Thursday 25 June 2015

Eruptions on Mount Bulusan.

Mount Bulusan, a 1565 m stratovolcano (cone shaped volcano made up of layers of ash and lava) on the southern tip of the Bicol Peninsula on Luzon Island, in the Philippines, began erupting slightly after 9.45 am local time on Friday 1 May 2015, with a small explosive eruption producing an ash column that rose 250 m above the summit of the volcano. This was the first eruption on the mountain since May 2012, though a series of small Earthquakes (often indicative of magma moving into chambers beneath a volcano) were reported under Mount Bulusan in July 2014. A second small eruption occurred later that day, along with a series of Earthquakes beneath the mountain, causing the Philippine Institute of Volcanology and Seismology to issue a warning against people entering the 'permanent danger zone' around the volcano, which in the case of Mount Bulusan extends 4 km from the summit due to the danger of lahars (extremely rapid floods of ash-laden mud).

An ash column over Mount Bulusan on 21 June 2015. Benedict Del Valle Ocampo/Facebook/Earth on Fire.

Slightly after 9.45 pm local time on Wednesday 6 May a small explosion was recorded in a vent on the northwest flank of the volcano, again producing a 250 m ash column. This was determined to have been phreatic in origin, i.e. caused by hot magma coming into contact with liquid water. Small ash-falls were recorded by several local communities, and steam was observed to be emitted from several other vents on the flanks of the volcano.

Ash column produced by an explosive eruption on Mount Bulusan on 16 June 2015. Ronald Belleza/Bicol Today.

A series of small Earthquakes and steam emissions were recorded from Mount Bulusan between 13 and 19 May, but no further eruptions. Then on 16 June a 10 minute eruption occurred slightly after 11.00 am, this also being thought to be phreatic in origin, and producing an ash column 1 km high. A second smaller eruption was recorded at about 11.20 am local time, combined with a series of small Earthquakes. Another small explosive eruption was recorded close to the summit of Mount Bulusan on Thursday 18 June, and on Friday 19 June a seven minute eruption starting at about 2.45 pm local time created a 1.5 km ash column that drifted to the west, causing ash falls in several local communities. A smaller eruption later that afternoon caused a 250 m ash column which drifted to the southwest. A small eruption at about 1.15 pm local time on Sunday 21 June produced a 150 m ash-and-stream plume that drifted to the east. Ash falls were also recorded by several local communities from this event. Another small eruption was recorded slightly before 10.10 pm local time on Tuesday 23 June.

The location of Mount Bulusan. Google Maps.

The geology of the Philippines is complex, with the majority of the islands located on the east of the Sunda Plate. To the east of this lies the Philippine Sea plate, which is being subducted beneath the Sunda Plate (a breakaway part of the Eurasian Plate); further east, in the Mariana Islands, the Pacific Plate is being subducted beneath the Philippine Sea Plate. This is not a smooth process, and the rocks of the tectonic plates frequently stick together before eventually being broken apart by the rising pressure, leading to Earthquakes in the process. Material from the subducting Philippine Plate is heated by the temperature of the Earth's interior, causing lighter minerals to melt and the resultant magma to rise through the overlying Sunda Plate, fueling the volcanoes of the Philippines.

Subduction beneath the Philippines. Yves Descatoire/Singapore Earth Observatory.

See also...

The United States Geological Survey recorded a Magnitude 5.3 Earthquake at a depth of 10 km about 37 km off the east coast of Luzon Island in the...

The Philippine Institute of Volcanology and Seismology has recorded an increase in seismic activity over the past 24 hours (Saturday 28-Sunday 29 June 2014) beneath Mount Mayon, a 2463 m stratovolcano (cone shaped volcano) on southern Luzon Island. White smoke has also been seen...

ive people are reported to have been killed in an eruption on Mount Mayon, an active stratovolcano (cone shaped volcano) on Luzon Island in the Philippines...

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