Phreatic eruptions at Mayon volcano, Alert Level remains at 2, Philippines

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Two phreatic eruption events were observed at Mayon volcano, Philippines late November 25 into 26, 2018. Alert Level remains at 2. The public is reminded that sudden explosions, lava collapses, pyroclastic density currents or PDCs and ashfall can still occur and threaten areas in the upper to middle slopes of the volcano. 

The eruptions were observed between 23:59 UTC, November 25 and 00:05 UTC, November 26 (07:59 to 08:05 PST), PHIVOLCS reports.

The events generated grayish to grayish white ash plume that rose 300 to 500 meters above the summit before drifting southwest. 

Two volcanic earthquakes were registered in 24 hours to 00:00 UTC, November 26 as well as moderate emission of white steam-laden plumes that crept downslope before drifting west-southwest. Fair crater glow from the summit could be observed at night.

Sulfur dioxide (SO2) emission was measured at an average of 1943 tonnes/day on November 25, 2018.

Precise leveling data obtained between October 22 and 31, 2018 indicate inflation of the edifice in the southeast sector while the north sector indicate short-term deflation relative to August 30 to September 3, 2018. The volcano generally remains inflated relative to 2010 baselines.

Electronic tilt data further show pronounced inflation of the mid-slopes beginning June 25, 2018, possibly due to aseismic magma intrusion deep beneath the edifice.

PHIVOLCS maintains Alert Level 2 – moderate level of unrest.

The public is reminded that sudden explosions, lava collapses, pyroclastic density currents or PDCs and ashfall can still occur and threaten areas in the upper to middle slopes of Mayon.

PHIVOLCS recommends that entry into the 6 km (3.7 miles) radius Permanent Danger Zone or PDZ and a precautionary 7 km (4.3 miles) Extended Danger Zone or EDZ in the south-southwest to east-northeast sector, stretching from Anoling, Camalig to Sta. Misericordia, Sto. Domingo must be strictly prohibited.

People residing close to these danger areas are also advised to observe precautions associated with rockfalls, PDCs and ashfall.

Civil aviation authorities must advise pilots to avoid flying close to the volcano’s summit as airborne ash and ballistic fragments from sudden explosions and PDCs may pose hazards to aircrafts.

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A powerful eruption took place at the volcano around 04:45 UTC on January 22, 2018 (12:45 local time), producing a column of ash that rose up to 7.6 km (25 000 feet) above sea level. The event forced PHIVOLCS to raise the Alert Level to 4.

More than 80 000 people living near the volcano were evacuated before and after this event.

The Alert Level was lowered to 3 on March 6 and to 2 on March 29.

A moderately strong phreatic eruption took place at 04:34 UTC (12:34 local time) on July 1. A light gray ash column reached an altitude of about 500 m (1 640 feet) above the crater.

Geological summary

Beautifully symmetrical Mayon volcano, which rises to 2 462 m (8 077 feet) above the Albay Gulf, is the Philippines’ most active volcano. The structurally simple volcano has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions at this basaltic-andesitic volcano date back to 1616 and range from strombolian to basaltic plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows.

Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas.

Mayon’s most violent eruption, in 1814, killed more than 1 200 people and devastated several towns. (GVP)

Featured image credit: Kurt Fredrickson / Smithsonian Institution

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