Sunday, 14 August 2016

Thousands evacuated after landslide dams river in Sikkim, India,

Thousands of people have been forced to evacuate their homes in Sikkim and West Bengal after a landslide blocked the River Kanaka in the Dzongu Forest in East Sikkim District, above the Teesta Low Dam Project, threatening the towns of Teesta, 29 Mile, Dikchu, Makha, Singtam and Rangpo on Saturday 13 August 2016. The landslide dam is about 50 m wide, and has created a new dam lake which has submerged the Kanka Bridge and parts of the villages of Mentyam and Lingthem, as well as about 300 m of roads.

Cloud of duct created by the 13 August 2016 River Kanaka landslide. Voice of Sikkim.

The River Kanaka is a tributary of the River Teesta which joins it above the Teesta Low Dam Project, a hydroelectric dam operated by the state-owned National Hydroelectric Power Corporation Ltd. The dam reservoir has been emptied as a precaution, though dams of this type are not intended to stop sudden floods of this kind.

The flow of the Kanaka River in Upper Dzongu from Singhik view point, before and after the 13 August 2016 landslide. Darjeelig News.

August is peak monsoon season in East Sikkim District, with rainfall for the month averaging 574 mm. 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.

 Debris from the 13 August 2016 Kanaka River landslide. Village of Mentyam in the foreground. Voice of Sikkim.

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.  

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

See also...

http://sciencythoughts.blogspot.co.uk/2016/08/ninety-one-confirmed-deaths-in-bihar.htmlNinety-one confirmed deaths in Bihar flooding.                                                Ninety-one people have been confirmed dead in flooding in Bihar State this Monsoon Season. Twenty eight of these deaths have been recorded in Purnea...

http://sciencythoughts.blogspot.co.uk/2016/07/woman-killed-by-landslide-in-guwahati.htmlWoman killed by landslide in Guwahati, Assam.                                                            A woman has been killed by a landslide in the Chandmari District of Guwahati, in Assam State, India, on Wednesday 20 July 2016. Malati Das was killed when her home was engulfed by a...
http://sciencythoughts.blogspot.co.uk/2016/01/landslide-kills-one-in-darjeeling.htmlLandslide kills one in Darjeeling District, West Bengal State, India.                                        One person has died and another five have been treated for injuries following a landslide at Bhotey Bhir in Darjeeling District, West Bengal State, India...
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