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Powerful phreatic eruption at Bulusan volcano, Philippines

bulusan phreatic eruption june 5 2022

A powerful phreatic eruption took place at Bulusan volcano, Philippines at 02:37 UTC (10:37 LT) on June 5, 2022. As a result, the Philippine Institute of Volcanology and Seismology raised the Alert Level for the volcano from 0 to 1.

  • The last eruption of this volcano was on June 5, 2017 (VEI 1) – exactly 5 years ago.
  • Ashfall has been reported in Juban and Casiguran, Sorsogon.

The eruption lasted 17 minutes and was recorded by seismic and infrasound monitoring by the Bulusan Volcano Network (BVN).1

The event was poorly visible through cloud cover over the edifice although a steam-rich grey plume at least 1 km (3 280 feet) tall was observed from Juban, Sorsogon and was subsequently observed to drift west.

According to the Tokyo VAAC, ash cloud top reached an 2.7 km (9 000 feet) above sea level at 03:40 UTC.

Thin fine ashfall fell on the general northwestern sector of the edifice and affected the barangays of Puting Sapa, Añog, Guruyan, Catanusan, Buraburan, Bacolod, and Sangkayon in Juban and Bolos in Irosin, Sorsogon Province.2

Rumbling sounds and sulfurous odor were also observed by residents of Brgys. Añog, Guruyan, and Catanusan.

Image credit: Sorsogon Provincial Information Office
ashfall bulusan volcano eruption june 5 2022 b - by Sorsogon Provincial Information Office
Image credit: Sorsogon Provincial Information Office
ashfall bulusan volcano eruption june 5 2022 d - by Sorsogon Provincial Information Office
Image credit: Sorsogon Provincial Information Office

After the eruption, degassing was observed from the northwest vent on the summit for the first time this year.

A total of 27 weak volcanic earthquakes were recorded through 8:00 UTC today by the Bulusan Volcano Network.

Fine ashfall can cause irritation and breathing problems, especially among the vulnerable population – the elderly, children, expecting mothers and those with respiratory disorders – and can be particularly dangerous when inhaled in copious amounts. In addition, ashfall even when thin but having high amounts of sulfur can also cause irritation.

Affected populations are advised to protect their mouths and noses using N95 grade facemasks or wet cloth or towel. Motorists are advised to drive with extreme caution as ash can cause poor visibility and, when wet, can make roads slippery.

Prior to the eruption, the BVN recorded 77 volcanic earthquakes in the past 24-hour observation period.

Ground deformation data from continuous GPS monitoring indicate that the Bulusan edifice has been generally inflated since July 2020, while electronic tilt monitoring recorded a sudden but isolated inflation of the southeast lower slopes only since April 2022.

These parameters indicate that volcanic processes are underway beneath the edifice that are likely caused by shallow hydrothermal activity.

earthquakes under bulusan volcano june 4 - 5 2022
Figure 1. Earthquake records for the past 24 hours from the Upper Slope (VBUS) Observation Station on Bulusan Volcano. High frequency volcanic earthquakes (HFVQs) are indicated by orange dots, the 02:37 UTC eruption is indicated by the long off-scale (red) signal. Credit: PHIVOLCS
Seismic waveform, frequency spectra and frequency distribution - explosion signal - bulusan volcano eruption june 5 2022
Figure 2. (A) Seismic waveform, frequency spectra and frequency distribution of the 10:37AM eruption today recorded by the Upper Slope (VBUS) and Gubat, Sorsogon borehole (VBGB) Observation Stations. (B) Explosion signal recorded by infrasound sensors of the Bulawan, Irosin, Sorsogon (VBUS) station on Bulusan and the Anoling, Daraga, Albay (VMAN) station on Mayon Volcano. Credit: PHIVOLCS
gps station velocities for bulusan volcano from january 2020 to may 2022
Figure 3. (A) GPS station velocities for Bulusan from January 2020 to May 2022. with respect to Bulawan, Irosin station (VBBU) in general do not resemble volcanic ground deformation. (B) GPS inter-station baselines record a general inflation of the edifice since July 2020, partly affected by the M6.6 18 August 2020 Masbate Earthquake. Credit: PHIVOLCS
short-term ground tilt data since october 2021 bulusan volcano
Figure 4. Short-term ground tilt data from the 4-station electronic tilt array on Bulusan since October 2021. The edifice has been deflating in the short-term except for a pronounced inflation of the southeast lower slopes (VBPA; Patag, Irosin, Sorsogon Observation Station) beginning April 2022. Credit: PHIVOLCS

Alert Level 1 status remains in effect over Bulusan Volcano, which means that it is currently in an abnormal condition.

Local government units and the public are reminded that entry into the 4 km (2.5 miles) radius Permanent Danger Zone (PDZ) must be strictly prohibited and that vigilance in the 2 km (1.2 miles) Extended Danger Zone (EDZ) on the southeast sector must be exercised due to the increased possibilities of sudden and hazardous phreatic eruptions that can occur without warning, PHIVOLCS said.

“Civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft.

“Furthermore, people living within valleys and along river/stream channels especially on the southeast, southwest and northwest sector of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur.”

Geological summary

Luzon’s southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter (6.8 miles) dacitic-to-rhyolitic Irosin caldera, which was formed about 36 000 years ago. Bulusan lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic Bulusan complex.

Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit of 1 565-m-high (5 134  feet) Bulusan volcano is unvegetated and contains a 300-m-wide (984 feet), 50-m-deep (164 feet) crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded at Bulusan since the mid-19th century.3

References:

1 BULUSAN VOLCANO UPDATE – PHIVOLCS – 05 June 2022 11:40 P.M. (LT)

2 BULUSAN VOLCANO UPDATE – PHIVOLCS – 05 June 2022 08:00 P.M. (LT)

3 Bulusan – Geological summary – GVP

Featured image credit: Il Mondo dei Terremoti

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