Sunday 11 May 2014

Seismic swarms beneath Cerro Negro de Mayasquer.

Concern is rising in Colombia and Ecuador following a rise in seismic activity beneath Cerro Negro de Mayasquer, a volcano in the Andes straddling the border between the two countries not thought to have been active since the Late Pleistocene. A network of seismic monitors at the volcano began to detect microseismic activity beneath the volcano in March 2014, since when the level of activity has risen sharply - although the seismic network has only installed in November 2013, following fumarole activity (gas emissions) on the mountain. The data being collected by volcanologists from the Volcanological and Seismological Observatory of Pasto and the Geological Survey of Colombia suggests that the earthquakes comprise a mixture of micro-tectonic quakes, caused by rocks fracturing under pressure, and long period quakes, due to fluid movement within the rocks, a combination which strongly suggests that fresh magma is moving into chambers beneath the volcano.

The locations of recent Earthquakes beneath Cerro Negro de Mayasquer. Institutio Geofisício Escuala Politécnica Nacional.

Over 9000 Earthquakes occurred beneath the mountain between 29 April and 5 May 2014, the largest of which, with a Magnitude of 4.8, occurred on 30 April, slightly before 0.45 am local time, and was felt across much of the region. The have subsequently been five further quakes with Magnitudes in excess of 3.0. Prior to this Cerro Negro de Mayasquer is thought to have been inactive for about 160 000 years; reports of a small eruption in 1936 witnessed are now believed to have been an eruption on Reventador in Ecuador.

Aerial photograph of Cerro Negro de Mayasquer in September 2006. Geological Survey of Colombia.

Like all South American volcanoes Cerro Negro de Mayasque owes its existence to the subduction of the Nazca Plate (which underlies the southeast Pacific) beneath South America. The Nazca Plate is being pushed from the east and forced down into the Earth's interior beneath South America. As it sinks rocks in the crust melt, and the lighter portions of it rise up through the overlying South American Plate to form volcanoes at the surface. These are dotted throughout the Andes Mountains; a range of mountains that is formed by a mixture of volcanism and crumpling of the South American Plate where is is forced against the Nazca Plate.

The approximate location of Cerro Negro de Mayasquer. Google Maps.

See also...

Mount Tungurahua, a stratovolcano (a 'conventional' cone-shaped volcano, the sort you see in Hollywood movies) located in the Sangay National Park in Ecuador, overlooking the town of Baños de Agua Santa, erupted suddenly at about 6.10 pm local time (about 11.10 pm GMT) on Friday 4 April 2014, producing a column of ash rising 10 km above the summit of the volcano. The initial eruption was followed by a number of smaller eruptions and earthquakes.

The United States Geological Survey recorded a Magnitude 5.0...

The United States Geological Survey recorded a Magnitude 4.5...

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