3.2.3. Landslides and Man Induced Landslides

Landslides always exist on this planet and the term landslide is used to describe a wide variety of processes that result in a downward movement of rocks under gravitational forces. In other words, mass movement of rocks, debris, and soil down a slope of land.

A landslide is a natural phenomenon where a large amount of earth material such as rocks, soil, and debris slide down a slope. This happens because of gravity pulling the material down. Landslides can occur in many places but are mostly associated with steep slopes where the downward pull is strong enough to move the heavy materials. They can be triggered by various factors such as heavy rain, earthquakes, volcanic eruptions, and human activities.

Think of a pile of sand on a beach. If you keep adding more sand to the top of the pile, at some point, it will become too heavy and start to slide down. Similarly, when the conditions are right, rocks and soil can start to slide down a hillside, especially when they become wet from rain.

Landslides are primarily associated with steep slopes. Surface run-off and changes in drainage also cause landslides. Landslides can also be initiated by rainfall; earthquakes; volcanic activity, changes in groundwater movement or any combination of these factors.

Several natural factors can lead to landslides. Steep slopes are the most common areas for landslides. Heavy rain can saturate the ground, making it easier for soil and rocks to slide. Earthquakes shake the ground, which can disturb loose materials. Volcanic eruptions can displace soil and rocks. Additionally, if groundwater levels change, they can destabilize a slope’s materials, causing a landslide.

Imagine a steep hill after a heavy rainstorm. As the ground gets soaked, it becomes slippery. If enough water accumulates, it’s like someone pushing a pile of wet sand - it could easily slide down. Similarly, an earthquake can shake the hill and cause the earth to tremble and slide.

Debris-flows can travel down a hillside at speeds up to 200 miles per hour (more commonly, 30 – 50 miles per hour) depending on the slope angle, water content, and type of earth and debris in the flow.

Debris-flows refer to a mixture of water, soil, and debris that flows rapidly down slopes. The speed of this movement can vary greatly. On steep slopes with lots of water, debris-flows can reach very high speeds, potentially resulting in significant destruction. The speed also depends on the type of materials in the flow; loose and wet debris flows faster than dry and compact debris.

Picture a mudslide after it rains heavily. If it's very wet and the slope is steep, it can rush down like a fast-moving river, creating a powerful flow that can sweep away anything in its path, much like how a rushing river can carry away branches and debris during a flood.

While landslides are a naturally occurring environmental hazard they have recently increased in frequency in certain areas due to human activities. Building excavations collapses in mining (e.g.: coal mine) causes landslides. However, landslides can be triggered by human beings by induced changes in the environment.

Humans can inadvertently contribute to landslides through activities such as construction, mining, and deforestation. When we excavate the ground to build structures, it removes the stability of the soil, making it more susceptible to sliding. Similarly, cutting down trees removes roots that hold the soil together, which increases the risk of landslides. These actions have led to an increase in landslides in areas that were once stable.

Think of a tall tower of blocks that’s been built up; if someone takes a few blocks away from the bottom quickly, the whole tower can start to topple over. This is similar to what happens with hills; when we remove vegetation or change the ground structure, it can lead to landslides.

Simply landslides can be explained in three ways: (a) Inherent of rocks (weakness in the structure of a rock); (b) Due to heavy seismic or volcanic activity; (c) Due to various environmental conditions.

Landslides can result from several inherent weaknesses in the local geology. Faulty rock structures can make areas more prone to landslides. Additionally, landslides can be triggered by natural disasters like earthquakes and volcanic activity, which disturb the ground. Environmental conditions such as heavy rains or rapid snowmelt can also lead to instability, making it easier for debris to slide.

Think about a structure built on a shaky table. If someone bumps the table (like an earthquake), any items on it might fall. Similarly, rocks in the earth can have weak points that are disturbed by earthquakes or heavy rain, causing landslides.

--