Bulusan is classified by volcanologists as a stratovolcano (or a composite cone) and covers the northeast rim of Irosin caldera that was formed about 40,000 years ago. It has a peak elevation of 1,565 m (5,135 ft) above sea level with a base diameter of 15 km (9.3 mi).
Around the mountain are four craters and four hot springs. The first crater, called Blackbird Lake, is 20 m (66 ft) in diameter and 15 m (49 ft) deep. The second crater is oval, with dimensions of 60 by 30 m (197 by 98 ft) and 15 m (49 ft). The third crater is about 90 m (300 ft) in diameter and 20 m (66 ft) deep, while the fourth, which is near the northeastern rim opened during the 1981 eruption. There is also a 100-metre (330 ft) fissure measuring 5 to 8 m (16 to 26 ft) wide below this crater.
There are evacuation procedures in place for parts of the peninsula; the farms nearest the volcano are to be evacuated, and many village schools will be closed if a more destructive eruption is possible.
Recent activity
March–June 2006
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) declared alert level 1 on March 19, after it recorded increased seismic unrest. On June 8, volcanologists raised the alert level to 2 (moderate level of seismic unrest) after the volcano spewed ash. On June 9, the resulting ash cloud damaged a number of houses in the nearby town of Casiguran, 5 kilometres (3.1 mi) north of the volcano, and reached Sorsogon City, about 20 kilometres (12 mi) north of Bulusan.
On June 13, volcanologists said new craters were created by mild explosions. Aside from the new craters, two of the volcano's existing four craters appeared to have merged and cracks were observed on the western rim of the summit crater. Another eruption took place on April 8, 2007.[5]
July–October 2007
Mount Bulusan in active mode in February 2007
Following some signs of volcanic activity, on the morning of July 31, 9:37am (local time), there was a loud explosion described by locals as "like a bomb going off". A cloud of steam and ash shot into the air from Mount Bulusan to a height of 5 kilometres (3.1 mi), drifting and blanketing the surrounding countryside. The eruption lasted for 20 minutes.[6]
November 2010
On November 7, PHIVOLCS recorded increased seismic activity at Bulusan Volcano, 24 hours after it spewed a 600-metre (2,000 ft) ash column and grayish steam on November 5. State volcanologists noted that at least 10 volcanic earthquakes and four explosion-type events were documented after the emission of ash and steam at 8a.m. on November 5. PHIVOLCS also noted that steaming activity was characterized by strong emission of white steam column that reached a maximum height of 200 meters above the crater rim. It warned the public not to enter the four-kilometer permanent danger zone from the volcano. People near the valleys and streams were also advised to be "extra alert" against sediment-laden stream flows in the event of heavy rains.[7] More ash ejection was reported on November 8–9, with ash fall in Juban and Irosin . A PHIVOLCS bulletin on November 9, stated that eight volcanic earthquakes were recorded from the volcano during the past 24 hours and weak to moderate emission of ash explosion was observed. PHIVOLCS also warned residents near valleys and streams against sediment-laden stream flows in the event of heavy and continuous rainfall.[8]
February 2011
After months of little activity, the volcano suddenly erupted and released a plume of ash 2 kilometres (1.2 mi) high, after water reacted with the hot magma. PHIVOLCS said such explosions were likely to continue for the coming weeks. Initially, hundreds of nearby residents evacuated on their own, but the government stepped in to evacuate thousands more, and imposed a 4-kilometre (2.5 mi) travel ban around the crater. They also advised airplanes to avoid the immediate perimeter due to ash and debris in the air.[9][10]
July 2014
On July 13, during the 24-hour observation period, the seismic network detected thirteen volcanic earthquakes.[11]
May–June 2015
Mount Bulusan ejected a 250 m (820 ft) ash plume on May 1, at around 9:46 pm, lasting for 3.5 minutes. The incident was classified as a "minor explosion event" by PHIVOLCS leading to the raising of alert level 1 (abnormal activity) for the surrounding area. A second ash explosion lasting for five minutes also occurred on the same day. PHIVOLCS determined the cause of the eruptions to be hydrothermal activity beneath the volcano. People were advised not to enter the 4 km (2.5 mi) permanent danger zone. Further advisories were given to low-flying aircraft against the dangers of sudden phreatic eruptions, and to local residents near rivers and streams in case of lahar flows.[12][13][14] There were also concerns that rains from Typhoon Noul could trigger lahars and mudslides near the mountain.[15] However, after Noul recurved to the north, the threat did not materialize and the evacuees were permitted to return to their homes.[16]
On June 16, Mount Bulusan generated two volcanic eruptions with the first one recorded at 11:02am which lasted for 10 minutes producing a one kilometer high grayish steam and ash plume and accompanied by rumbling sounds. The second one was recorded at 11:20am which lasted for a minute producing only a small ash plume.[17] On June 18, the volcano once again erupted but was not observed visually due to thick clouds covering the summit. Prior to the eruption, rumbling sounds was heard between 5:00am to 7:00am by residents of the village of Monbon in Irosin town. The next day, June 19, Bulusan erupted yet again at around 2:55pm producing a 1.5-kilometer high ash plume.[18]
June 2016
On June 10, almost a year after its last eruption, Mount Bulusan erupted again at 11:35am. The eruption lasted for five minutes and generated an ash plume measuring 6,562 feet or some 2,000 meters.[19] According to PHIVOLCS, the eruption was phreatic in nature and had a shallow source, with the ash drifting northwest to the direction of Juban town.[20] While the PHIVOLCS did not raise the alert level 1 in the volcano, it advised residents not to enter the four-kilometer permanent danger zone and warned pilots not to fly near the volcano.[21]
December 2016
On December 29, Mount Bulusan had a phreatic eruption, shooting a plume of ash about two kilometers high. It happened 2:40pm local time and lasted for about 16-minutes. The eruption prompted PHIVOLCS to raise Alert level 1 for the surrounding areas and remind the public not to enter the 4-kilometer radius permanent danger zone.[22]
May 2019
On May 6, PHIVOLCS reported that two volcanic earthquakes were recorded during the past 24 hours. Wispy emission of white steam-laden plumes from the active vents was observed. Alert level 1 (abnormal) status remained in effect.[23]
July 2020
PHIVOLCS raised the alert status of Bulusan Volcano from alert level 0 to alert level 1 after an increase in seismic activity was observed in the past days.[24]
Timelapse video of Bulusan Volcano after its eruption on June 12, 2022
May 2021
On May 11, PHIVOLCS raised the alert status of Bulusan Volcano from alert level 0 to alert level 1 due to increased seismic activity since May 8.[25]
June 2022
On June 5, PHIVOLCS reported that Mount Bulusan had a phreatic eruption with a height of about one kilometer, and the alert level status was raised to alert level 1.[26] Ash fall was reported in Juban and Casiguran.[27][28][29] The DOH advised the public to remain indoors.[30] The local government of Juban ordered residents to evacuate from affected areas.[31] The NDRRMC reported at least 180 individuals from Juban were evacuated.[32] On June 12, a phreatic eruption took place at 3:37 am (local time) and lasted for about 18 minutes.[4]
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