Monday 8 August 2016

Landslides kill at least 40 as Tropical Storm Earl makes landfall in Mexico.

At least 40 peoplehave died in the Mexican states of Puebla and Veracruz after Tropical Storm Earl made landfall on Saturday 6 August 2016, brining heavy rain across the region. The highest number of casualties happened in the township of Huaucinango in northern Puebla State, where a number of mudslides and hillslope collapses occured. Three people also died in the nearby town of Tlaola. 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 aftermath of a landslide at Xaltepec in northern Puebla on 7 August 2016. Pablo Spencer/AP.

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.

 Damaged homes at Huauchinango in northern Puebla after a landslide on 7 August 2016. Reuters.

The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides.

See also... on Mount Popocatépetl                 The Mexican National Centre for Disaster Prevention reported an  eruption on Mount Popocatépetl, a stratovolcano (cone shaped volcano made up of layers of ash and lava) in the central part of the country, on Sunday 12 June 2016. This began with the... on Mount Popocatépetl.             Mount Popocatépetl in southern Mexico underwent a major eruption on Monday 18 April 2016, producing a column of ash rising 3 km above the summit and throwing incandescent material (glowing hot rocks... Patricia: The most severe storm ever recorded causes widespread flooding but relatively few casualties.                  Hurricane Patricia formed as a tropical depression over the eastern Pacific Basin in mid-October 2015, before increasing rapidly in intensity on 22 October...
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