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Mount Bulusan
Mount Bulusan
Mount Bulusan
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Mount Bulusan, also known as Bulusan Volcano, is a stratovolcano on the island of Luzon in the Philippines. Located in the province of Sorsogon in the Bicol Region, it is 70 kilometres (43 mi) southeast of Mayon Volcano and approximately 390 kilometres (240 mi) southeast of Manila. Bulusan is one of the active volcanoes in the Philippines.

Key Information

Physical features

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Bulusan is classified by volcanologists as a stratovolcano (or a composite cone) and covers the northeast rim of Irosin caldera that was formed about 36,000 years ago. It has a peak elevation of 1,535 m (5,036 ft) above sea level with a base diameter of 15 km (9.3 mi). [1]

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. [citation needed]

The volcano's hot springs are:

  • Mapaso
  • Masacrot
  • San Benon
  • San Vicente

Adjacent volcanic edifices are:

  • Mount Batuan
  • Mount Binitacan
  • Mount Calaunan
  • Mount Calungalan
  • Mount Homahan
  • Mount Jormajan
  • Mount Juban
  • Mount Tabon-Tabon

Eruptions

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Bulusan is generally known for its sudden, steam-driven or phreatic explosions. It has erupted 15 times since 2016 and is the fourth most active volcano in the Philippines after Mayon, Taal, and Kanlaon.

Evacuation procedures

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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

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March–June 2006

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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.[4]

July–October 2007

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Mount Bulusan in active mode in February 2007

Following some signs of volcanic activity, on the morning of July 31, 9:37 am (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.[5]

November 2010

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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 8 a.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.[6] 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.[7]

February 2011

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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.[8][9]

May–June 2015

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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.[10][11][12] There were also concerns that rains from Typhoon Noul could trigger lahars and mudslides near the mountain.[13] However, after Noul recurved to the north, the threat did not materialize and the evacuees were permitted to return to their homes.[14]

On June 16, Mount Bulusan generated two volcanic eruptions with the first one recorded at 11:02 am 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 11:20 am which lasted for a minute producing only a small ash plume.[15] 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 5:00 am to 7:00 am by residents of the village of Monbon in Irosin town. The next day, June 19, Bulusan erupted yet again at around 2:55 pm producing a 1.5-kilometer high ash plume.[16]

June 2016

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On June 10, almost a year after its last eruption, Mount Bulusan erupted again at 11:35 am. The eruption lasted for five minutes and generated an ash plume measuring 6,562 feet or some 2,000 meters.[17] 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.[18] 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.[19]

December 2016

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On December 29, Mount Bulusan had a phreatic eruption, shooting a plume of ash about two kilometers high. It happened 2:40 pm 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.[20]

July 2020

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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.[21]

Timelapse video of Bulusan Volcano after its eruption on June 12, 2022

May 2021

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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.[22]

August 2021

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On August 18, PHIVOLCS lowered the alert level of Bulusan from alert level 1 (low-level unrest) to alert level 0 (normal) after the volcano returned to normalcy following a general decline in volcanic earthquakes, ground deformation, gas emission, and surface activity. [23]

June 2022

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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.[24] Ash fall was reported in Juban and Casiguran.[25][26][27] The DOH advised the public to remain indoors.[28] The local government of Juban ordered residents to evacuate from affected areas.[29] The NDRRMC reported at least 180 individuals from Juban were evacuated.[30] On June 12, a phreatic eruption took place at 3:37 am (local time) and lasted for about 18 minutes.[31]

April 2025

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At 4:36 am on April 28, Bulusan underwent a phreatic eruption that lasted 24 minutes and emitted a bent plume that rose 4,500 meters above the crater before drifting to the general west. A pyroclastic density current (PDC) descended the southwestern slopes, traveling within 3 kilometers from the summit vent of the volcano. The eruption prompted PHIVOLCS to raise Alert Level 1 on the volcano again.[32] Sixty-one people were evacuated from the vicinity.[33] A second phreatic eruption occurred at 7:43 pm on April 29, lasting for 1 hour and 17 minutes and emitting a plume that drifted southwest.[34]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Mount Bulusan

View on Grokipedia
from Grokipedia
Mount Bulusan, also known as Bulusan Volcano, is an active located at the southeastern end of the Bicol volcanic arc in Province, on the island of in the , with coordinates approximately 12.77°N, 124.06°E. It rises to a summit elevation of 1,535 meters above sea level and features a 300-meter-wide, 50-meter-deep at its unvegetated peak, flanked by several intra-caldera lava domes and cones, including Mount Jormajan. The volcano forms part of the Bulusan Volcano Natural Park, a encompassing diverse ecosystems and hot springs, and is situated on the northeastern rim of the 11-kilometer-wide Irosin Caldera, which formed around 35,000–40,000 years ago due to a major . Geologically, Bulusan is a young andesitic resulting from the subduction of the Philippine Sea Plate beneath the Sunda Plate along the , contributing to the region's high volcanic activity. It is classified as one of the ' potentially active volcanoes by the Philippine Institute of Volcanology and Seismology (PHIVOLCS), ranking as the fourth most active in the country after , , and . The volcano's eruptive history includes at least 24 confirmed eruptions over the past 10,000 years, with 22 documented historical events since 1852, primarily consisting of moderate and phreatomagmatic explosions that produce ash plumes, steam emissions, and occasional mudflows during heavy rains. Notable eruptions include a series from to 1922 involving explosive activity and lava flows, and more recent events in 2011, 2016, and June 2022, when ash plumes rose up to 1 kilometer and sulfur dioxide emissions peaked at around 1,900 tonnes per day. In 2025, Bulusan exhibited increased unrest, with PHIVOLCS raising the alert level to 1 in May due to 18–124 daily volcanic earthquakes, gas-and-steam plumes up to 400 meters high, and sulfur dioxide fluxes of 466–1,117 tonnes per day; this alert level remains in effect as of November 2025. The primary hazards from Bulusan include sudden eruptions, ashfall affecting nearby communities, lahars (volcanic mudflows) triggered by rainfall on loose deposits, and potential pyroclastic flows or lava flows during magmatic events, prompting a permanent 4-kilometer-radius danger zone around the summit. Culturally, the volcano holds significance in local Bicolano , such as the of Bulusan and Agingay, and is commemorated annually through festivals like the street-dancing event on July 24 in nearby areas.

Geography and Location

Name and Etymology

Mount Bulusan, known locally as Bulusan Volcano, derives its name from the Bicol word bulos, which translates to "flow" or "waterflow" in the Bikol Central dialect, alluding to the volcano's prolific springs and streams that originate from its slopes. This etymology underscores the mountain's role as a vital hydrological feature in the region, where rainwater and geothermal influences contribute to an abundance of freshwater sources feeding local rivers and communities. Alternative interpretations connect the name directly to the surrounding landscape of the Bulusan municipality, emphasizing it as "a place where water flows," with cascading waters from the volcano nourishing irrigation systems, nearby rivers, and coastal outlets. These associations highlight the integral bond between the volcano and the area's water-dependent ecosystem, a characteristic evident in the dense network of streams and springs that define the terrain. In pre-colonial Bicolano culture, the naming reflects indigenous reverence for natural water elements, as seen in local such as the of Si Bulusan nan Si Agingay, which portrays Bulusan as a heroic figure tied to the origins of the volcano's lakes and the life-giving flows they produce. This narrative, rooted in oral traditions, illustrates how Bicolano communities historically personified the mountain's aqueous bounty, embedding it within their mythological worldview long before colonial influences.

Position and Accessibility

Mount Bulusan is located in Province in the of the , on the island of , at the southeastern end of the Bicol Volcanic Chain. Its summit is positioned at coordinates 12°46′12″N 124°03′00″E, with an elevation of 1,535 meters (5,036 ft). The volcano occupies a strategic position within the province, near the municipalities of Bulusan and , and serves as a key geographical feature approximately 500 kilometers southeast of . Access to Mount Bulusan primarily involves travel along the Maharlika Highway, the main arterial road connecting to the , leading to . From , visitors can proceed via local buses or jeepneys to the town of Bulusan, a journey of about 55 kilometers that takes roughly 1.5 to 2 hours depending on road conditions. Upon reaching Bulusan town, tricycles or short van rides transport travelers to the entrance of Bulusan Volcano Natural Park, located approximately 5 kilometers from the town center. Hiking trails to the 's begin at the park's main near Bulusan Lake, offering routes that vary in difficulty and length, typically requiring 4 to 7 hours for an ascent through forested paths and volcanic terrain. Permits are required for trekking and can be obtained at the park station, with guided tours recommended due to the active nature of the and potential hazards.

Physical and Geological Features

Stratovolcano Structure

Mount Bulusan is a situated within the Philippine Mobile Belt, a tectonically active region shaped by the oblique subduction of the Philippine Sea Plate beneath the Eurasian Plate along the . This subduction process generates that rises to form volcanic arcs, including the Bicol arc where Bulusan is positioned at the southeastern terminus. The 's edifice was constructed within the 11-km-wide Irosin caldera, formed by a major approximately 36,000 to 40,000 years ago, as evidenced by of associated deposits. Following this caldera-forming event, subsequent phases of volcanic activity built the prominent cone through layered accumulation of materials over millennia. The stratovolcano's structure comprises alternating layers of andesitic to dacitic lava flows, pyroclastic deposits from , and sediments from rain-induced mobilization of volcanic debris. Lavas in the Bulusan complex predominantly exhibit andesitic compositions, with subordinate basaltic and dacitic varieties, reflecting the magmatic evolution driven by subduction-related . Overall, the edifice features a base diameter of approximately 10 km and rises to a of 1,535 m above , forming a classic conical profile typical of stratovolcanoes in convergent margins.

Craters, Lakes, and Hydrothermal Activity

Mount Bulusan's features a prominent 300-meter-wide and 50-meter-deep located at the of 1,535 meters above , formed through repeated explosive activity and containing multiple vents, including the main Blackbird Crater and three smaller explosion pits on the southeastern flank. This crater structure reflects the volcano's stratovolcanic nature, with additional vents on the northwestern and northern sides contributing to episodic gas emissions. Within the volcanic complex, two notable lakes are present: Aguingay Lake, situated at about 890 meters elevation between the main peak and Sharp Peak, and the intermittent Blackbird Lake in the summit crater. These water bodies primarily form from rainwater accumulation, supplemented by minor hydrothermal inputs, though Aguingay Lake is characterized as a vast plain that floods during the . Hydrothermal activity at Mount Bulusan is evident through active fumaroles at the summit, where superheated solfatara vents release gas-and-steam plumes, and peripheral hot springs in the and thermal areas. The hot springs exhibit bicarbonate-type waters with temperatures below 65°C and near-neutral , while those at (also known as Buhang) are chloride-bicarbonate type, reaching 45°C with around 6.2, indicating mixing of meteoric and influenced by magmatic volatiles. Sulfur deposits and sulfate-rich waters (up to 601 mg/L SO₄) around these sites, along with elevated emissions averaging hundreds of tons per day, underscore the ongoing transfer of magmatic heat to the surface. Recent observations indicate fluctuations in lake levels, particularly for Aguingay Lake, which dries up completely during the summer due to reduced , while the small Blackbird Lake in the summit crater remains non-persistent and varies with seasonal rainfall.

Historical Eruptions

19th Century Eruptions

The documented volcanic activity at Mount Bulusan during the represents the earliest phase of recorded eruptions, characterized by sparse historical accounts due to limited scientific monitoring at the time. The first confirmed event occurred in , manifesting as a from the summit crater, described as a light outburst accompanied by the ejection of ashes. This activity aligns with the 's typical explosive style, though specific plume heights or secondary effects like lahars were not detailed in contemporary reports. Further eruptions were recorded in 1886 (mild eruption), 1889 (light outburst with ejection of ashes), and 1892 (mild eruption), all from the summit . A notable took place in 1894, classified as with a light outburst and ash ejection from the summit . Overall, these 19th-century eruptions were minor events with no recorded fatalities or major damage.

20th Century Eruptions

The marked a period of sporadic but notable volcanic activity at Mount Bulusan, with eruptions transitioning from magmatic events in the early decades to predominantly and phreatomagmatic explosions later on. These events were documented through instrumental and eyewitness accounts, providing more reliable compared to earlier historical reports. Activity often involved emissions, ejections, and occasional associated hazards like lahars, though no major loss of human life was recorded except in one instance. The initial significant unrest began in October 1918 and continued intermittently until 1922, featuring a series of 17 explosive eruptions that produced ash clouds, with dust and sand drifting southwest from the summit crater. Lava flows descended the south-southwest ravine during this period, accompanied by jets of vapor and a thick blackish cloud exceeding 2,000 m that drifted west, indicating magmatic involvement and possible dome growth or pyroclastic flows (nuées ardentes). In December 1918 specifically, rumbling sounds, light seismic shocks, and lava caused widespread alarm in nearby towns and barangays, though no evacuations were reported. Following a period of relative quiescence, activity resumed in June 1928 with ejections from the summit, producing minor steam-and- plumes but no reported flows or significant impacts. The then erupted strongly on , 1933, in what newspaper accounts described as a vigorous event generating emissions and a powerful (referred to as a "tidal wave" in contemporary reports), which caused extensive damage to and resulted in nine fatalities downstream. This eruption highlighted Bulusan's potential for sudden explosive phases, though detailed plume heights or flow extents remain undocumented in available records. After 45 years of dormancy, unrest reemerged in late 1978 with multiple explosions on July 29, August 2, 4, and 14, ejecting dark-colored smoke and -laden steam from the summit . This initiated a prolonged episode of intermittent phreatomagmatic activity through 1981, characterized by ejections and increased that prompted evacuations from nearby barangays in Sorsogon Province to mitigate risks from falling debris and potential flows. In 1981, the most intense phase occurred, beginning on April 9 with explosive ejections producing plumes up to 4 km high; accumulations of 4 mm of fell in areas downwind, and a new (approximately 90 m in diameter and 20 m deep) opened near the northeastern rim. The 1981 events reached a (VEI) of 3, underscoring their moderate scale. Lahars generated during heavy rains in this period affected river valleys, though specific casualties were limited. Overall, 20th-century eruptions at Bulusan exhibited clustered patterns, with early magmatic phases giving way to more frequent phreatic events by the late century, suggestive of ongoing ascent interacting with the volcano's extensive hydrothermal system. These activities occasionally activated hydrothermal features, such as increased fumarolic emissions in the craters.

Recent Volcanic Activity

2006–2007 Phreatic Events

The 2006–2007 phreatic events at Mount Bulusan marked the onset of heightened unrest at the following a period of relative quiescence since 1995. These steam-driven explosions resulted from the interaction of rising magmatic gases and heat with shallow , producing ash plumes without any observed lava or magmatic material in . Seismic swarms, characterized by explosion-type earthquakes, often preceded the eruptions, signaling increased fluid movement beneath the summit crater. In –June 2006, Bulusan experienced at least four significant eruptions, beginning with an event on 21 that generated a 1.5 km-high ash plume drifting southwest, depositing light in seven barangays across and Juban municipalities. Subsequent explosions occurred on 29 April (plume ~1.6 km high, ashfall in nearby communities), 25 May (light up to 2 mm thick in eight western and southwestern villages including Juban and ), and 7 (2 km-high ash-and-steam plume drifting north-northwest, light ashfall up to 20 km away in 11 barangays). The Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the alert level to 2 on 7 , establishing a 4 km permanent danger zone around the summit due to ongoing unrest. These events caused minor crop damage from ash accumulation, particularly in rice and vegetable fields in Casiguran, and led to temporary school closures in affected areas; no direct fatalities were reported, though one indirect death from ash-induced occurred on 10 . Activity continued into late 2006 and 2007, with phreatic explosions persisting through . In July–October 2007, three notable events included increased seismic swarms from late , followed by explosions on 4 (two short bursts) and a major eruption on 10 that produced a 4.5 km-high ash-and-steam plume lasting 9 minutes and drifting southeast and south-southwest, with light ashfall (trace to 5 mm) in , Casiguran, Gubat, Juban, and Bulan. Additional explosions on 19 and 23 generated plumes up to 2.6 km high, accompanied by rumbling sounds heard up to 6 km away. Overall, the 2006–2007 sequence involved 19 distinct eruptions in 2006 and 7 in 2007, each ejecting fine dispersed by , with average volumes around 10^5 m³ per event. Impacts remained localized, including further losses from and brief disruptions to communities, but no lives were lost directly to the eruptions. These events shared characteristics with later ash emissions in 2015–2016, involving similar steam-driven mechanisms.

2010–2011 Explosive Eruptions

Mount Bulusan's volcanic unrest in late 2010 and early 2011 was marked by a series of explosions, driven by interactions between magma-heated and the shallow hydrothermal system, leading to sudden steam-and-ash emissions. This period followed a quiet phase since 2007 and was preceded by escalating , with the Philippine Institute of Volcanology and Seismology (PHIVOLCS) recording more than 200 volcanic earthquakes over the weeks leading up to the main events, signaling fluid movement beneath the edifice. The initial major activity occurred on 12 2010, when a generated an column reaching 1.5 km above the rim, drifting westward and depositing fine over nearby villages in province. The event lasted approximately 20 minutes, accompanied by rumbling sounds heard up to 10 km away and incandescent ejecta visible at night, though no significant pyroclastic flows were confirmed beyond minor hot material on the upper flanks. Earlier minor explosions on 6, 8, and 9 had produced smaller plumes up to 1 km high, but the 12 blast prompted heightened monitoring due to its intensity. Activity intensified in early 2011, culminating in two closely spaced eruptions on 21 . The first at 9:12 a.m. and the second at 10:27 a.m. produced gray plumes rising to 3-4 km above the , drifting southwest and blanketing communities in , Juban, and Bulan with up to 2 mm of . was reported as far as 10 km distant, and the explosions lasted several minutes each, with no lava emission but potential for minor ballistic . Heavy rains in late triggered small lahars along drainages, including the Puting Bato River, depositing sediment and prompting warnings for channel-confined flows. In response, PHIVOLCS raised the alert level to 1 (indicating low-level unrest) following the November events and maintained it through 2011, enforcing a 4 km permanent danger zone around the summit to mitigate risks from sudden blasts and ashfall. Approximately 500 families—around 1,000 residents—from villages in and Juban were evacuated in mid-November 2010, with similar advisories issued in February to avoid drainages prone to lahars. Seismic and visual monitoring data from this period underscored the hydrothermal nature of the unrest, with no signs of magmatic ascent.

2015–2016 Ash Emissions

During 2015, Mount Bulusan exhibited intermittent phreatic explosions characterized by steam-and-ash emissions, similar in mechanism to the 2006–2007 events where superheated water flashed to steam upon contact with hot rocks or magma. On May 1, a five-minute explosion from the summit crater produced a plume rising 200 meters that drifted west-northwest, depositing light ashfall in villages southwest and northwest of the volcano, including areas in Juban and Irosin up to 12 km away. This was followed on May 6 by a 3.5-minute phreatic explosion from a vent on the upper northwest flank, generating a 250-meter plume drifting west and causing ashfall in southwestern villages such as Cogon and Tinampo, about 8 km distant. A third notable event occurred on June 16, when a 10-minute explosion from the summit crater ejected a plume to 1 km that drifted west-southwest, leading to ashfall in northwestern areas including Juban, up to 11 km away. Seismic unrest accompanied these explosions, with up to 62 volcanic earthquakes recorded immediately after the May 1 event, though overall seismicity remained low to moderate afterward, averaging fewer than 24 events per month through the end of 2015. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the alert level to 1 following the May explosions, indicating abnormal conditions and enforcing a 4-km permanent danger zone. Activity persisted into 2016 with a single prominent on June 10, lasting five minutes and producing a grayish plume that rose 2 km above the northwest summit vent before drifting northwest; this event was preceded by increased rockfalls and rumbling sounds reported in nearby areas. Light ashfall affected villages in Juban and , though no significant seismic swarm was noted immediately prior. By December 2016, emissions had diminished to minor steam venting from the summit, accompanied by elevated fluxes averaging 559–1,255 tons per day, signaling ongoing magmatic but reduced eruptive intensity overall. PHIVOLCS maintained Alert Level 1 throughout the period, reflecting a trend of waning activity compared to the more frequent explosions of 2015.

2020–2022 Unrest and Phreatic Activity

The period from 2020 to 2022 marked a phase of heightened unrest at Mount Bulusan, characterized by increased , ground deformation, and elevated (SO₂) emissions indicative of magmatic processes beneath the , though no confirmed strombolian eruptions occurred. In 2020, the Bulusan Volcano Network recorded 72 volcanic earthquakes between 3 and 7 , including 43 low-frequency events associated with movement, alongside ongoing edifice detected since February 2020 and diffuse white gas-and-steam plumes rising from the southeastern vent. This unrest prompted PHIVOLCS to raise the alert level to 1 on 6 , the first such elevation in decades signaling abnormal conditions potentially driven by magmatic ascent, with the permanent danger zone maintained at 4 km. The alert was lowered to 0 on 26 October after declined. Activity intensified in , with multiple episodes of unrest reflecting sustained magmatic influence. From 7 to 11 May, 186 volcanic earthquakes were detected, accompanied by continued inflation on electronic tiltmeters, leading to the alert level being raised to 1 on 11 May. SO₂ emissions peaked at 48 tons per day on 20 May, well above baseline levels, suggesting from a shallow magmatic source. On 12 June, 95 weak volcanic earthquakes occurred alongside diffuse steam plumes from the southwestern vent drifting west-northwest, though no explosive bursts were reported during May to August. Heightened monitoring, including seismic, GPS, and gas sampling networks, was maintained throughout this period to track potential escalation. The alert level remained at 1 until late . In 2022, unrest culminated in explosions likely triggered by magmatic gases interacting with , producing plumes and expanding hazards. On 5 June, a lasted approximately 17 minutes, generating a 1 km-high plume that deposited fine in areas northwest of the volcano, prompting an alert level raise to 1 and a temporary extension of the danger zone to 6 km in some sectors. Another event on 12 June endured 18 minutes, producing grayish plumes 400–750 m tall that caused up to 50 km northwest, with SO₂ emissions measured at 1,900 tons per day on 11 June indicating significant magmatic . These events featured seismic signals consistent with sudden release but lacked ballistic or lava fountains typical of strombolian style; instead, they involved steam and expulsion. persisted with 213 earthquakes from 24 to 29 June, including a magnitude 3.5 event, and a on 26 June affected channels. The alert level was lowered to 0 on 21 August as parameters normalized.

2025 Eruptions and Seismic Swarms

On April 28, 2025, Mount Bulusan experienced a from its summit crater, lasting approximately 24 minutes based on seismic and records. The event generated a voluminous plume rising to 4,500 meters above the crater, drifting west to southwest, accompanied by a extending about 3 kilometers down the southeast flank. Ashfall was reported in Barangays Casigura and Monbon in Juban, , prompting evacuations within the 4-kilometer permanent danger zone and expansion to a 6-kilometer extended zone for potential risks. A second occurred on April 29 at 7:43 PM, lasting 77 minutes and producing a plume that drifted southwest, with ashfall affecting nearby areas in . In response, the Philippine Institute of and (PHIVOLCS) raised the alert level to 1, indicating abnormal conditions driven by hydrothermal processes, with close monitoring for possible phreatomagmatic escalation. Seismic activity at Mount Bulusan increased notably starting October 11, 2025, with the volcano-tectonic network recording 72 earthquakes over a 24-hour period, signaling heightened unrest likely related to fluid movement within the edifice. Sulfur dioxide (SO₂) emissions, measured at an average of 31 tonnes per day on October 9, remained below the baseline of 200 tonnes per day at that time, but subsequent observations showed a rise, reaching 1,006 tonnes per day by November 7. No eruptive activity occurred during this period, though steam plumes up to 50 meters high were observed drifting southwest, and ground deformation indicated edifice inflation. Seismicity decreased in early November, leading PHIVOLCS to lower the alert level to 0 on November 12, 2025, as activity subsided to baseline levels. As of November 19, 2025, the volcano remains at Alert Level 0 with no significant unrest reported. These 2025 events echo patterns of magmatic unrest seen in the 2020–2022 activity, suggesting persistent subsurface processes but with a focus on and seismic indicators in the current phase.

Hazards and Mitigation

Monitoring Systems

The monitoring of Mount Bulusan is primarily overseen by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) through the Bulusan Volcano Observatory (BVO), established in 1980 and relocated to in 2004. The core infrastructure is the Bulusan Volcano Network (BVN), which comprises nine broadband seismic stations for detecting earthquakes and tremors, six continuous (GPS) stations, two electronic tiltmeters, and IP cameras for real-time visual surveillance of the summit and flanks. These solar-powered, autonomous systems transmit data in real-time to PHIVOLCS headquarters in via WiFi, LTE, or , enabling rapid assessment of volcanic unrest. Gas emissions are tracked using Differential Optical Absorption Spectroscopy () to measure sulfur dioxide (SO₂) flux from the summit vents, a key indicator of magmatic activity. During periods of unrest, SO₂ emissions typically range from 500 to over 5,000 tons per day, far exceeding the baseline of 200 tons per day, as observed in events with sustained . Deformation monitoring complements this through the continuous GPS network, which records ground or associated with movement, and tiltmeters that detect subtle changes in the volcano's slope orientation. PHIVOLCS employs a five-level alert system to interpret monitoring data and guide public safety responses, ranging from Level 0 (normal background activity) to Level 5 (hazardous eruption in progress). A 4-kilometer permanent danger zone (PDZ) encircles the at all times due to risks from sudden explosions, rockfalls, and landslides, with expanded zones declared at higher alert levels based on escalating parameters like swarms or ejections. These systems were instrumental in detecting the seismic swarms and elevated emissions during the 2025 volcanic unrest, including the April and October seismic swarm. For example, in October 2025, the network detected 72 volcano-tectonic earthquakes on October 11, with low SO₂ emissions of 31 tonnes/day; the alert level was subsequently lowered from 1 to 0 on October 26, 2025.

Evacuation and Preparedness Measures

The permanent danger zone around Mount Bulusan's summit is defined as a 4-kilometer radius, where entry is strictly prohibited at all times due to risks of sudden explosions, rockfalls, and landslides. During periods of elevated unrest, such as Alert Level 3 or higher, this zone is expanded to 6–10 kilometers to account for potential pyroclastic flows, ashfalls, and lahars, with specific advisories issued based on monitoring data. Evacuation plans for communities near Mount Bulusan include pre-designated centers in the municipalities of Bulusan and Juban, , capable of accommodating thousands of residents from high-risk barangays. These plans, developed in response to unrest since 2006, incorporate annual drills coordinated by local governments and the Philippine Institute of Volcanology and Seismology (PHIVOLCS) to simulate eruptions and ensure rapid response. The drills emphasize routes out of danger zones, assembly points, and coordination with services, fostering readiness for sudden events. PHIVOLCS issues regular advisories to educate residents on volcanic hazards, including risks along drainages like the Bulusan and Talisay rivers, where heavy rains can mobilize and . Communities are instructed to use protective or wet cloths during ashfalls to prevent respiratory issues, avoid low-lying areas prone to flooding, and adhere to no-entry policies in restricted zones. Historical implementations of these measures have proven effective, as seen in the 2011 eruptions when proactive evacuations from affected barangays prevented any casualties despite ashfall impacting nearby areas. Similarly, during the April 2025 phreatic eruption, over 2,400 residents were successfully evacuated to centers in Juban and surrounding towns, resulting in no reported injuries or fatalities.

Ecology and Cultural Significance

Biodiversity and Natural Park Status

The Bulusan Volcano Natural Park spans approximately 3,640 hectares of pristine encircling Mount Bulusan. Initially protected in , it was reclassified as a natural park under No. 421 on November 27, 2000, and further designated under the Expanded National Integrated Protected Areas System (NIPAS) in 2018 to preserve its ecological integrity. Designated under the National Integrated Protected Areas System (NIPAS) Act of 1992, the park serves as a critical for endemic and , qualifying it as a Key Area due to its support for significant populations of Luzon Endemic Bird Area restricted-range birds. The diverse ecosystems, ranging from lowland dipterocarp forests to montane mossy forests, harbor unique flora, including the endemic fern Pronephrium bulusanicum, which thrives in the volcanic soils and humid conditions. Additionally, the park is home to Canarium ovatum, the pili nut tree, which grows abundantly in the surrounding rainforests and contributes to the region's botanical diversity. The fauna of the park is equally remarkable, featuring mammals such as the Philippine brown deer (Rusa marianna), (Sus philippensis), and Luzon giant cloud rat (Phloeomys cumingi), alongside a variety of herpetofauna including the rough-backed forest frog (Platymantis corrugatus) and sailfin water lizard (Hydrosaurus pustulatus). Avian diversity is particularly high, with important populations of endemic species like the Luzon tarictic hornbill (Penelopides manillae) and (Nisaetus philippensis), supporting numerous threatened and restricted-range birds within the Luzon Endemic Bird Area. Bulusan Lake, a tectonic within the park, sustains rich aquatic ecosystems, hosting 21 species of freshwater fish—of which 15 are endemic, including the Bicol endemic goby (Redigobius dispar)—as well as diverse amphibians adapted to its forested margins. Conservation efforts in the park address ongoing challenges posed by human activities, including slash-and-burn agriculture (kaingin), , fuelwood gathering, and , which have led to habitat degradation over the years. , while promoting awareness and local economies, contributes to trail erosion and disturbance along popular routes, necessitating strategies like regulated visitor access and trail maintenance to mitigate impacts on sensitive habitats. These measures aim to balance protection with sustainable use, ensuring the park's role as a vital refuge for Luzon's endemic .

Local Cultural Role and Human Impacts

Mount Bulusan holds a prominent place in Bicolano , often depicted as a sacred entity intertwined with water spirits and natural forces. Local legends portray the as the dwelling of a mighty spirit that governs the land, ensuring prosperity for obedient inhabitants while punishing disobedience with eruptions or floods. One enduring tale recounts the village of Aguingay, submerged by divine wrath to form Lake Aguingay, symbolizing the volcano's role as a guardian of water sources that sustain the region. Another narrative, "Si Bulusan nan si Agingay," describes a harmonious couple living beneath the , whose story underscores themes of balance between human life and the mountain's volatile power. These myths associate Bulusan with Bicolano water deities, such as Tubigan, the god of water, reflecting the volcano's vital contribution to rivers, springs, and lakes that define local identity. Cultural reverence manifests in annual festivals that weave volcanic themes into community celebrations. The Agingay Festival, held every July 24 in Bulusan, honors the legend of the twin lakes through street dances, processions, and rituals that highlight the volcano's mystical origins. Similarly, the Bulusan Festival, part of the broader Kasanggayahan Festival in October, features performances and exhibits that celebrate the mountain's enduring presence in 's heritage. The annual fiesta for Saint James the Greater, the patron saint of Bulusan, includes prayers for protection from eruptions, blending Catholic traditions with pre-colonial about the volcano's spirit. The local economy in Bulusan municipality relies heavily on agriculture and ecotourism, both shaped by the volcano's fertile slopes and natural attractions. Coconut and abaca farming dominate, with the volcano's nutrient-rich soils supporting these crops that form the backbone of livelihoods in Sorsogon Province. Ecotourism, centered on Bulusan Volcano Natural Park, draws visitors to its lakes, trails, and biodiversity, generating income through guided tours and homestays that employ a significant portion of the local population. These sectors intertwine, as park ecosystems support agro-based activities, though volcanic activity periodically disrupts farming and tourism revenues. Volcanic events since 2006 have inflicted notable human impacts on surrounding communities, primarily through ashfall and lahars rather than direct fatalities. eruptions and ash emissions have triggered respiratory issues, with fine particles irritating airways and exacerbating conditions like , particularly among children and the elderly in affected barangays. Lahars, often rain-induced following eruptions, have displaced thousands of families; for instance, the 2006 activity prompted evacuations of several hundred households, while the 2022 eruption affected over 3,000 families in Juban and through mudflows and ash accumulation. In April 2025, a produced ash plumes up to 500 meters high, causing light ashfall in nearby areas, temporary evacuations, and increased respiratory concerns, though no fatalities were reported. No direct deaths from eruptions have occurred in this period, though indirect hazards like typhoon-triggered lahars in 2006 caused fatalities. In response, communities around Bulusan have implemented community-based disaster risk reduction (CBDRR) programs since 2010, enhancing local resilience through . These initiatives, supported by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and local governments, involve hazard mapping, early warning systems, and drills tailored to volcanic threats. In , CBDRR efforts include integrating risk assessments into municipal plans, training volunteers for evacuation, and fostering cooperation among residents to mitigate ash and effects. Such programs have improved adaptive capacities, reducing vulnerability in high-risk areas like Puting Sapa and Mapaso.

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