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The Himalaya, as the name echoes in the mind, gives a picture of abundant snow, glaciers, high mountain peaks, breathtaking hilly landscapes, lush green forests, rich biodiversity, perennial rivers, water streams, deep river valleys, hard rocks and above all, a soothing place where one can rejuvenate oneself through exploring the nature, taking the adventure of trekking, mountain climbing or meditating in the serene environment. The Himalayas represent a unique ecosystem, protecting us from the extremities of weather. The Himalayan range stretches across five countries: India, Nepal, Bhutan, China, and Pakistan and covers approximately 2,400 km from west to east.
However, in the last few decades, the Himalayan region has witnessed a frequent and increased number of disasters,
which signal something unwarranted is happening to this ecosystem. In order to understand the reason, let us briefly understand how the Himalayan mountain system evolved and why natural hazard is part of this region.
GEODYNAMICS
The earth has continuously evolved to its present state through continuous geodynamic earth system processes operating into it over a journey of approximately 4.6 billion years. These processes are still working and continuously shaping the earth. That’s why we call the earth an active planet. Plate tectonics theory explains the present shape and position of the landmasses on the earth, which were arranged together as a single unit, called Pangea, in the southern hemisphere around 230 million years ago. The Pangea broke apart in several parts due to various internal and external processes associated with the earth. These broken plates started moving northward due to convection currents deep inside the earth. The convergence of the Indian and Eurasian plates caused the collision of two continents (approximately 50 Ma). The Himalayas, the youngest mountain belt and most fragile mountain system on earth, are a byproduct of this collision. The convergence is still going on, and the Indian plate is continuously pushing the Eurasian plate. Due to this continuous convergence, stress is accumulating in the Himalayan crust. Subsurface rocks accumulate these stresses up to the threshold limit. Once the threshold is reached, stress is released. This release of energy is reflected as earthquakes.
Besides these stress accumulations, other geological processes like weathering, erosion, sedimentation, and climate tectonics interplay are the driving factors that continuously operate on different spatio-temporal scales. This makes
the Himalayan mountain system tectonically active where both endogenous and exogenous processes are giving shape to its topography.
The Himalayan region is highly prone to different natural hazards due to its rugged terrain, seismic activity, high levels of precipitation, and human interventions. These factors create a delicate balance but can trigger catastrophic landslides, flash floods, cloud bursts, etc., when disturbed. These events pose a severe threat to the ecosystems, human settlements, infrastructure, and the overall environmental stability of the region. Over the last decade, more than 10,000 casualties have been caused by landslides in the Himalayas.
Each Himalayan region has its history of natural hazards. In Uttarakhand, for instance, the first reported landslide occurred in Nainital in September 1880 due to which as many as 151 people lost their lives.
In July 1983, extreme rainfall caused the flood in the Karmi because of which the mobilised slope debris created a 40
m high landslide dam that impeded the flow of the river. Within a short period of time, the dam burst and killed 150 people and 20 animals.
18 August 1998 was the most dreadful day for the Malpa Village. On that day a huge rain-induced rock fall killed 250 people and buried 800 cattle under 90 m of heavy debris. Similarly, severe rain in the Madhmaheshwar Valley destroyed the villages of Benti and Pundar and blocked the flow of the Madhmaheshwar river. In this disaster, 101 people and 500 animals were killed.
Who can forget the disaster of June 2013, popularly known as the Kedarnath disaster? The convergence of mid-latitude westerlies and the Indian summer monsoon caused the heavy rainfall on 16 and 17 June 2013. This heavy rain resulted in flash floods in many streams and rivers causing several new and reactivated landslides in various parts of the state. The intensity and magnitude of this disaster destroyed the state’s infrastructure, and the catastrophic landslides generated a massive amount of sediment in the mountain terrain, leading to flash floods and great damage to infrastructure.
In 2023, Himachal Pradesh experienced one of its worst disasters due to extreme weather situations leading to devastating landslides, widespread damage and collapse of several buildings. News of the disaster was pouring
in from every corner of the state but Kullu, Mandi, Shimla, Sirmaur, Solan and Chamba districts were some of the
worst affected.
The above are very few examples of natural hazards in the Himalayan region. Although the immediate cause seems to be excessive rainfall, there are other factors that cause slope destabilization in the region. Let us understand the landslide phenomenon in simple words, its causes, impacts, mitigation strategies, and future outlook regarding
landslides in the Himalayas.
LANDSLIDE
A landslide is defined as a mass movement (of soil, rocks and other material) on a slope due to gravity. Although there is considerable debate on the definition of landslide considering various technicalities, mass movement along a slope or along a weak plane is the gist of all definitions.
The Himalayan mountain system is the youngest mountain system on the earth, and therefore, the rocks of the region are fragile. The steep slopes of the Himalayas are composed of a variety of rocks, including schists, gneisses, quartzites, and granites. These rock types have different strengths, which vary in their resistance to weathering
and erosion, leading to differential erosion rates that can weaken slopes over time. Moreover, jointed and fractured
rocks create zones of weakness, which are prone to failure, particularly when exposed to heavy rainfall or earthquakes.
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The Himalayan region experiences several types of landslides, each of which can have devastating consequences. The most common types of landslides in the region are:
- Rockfalls: When a large mass of rock becomes dislodged from a slope and falls down the mountain, it is known as a rockfall. Rockfalls are particularly dangerous along roads and highways, where they can block roads or damage vehicles and infrastructure.
- Debris flows: Debris flows are fast-moving masses of mud, rocks, and other materials that flow down slopes during heavy rainfall or rapid snowmelt periods. These flows can bury entire villages and cause widespread destruction.
- Slumps: A slump is a type of landslide where a mass of earth moves down a slope in a rotational manner. This type of landslide is slower and less destructive than debris flows but can still cause significant damage to infrastructure and agriculture.
- Creeps: Creep is the slow, gradual downhill movement of soil and rock. Although this process is much slower than other types of landslides, it can cause long-term damage to buildings, roads, and pipelines.
- Glacial Lake Outburst Floods (GLOF): A Glacial Lake Outburst Flood, or GLOF, is a sudden release of water from a lake fed by glacier melt that has formed at the side, in front, within, beneath, or on the surface of a glacier. GLOF events occur in higher reaches of mountains, but they remain a persistent threat to downstream communities.
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FACTORS FOR LANDSLIDE
Climate
During the rainy season, flash floods and landslides usually occur due to extreme rainfall events. The climate of the Himalayas is characterised by a distinct monsoon season, which brings heavy rainfall to the region, particularly between June and September. The intense rainfall saturates the soil, increasing pore water pressure and reducing the shear strength of the slope materials. This often results in shallow landslides, where the top layer of soil and debris slides down the slope. However, the entire slope can fail in some cases, leading to large-scale landslides.
At the end of the month of July 2024, people in Wayanad, Kerala, witnessed the deadliest landslides. The main cause of these series of landslides was torrential rainfall. Because of the collapsed slopes, debris flow consisting of mud, water and boulders engulfed the villages located downslope causing more than 420 casualties, 397 injuries and more than 120 people missing.
Glaciers
Glacial meltwater also contributes to landslides in the Himalayas, particularly in the higher reaches of the mountains. The glaciers in the region are receding due to climate change, and the meltwater can infiltrate the ground, lubricating the slopes and triggering landslides. In some cases, glacial lake outburst floods (GLOFs) occur when the natural dam of a glacial lake fails, releasing a large volume of water that can erode slopes and cause landslides downstream.
Anthropogenic Activities
Human activities have exacerbated the occurrence of landslides in the Himalayas. Deforestation, unplanned urbanization, and infrastructure development, such as roads, dams, and hydropower projects, have all contributed to slope destabilisation directly or indirectly. The construction of roads and highways in the Himalayas often involves cutting into steep slopes, which disturbs the natural slope stability and can trigger landslides. The excavation of materials, improper drainage systems, and the use of heavy machinery further destabilise the slopes. The earthquakes that occur frequently in the region also interact with these weakened slopes, causing massive landslides.
Deforestation
The forests play a crucial role in stabilising slopes by binding the soil with their roots and reducing surface runoff. However, rapid deforestation in the region has stripped the slopes of their natural protective cover.
IMPACT OF LANDSLIDES
The impacts of landslides in the Himalayas are widespread and far-reaching, affecting not only human populations but also the environment, economy, and infrastructure.
Mitigation Strategies
Mitigating the risk of landslides in the Himalayas requires a multifaceted approach that includes both structural and non-structural measures. While it is impossible to completely eliminate the risk of landslides, the following strategies can help reduce their frequency and impact.
i. Focused Research
Researches undertake landslide susceptibility mapping to infer the probability of landslide in specific areas. Most of the susceptibility mapping is based on satellite images. This should include field base parameters along with geophysical mapping of susceptible zones. Research should be focused toward understanding the landslide process in real time rather than reporting events.
ii. Early Warning System
One of the most effective ways to mitigate landslides is to implement early warning systems that can detect the signs of an impending landslide. These systems use a combination of sensors, satellite imagery, and ground observations to monitor changes in the slope and weather conditions. When a landslide is imminent, warnings can be issued to the affected communities, allowing them to evacuate and take protective measures.
iii. Slope stabilization
To stabilize the slopes in order to prevent landslides, structural measures such as retaining walls, terracing, and rock fall barriers need to be implemented rigorously. These measures are particularly important along roads and highways, where landslides are more likely to occur. Additionally, reforestation and afforestation efforts can help stabilize slopes by restoring the natural vegetation that holds the soil in place.
iv. Land use planning
This includes restricting development in high-risk areas and enforcing building codes that require structures to be designed to withstand landslides. In some cases, it may be necessary to relocate entire communities away from vulnerable slopes. Efforts should be made to define the carrying capacity of the region.
v. Community preparedness & awareness
Educating communities about the risks of landslides and how to prepare for them is a key component of disaster mitigation. This includes training local residents in emergency response procedures, such as evacuation and first aid. There must be efforts in raising awareness about the importance of maintaining slope stability through reforestation and proper drainage management.
vi. Adaptation
Given the Himalayas’ tectonic activity, integrating seismic risk management with landslide mitigation strategies is essential. Additionally, climate adaptation plans should consider both the increasing rainfall due to climate change and the retreating glaciers, which both aggravate landslide risks.
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Landslides in the Himalayas are a natural consequence of the region’s geology, climate, and tectonic activity. However, human interventions and climate change have aggravated the frequency and intensity of these events. It is therefore crucial to adopt a holistic approach that combines traditional knowledge with modern technology to mitigate the impacts of landslides in the region. This will involve strengthening early warning systems, promoting sustainable development practices, enhancing community preparedness, and investing in research to better understand the complex dynamics of landslides.
As climate change is the bitter truth for the world today, it is expected that the frequency and intensity of landslides will increase in the Himalayas. Glaciers will continue to retreat, monsoon patterns may become more erratic, and extreme weather events will become more common. Therefore, it is essential that governments, communities, and international organizations work together to develop long-term strategies for landslide risk management in the Himalayas.
*The writer is Scientist ‘E’ at the Wadia Institute of Himalayan Geology.
