Thursday 13 September 2012

Seismic activity beneath Apoyeque.

Apoyeque is a shield volcano located on the Chiltepe Peninsula on Lake Managua in Nicaragua. It has two lake-filled craters, Apoyeque to the northwest and Jiloá (or Xiloá) to the southeast. To make matters more confusing the name Apoyeque is sometimes reserved for the east crater alone, with the whole complex being called Chiltepe. There are also two lava domes (circular or mound-shaped formations, produced by the slow eruption of viscous lava), Talpetatl and Miraflores.

Space Shuttle Image of the Chiltepe Peninsula, the greenish lake to the left is Apoyeque, the darker blue lake to the right is Jiloá. Smithsonian Global Volcanism Project/NASA.

Apoyeque is last thought to have erupted in about 50 BC, but that eruption is thought to have been spectacular, with around 18 km³ of material being ejected, one of the largest known eruptions ever. The volcano is also thought to have undergone massive eruptions in around 1050 BC, 2550 BC and 4160 BC.

Footprints at Acahualinca near Managua in a ~7500 year old mudflow, preserved by an overlying ~6500 year old ash-fall from Jiloá. Smithsonian Global Volcanism Project/Jaime Incer.

On Thursday 6 September 2012, the Nicaraguan Institute of Territorial Studies recorded the first of a series of Earthquakes beneath Apoyeque that lasted for three days. In total 17 small quakes were recorded with Magnitudes between 2.3 and 3.7 at depths of between 2.8 and 6 km. Monitoring such quakes is important because they can indicate the movement of magma into chambers beneath the volcano, which may in turn be a forerunner to an eruption.

Apoyeque last underwent a period of seismic activity in 2009, and prior to this in 2001. It also undergoes occasional periods of fumarole activity (gas emissions).

Aerial Photograph of the two crater-lakes. Jiloá on the left and Apoyeque on the right. Smithsonian Global Volcanism Project/Jaime Incer.

Nicaragua is located on the southern edge of the Caribbean Plate, which underlies Central America as well as the Caribbean Sea. To the south the Cocos Plate, which underlies part of the eastern Pacific, is being subducted beneath the Caribbean Plate along the Middle American Trench, passing under Central America as it is sinks into the Earth. As it is subducted the Cocos Plate is being partially melted by the heat of the planet's interior and the friction caused by its dragging under the Caribbean Plate, producing liquid magma, which then rises through the overlying plate fueling the volcanoes of Central America.

Diagrammatic representation of the Cocos Plate passing beneath the Central American Plate, showing how it fuels the volcanoes of Central America. VCS Mining.

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