Sciency Thoughts: Cox's Bazae

Sunday, 23 July 2017

Student killed by landslide at Himcchahari in Cox's Bazar District of Bangladesh.

A second year student at Dhaka University was killed and two others injured after a landslide close to a waterfall at Himchhari in the Cox's Bazar District of Chittagong, Bangladesh, on Saturday 22 July 2017. Sabbir Alam Ridwan was hit by a collapsing hillside at about 4.30 pm local time, and reportedly died instantly of head injuries. The two other students were treated for injuries in a local hospital. The incident happened after two days of heavy 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.

Sabbir Alam Ridwan of Dhaka University, killed by a landslide at Himchhari in Cox's Bazar on 22 July 2017. The Daily Star.

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.

Seven confirmed deaths and around 150 missing after Cyclone Mora makes landfall in Bangladesh.

Seven people have been confirmed dead and about 150 are still missing after Cyclone Mora made landfall in eastern Bangladesh on Tuesday 30 May 2017. The cyclone caused widespread flooding in Chittagong and Cox's Bazar districts, washing away many homes in low lying areas. Coastal communities and Rohingya refugees living in camps close to the border with Myanmar are thought to have been the worst hit. Most of the missing people are fishermen caught at see by the storm; ships from the Indian and Bangladeshi navies are searching for survivors.

Damaged homes in Cox'x Bazar district following Cyclone Mora. Munir Uz Zaman/Reuters.

Tropical storms 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.