Three people have died and several more are missing following a landslide in Assam State, India, on Saturday 14 May 2022. The incident happened in the evening when part of a hillslope in Dimo Hasao District collapsed following several days of heavy rain in the area associated with the Indian Monsoon Season. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.
The incident comes amid widespread flooding in Assam, which has displaced thousands of people in five districts, and at least eighty homes destroyed in 10 villages. Numerous roads and rail lines have been swept away, severely hampering travel within the state. Monsoon Season typically lasts from May to October each year in Assam, and frequently brings with it flooding and related events. However, this year many areas of the state also had unusual pre-monsoonal rains through much of April, which led to the ground already being waterlogged by the time the monsoon arrived, and therefore a much more rapid onset of flooding problems.
Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea.
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