Sunday 4 August 2013

Further eruptions on Mount Tungurahua.

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 which has been intermittently active since 1999 (prior to which it had been inactive for about 75 years), with major eruptions in August 2006, February 2008, May 2010, December 2010 and April 2011, increased its activity sharply in mid July, leading to the evacuation of 200 people from its immediate vicinity after an eruption on 14 July that produced a 5 km high ash column. On 16-17 July the summit of the volcano was obscured by cloud, but several large explosions were heard and blocks of incandescent rock observed raining down the mountain's flanks. On 18-19 the summit was visible, and observers witnessed a number of small eruptions, throwing additional material down the flanks. Throughout this time seismic activity remained high, with a dozens of small tremors and several sustained Earthquakes each day. On 19 July another ash column was produced, this time rising 1 km above the summit and drifting to the southwest; ashfalls were reported in Choglontus and El Manzano, both to the southwest of the volcano. 

Incandescent material being ejected from the crater of Tungaruhua on 19 July 2013. Fuente Ramón/Observatorio del Volcán Tungurahua/Instituto Geofisico de la Escuela Politecnica Nacional.

20 July saw a further escalation in activity on Tungurahua, with 127 sustained Earthquakes, 71 smaller tremors and 43 explosions heard. On 21 July there were 220 Earthquakes and three major explosions, accompanied by blocks being thrown from the crater onto the flanks of the volcano. A 5 km high column of ash was produced, and settlements to the southwest and northwest reported ashfalls. The eruptive activity continued overnight into 22 July, with material being thrown down the flanks of the mountain and explosions shaking structures close by. Activity decreased over 22-23 July, with smaller columns of ash reaching 1-1.5 km and drifting to the west and 22-40 Earthquakes per day.

On 24 July the summit of the mountain was again obscured by cloud, but an ash column rising 5 km and drifting to the west could be seen, and ashfalls were reported in settlements up to 25 km away. Ashfalls continued through 25 July, with another explosive eruption producing another column, this time 1.5 km high, in the evening. Further eruptions were seen on 26-27 July, along with minor ashfalls and explosions that rattled windows 8 km away. On the morning of 28 July a number of smaller explosions heard, and a pyroclastic flow (avalanche of hot ash and rocks) seen on the northern flank of the volcano. Ashfalls were reported in Tisaleo, 29 km to the northwest. Explosions continued into 29 July, when a 2 km ash column was observed.

An ash column over Tungurahua on 28 July 2013. Correo del Orinoco.

The current Tungurahua volcano is the third on the site, referred to by volcanologists as Tungurahua III. The first volcano on the site, Tungurahua I, built up and then collapsed some time in the Mid-Pleistocene. This was followed by Tungurahua II, which started to grow about 14 000 years ago, then collapsed about 3000 years ago. The current volcano has been growning since this time, and lies within the caldera of Tungurahua II.

The approximate location of Mount Tungurahua. Google Maps.

Like all South American volcanoes Tungurahua 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 subduction of the Nazca Plate beneath the South American Plate. Marot et al. (2012).

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