Sunday, 18 November 2018

Landslide kills four in Tamil Nadu.

Four workmen have died in a landslide in the Dindigul District of Tamil Nadu on Saturday 17 October 2018. The four men were staying in a temporary shelter at Chinnapallam, near Kodaikanal, when a section of hillslope collapsed onto it, killing them. The men have been identified as Ravi, 50, Rajendran, 48, Soundararajan, 40, and Karthik, 21, all from the city of Salem 200 km to the northeast of the effected area. The incident occurred following heavy rains in Tamil Nadu associated with Cyclone Gaja, which swept across the state the day before. 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. 

Temporary shelter for workers hit by a landslide in Dindigul District, Tamil Nadu, hit by a landslide on Saturday 17 November 2018, killing four men. Times of India.

Tropical storms (referred to as Cyclones in the Indian Ocean) are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

Hillside above the landslide that killed four workers in Dindigul District, Tamil Nadu, on Saturday 17 November 2018. The Hindu.

 Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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