Thursday 27 October 2016

Landslide kills seven in Antioquia Province, Colombia.

Seven people are known to have died and it is feared that more people may be buried, following a landslide in Antioquia Province, Colombia, on the morning of Wednesday 26 October 2016. The andslide hit a four lane highway about 12 km to the north of the provincial capitol, Mendalin, covering about 200 m of road and burying a number of vehicles. The incident is reported to have happened following a period of heavy rain. 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 scene of the 26 October 2016 Antioquia landslide. AFP.

Antioquia is a mountainous province with several distanct climate zones. The Medallin area is considered to gave a monsoon climate, with a to peaks in rainfall in May and October. Two hot wet seasons per year is normal on the equator, where the Sun is highest in the sky around the equinoxes and lowest at the solstices, as opposed to the situation at higher latitudes, where the Sun is highest at one solstice and lowest at the other.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year. 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.

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

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