Wednesday 26 July 2017

Five killed by landslide at Ramu in Cox's Bazar District of Bangladesh.

Five people have been killed and another five injured by a landslide in the village of Ramu in the Cox's Bazar District of Chittagong, Bangladesh,which occurred at about 3.00 am local time  on Tuesday 25 July 2017. Two of the dead have been identifies as children aged five and seven, who were buried when a mass of mud engulfed their home, with their parents among the injured. In the 24 hours before the incident the area received about 20 cm of rain, associated with the Asian summer monsoon. Landslides are a common problem after severe weather, 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 approximate location of the 25 July 2017 Cox's Bazar landslide. Google Maps.

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.

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