Saturday, 21 July 2012

Seismic activity on Mount Cumbal, Colombia.

Cumbal is the most southerly active volcano in Columbia; it is a stratovolcano (conventional cone-shaped volcano made up of layers of lava and ash) elongated along a northeast-southwest axis, giving it an oval shape. It has undergone two major eruptions in recorded history; one in 1877 and one in 1926. There is a lava-dome within the 250 m wide central crater (i.e. a dome formed by the injection of magma beneath the surface which has never erupted, but has caused uplift), which produces fumaroles (gas emissions) and steam plumes from time to time. There are also hot springs on the southeastern flanks.

Mount Cumbal, Colombia. Land of Winds.

On 10 July 2012, the Instituto Colombiano de Geología y Minería reported that it had recorded a steady rise in seismic activity (Earth tremors) over recent months. Such movements beneath volcanoes can be significant, as they are often caused by the arrival of fresh magma, which may indicate that a volcano is about to undergo an eruptive episode. The most recent period of seismic unrest on Mount Cumbal occurred in 1988, which led to an increase in fumarole activity, but not to an eruption. However this was accompanied by a similar increase in seismic activity on the nearby Mount Gaelras, which did develop into a full eruptive episode, culminating in the deaths of six volcanologists and three tourists visiting the volcano in 1993.

Cumbal itself is more infamous for the fatalities caused by a man-made disaster; in January 2002 a commercial airliner flew into the side of the volcano in heavy fog, killing all 94 passengers and crew onboard. 

Debris on Mount Cumbal following the 2002 air-crash. AirDisaster.com.

Cumbal is located in the Andes Mountains, which run along the entire west coast of South America from Columbia to southern Chile. These owe their origin to the subduction of the Nazca Plate which underlies the southeast Pacific beneath the South American Plate. The Nazca Plate is being subducted beneath the South American Plate along almost the entire of South America's west coast. As this happens it causes crumpling in the South American Plate, leading to uplift in the Andes. At the same time the underlying Nazca Plate is being heated by a combination of friction with the overlying South American Plate and the heat of the Earth's interior, causing it to partially melt. Some of the melted material then rises through the overlying South American Plate, fueling volcanoes scattered throughout the Andes Mountains.

Simple diagram showing the passage of the Nazca Plate beneath the South American Plate, and the formation of magma which fuels the Volcanoes of the Andes. PlateTectonics.com.


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