Raigad landslides

Subject: Geography

Section: Physical geography

Context: Recent Raigad landslides

Landslide Causes

Geological causes
- Weak or sensitive materials
- Weathered materials
- Sheared, jointed, or fissured materials
- Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, contact, and so forth)
- Contrast in permeability and/or stiffness of materials
Morphological causes
- Tectonic or volcanic uplift
- Glacial rebound
- Fluvial, wave, or glacial erosion of slope toe or lateral margins
- Subterranean erosion (solution, piping)
- Deposition loading slope or its crest
- Vegetation removal (by fire, drought)
- Thawing
- Freeze-and-thaw weathering
- Shrink-and-swell weathering
Human causes
- Excavation of slope or its toe
- Loading of slope or its crest
- Drawdown (of reservoirs)
- Deforestation
- Irrigation
- Mining
- Artificial vibration
- Water leakage from utilities

Types of Landslides

Falls: It happens due to the abrupt movements of the mass of geologic materials, such as rocks and boulders, that become detached from steep slopes or cliffs.
Topples: It happens due to the forward rotation of a unit or units about some pivotal point, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks.
Slides: In this type, rocks, debris, or soil slide through slope forming material.
Spread: It usually occurs on very gentle slopes or flat terrain.

Landslides and India

Landslides and avalanches are among the major hydro-geological hazards that affect large parts of India.
Around 15% of the country’s region is prone to landslides. The Himalayas of Northwest and Northeast India and the Western Ghats are two regions of high vulnerability.
Some major recent incidents are Kerala (2018), Himachal Pradesh (2018), Uttarakhand (2018), Tamenglong-Manipur (2018), and Kalikhola, Manipur (June 2017).