a short essay on landslide

ENCYCLOPEDIC ENTRY

A landslide is the movement of rock, earth, or debris down a sloped section of land.

Earth Science, Geology, Geography, Human Geography, Physical Geography

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A landslide is the movement of rock , earth , or debris down a sloped section of land. Landslides are caused by rain , earthquakes , volcanoes , or other factors that make the slope unstable . Geologists , scientists who study the physical formations of Earth, sometimes describe landslides as one type of mass wasting . A mass wasting is any downward movement in which Earth's surface is worn away. Other types of mass wasting include rockfalls and the flow of shore deposits called alluvium . Near populated areas, landslides present major hazards to people and property. Landslides cause an estimated 25 to 50 deaths and $3.5 billion in damage each year in the United States.

What Causes Landslides?

Landslides have three major causes: geology , morphology , and human activity.

Geology refers to characteristics of the material itself. The earth or rock might be weak or fractured , or different layers may have different strength and stiffness.

Morphology refers to the structure of the land. For example, slopes that lose their vegetation to fire or drought are more vulnerable to landslides. Vegetation holds soil in place, and without the root systems of trees , bushes , and other plants , the land is more likely to slide away.

A classic morphological cause of landslides is erosion , or weakening of earth due to water. In April 1983, the U.S. town of Thistle, Utah, experienced a devastating landslide brought on by heavy rains and rapidly melting snow . A mass of earth eventually totaling 305 meters (1,000 feet) wide, 61 meters (200 feet) thick, and 1.6 kilometers (one mile) long slid across the nearby Spanish Fork River, damming it and severing railroad and highway lines. The landslide was the costliest in U.S. history, causing over $400 million in damage and destroying Thistle, which remains an evacuated ghost town today.

Human activity, such as agriculture and construction , can increase the risk of a landslide. Irrigation , deforestation , excavation , and water leakage are some of the common activities that can help destabilize, or weaken, a slope.

Types of Landslides

There are many ways to describe a landslide. The nature of a landslide's movement and the type of material involved are two of the most common.

Landslide Movement

There are several ways of describing how a landslide moves. These include falls , topples , translational slides , lateral spreads , and flows. In falls and topples, heavy blocks of material fall after separating from a very steep slope or cliff. Boulders tumbling down a slope would be a fall or topple. In translational slides, surface material is separated from the more stable underlying layer of a slope. An earthquake may shake the loosen top layer of soil from the harder earth beneath in this type of landslide. A lateral spread or flow is the movement of material sideways, or laterally. This happens when a powerful force, such as an earthquake, makes the ground move quickly, like a liquid.

Landslide Material

A landslide can involve rock, soil, vegetation, water, or some combination of all these. A landslide caused by a volcano can also contain hot volcanic ash and lava from the eruption . A landslide high in the mountains may have snow and snowmelt . Volcanic landslides, also called lahars , are among the most devastating type of landslides. The largest landslide in recorded history took place after the 1980 eruption of Mount St. Helens in the U.S. state of Washington. The resulting flow of ash, rock, soil, vegetation and water, with a volume of about 2.9 cubic kilometers (0.7 cubic miles), covered an area of 62 square kilometers (24 square miles).

Other Factors

Another factor that might be important for describing landslides is the speed of the movement. Some landslides move at many meters per second, while others creep along at an centimeter or two a year. The amount of water, ice , or air in the earth should also be considered. Some landslides include toxic gases from deep in Earth expelled by volcanoes. Some landslides, called mudslides , contain a high amount of water and move very quickly. Complex landslides consist of a combination of different material or movement types.

Martian Landslide In December 2008, scientists announced that they had found evidence of the largest landslide ever. Because of a giant asteroid impact billions of years ago, the smooth northern hemisphere of Mars is sharply separated from the irregular southern highlands. Arabia Terra, a previously unexplained plateau between the two regions, is thought to have been formed by an enormous landslide immediately after the impact. The land mass that slid north to form Arabia Terra was the size of the entire United States!

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What is Landslide?

Have you seen or heard of a mass movement land? Have you noticed the news that some roads in the mountains were closed due to landslides? Well, in this article, we will only discuss this mass movement of landmass. We will learn about the meaning of landslides, the impact of landslides, the causes of landslides, efforts to prevent or overcome them and so on. This article will help you understand a very important geographical phenomenon, namely landslides and related concepts.

Landslides are a natural phenomenon, but it involves many human activities which lead to the mass movement of landmass. In recent times we find the causes of landslides increasing day by day and the primary cause is deforestation. To survive, one needs to keep a check on these human activities.

More on the Topic

The movement of the rocks or debris etc., on a slope downwards, is called a landslide. It is a type of "mass wasting ", which refers to the movement of any mass, soil, or rocks under the influence of gravity. It is one of the natural hazards and can be a disaster if the damages occur in large amounts.

According to the Oxford learners dictionary, "landslides is a mass of earth, rock, etc. that falls down the slope of a mountain or a cliff ".

Types of Landslides

They can occur because of various reasons. We can classify them into four categories which are mentioned below:

Falls Landslides  

It means falling of some material or debris or rocks etc., from a slope or a cliff which leads to a collection of this debris at the base of the slope.

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Topple Landslides

These can occur because of some fractures between the rocks and the tilt of the rocks because of gravity without collapsing. Here, we see the forward rotational movement of the material.

It is a kind of landslide when a piece of the rock slides downwards and gets separated from it.

It happens on flat terrain and gentle slopes and can occur because of softer material.

Causes of Landslide

Landslides are caused by various factors, which are mentioned below:

It can be caused because of heavy rain.

Deforestation is also one of the main reasons for landslides because trees, plants, etc., keep the soil particles compact and due to deforestation, the mountain slopes lose their protective layers because of which the water of the rain flows with unimpeded speed on these slopes.

It can be caused by earthquakes as well.

For example, in the Himalayas, the tremor occurred because earthquakes unstabilized the mountains, which led to landslides.

Volcanic eruptions in specific regions can also cause landslides.

Landslides often occur in mountain regions while making roads and construction; a large number of rocks has to be removed, which can cause landslides over there.

In the regions of North East India, landslides occur because of shifting agriculture.

Due to the increasing population, a large number of houses are being created, which leads to the creation of a large amount of debris which can cause landslides.

Effects of Landslide

Let us look at the effects of landslides in points:

Landslides can disturb the social and economic environment with the number of other damages which are mentioned below:

Short Term Impacts

The natural beauty of the area is damaged.

Loss of life and property

Destruction of railway lines

Channel blocking because of the falling of rocks.

It leads to the diversion of river water, which can cause floods as well.

Long Term Impacts

Landscape changes can be permanent.

The loss of fertile land or cultivation land.

Erosion and soil loss can lead to environmental problems.

Population shifting and migration.

Effects on the sources of water.

Some roads can be damaged or closed permanently.

Prevention and Mitigation

The following measures can be taken in this regard:

The country should identify the vulnerable areas and actions should be taken in this regard on a priority basis.

Early warning systems and monitoring systems should be there.

Hazard mapping can be done to identify the areas which are more prone to landslides.

Restriction on the construction in the risky areas should be imposed.

Afforestation programs should take place.

Restricting development in landslide areas and protecting the existing ones.

The country should specify codes or standards etc. For the construction of the buildings and other purposes in such areas of risk.

Insurance facilities should be taken by the people to deal with the loss.

Terrace farming should be adopted in hilly areas.

Response teams should be quick to deal with landslides if they occur.

Landslides in India

It is one of the natural hazards in India, which affects 15% of the geographical area of our country. Due to several factors, India is divided into the following vulnerability zones, which are shown in the table below:

Did You Know?

The North India Flood Mudslides that occurred in Kedarnath, India in June 2013 was one of the deadliest landslides in the world. Around 5700 people died in this disaster. It was one of the worst disasters ever to occur in India.

Thus, in this article, we have covered a very important topic namely landslides. We have covered its related concepts like causes, effects, prevention, and mitigation, etc. Hence, it is very important to learn these kinds of topics. These notes will help you in Geography, Environment, and Disaster Management. So, we have read about the landslide information, effects of landslides, etc. Let's look at some FAQs in the following.

FAQs on Landslide

1. What is meant by a landslide?

Also known as a mass movement of landmass, Rocks, rubble, etc. A landslide is called an avalanche. It is a kind of "mass movement" which refers to the movement of any kind of mass, soil or rock under gravity. This is a natural hazard and can be catastrophic if the damage is large. Landslides mostly happen in hilly regions. Many factors involve landslides and we need to be careful and aware of these factors. We can learn in detail about landslides on the website of Vedantu for free.

2. What are the causes and effects of landslides?

Landslides can be caused by a combination of factors, both man-made and geological. Landslides must occur when the subsoil loses its ability to withstand the pressure of the part above it. It is estimated that it will surrender by force, and depending on the earth, the earth can only cover a short distance or even a few kilometers.

Some cases are more tragic than others due to soil moisture and other conditions, but in all cases, the worst-case scenario needs to be prepared. Landslides are caused by heavy rains, earthquakes, deforestation, volcanic eruptions, construction of roads, buildings or houses, and so on. causing. It can have a variety of short-term and long-term effects on the environment, area and people. Can cause loss of property and life. Can damage the natural environment, means of transportation or communication can block roads, railroads, rivers and so on.

3. Is it possible to predict landslides?

Landslide prone areas are quite predictable but timing is not. One of the main ways to predict them is to look at areas where they have appeared before. Areas that have experienced landslides are likely to occur in the future. Scientists are studying existing landslides to see the factors that caused them to collapse. Mountain slopes, hills or cliffs. Existing drainage. Erosion, which is especially common near riverbanks and rocky sides. Excessive rainy season.

A place that is saturated with water that is not wet. Mountainous area with freezing point. Man-made projects such as road construction in steep areas, quarrying and mining. It's important to remember that our landscape is constantly evolving, so landslides can happen almost anywhere if the environment allows them.

4. What are Countermeasures and protection against landslides?

Landslides are a constant threat to human life and livelihoods throughout much of the world, especially in some areas where population and economic growth are high. This risk is mainly mitigated by preventive measures, such as limiting or even removing people from areas previously affected by landslides, limiting certain types of land use where slope stability is present, and setting up warning systems based on slope control. soil conditions such as rock and soil pressure, slope displacement and groundwater levels.

There are also various direct methods to prevent landslides; This includes changes in slope geometry, the use of materials to strengthen slope materials, installation of structures such as poles and retaining walls, grouting at rock joints and fractures, bending of debris and drainage paths on the surface and underwater. Such a direct method is limited by the cost, extent and frequency of landslides and the size of the human settlement at risk.

Causes, Effects and Types of Landslides

Landslides are among the many natural disasters causing massive destructions and loss of lives across the globe. According to a survey study by the International Landslide Centre at Durham University, UK, 2,620 fatal landslides occurred between 2004 and 2010. These landslides resulted in the death of over 32,322 people. The figure does not include landslides caused by earthquakes . This research result is astonishing considering the number of people killed by landslides. It is, thus, paramount to know the causes and warning signs of a potential landslide to minimize losses.

A landslide, sometimes known as landslip, slope failure or slump, is an uncontrollable downhill flow of rock, earth, debris or the combination of the three. Landslides stem from the failure of materials making up the hill slopes and are beefed up by the force of gravity. When the ground becomes saturated, it can become unstable, losing its equilibrium in the long run. That’s when a landslide breaks loose. When people are living down these hills or mountains, it’s usually just a matter of time before disaster happens.

Causes of Landslides

While landslides are considered naturally occurring disasters, human-induced changes in the environment have recently caused their upsurge. Although the causes of landslides are wide ranging, they have 2 aspects in common; they are driven by forces of gravity and result from failure of soil and rock materials that constitute the hill slope:

Natural Causes of Landslides

Long-term climatic changes can significantly impact soil stability. A general reduction in precipitation leads to lowering of water table and reduction in overall weight of soil mass, reduced solution of materials and less powerful freeze-thaw activity. A significant upsurge in precipitation or ground saturation would dramatically increase the level of ground water. When sloped areas are completely saturated with water, landslides can occur. If there is absence of mechanical root support, the soils start to run off.

Earthquakes

Seismic activities have, for a long time, contributed to landslides across the globe. Any moment tectonic plates move, the soil covering them also moves along. When earthquakes strike areas with steep slopes, on numerous occasion, the soil slips leading to landslides. In addition, ashen debris flows instigated by earthquakes could also cause mass soil movement.

Weathering is the natural procedure of rock deterioration that leads to weak, landslide-susceptive materials. Weathering is brought about by the chemical action of water, air, plants and bacteria. When the rocks are weak enough, they slip away causing landslides.

Erosion caused by sporadic running water such as streams, rivers, wind, currents, ice and waves wipes out latent and lateral slope support enabling landslides to occur easily.

Volcanic eruptions can trigger landslides. If an eruption occurs in a wet condition, the soil will start to move downhill instigating a landslide. Stratovolcano is a typical example of volcano responsible for most landslides across the globe.

Forest fires

Forest fires instigate soil erosion and bring about floods , which might lead to landslides

Steeper slopes coupled with gravitational force can trigger a massive landslide.

Human causes of landslides

Mining activities that utilize blasting techniques contribute mightily to landslides. Vibrations emanating from the blasts can weaken soils in other areas susceptible to landslides. The weakening of soil means a landslide can occur anytime.

Clear cutting

Clear cutting is a technique of timber harvesting that eliminates all old trees from the area. This technique is dangerous since it decimates the existing mechanical root structure of the area.

Effects of Landslides

Lead to economic decline.

Landslides have been verified to result in destruction of property. If the landslide is significant, it could drain the economy of the region or country. After a landslide, the area affected normally undergoes rehabilitation. This rehabilitation involves massive capital outlay. For example, the 1983 landslide at Utah in the United States resulted in rehabilitation cost of about $500 million. The annual loss as a result of landslides in U.S. stands at an estimated $1.5 billion.

Decimation of infrastructure

The force flow of mud, debris, and rocks as a result of a landslide can cause serious damage to property. Infrastructure such as roads, railways, leisure destinations, buildings and communication systems can be decimated by a single landslide.

Loss of life

Communities living at the foot of hills and mountains are at a greater risk of death by landslides. A substantial landslide carries along huge rocks, heavy debris and heavy soil with it. This kind of landslide has the capacity to kills lots of people on impact. For instance, Landslides in the UK that happened a few years ago caused rotation of debris that destroyed a school and killed over 144 people including 116 school children aged between 7 and 10 years. In a separate event, NBC News reported a death toll of 21 people in the March 22, 2014, landslide in Oso, Washington.

Affects beauty of landscapes

The erosion left behind by landslides leaves behind rugged landscapes that are unsightly. The pile of soil, rock and debris downhill can cover land utilized by the community for agricultural or social purposes.

Impacts river ecosystems

The soil, debris, and rock sliding downhill can find way into rivers and block their natural flow. Many river habitats like fish can die due to interference of natural flow of water. Communities depending on the river water for household activities and irrigation will suffer if flow of water is blocked.

Types of Landslides

Falls are sudden movements of loads of soil, debris, and rock that break away from slopes and cliffs. Falls landslides occur as a result of mechanical weathering, earthquakes, and force of gravity.

This is a kind of mass movement whereby the sliding material breakaways from underlying stable material. The kinds of slides experienced during this type of landslide include rotational and transitional. Rotational slides are sometimes known as slumps since they move with rotation.

Transitional slides consist of a planer or 2 dimensional surface of rupture. They involve landslide mass movement following a roughly planar surface with reduced rotation or backward slanting. Slides occur when the toe of the slope is undercut. They move moderately, and the consistency of material is maintained.

Topple landslides occur when the topple fails. Topple failure encompasses the forward spinning and movement of huge masses of rock, debris, and earth from a slope. This type of slope failure takes place around an axis near or at the bottom of the block of rock. A topple landslide mostly lead to formation of a debris cone below the slope. This pile of debris is known as a Talus cone.

They are commonly known as lateral spreads and takes place on gentle terrains via lateral extension followed by tensile fractures.

This type of landslide is categorized into five; earth flows, debris avalanche, debris flow, mudflows, and creep, which include seasonal, continuous and progressive.

Flows are further subcategorized depending upon the geological material, for example, earth, debris, and bedrock.

The most prevalent occurring landslides are rock falls and debris flow.

The study of landslides is critical considering the annual economic losses they bring. Globally, landslides result in expenditure of billions of dollars towards rehabilitation of affected areas. Due to these astonishing annual losses, most governments have instituted bodies to deal specifically with landslides. For example, the U.S. government created the National Landslide Information Centre to collect and distribute all kinds of data related to landslides. The body is intended to cater to landslide researchers, geotechnical practitioners involved in landslide mobilization and other individuals and organizations focused on landslide hazard analysis and mitigation. The aim is to reduce the financial burden and deaths from landslides.

Photo by: flickr

I am Sonia Madaan, a mother with a passion for science, computing, and environmental issues. Motivated by my passion and education, I started a website to spread awareness about climate change and its causes, like rising greenhouse gas levels. You can read more about me here .

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Landslides don’t attract the same media attention as more familiar geological hazards such as earthquakes and volcanoes. And yet they can be just as disastrous and, in fact, 2014 has been a particularly bad year.

In Hiroshima, Japan, a series of landslides has left 39 people confirmed dead and a further 52 missing. In March a hillside collapsed in Washington state, US, leaving 43 dead, and in May massive mudslides in Afghanistan caused several thousand deaths. In early August, landslides in Nepal left almost 200 dead or missing .

Landslides can vary greatly in speed, water content and size. Different landslides can look very different and can vary greatly in their destructive power – size is not everything. Nevertheless, they pose a significant hazard to human life, buildings and transport routes.

Statistics about deaths from landslide-generated disasters can be a little difficult to come by, since some agencies group “wet” landslides with floods and damage caused by landslides generated during earthquakes are often classed as earthquake damage.

The recent Japanese landslides, for example, are mud flows or debris flows (a watery mix of rock and soil) generated from a slope collapsing further up river. Heavy rainfall had caused large volumes of slope collapse material to be incorporated into the river waters, giving the mud flows and debris flows, which have overwhelmed villages within the mountain valleys. Villages built a little further up from the floor of the valleys will be much less prone to the destructive debris flows, which occur in the base of the mountain valleys.

Major league disasters

Landslides tend to be most frequent and destructive in steep mountainous areas, as they are an expression of a natural process which reduces steep slopes to less steep slopes. Data collected over many years suggests that landslides are ranked 7th in the natural disaster table well after the major historical killers of droughts, floods and storms, but close on the heels of earthquakes and volcanic eruptions.

Landslides generally require a trigger, most commonly extreme rainfall or large earthquakes. Earthquakes initiate landslides by locally – and very briefly – changing the gravity experienced by a slope, which tips it beyond its stability point. Extreme rainfall temporarily drives the water pressure within a slope to a critical level; the stresses within the slope then exceed their stability point and the land begins to slip down the slope. Landslides are then driven simply by gravity, often assisted by a loss of strength in the region at the base of the slide.

So parts of the world with steep slopes, intense rainfall and large earthquakes tend to be most prone to this kind of geological disaster.

A man-made natural disaster?

But they aren’t always massive, deadly disasters. Smaller, often more benign landslides can be initiated by roadway construction, building works, river or wave/tidal undercutting of slopes. If engineers or builders mess up and make a slope too steep, it may no longer be held up by the intrinsic strength of the rock.

In the same way, apparently simple things like leaky water pipes or inadequate drainage on man-made slopes can also start landslides . This is particularly so water is either retained in, or drains particularly slowly from, the rock or soil of the slope. Certain kinds of clays are particularly notable for these features – and this seems to have exacerbated the landslides at Hiroshima.

Such conditions are generally well understood by geo-technical engineers, so can normally be predicted in artificial slopes. Next time you are on a train or car look out for adjacent slopes which have lines of gravel or rock-fill running down them to drain the water away. These have been assessed by engineers as potential unstable slopes, should the area be exposed to heavy rainfall over long periods of time.

A lack of trees can also make steep slopes more prone to landslide, since trees naturally intercept and slow heavy rainfall and their roots help bind the soil together. This is another example of natural and man-man factors overlapping – environmentalists blamed deforestation for a recent landslide in India which killed 30 people.

These facts gives clues as to how to limit landslides (triggered by heavy rainfall) on natural slopes, by managing water flow across slopes, limiting water ingress into slopes and by planting tree cover to slow water delivery into water courses and so provide natural slope binding.

The most destructive landslides of all are those that end up in water (or occur on underwater slopes) and generate tsunamis. For example, this kind of destruction can happen if a volcano flank collapses into water while erupting.

Indeed, the largest tsunami ever recorded was set off by a landslide in Lituya Bay, Alaska, in 1958. Waves reached a height of more than 500m, far taller than any skyscraper built at the time, but killed just five people in the sparsely populated fjord.

Fortunately such disasters have been very rare in human history – the 1792 Unzen eruption , earthquake, landslide and tsunami, which killed 15,000 people in Japan is a notable instance. However we know from geological evidence on the sea floor, for example around the Canary Islands, that mega-tsunamis must have been generated by similar slides – landslides that would make 2014’s crop seem tiny by comparison.

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• What is a landslide? Types, causes, effects & prevention

Andrew Lees

Subscribe to our newsletter, what is a landslide types, causes, effects & prevention.

by Andrew Lees, on September 09, 2021

This guide explains landslides, outlining what they are and the various types, the factors that can cause landslides to occur and the main landslide prevention techniques used in engineering and construction. Use the links below to jump to the sections you’re most interested in:

What is a landslide?

Types of landslide movement.

• What causes a landslide?

The varying effects of landslides

• Preventing a landslide

Repair of failed slopes

A landslide is defined as the movement of a mass of earth, rock or debris down a slope. They are a type of “mass wasting” which is the name for any down-slope movement of soil and/or rock under the direct influence of gravity. This movement is caused by the self-weight of the material, under the force of gravity, and can take the form of falls, topples, sliding, spreading or flows (mudflows or waste flows).

Although landslides often have the same negative effects on their surroundings, there are many diverse types with varying sizes, shapes, movement speeds and characteristics. The four main types of landslides are:

• S lides (including rotational landslides and translational landslides)
• Flows  

The landslide types each have their own unique cause, read on to get a better understanding of each type and why they occur.

   1. Falls

With vertical or steep slopes such as cliffs , a landslide will often take the form of a fall – this is where material collapses from the slope, falls downwards, and collects towards the base. As a result, we can recognise the occurrence of a fall and differentiate it from the other landslide types by the accumulation of earth, rock and debris at the bottom of a steep slope. 

     2. Topples

As the name suggests, a topple is a type of landslide where the rock, earth or debris rotates forwards away from slope and literally topples downwards. Under normal circumstances, there will be an axis at or close to the bottom of the slope about which the rotation occurs.

     3. Slides

In cases where a slide landslide occurs, the failure in the slope takes place at depth below the surface. The material above this point then slides downwards along a slip surface (or ‘rupture’). This type of slide landslide can either be rotational or translational.

   4. Rotational

We can spot rotational slides in cases where the slip surface is curved (often like the surface of a spoon) – this is referred to as a listric rupture or slip surface. As a result of this appearance, rotational landslides are sometimes called ‘slumps’.

   5. Translational

Where a landslide occurs along the surface of a fault, joint or bedding plane, it is said to be translational or ‘planar’. Often causing huge damage, translational landslides can result in the rapid movement of material down a slope. The speed of the slide ultimately depends on how deep the underlying fault is.

   6. Flows

If water – or another form of fluid – is involved, then a flow can occur. This is a movement of fluid along with any other material that is being carried in it. A flow could consist of mud, debris or even rock (known as a rock avalanche).

What causes a landslide? 

Landslides are caused by agitation to the layers of earth beneath the surface. There are four common factors that can trigger a landslide: the weight, angle, geometry and strength of the external force. All of these factors can place pressure upon the internal strength of the soil, leading to the stability to fail and a landslide to happen.

Let’s take a deeper look into the different cause of landslides:

Water plays an integral part in the many causes of landslides, and is actually the most common cause of a landslide trigger mechanism. Soil that is already facing instability can be at risk of sliding when water increases the hydrostatic pressure while at the same time weakening the soil further. An increase in water can originate from a number of natural causes and other human related activities including: rainfall, snowmelt, stream erosion, burst water mains, floods.

Soil strength and slope angle

Different soil types can support different slope angles. The maximum stable slope face angle depends upon the internal strength of the soil and the forces acting on it. Some slopes that have been stable for many years can suddenly fail due to a trigger mechanism such as a change in soil strength or surcharge loading.

External activity

A landslide can be caused by a number of external factors other than water and soil stability.  Primarily earth vibrations such as earthquakes, volcanic eruptions and human activity (mining or traffic) are the obvious causes. A slope’s strength can also be impacted by the removal of vegetation, weathering – where a material’s strength is reduced due to freeze thaw cycles and mineralogical changes – and the arrangement of the rock layers..

Landslides are not uncommon. They occur in all regions across the globe, with varying degrees of severity. Many are minor slope failures with minimal consequences, where even local people may be unaware of the landslide. At the other end of the scale are humanitarian disasters involving catastrophic loss of life and destruction. In between these extremes are a variety of landslide types, including both minor and major failures, resulting in differing degrees of damage to buildings, properties, businesses, people and animals.

Landslide prevention techniques

The easiest way to prevent a landslide is to avoid building in areas that are – or might become – prone to landslides. However this is not always an option; unique assessments are often used to show the conditions for a landslide exist. In such cases, there are measures that can be taken to reduce the potential for a landslide to occur, such as steep slope reinforcement, installing structures using pile foundations and checking surface drainage.

Surface drainage

Surface drainage can be installed to reroute surface water away from a slope, thus reducing the likelihood of a landslide. In high rainfall areas, erosion protection via surface drainage – both at the toe and on the surface – can be very effective, positively impacting the maintenance of the angle of the slope. An alternative option is almost the opposite of this, where removing material from the top of the slope or adding a toe berm can reduce the effective slope angle and loading, thus reducing the risk of a landslide and increasing safety.

Construction of safe steep slopes

Sometimes it is desirable to construct earth slopes or embankments with steep faces. Steep slopes  reduce land take and are lower in cost than constructing vertical retaining walls. The steep slope can be made stable and prevent landslides by the inclusion of soil reinforcement in the form of high strength geogrids. Tensar have developed systems for the design and construction of reinforced soil slopes up to 70° face angle: TensarTech Natural Green and TensarTech GreenSlope .

Ultimately, the only way to increase the strength and stability of slopes prone to landslides is by major engineering works. Several options are available including soil nailing and earth retaining structures.

Landslides affecting infrastructure are not an uncommon occurrence, as road and rail embankments can slide, and steep faced cuttings in soil and rock can fail. Where landslides occur in embankments or soil cuttings, the failed material is often removed from site and replaced with a material that has greater strength – usually quarried rock or aggregate. This is expensive and disruptive, and clearly not ideal.

This guide has explained what a landslide is, the different types of landslides, the varying effects, how to prevent them and how failed slopes are repaired. If you’ve found this post useful, you may also want to read some of our other articles:

• What is the shear strength of soil?
• Types of pavement and road construction methods
• Geogrids: A different way of thinking

To find out more about how Tensar products support slo pe design and construction processes, visit our Tensar geogrids and geosynthetic construction solutions pages.

Got a burning question about geotechnical engineering? 

Why not drop us a line at [email protected]  and the answer to your question may feature in a future episode of Ground Coffee!

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What are landslides & how can they affect me?

Dixie fire debris-flow deposit, new zealand landslides, home damaged by rainfall-triggered debris flow - carrol county, kentucky.

Landslides occur in all 50 states and territories, and they affect lives, property, infrastructure, and the environment. Landslides are the downslope movement of earth materials (rock, debris, and soil) at rates that range from inches per year to tens of miles per hour. Some landslides can move faster than a person can run and can happen with no notice or can take place over days, weeks, or longer

Landslides can bury homes, damage critical infrastructure , block or damage roads and rail lines, and disrupt vital utilities and communication lines.  Landslides can happen with no notice or can take place over a period of days, weeks, or longer. Landslides are unpredictable. A slow-moving landslide can rapidly change to a fast-moving landslide. Some fast-moving landslides can travel thousands of feet, even across flat ground. A landslide can remain inactive for centuries and then suddenly start moving again. Although not as dangerous to human life as fast-moving landslides, a slow-moving landslide that may be moving a few inches per year can, over periods of months to years, severely damage and destroy building, roads, pipelines, and other utilities built on and adjacent to the landslide.

Types of landslides

_________________________________________________________________________

Landslides come in many varieties, from small rockfalls or debris flows (mudflows) that occur quickly to mountain-sized slides that move for centuries. Many landslides are complex and involve a variety of landslides themselves, such as large, slow-moving landslides that produce smaller but rapid debris flows.

Causes of landslides

Landslides can be triggered by rainfall from hurricanes and rainstorms, ground shaking from earthquakes , and volcanic activity . Human activity commonly triggers landslides, such as modifying (grading) a slope, removing vegetation, or channeling water onto a slope. Local terrain conditions, such as slope steepness and curvature, and geologic materials make hillslopes more or less likely to experience landslides.

A landslide that moves into water can produce a displacement wave, which is a type of tsunami. The largest displacement wave in the world occurred in 1958 in Lituya Bay, Alaska when an earthquake triggered a landslide that rapidly moved into the bay. The resulting displacement wave was over 1,700 feet high and stripped trees and soils from the slopes along the Lituya Bay.

Areas recently burned by wildfires can be more susceptible to landslides from rainfall. Fire can destroy vegetation and alter soil properties, such that water is repelled by a soil. During a rain event over a burned area, the soils may not be able to absorb water and instead, the water beads on the surface. If the soils are on a slope, the water will flow downslope and can rapidly increase in volume, picking up debris. 

 In the right conditions, the water can collect sufficient soil, rocks, and other debris and become a debris flow, which are very dangerous to those living downslope. Debris flows can damage or destroy roads, building, and other infrastructure far outside of the burned area.

Related Information - Postfire Debris Flows

Postfire Landslide Monitoring Station: “Maria Ygnacio” (2019 Cave Fire) near Santa Barbara, California

Impacts of landslides, ___________________________________________________________________________________________.

Landslides can have cascading consequences; for example, a landslide can form a debris dam that blocks a stream channel, forming a pond. The rising pond water can eventually breach the debris dam which can lead to downstream flooding. Or a landslide-damaged road can cause closures, forcing vehicles to take alternate routes for weeks to months. This can impact local economies and hinder emergency response .  The frequency and size of landslides are expected to grow in areas due to climate change, which is increasing rainfall intensity that can trigger landslides. Climate change is also linked to more frequent and severe wildfires and recently burned areas can experience increased occurrence of landsliding due to the fire altering the soil and vegetation.  

In the United States, financial loss from landslide damages is not well-documented; however, landslides are estimated to cause billions of dollars in damage and multiple deaths annually. In additional, indirect loss from landslides, such as cost to commercial traffic due to extended road closures by landslide damage, are also not well understood.  

More importantly, if a home is damaged by a landslide, the typical homeowner’s insurance policy does not cover earth movement. So, the damage to a home from a landslide may be entirely covered by the homeowner.  

People who live in areas with landslide hazards should learn the signs of a landslide and learn what to do after a landslide occurs.    

Related Content

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Glenwood Canyon, Colorado, Flooding and Debris Flows: 2021

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Forecasting the frequency and magnitude of postfire debris flows across southern california, the influence of frost weathering on the debris flow sediment supply in an alpine basin.

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Landslides: Types, Causes, Consequences, Prone Areas, Mitigation Strategies & More

Landslides , a geological phenomenon with the potential to cause widespread devastation, are one of the most prominent disasters of concern for India. As societies expand into hilly and mountainous regions, the understanding of landslides becomes crucial for sustainable development and disaster preparedness. This article of NEXT IAS aims to explain various aspects of Landslides , including their types, causes, consequences, and mitigation strategies.

What is Landslide?

Landslides are a geological phenomenon that involves the sudden and rapid movement of a mass of rock, soil, or debris down a slope under the influence of gravity.

Characteristics of Landslide Prone Areas

Landslides , usually, occur in areas having one or more of the following characteristics:

• Steep terrain such as hilly or mountainous areas.
• Presence of joints and fissures.
• Presence of loosely-packed or weathered material
• Any area that has been burned by wildfires
• Any area that has been modified due to human activities, such as deforestation or construction
• Channels along a river-stream
• Any area where surface runoff is directed or land is heavily saturated with water.

Causes of Landslides

A variety of causes act as a trigger for a landslide . Some of the major causes of landslide can be seen under the following two heads:

Natural Causes

A myriad number of natural processes can trigger a landslide. Some prominent of them are:

• Heavy Rainfall – Heavy rainfall is one of the most common triggers of landslides. It increases pore water pressure as well as the weight of soil by making it saturated.
• Erosion – Clay and vegetation present within the soil or rock act as cohesive elements and help bind particles together. By removing these cohesive elements, erosion makes an area more prone to landslides.
• Earthquakes – intense ground shaking due to earthquakes causes instability in rocks and soils, thus triggering landslides.
• Volcanic Eruptions – Ash and debris deposited by volcanic eruptions overload slopes while the accompanied seismic activity causes instability. All these, together, trigger landslides.

Anthropogenic Causes

Several human activities can directly or indirectly influence the occurrence and magnitude of landslides. Some prominent such activities include:

• Deforestation – By holding soils as well as obstructing the flow of falling debris, vegetation cover plays an important role in preventing landslides in any area. Deforestation takes away this preventive cover and increases vulnerability to landslides.
• Encroachment in Vulnerable Terrains – Of late, humans have been encroaching in landslide-prone areas such as hilly terrains. This has led to increased construction activities in these areas and increased chances of landslides.
• Uncontrolled Excavation – Unauthorized or poorly planned excavation activities, such as mining, quarrying, etc destabilize slopes and increase the chances of landslides.
• Climate Change – Climate change caused by various anthropogenic activities has led to abrupt alterations in precipitation patterns and increased frequency of extreme weather events. All these, in turn, have increased the frequency as well as the severity of landslides .

Types of Landslides

Based on the type of movement involved, there are mainly 4 types of landslides:

• Falls – They refer to the type of landslide that involves the collapse of material from a cliff or steep slope, which then falls down the slope and collects near the base.
• Topples – Under this type of landslide , the falling mass undergoes forward rotation and movement around an axis or point at or near the base.
• Slides – Under this type of landslide, there is a distinct zone of weakness that separates the moving material from a more stable underlying material.

There are two major types of slides:

• Rotational Slide – In this type of slide, the surface of rupture is curved concavely upward and the slide movement of the falling mass is rotational about an axis that is parallel to the ground surface and transverse across the slide.
• Translational Slide – In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting.
• Flows – This type of landslide involves the movement of material down a slope in the form of a fluid.

There are different types of flows:

• Mud Flow – It involves the movement of wet material of which a majority portion is comprised of sand, silt, and clay-sized particles.
• Debris Flow – Masses such as loose soils, rocks, and organic matter combine with water to form a slurry. It, then, flows down a slope.
• Rock Flow or Rock Avalanches – a specific type of landslide or mass movement involving the flow of rock material downslope.

Impacts of Landslides

Some of the key impacts of landslides can be seen as follows:

• Loss of human and animal lives.
• Damage to infrastructure and properties such as homes, roads, etc.
• They can bury or wash away agricultural land, thus affecting agriculture.
• The aftermath of landslides may mean the displacement of local communities.
• Landslides, often, block transportation routes such as roads. This, then, has its own repercussions.
• The movement of huge mass during landslides can alter the natural landscape of a region. This, in turn, affects the ecosystem, water courses, etc.

Landslide Prone Areas in India

ISRO has recently released the Landslide Atlas of India . As per this atlas, some of the prominent statistics regarding landslides in India are as follows:

• India is among the top five landslide-prone countries in the world.
• Excluding snow-covered areas, around 12.6 percent of India’s geographical land area is prone to landslides.
• About 66.5 percent from the North-Western Himalayas
• About 18.8 percent from the North-Eastern Himalayas
• About 14.7 percent from the Western Ghats.

As per the Landslide Atlas of India, major landslide prone areas in India are as follows:

• The Northeastern Region (comprises about 50 percent of the total landslide prone areas in India)
• Areas of Uttarakhand, Himachal Pradesh, and Jammu & Kashmir lying along the Himalayas.
• Areas of Maharashtra, Goa, Karnataka, Kerala, and Tamil Nadu lying along the Western Ghats.
• The Araku region in Andhra Pradesh along the Eastern Ghats.

Measures Taken in India

Some of the prominent measures taken for proper management of landslides in India are as follows:

• The Disaster Management Act, of 2005 provides a comprehensive legal and institutional framework for the management of various disasters including landslides.
• The National Landslide Risk Management Strategy (2019) covers all aspects of landslide disaster risk reduction and management, such as hazard mapping, monitoring, and early warning systems.
• The National Disaster Management Authority (NDMA) has issued Guidelines on Landslide Hazard Management (2009) that outline the steps that should be taken to reduce the risk of landslides.
• The National Institute of Disaster Management (NIDM) has been providing capacity building and other support to various national and state-level disaster management authorities.
• Efforts have been made towards better prediction of weather . E.g. Ensemble Prediction System. This will help predict disasters like landslides.

Suggested Measures

• Promotion of terrace farming can help reduce landslide risks.
• Afforestation and construction of bunds to reduce the flow of falling materials.
• Retaining walls can be built on mountain slopes to stop the falling materials coming down.
• As suggested by the 10th FYP, mitigation measures should be built into the development process itself.
• A more granular Hazard Mapping to have accurate knowledge of prone areas.
• Traditional knowledge of the local community should be used to tackle such kinds of disasters.
• Education and training can help ensure the preparedness of the disaster management authorities as well as the local community.

Landslides as one of the prominent disasters concerning India have far-reaching consequences. As societies continue to expand into vulnerable regions, a proactive approach to landslide prevention and mitigation becomes imperative. The measures suggested as above can help in this direction.

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Disaster Management: Types, Steps & Measures

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Essay on landslides: factors, types and methods.

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The landslide hazard causes severe loss of life, injury, damage to property, destruction of communication networks and loss of precious soil and land. Although the occurrence of landslides is . declining all over the world due to greater scientific understanding and public awareness, in many areas the mounting pressure of population at the base of slopes, canyons and unstable borders of plateau have led to an increase in dangers due to landslides. Landslides are universal phenomena, but more than being ‘natural hazards’, they are induced by human activity.

M.A. Carson and M.J. Kirkby (1972) divided hill slopes into (i) weathering-limited slopes and (ii) transport-limited slope. In the former case, rock disintegrates in situ, whereas, in the latter case, slopes are covered by thick soil or disintegrated rock materials, known as regolith. Due to the presence of regolith, transport-limited slopes experience frequent landslides.

The term, ‘landslide’ encompasses falling, toppling, sliding, flowing and subsidence of soil and rock materials under the strong influence of gravity and other factors. Some geomorphologists thus prefer to use the term mass movement instead of landslides. The resultant landforms produced by mass movements are termed mass wasting. Mass movement occurs when the slope gradient exceeds its threshold angle of stability.

Factors Responsible for Landslides:

Slope instability may be caused by removal of lateral or underlying support, mainly by river erosion and road cuts, landfill dumping, faulting, tectonic movement or the creation of artificial slopes by constructional activities.

Weathering involves rock disintegration, causing weakening of soil and decreased resistance to shearing. A Significant cause of landslide is related to increased water infiltration which causes saturation of soil. It may be due to ploughing or poor organisation of drainage on a sloping area that has under-gone modification due to deforestation and urbanisation. Pour water pressure is increased by soil saturation which results in a positive force on the slope.

Landslides due to slumping may occur due to construction of settlement built on filled up land that suffers from poor compaction or engineering. In forests, timber harvesting may negatively affect slope stability. Tractors, in general, cause immense damage as runoff follows the wheelings.

Apart from the above-mentioned forces, the causes of slope failure may be distinguished as (i) immediate causes such as vibrations, earthquake tremors, heavy precipitation and freezing and thawing; and (ii) long-term causes such as the slow and progressive steepening of the slope.

R.U. Cooke and J.C. Doornkamp (1974) suggested a few factors that contribute to landslides.

(i) Factors leading to accelerated shear stress:

a. Surcharge i.e., loading of the crest of slopes with an additional load;

b. Undermining of slope;

c. Lateral pressure exerted on cracks due to factors like freezing.

(ii) Factors that cause reduced shear strength:

a. Characteristic of some soil particles like clay to swell and shrink alternatively in wet and dry periods;

b. Rock structure such as faults, joints, bedding etc.;

c. Pore-pressure effects;

d. Drying and desiccation;

e. Loss of capillary action;

f. Crumbling soil structure that leads to reduced cohesion in soil.

According to Cooke and Doornkamp, the process of movement which follows planes is called shear. Applied forces are called stresses. Slope failure takes place as a result of shear stresses operational along straight or curved shear planes.

Strain is the deformation caused by movement. If it is the result of shear stresses it is called shear strain. The amount of resistance offered by the slope to movement is measured by the strength of the slope. The component of this which is directed against shear stresses is termed the shear strength.

Types of Landslides:

Landslides are extremely complicated and varied phenomena. They differ in terms of sliding, flowing, creeping, toppling or speed of movement so markedly that it is extremely difficult to combine all these diagnostic phenomena into a standard taxonomy.

Classifications of landslides have been attempted by T.H. Nilsen (1979), R.J. Blong (1973), A.J. Nemcock (1972), A.W. Skempton and J.N. Hutchinson (1964), and D.J. Varnes (1978).

The scheme advanced by Varnes has received widest acceptance:

1. Rotational slide:

It is a classic form of landslide. Some cases produce multiple regressive phenomena when continued instability produces new head carps to develop progressively up the slope.

2. Translational slide:

It involves relatively flat, planar movement following the surface. This type of movement is found in bedding planes made of sedimentary or metamorphic rocks dipping in the direction of slope,

3. Roto-translational slide:

It is a complex type where ‘a combination of slip along a circular arc and a flat plane is found.

4. Soil-slab failure:

In this case, a slab of saturated regolith is converted into a thick liquid. So the speed of landslide accelerates to as high as 10m/sec.

5. Debris slide or avalanche:

It occurs in surface deposits of granular materials. The surface of rupture is almost parallel to the inclination of bedrock.

6. Debris flow:

It occurs when debris is saturated with water. When rigid solid also falls along with the sliding mass, the phenomenon is called plug flow.

These take place through air; for example, jointed weathered rock falls from vertical cliffs.

8. Topples:

After detachment from cliffs the outward rotation of angular blocks and rock columns cause toppling.

9. Mudflow:

It contains 20 to 80 per cent fine sediments saturated with water. Friction is caused by viscous movement that generates enough power to carry even large boulders.

10. Soil creep:

It is the least destructive of landslide phenomena. Creep is slow and superficial.

PE. Kent (1966) proposed a hypothesis based on fluidisation of rock mass. He said that accumulated stress within rock particles causes compression of air in the pore spaces. This results in a fast-moving stream of debris. A. Heim (1932) held elasto-mechanical collisions responsible for landslides. His emphasis was on exchange of stresses between solid particles rather than fluids.

Methods to Minimise Damage:

R.U. Cooke (1984) and W.J: Kochelman (1986) have proposed some methods for reducing the landslide hazard.

1. Avoidance:

One way is to avoid landslides by controlling the location, timing and nature of development.

The measures include:

i. Bypassing unstable areas; putting restrictions on land use;

ii. Mapping of hazard-prone areas and land use zoning;

iii. Acquiring and restructuring of public property;

iv. Spreading social awareness among people;

v. Disclosing the nature of hazard to prospective property buyers;

vi. Promoting insurance against hazard;

vii. Giving financial assistance such as loans, tax credits, etc., to promote the reduction of the hazard.

2. Reducing shear stress:

One could reduce shear stress:

i. Limit or reduce angles of slope, cut and fill;

ii. Limit or reduce unit lengths of slope;

iii. Remove unstable material.

3. Reducing shear stress and augmenting shear resistance:

This could be achieved through an improved drainage system which involves

i. Improving surface drainage that covers terrace drains and other drains;

ii. Improving subsurface drainage;

iii. Controlling unsustainable agriculture.

4. Increasing shear resistance:

This would be through

i. Retaining structures such as cribs or building retaining walls;

ii. Adoption of engineering methods by piling, tie-rods, anchors etc.;

iii. Building hard surface e.g., concrete surface;

iv. Controlling fill compaction.

Related Articles:

• Issues Related to Landslides – Explained!
• Paragraph on Landslides in India

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Landslide Definition, Causes, Types, Effects, and Prevention

• Updated on  
• Dec 2, 2023

Landslides, also known as landslips, are the most destructive type of natural phenomenon that causes significant damage to human life and property. In simple words, landside refers to the massive movement of rock, debris, soil, or earth in a downward slop-like movement. This is because gravity is the primary driving force. Moreover, they can occur anywhere in the world but are specifically more common in mountain regions that have steep slopes. Now that we know about the landslide definition, let us explore the causes, effects, types, and prevention of landslides, 

Causes of Landslide

After the landslide definition comes its primary causes. Landslides generally occur when the slope undergoes some processes that change its overall condition and make it unstable. It can also occur when any type of shear stress exceeds the sheer strength of or the resistance strength of the materials that join to form the slope.

Natural causes of landslides include:

• Increase in water content due to snow or glacier melting 
• The rising of groundwater due to rainwater infiltration
• Loss of soil structure or nutrients due to wildfire 
• Erosion due to water bodies 
• Physical or chemical weathering 
• Earthquakes
• Volcanic eruptions 

Human activities that cause landslides include:

• Deforestation
• Over cultivation of land
• Heavy and consistent construction 
• Blasting and mining activities 

Also Read: What is a Natural Disaster? Types, Causes, Events

Effects of Landslide

The aftermath of a landslide can be extensive and unimaginable. 

• Landslides can lead to the loss of human lives. 
• It can cause destruction to the infrastructure of the affected regions.
• Landslide disasters can also damage natural resources.
• It can also block water bodies which further increases the risk of flooding. 
• Farmers can lose their crops and livestock which can deteriorate their living conditions. 
• It can also cause roadblocks and make transportation impractical. 

Types of Landslide

Interestingly, landslides are classified based on the type of movement they show. Generally, there are four types of movements such as falls, slides, topples, and flows. Let’s explore them in more detail.

Falls 

• Falls are sudden movements or landslides that include the breaking away of soil, debris, and rock from slopes and cliffs. 
• Characteristics of fall landslides include contents free falling from height through the air and bouncing and rolling over. 

Slides 

• As the name suggests, slides include the material slipping or dropping along a rupture or slip surface.  
• The top of this type of landslide has a scarp which is a steep drop as well as a flat portion behind it which is called the bench.
• Slide-type landslides are of two types, rotational slides (slumps) and translational (planar) slides. 

Also Read: What is Soil Erosion? Definition, Causes, Effects and Prevention

Topples 

• Topples are a bit different from other types of landslides.
• They include a mass of rock or debris falling in the forward direction out of a slope. 
• They are more common at the bottom of the block of the rock. 
• Ice melt and weathering can cause topple landslides. 

Flows 

• As the name implies, flow-type landslides include the mass movement of debris, soil, and rocks from a slop in the form of a fluid. 
• Flow landslides leave behind an upside-down funnel-shaped deposit. This place signifies where the material has stopped flowing. 
• It can include mud, debris, and rock avalanche flows. 

Also Read: What are 10 Ways to Reduce Pollution?

Prevention of Landslide Tips

The concept of prevention is better than cure goes for various aspects of our lives. For instance, although one cannot truly avoid landslides completely forever, numerous ways can mitigate their effects and help to reduce the frequency. Here is what the prevention of landslides includes:

• Steps can be taken to identify landslide-prone areas and ask the residents to vacate the area during monsoons. 
• Monitoring and warning systems can be made better. 
• The government can impose restrictions on heavy construction activities. 
• Deforestation should be avoided and awareness should be spread about the need for afforestation.
• Water drainage systems and management should be improved.
• Evacuation plans should be made in advance to deal with unforeseen situations. 

Also Read: Essay on Save Trees: Trees for Generation

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To explain the landslide definition in a few words, landslides are nothing but a large mass of soil, rocks, mud, and land that slide from the earth’s surface in a downward direction. This happens when external or internal shear stress somehow exceeds the resistance strength of the slope.

Landslides are of different types and can occur due to a wide range of reasons such as deforestation, earthquakes, an increase in water concentration, etc. Moreover, this sudden movement of massive earth, rocks, mud, and debris can cause major damage to human life, infrastructure, property, and more.  

The four types of landslides include falls, topples, slides, and flows. 

Hope you have fun learning this informative content on landslide definition, causes, types, effects, and prevention. For more information about such informative articles, check the  trending events  page of  Leverage Edu .

Parul Sharma

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Landslides are more widespread than any other geological event, and can occur anywhere in the world. They occur when large masses of soil, rocks or debris move down a slope due to a natural phenomenon or human activity. Mudslides or debris flows are also a common type of fast-moving landslide.

Landslides can accompany heavy rains or follow droughts, earthquakes or volcanic eruptions. Areas most vulnerable to landslides include:

• steep terrain, including areas at the bottom of canyons;
• land previously burned by wildfires;
• land that has been modified due to human activity, such as deforestation or construction;
• channels along a stream or river;
• any area were surface runoff is directed or land is heavily saturated.

Between 1998-2017, landslides affected an estimated 4.8 million people and cause more than 18 000 deaths. Climate change and rising temperatures are expected to trigger more landslides, especially in mountainous areas with snow and ice. As permafrost melts, rocky slopes can become more unstable resulting in a landslide.

Landslides can cause high mortality and injuries from rapidly flowing water and debris. The most common cause of death in a landslide is trauma or suffocation by entrapment.

Broken power, water, gas or sewage pipes can also result in injury or illness in the population affected, such as water-borne diseases, electrocution or lacerations from falling debris. People affected by landslides can also have short- and long-term mental health effects due to loss of family, property, livestock or crops.

Landslides can also greatly impact the health system and essential services, such as water, electricity or communication lines.

The magnitude of the physical and human costs from landslides can be reduced if adequate emergency prevention, preparedness, response and recovery measures are implemented in a sustainable and timely manner. 

WHO works with Member States to build resilient and proactive health systems that can anticipate the needs and challenges during emergencies so that they are more likely to reduce risks and respond effectively when needed. 

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Landslides pose a recurrent hazard to human life and livelihood in most parts of the world, especially in some regions that have experienced rapid population and economic growth . Hazards are mitigated mainly through precautionary means—for instance, by restricting or even removing populations from areas with a history of landslides, by restricting certain types of land use where slope stability is in question, and by installing early warning systems based on the monitoring of ground conditions such as strain in rocks and soils, slope displacement, and groundwater levels. There are also various direct methods of preventing landslides; these include modifying slope geometry, using chemical agents to reinforce slope material, installing structures such as piles and retaining walls, grouting rock joints and fissures , diverting debris pathways, and rerouting surface and underwater drainage. Such direct methods are constrained by cost, landslide magnitude and frequency, and the size of human settlements at risk.

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• Review Article
• Published: 21 July 2020

Life and death of slow-moving landslides

• Pascal Lacroix   ORCID: orcid.org/0000-0003-1282-9572 1 ,
• Alexander L. Handwerger   ORCID: orcid.org/0000-0001-9235-3871 2 , 3 &
• Grégory Bièvre 1  

Nature Reviews Earth & Environment volume  1 ,  pages 404–419 ( 2020 ) Cite this article

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• Natural hazards

In the most destructive and catastrophic landslide events, rocks, soil and fluids can travel at speeds approaching several tens of metres per second. However, many landslides, commonly referred to as slow-moving landslides, creep at rates ranging from millimetres to several metres per year and can persist for years to decades. Although slow-moving landslides rarely claim lives, they can cause major damage to infrastructure and sometimes fail catastrophically, transitioning into fast-moving landslides that can result in thousands of casualties. In addition, slow-moving landslides are highly erosive features that control the landscape morphology in many mountainous regions (such as the California Coast Ranges or the Apennines). The persistent and long-term motion of slow-moving landslides provides an exceptional opportunity to investigate landslide processes and mechanisms. In this Review, we examine the environmental conditions (such as geology, climate and tectonics) of slow-moving-landslide-prone regions, analyse the forcings (for example, precipitation and groundwater, earthquakes, river erosion, anthropogenic forcings and external material supply) that drive their motion and investigate the subsequent implications of the different forcings on landslide dynamics. We then discuss circumstances in which slow-moving landslides can accelerate rapidly, move large distances or even fail catastrophically. Finally, we provide new perspectives and challenges for future landslide research.

Slow-moving landslides occur all around the world in mechanically weak rock and soil.

The persistent and long-term motion of slow-moving landslides provides an exceptional opportunity to investigate landslide processes and mechanisms.

The landslide velocity is modulated by external forcings (such as precipitation, earthquakes, material supply and anthropogenic activity).

Slow-moving landslides can sometimes accelerate rapidly and fail catastrophically.

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Acknowledgements

Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA). P.L. and G.B. are part of LabEx OSUG@2020 (ANR10 LABX56).

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Lacroix, P., Handwerger, A.L. & Bièvre, G. Life and death of slow-moving landslides. Nat Rev Earth Environ 1 , 404–419 (2020). https://doi.org/10.1038/s43017-020-0072-8

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[Commentary] On the trail of the Wayanad landslide

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• On July 30, 2024, a massive landslide struck the Vellarimala hill ranges in Wayanad district, Kerala, causing fatalities and widespread destruction.
• Heavy rainfall triggered the landslide. Deforestation, land-use changes, improper drainage, and past landslides are contributing factors. Human activities like agriculture, construction, and quarrying have made the landscape more susceptible.
• Implementing site-specific land-use policies, managing natural drainage, and setting up local landslide early warning systems (LEWs), public awareness, community involvement, and advanced techniques like seismic noise imaging are crucial for understanding and mitigating landslide risks.
• The views in the commentary are that of the author.

It was like any other day in a rainy season. The people of Vellarimala hill ranges in the Western Ghats of Wayanad district of Kerala had little inkling of what was in store when they went to sleep on the night of July 29. They didn’t realise that the land under their feet was slowly beginning to shift. The ground finally slipped in its entirety in the early hours of July 30, which turned out to be the biggest landslip disaster in the history of Kerala.

The twin landslides – the initial slip at around 1 am and a more devastating one with gushing muddy water and massive boulders around 4 am wiped out the Mundakkai and Chooralmala settlements of Meppadi panchayat, killing more than 360 people at the time of writing and many missing, leaving a trail of destruction and transforming a green rolling hilly landscape into a valley of death and mayhem.

A landslip or landslide can be defined as the movement of rock, earth, or debris down a sloped section of land, caused generally by rain, although earthquakes and volcanoes can also trigger them. Landslides are also described as a type of mass wasting . The Mundakkai landslide disaster is the worst in Kerala’s modern history. The region experienced torrential rains of as much as 572 millimetres in about 48 hours before the event.

Landslides have become a common phenomenon in India’s southwest state of Kerala during the monsoon season. Some of them turn out to be massive and consequently disastrous, like the one that occurred in Mundakkai on July 30.

The satellite imagery released by the Indian Space Research Organisation (ISRO)’s National Remote Sensing Centre (NRSC) on August 1 indicates that about 86000 square metres of land have moved down the hill. The run-out zone stretches about eight km from the crown zone of the hills along the course of Iruvanjipuzha, a major tributary of the Chaliyar river that flows close to the impacted area. The pre-event images captured by the Cartosat 3 satellite on May 22, 2023, reveal the crown zone impacted by an older landslide. The post-event images were captured by the RISAT satellite a day after the landslip on July 31. The RISAT satellite is a radar imaging reconnaissance satellite built by the ISRO.

Previous studies in the area

An expert committee constituted by the Kerala government visited many sites in Wayanad and submitted a report in 2009. The report identified many factors that trigger landslides in the region.

The expert committee also visited sites in the Meppadi panchayat in Wayanad (from where the recent landslide disaster was reported) and found that proper drains were lacking for the movement of the stormwater. They cautioned that the area receives very high rainfall and that all the rainwater is filtered into the soil, which can cause piping (subsurface soil erosion), leading to rotational-type slide movement. The report reveals a previous landslide at Mundakkai, the site of the current disaster, in 1984 that claimed 14 lives and destroyed some agricultural land.

The satellite imagery released by the NRSC, mentioned earlier, also identifies the lobe of an old landslide. This imagery is convincing of the fact that the headwater region of the river has been the site of landslides in the past.

The location of the landslide in Mundakkai and Chooralmala was about 2-3 km from Puthumala , where a similar type of mass wasting had occurred on August 29, 2019, and killed 17 people. The post-landslide studies conducted by a group of researchers from the Central Coastal Agricultural Research Institute, Goa, published in 2020, indicated that the Puthumala event started as one of those smaller landslides deep inside the forest. It gained momentum in the lower reaches of the hill, where the soil structure was fragile and over-saturated with rainwater. It turned into a massive slide filled with rocks and mud, bringing down a part of the hill.

The way the landslide unfolded in Mundakkai on July 30, 2024, somewhat mimics its predecessor, the 2019 Puthumala event. While the high-intensity rainfall was the major trigger that acted as a tipping point in both these events, the Mundakkai event, which started as a minor event, picked up momentum and became a major disaster.

Factors causing landslides in Kerala

According to the researchers at the Department of Civil Engineering and Yardi School of Artificial Intelligence at the Indian Institute of Technology-Delhi, who developed the India Landslide Susceptibility Map (ILSM), 4.75% of India is very highly susceptible to landslides. Among the Indian states outside of the Himalayan region, Kerala is the most vulnerable to landslides. According to the landslide susceptibility map of Kerala, an area of 3300 and 2886 Sq. km.  is highly and moderately susceptible to landslides, respectively.

The changed climatic factors, like the intensification of short-duration heavy rainfall with increased atmospheric moisture, are dominant triggers for heavy landslides in Kerala. In addition to the intensity of precipitation, various hydraulic and mechanical properties of the topsoil can influence the occurrence or non-occurrence of a landslide. Studies indicate that the slope angle, shear strength of the soil (that depends on the grain size distribution and particle interlocking), and initial pore-water conditions have the greatest impact on slope safety. External forcings can perturb the natural factors and their impacts are generally determined by the scale of human activities brought about by land utilisation, construction, and agricultural activities. They affect the landscape, soil structure, and natural drainage, leading to slope instability and hydrologic properties such as surface runoff and infiltration.

One alternate view is that the recent Mundakkai landslide occurred inside a dense forest, and therefore, it was naturally formed with no contribution from anthropogenic activities . But the question here is why the smaller landslips at the top transformed into massive mass wasting at the lower levels of the slope along its flow path. This transformation could have happened because the water-carrying capacity of the soil at the lower levels deteriorated over the past several decades because of anthropogenic activities. This could be one possible reason why the 1984 landslide in Mundakkai did not spiral into a major one, as the integrity of the soil in that area was relatively better at that time.

Among the anthropogenic factors that affect the landscape, deforestation and alterations to the natural vegetation to prepare farmlands are critical. These activities to clear the land for cash crops like tea, rubber, coffee, and cardamom started during British rule. Over more than two centuries, these activities have gradually changed the soil and hydrological conditions in many parts of Wayanad, impacting the pattern of groundwater discharge. While the large trees were removed, their root systems remained buried. Over long periods, they have decayed, leaving large cavities, some of which are interconnected and act as fast subterranean flowage channels, causing soil piping and ground collapse. The lack of adequate measures to protect the soil profile adds to this problem. For example, in the absence of stubble mulching, which the local farmers do not practise, the soil gradually depletes in its organic content, facilitating faster hydraulic conductivity and rapid transport of subterranean water. Any fresh plantation activities also alter the infiltration and the water-bearing capacity of the underlying soil layers.  First, there is tilling and loosening of topsoil.  Then, there are arrangements for irrigation.

Take the case of rubber tree re-plantation, wherein mature trees are slaughtered after their lifespan and fresh saplings are planted. Both tilling of the land and irrigation are required, which are usually done by making rainwater pits. It is a common practice to use heavy machinery for these activities, which not only disturbs the soil structure but also increases infiltration and reduces surface runoff. Over time, the excessive infiltration facilitated by the water pits tends to weaken the contact of the overlying soil layer with the bedrock, triggering movements. Usually, this contact is marked by a layer of clay, which facilitates movement under wet conditions. Construction of poorly rubble masonry walls, houses, or other structures also obstructs the low-order drainage and restricts the natural surface runoff. Therefore, experts have recommended strict land use policies to avoid such pitfalls. Excessive quarrying also has a significant impact on the landscape, affecting the natural hydrological conditions. Quarrying removes topsoil, which is essential for sustaining the vegetation. The effects of using explosives and machinery such as backhoes to transport the material have adverse effects on the landscape. These activities create fresh fractures and open up older ones, altering the movement of water.  They eventually destabilise the ground, leading to increased soil erosion, which leads to the overall instability of the hill slopes. Although recognised to have many adverse effects, the impacts of quarrying are not well-documented, and they need to be studied in detail in the context of landslide hazards.

Mitigating risks

The frequency and individual sizes of landslides can be reduced by following site-specific and scientific utilisation of land considering the carrying capacity of hilly terrains. Natural drainage management should also be a priority. It is important to collect historical and geological data on the previous landslides, if any, from the vulnerable regions. In hindsight, the information on the 1984 Mundakkai and the 2019 Puthumala landslides, which occurred near Mundakkai, should have been appropriately used to model the landslide vulnerability of the region. This should have helped to understand the possible scale of a future incident and caution the public. In such a scenario, the pre-identified slopes could have been treated as sites to establish local landslide early warning systems (LEWs) to monitor the slope movement. It is also imperative to collect site-specific data on the varying thicknesses of the soil profile and understand its compositional and water percolation properties. A more intense network of rain gauges and arrangements to monitor surface runoff and infiltration could help in monitoring the surface and groundwater movements. If such experiments are successful, they would help to establish the threshold relationship between slope properties and the likelihood of a landslide. Seismic noise imaging is another useful technique to estimate the thickness and water-bearing capacity of the underlying soil layers and their vulnerability to sliding. In the Idukki region of Kerala, where rains have selectively triggered landslides in 2018, hill slopes with shallower soil profiles were found to be more prone to sliding. In contrast, regions with thicker soil profiles seemed stable. Such techniques that correlate subsurface conditions with incidences of landslides help to make an inventory of triggering conditions.

Creating public awareness is an important factor in risk reduction. High-resolution maps depicting landslide vulnerability should be brought to the attention of residents.  It is also important to involve community groups in the discussions on risk reduction, capacity building, and disaster resilience. An exemplary example of community participation in the forecast efforts originated near Mundakkai, the site of the current landslide disaster. The investigators at the Hume Centre for Ecology and Wildlife Biology at Kalpetta, Wayanad, were able to issue a warning to the district authorities regarding the landslide about 16 hours before the event. They used the measure of rainfall from their rain gauge established in Puthumala, not far from Mundakkai. They found that the rainfall was about 572 mm, more than what was measured when the landslide occurred at Puthumala in 2019. The warning, however, was not taken seriously by the district authorities. An effective approach to disaster mitigation efforts involves fostering the participation and empowerment of community members. The Wayanad disaster should mark the beginning of a new learning curve.

The author is an adjunct professor at the National Institute of Advanced Studies, Bengaluru, and the director of the Consortium for Sustainable Development, Connecticut, U.S.A.

Banner image: Rescue efforts underway in Wayanad. Image by Public Relations Department Government of Kerala.

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Wayanad landslide tragedy: Balancing nature and development

The serene and picturesque district of Wayanad, Kerala, recently witnessed a catastrophic landslide, leading to immense loss of life and property. On the fateful night of July 30, 2024, Wayanad, known for its lush greenery and scenic landscapes, was struck by a massive landslide. Triggered by incessant rainfall over several days, the landslide wreaked havoc in the Meppadi area in Chooralmala and Mundakkai, burying houses, roads, and farmlands under tons of mud and debris.

The immediate aftermath was a scene of devastation – collapsed buildings, uprooted trees, and a desperate search for survivors. Rescue teams are battling treacherous conditions, including waterlogged terrain, as they comb through the ruins of homes and buildings searching for missing people.

NRSC has quantified the destruction caused by the Wayanad landslide  through before-and-after images, indicating a land displacement of around 86,000 square meters in Chooralmala. High-resolution satellite images from July 31st provide a clear picture of the landslide in Wayanad, revealing an 8-kilometer debris flow from its origin to its endpoint. The powerful force of the debris flow has widened the Iruvaniphuza River, causing its banks to collapse and damaging nearby homes and infrastructure, according to NRSC. The NRSC images reveal evidence of an earlier landslip that got reactivated in the same area, highlighting its susceptibility to such events.

A staggering 49.7% of Kerala, equivalent to 19,301 square kilometers, is susceptible to landslides , according to the Geological Survey of India. According to the National Centre for Earth Sciences, a significant portion of Kerala – approximately 4.71% – is classified as highly susceptible to landslides . An additional 9.77% of the state is considered to be at low risk. The talukas of Devikulam, Vythiri, Nilambur, Mannarkkad, and Ranni are hotspots for landslide occurrences.

Out of the thirty most landslide-susceptible districts nationwide, ten are in Kerala, including Wayanad at number thirteen, as per the landslide atlas released by the Indian Space Research Organisation's (ISRO) National Remote Sensing Centre last year . A staggering 59% of Kerala's landslides occur in plantation areas, highlighting the region's vulnerability. Studies reveal that 90,000 square kilometers of the Western Ghats and Konkan coast are susceptible to landslides. The report emphasises the heightened risk to residents in this region , particularly in densely populated Kerala.

Kerala has grappled with severe landslide crisis in the past also, with 2,239 incidents recorded between 2019 and 2022 . These disasters have resulted in significant loss of life, widespread agricultural devastation, and a substantial financial burden on the state government. A Geological Survey of India report details the tragic loss of 167 lives in five major landslides between 2019 and 2021 . However, the Kerala State Disaster Management Authority has reported no major landslide incidents in the past two years.

Climate change, coupled with the state's fragile terrain and deforestation , created the ideal conditions for the catastrophic landslides in Wayanad. The Wayanad tragedy, a direct result of relentless rains underscores the vulnerabilities of hilly regions to natural disasters. Global warming has intensified monsoon patterns, with increased frequency and intensity of rainfall events. Climate change-induced anomalies have made traditional weather predictions unreliable, leaving communities unprepared for such extreme events.

Wayanad, receiving heavy monsoon rains annually, experienced a significant deviation from its usual pattern, with intense downpours within a short span, leading to soil saturation and eventual collapse. A research from 2022 “ West coast India’s rainfall is becoming more convective ” indicates that this “may be connected to Arabian Sea warming, greater instability, and strengthened monsoon ascent over western India.”

Despite an orange alert issued by the India Meteorological Department (IMD), Wayanad district was inundated with over 500 mm of rainfall , far surpassing the forecasted amount, leading to catastrophic landslides. Wayanad's hilly terrain, coupled with loose soil composition, makes it susceptible to landslides. The steep slopes, when saturated with water, lose their stability, causing massive soil displacement.

The region has witnessed extensive deforestation for agriculture, plantations, and construction. The removal of vegetation , which acts as a natural stabilizer for the soil, has exacerbated the risk of landslides. A stark decline in Wayanad's forest cover has been documented. Once boasting approximately 85% forestation in the 1950s, the district experienced a dramatic loss of 62% of its green cover by 2018, according to a 2022 study published in the International Journal of Environmental Research and Public Health . Conversely, plantation coverage surged by a staggering 1,800% during the same period, the study said. Additionally, unplanned and rapid urbanisation has disturbed the natural drainage patterns, further destabilising the slopes .

Despite being a known landslide-prone area, the lack of robust early warning systems and preparedness measures significantly contributed to the scale of the tragedy. The absence of timely evacuations left many residents vulnerable.

Immediate impact and long-term consequences 

The landslide claimed over 250 lives so far, with many still missing. Rescue operations faced challenges due to the continuous rainfall and difficult terrain, hampering efforts to locate survivors buried under the debris. Hundreds of houses were destroyed or severely damaged. Critical infrastructure, including roads, bridges, and communication networks, was disrupted , isolating affected areas and complicating rescue and relief operations. Thousands of residents were displaced, forced to seek shelter in relief camps.

The destruction of agricultural land and plantations, the primary sources of livelihood for many, will plunge the local economy into distress. The landslide not only displaced human settlements but also caused significant environmental damage. Uprooted trees and vegetation loss have long-term ecological consequences, affecting biodiversity and local ecosystems.

The economic consequences of the landslide are far-reaching and profound. Beyond the immediate relief efforts, the arduous task of rebuilding homes, infrastructure, and agricultural livelihoods lies ahead. Smallholder farmers, plantation workers and others face a protracted recovery, jeopardising their economic stability. The toll on survivors, who have endured the loss of loved ones and homes, cannot be overstated.

Lessons learned and future directions

The Wayanad landslide tragedy has underscored the critical need for a comprehensive approach to disaster management and environmental sustainability. One of the primary lessons is the importance of investing in advanced meteorological and geological monitoring systems . Also, remote sensing technologies need to be complemented with on-ground sensors to anticipate landslides.

A recent study “Integrating real-time sensor data for improved hydrogeotechnical modelling in landslide early warning in Western Himalaya” , has developed a site-specific landslide early warning system with a specific focus on Chamoli’s unique landslide risks. This system emphasises the crucial role of real-time monitoring in assessing slope stability. By combining hydrogeological data with advanced machine learning techniques, the system can provide early warnings. There is a need to learn from such systems that incorporate climate and vegetation factors to improve landslide prediction accuracy.

These technologies can provide early warnings about potential landslides and other natural disasters, allowing for timely evacuations and thereby minimizing loss of life. For instance, real-time data collection and analysis can help predict heavy rainfall patterns and soil movement, providing crucial information to authorities and residents in vulnerable areas.

Community-based alert systems, which leverage local knowledge and resources, can significantly enhance preparedness . These systems involve training local volunteers to monitor environmental changes and disseminate warnings quickly. Such grassroots initiatives ensure that even remote communities receive timely alerts, bridging gaps that larger, centralised systems might miss.

Enforcing strict regulations against deforestation is vital in reducing landslide risks. Forests play a crucial role in stabilizing soil and maintaining the ecological balance. A government-appointed panel led by Madhav Gadgil proposed in 2011 that 75% of the Western Ghats, known for its rich biodiversity, be designated as an environmentally sensitive area. However, these recommendations were never implemented. Large-scale reforestation and afforestation projects are necessary to restore ecological balance.

Also, when disaster strikes, knowing what to do can mean the difference between life and death. That's why it's so important to prepare everyone in a community , from the youngest to the oldest. Practice drills, teach people what to do in an emergency, and make sure information is easy to find. Schools and community centers are perfect places to spread the word and make sure everyone feels prepared. By working together, we can build stronger, safer communities.

The heartbreaking loss of lives in the Wayanad landslide is a stark reminder that we must rethink how we live with nature. It's clear that we need to do more than just react to disasters; we need to prevent them. This means investing in smart systems to warn us of potential dangers, protecting our forests, and making sure our communities are ready for what nature throws our way. 

Science News by AGU

The 30 July 2024 Wayanad landslides in Kerala, India

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The Landslide Blog is written by Dave Petley, who is widely recognized as a world leader in the study and management of landslides.

On 30 July 2024, heavy rainfall triggered landslides in the Wayanad district of Kerala, India. At the time of writing, the confirmed loss of life has reached 392 people, with a further 150 people reported to be missing. In addition, there were at least 273 injuries.

The event is sufficiently significant that it has its own Wikipedia page , which reports 570 mm of rainfall in the two days leading up to the tragedy. The area affected, including the villages of Punjirimattom, Mundakkai, Chooralmala, Attamala, Meppadi and Kunhome, consists of tea farms built on steep slopes. Many of the people killed were worked in the farms, or were members of their families.

Obtaining optical satellite imagery of the area affected is extremely difficult during the monsoon period, but ISRO has released radar images of the site:-

The left (false colour optical) image shows the site prior to the 30 July 2024 event, whilst the image on the right provides radar data that shows the area after the Wayanad landslides. The Google Earth image below shows the site in April of this year:-

The location of the headscarp is [11.46544, 76.13576]. The images before the 30 July 2024 shows the presence of a long runout, channelised flow, which appears to have occurred in 2020. The landslide did not quite reach Mundakkai. As the ISRO imagery shows, the initial failure for the 30 July 2024 event occurred on the same slopes, but on a much larger scale, creating a series of channelised debris flows that ploughed through the villages.

The ISRO analysis suggests that the landslide covers an area of 86,000 m 2 , with a runout of 8 km.

The Indian Express has posted a video that shows drone footage of the aftermath of the landslides :-

The images are devastating. The scale of the disaster is revealed in this portion of the video:-

The Wikipedia article reveals a very strange element to the response to this disaster:-

“The Kerala state government issued an order to scientific and technology institutions prohibiting scientists from visiting the site or discussing the landslides or their potential causes. It said that prior approval from the Kerala State Disaster Management Authority would be required before beginning any research in a region affected by a disaster. Hours later, the gag order was revoked unconditionally. “

It is deeply unhelpful to hinder the efforts of the research community to understand the causes of landslides of this type.

Text © 2023. The authors.  CC BY-NC-ND 3.0 Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

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