Phreatic activity during 5-12 June 2022

Bulusan lies at the SE end of the Bicol volcanic arc in the Philippines. It is flanked by several other large intra-caldera lava domes and cones and its summit contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Moderate explosive eruptions have been recorded since the mid-19th century. The previous eruption period, during June 2017, consisted of weak phreatic explosions and produced minor ashfall in nearby villages (BGVN 42:08). This reporting period covers a new eruption period during June 2022, characterized by similar phreatic explosions, based on information from the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

Summary of activity during January 2020-May 2022. Activity since the last eruption in June 2017 mainly consisted of occasional volcanic earthquakes and weak gas-and-steam emissions, sulfur dioxide emissions were below detectable levels since 2018, and the frequency of volcanic earthquakes had been at baseline levels of 0-2 earthquakes/day since May 2019. During 3-7 July 2020 a total of 72 volcanic earthquakes were detected, which included 43 low-frequency events. Diffuse white gas-and-steam plumes rose from the lower SE vent. Ground deformation data from continuous GPS measurements indicated short-term inflation of the edifice since late February 2020. On 6 July the Volcano Alert Level (VAL) was raised to 1, but activity remained relatively low, and on 26 October the VAL was lowered to 0 (normal conditions). Diffuse white gas-and-steam plumes continued to rise from the summit vents.

Unrest increased again during 7-10 May 2021, according to PHIVOLCS. There was a total of 186 volcanic earthquakes detected during 7-11 May. Inflation that was first recorded on the upper flanks on 6 March had continued. Sulfur dioxide emissions peaked at 48 tons/day on 20 May 2021, which was still within baseline levels. The VAL was raised to 1 on 11 May. During 12 June a total of 95 weak volcanic earthquakes were detected, in addition to diffuse white gas-and-steam plumes rising from the SW vent. Seismicity declined to the baseline level of 2-3 volcanic earthquakes per day during 1 July-17 August 2021, during which a total of 109 weak events were recorded. Short-term inflation had been detected since July 2020.

Activity during June 2022. During 4-5 June, PHIVOLCS reported 77 volcanic earthquakes. Ground deformation data from continuous GPS monitoring indicated short-term inflation, and electronic tilt data recorded an inflation event on the SE lower slopes beginning in April 2022. A phreatic eruption occurred at 1037 on 5 June 2022 and lasted approximately 17 minutes, based on seismic and infrasound monitoring by the Bulusan Volcano Network (BVN). Though cloud cover obscured most visual observations, a gray ash plume seen from Juban (Sorsogon Province) rose at least 1 km high and drifted W. Ashfall was reported to the NW in Puting Sapa, Añog, Guruyan, Catanusan, Buraburan, Bacolod, and Sangkayon in Juban, and Bolos in Irosin, Sorsogon Province. Residents of Añog, Guruyan, and Catanusan also reported rumbling sounds and a sulfur odor. As a result, the VAL was raised to 1. After this event, gas-and-steam emissions rose from the main crater, as well as the NW summit vent. A total of 27 weak volcanic earthquakes were recorded until 1600 by the BVN.

Increased seismicity began at 0500 on 9 June, which included a total of 45 volcanic earthquakes, including two low-frequency events. Most of these events were low magnitude and shallow. Another phreatic explosion was detected by the BVN at 0337 on 12 June, which lasted 18 minutes, based on seismic records. The eruption plume was not visible in webcams, but residents of Inlagadian (Casiguran municipality) briefly saw incandescence at the base of a plume. An explosion was felt by residents within 5 km, including in the barangays of Añog (Juban) and Inlagadian. Rumbling was heard in Sitio Bagong Barrio, and in the barangays of Santa Lourdes (Barcelona), Inlagadian and San Juan (Casiguran), Bentuco (Gubat), and Añog, Calateo, and Puting Sapa (Juban). Sporadic ash emissions were detected starting at 0430; ash emissions were visible rising from six vents: Blackbird Crater (the main crater), three explosion pits in the summit crater, and two vents on the NW and N sides of the summit. Gas-and-steam and ash plumes rose 400-750 m above the summit and drifted several kilometers NW. Ashfall was reported in areas as far as 50 km NW in Sorsogon City and Palanas, Pilar, Sorsogon Province, across Sorsogon Bay, and as far as Anislag (Daraga, Albay). Minor ashfall was detected in several barangays in the municipalities of Casiguran, Juban, and Magallanes. Sulfur dioxide emissions averaged 1,900 tons/day during 5-12 June. According to a Rappler news article, more than 11,000 people (at least 2,800 families) in Juban evacuated, and flights in and out of the Bicol International Airport were cancelled.

Unrest persisted through the rest of June. Gas-and-steam emissions rose 100-500 m above the summit and drifted NW, WSW, SW, and W. Daily sulfur dioxide emissions were 559-1,255 tons/day. Seismicity increased on 20 June; during 0500-1145 a total of 65 volcanic earthquakes were detected, including one low-frequency volcanic earthquake, though most were weak shallow events. During 24-29 June the BVN detected a total of 213 volcanic earthquakes, the strongest of which was an Mw 3.5 that occurred at 2327 on 24 June. Residents of Irosin and Bulusan in the Sorsogon Province felt the earthquake. A small-volume lahar began approximately at 1904 on 26 June during a thunderstorm, based on seismic and infrasound data. The event lasted 54 minutes and the Bulusan Volcano Observatory (BVO) confirmed thin, channel-confined lahar deposits along the Calang Creek on the SW flank, in the Cogon barangay.

Seismicity decreased to background levels during the third week of July. During 25 July-6 August sulfur dioxide emissions were 230 tons/day. On 21 August PHIVOLCS lowered the Alert Level to 0, reporting that unrest continued to decline to background levels.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Rappler, Unit B, 3/F, North Wing Estancia Offices, Capitol Commons, Ortigas Center, Pasig City 1605, Bulusan Volcano erupts again, ash spreads to more areas, (URL: https://www.rappler.com/nation/phivolcs-bulusan-volcano-phreatic-eruption-advisory-june-12-2022-420am/).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

July 1978 (SEAN 03:07) Cite this Report

Small ash eruption

Bulusan ejected a grayish steam and ash cloud for about 30 minutes on 29 July, beginning at 1155. The cloud rose several hundred meters above the crater and deposited 1-7 mm of ash NE of the volcano. The eruption was accompanied by rumbling. Steam emission persisted after the eruption, and as of 3 August, white to dirty white vapor was being continuously emitted to about 100 m above the crater. COMVOL delineated a danger zone within 5 km of the summit, to be evacuated in the event of a major eruption. Bulusan last erupted in December 1933.

Information Contacts: G. Andal, COMVOL, Quezon City; AFP.

August 1978 (SEAN 03:08) Cite this Report

Brief ash eruption continues

A voluminous ash-laden cloud rose 2,500-3,000 m above the crater rim on 14 August, then was blown NE by the prevailing wind. The eruption, accompanied by hissing and rumbling sounds, began at 0545 and lasted about 30 minutes. A seismograph 5 km SSE of the crater was saturated by an explosion-type earthquake.

Further Reference. Aguila, L.G., 1978, The 1978 eruptions of Bulusan volcano: The COMVOL Letter, v. 10, nos. 3-4, p. 4-8.

Information Contacts: G. Andal, COMVOL, Quezon City.

January 1980 (SEAN 05:01) Cite this Report

Brief eruption with 1-km-high ash clouds

Bulusan began to erupt at 1301 on 27 December, ejecting significant amounts of ash to about 1 km above the summit. Ash was blown WSW by the prevailing wind. The eruption lasted for 1 hour and 13 minutes, and was accompanied by hissing and rumbling. As of early January, some activity was continuing.

Information Contacts: O. Peña, COMVOL, Quezon City.

February 1980 (SEAN 05:02) Cite this Report

Ash explosions and earthquakes

The eruption continued with a second explosion on 12 January at 1640. Ash rose about 500 m above the crater rim, then drifted NNW. COMVOL had predicted further activity in the Bulusan Volcano Bulletin dated 4 January, based on patterns exhibited during previous eruptions, especially the 1878 eruption.

Citing a COMVOL official, Kyodo radio reported that a third explosion occurred on 7 February, apparently ejecting ash to 6 km. Ash emission was continuing early the next day. Residents left the area, reportedly because of 28 volcanic earthquakes and two tectonic events.

Information Contacts: O. Peña, COMVOL, Quezon City; Kyodo Radio, Tokyo.

March 1980 (SEAN 05:03) Cite this Report

Occasional steam and ash explosions continue

Occasional explosions continued through March. The 7 February explosion began at 0215, after an increase in the number of volcanic earthquakes. Cauliflower-shaped, ash-laden clouds rose about 6 km above the crater rim before drifting SSW. Rumbling and hissing sounds accompanied the activity. Milder ejection of ash-laden steam clouds started at 1102 the next day, with light ashfall continuing until late afternoon on the volcano's SW sector. Another weak ash ejection occurred 9 February.

Clouds and rain made observation of the summit and collection of ashfall data difficult in March. A strong odor of H₂S was detected at San Benon station, 6 km SSW of the crater, at 0945-0950 and 1030-1200 on 10 March, but no ashfall was reported. On 22 March, light ashfall occurred from 1120 to 1135.

Three weak ejections of ash-laden steam clouds took place on 26 March. At 0449, a cloud rose to approximately 400 m above the crater rim before winds blew it NW. A second steam and ash column reached 500-700 m above the rim about 1200, and a third was ejected to 300 m height two hours later. About 2 mm of ash fell on a settlement 8 km NNW of the crater.

At 1525 the next day, a volcanic earthquake of intensity I on the Modified Rossi-Forel (MRF) scale was felt at Lake Bulusan station, 4.5 km SE of the crater. Rumbling and hissing sounds accompanied the earthquake. Ejection of ash-laden clouds was visible through weather clouds at the summit.

Information Contacts: O. Peña, COMVOL, Quezon City.

April 1980 (SEAN 05:04) Cite this Report

Moderate ash explosions follows mild activity

Almost daily mild ejection of ash-laden steam clouds characterized activity from 2 April until late in the month. The clouds rose 100-1,500 m above the summit. On 4, 5, 15, 17, and 22 April, light ashfalls took place on villages as much as 8 km from the crater in the volcano's NW and SW quadrants. Activity was sometimes accompanied by volcanic earthquakes, including B-type events at 1243 on 2 April and 0722, 0950, 1007, and 1627 on 4 April, and by hissing sounds.

At 1950 on 29 April, Bulusan erupted a series of dark, cauliflower-shaped ash clouds, forming a column that reached 3-4 km above the summit. About 2.5 mm of ash fell on SW flank villages. Hissing and intermittent rumbling sounds were heard during the ash ejection. The 29 April activity was preceded by about three days of increased seismicity, when seismographs recorded 170 volcanic earthquakes. Two of these were felt at intensity I on the Rossi-Forel scale at a COMVOL station.

Information Contacts: O. Peña, COMVOL, Quezon City.

June 1980 (SEAN 05:06) Cite this Report

Steam and ash emission

Occasional mild emission of ash-laden steam clouds continued through June. During June, some light ashfalls occurred on the S and SW flanks.

Information Contacts: O. Peña, COMVOL, Quezon City.

July 1980 (SEAN 05:07) Cite this Report

Ash eruption and earthquake swarm

An earthquake swarm began on 6 July, when 108 volcanic events were recorded in a 24-hour period. Six events were felt at intensities of I-IV on the MRF scale and were accompanied by rumbling. Seismicity peaked on 10 July with 189 recorded shocks, ten felt at intensities I-IV. The swarm declined gradually after the 10th.

On 19 July, ash-rich steam clouds rose about 6 km above the summit. About 3 mm of ash fell on villages to the SE. Seismicity increased again on 22 July, with 235 volcanic earthquakes recorded in 24 hours. Ten were felt at intensities up to IV. AFP reported a 24 July COMVOL announcement that persons living within 4 km of Bulusan had been instructed to evacuate because of the earthquakes. On 27 July, 323 events were recorded and eleven felt, again at intensities of as much as IV. The swarm was continuing as of 29 July.

Information Contacts: O. Peña, COMVOL, Quezon City; AFP.

August 1980 (SEAN 05:08) Cite this Report

Explosions and seismicity continue

Occasional explosions continued through late August. Four explosions have occurred since last month, on 30 July (the strongest) and 1, 5, and 24 August. Ash-laden steam clouds rose 4-7 km above the summit, depositing ash as much as 14 km from the crater. The maximum measured ashfall thickness was 3.5 mm. The explosions were preceded by earthquakes of intensities I-IV on the MRF scale, continuing the seismicity that began on 6 July. As of 28 August, occasional felt events were continuing.

Information Contacts: O. Peña, COMVOL, Quezon City.

September 1980 (SEAN 05:09) Cite this Report

Small ash ejection

Only one explosion was reported during September, a mild ash ejection on the 28th at 1155. The summit was covered by weather clouds, but seismographs in the area recorded the activity and villages in the SE sector of the volcano received traces of ashfall.

Information Contacts: O. Peña, COMVOL, Quezon City.

November 1980 (SEAN 05:11) Cite this Report

Seismic activity decreases

The most recent ash eruption, on 28 September, was followed by a series of volcanic earthquakes that became less frequent with time. Felt events of intensity I-II on the MRF scale have also occasionally been recorded.

Information Contacts: O. Peña, COMVOL, Quezon City.

April 1981 (SEAN 06:04) Cite this Report

Ash ejection and seismicity

Bulusan began to eject ash on 9 April at 1008, its first such activity since 28 September 1980. Eruption clouds reached 4 km height and deposited 4 mm of ash on villages on the W side of the volcano. AFP reports that the 9 April eruption lasted about 8 hours.

A second episode of ash ejection started 15 April at 1858. Lightning flashes were observed within the eruption clouds, which reached an approximate height of 8 km. Most of the ashfall was again on villages W of Bulusan, with accumulations of as much as 6 mm.

An earthquake swarm began 20 April. During the next seven days, 1,812 events were recorded, 64 of which were felt at MM I-V on the Modified Mercalli Scale and were accompanied by rumbling. On 27 April at 1745, renewed explosive activity produced ashfalls on villages SW of the crater. Clouds obscured the summit, preventing determination of the eruption column height. Seismicity has declined since then. No additional eruptive activity had occurred as of 11 May.

Information Contacts: O. Peña, COMVOL, Quezon City; AFP.

June 1981 (SEAN 06:06) Cite this Report

Earthquake swarm

Seismographs registered a local earthquake swarm 30 June-4 July. Of the 700 recorded events, eleven were felt at intensities I-II on the MRF scale and seven others were accompanied by rumbling. No eruption took place.

Information Contacts: O. Peña, COMVOL, Quezon City.

July 1981 (SEAN 06:07) Cite this Report

No eruption follows earthquake swarm

No eruption followed the 30 June-4 July earthquake swarm, and seismic activity at the volcano has remained relatively quiet since then.

Information Contacts: O. Peña, COMVOL, Quezon City.

June 1983 (SEAN 08:06) Cite this Report

Two small phreatic explosions from summit crater

Mild phreatic explosions from the summit crater occurred at 0515 on 25 June and 0515 on 29 June. Eruption clouds reached heights of 1,000 and 1,200 m. Between 1 and 2 mm of ash fell on the NW quadrant of the volcano but no damage was reported. An intermittent increase in steaming from the summit crater and vents on the upper W flank was noted about a month before the eruption. A week before the first explosion, the temperature of hot springs 4 km S of the summit crater increased by 2°C and their discharge rate increased by 4 l/s. No increase in seismicity was noted.

Information Contacts: O. Peña, PHIVOLCS, Quezon City.

April 1986 (SEAN 11:04) Cite this Report

Seismic swarm in summit caldera

A seismic swarm began on 19 April at 2022 and lasted for ~ 10 hours. A total of 229 volcanic earthquakes were recorded by most of the five seismic monitoring stations. The initial phase was characterized by high-frequency volcanic earthquakes, gradually replaced by low-frequency volcanic earthquakes during the peak and latter part of the activity. Three of the events were felt, with epicenters initially located ~ 7.4 km SE (azimuth 134°) of the summit crater, within the caldera.

No other significant change was observed. Steam emission remained weak and hot spring temperatures remained normal. Local seismicity gradually declined to a low level, with only 1 high-frequency volcanic earthquake recorded on 22 April.

The last eruption of Bulusan, in June 1983, was not preceded by an increase in seismicity, but hot spring temperatures had increased several degrees. The April 1981 eruption, however, was preceded by an 8-day earthquake swarm. A seismic swarm following that eruption did not culminate in additional eruptive activity.

Information Contacts: PHIVOLCS.

May 1987 (SEAN 12:05) Cite this Report

Seismic swarm and slightly increased steaming

Seismicity rose again to a high level on 5 May with two high-frequency and 18 low-frequency volcanic earthquakes recorded in the area of the volcano. The beginning of the swarm was accompanied by a slight increase in steam emission at an upper fissure. Five tectonic earthquakes with large maximum double amplitudes were recorded the same day. A total of 103 high-frequency and 308 low-frequency volcanic events were recorded by the 3-station seismic network during the entire crisis. This swarm occurred 55 days after the previous swarm on 3-21 March. A two-month recurrence had been recognized for seismic swarms prior to the May episode (figure 1).

Figure 1. Seismicity at Bulusan, January 1986-May 1987. Courtesy of PHIVOLCS.

Further Reference. Bautista, L.P., 1987, Volcano Update - Bulusan Volcano: PHIVOLCS Observer, v. 3, no. 2, p. 5.

Information Contacts: PHIVOLCS.

December 1987 (SEAN 12:12) Cite this Report

Strong volcanic earthquakes; weak steam emissions

Strong volcanic earthquakes were detected by the single instrument in operation at Bulusan from 22 October to 3 December (typhoons damaged the remainder of the seismic telemetry network). High-frequency earthquakes with S-P intervals ranging from 2.0 to 2.6 seconds were recorded on 22, 23, and 31 October, and 3 December. The 22 October earthquake was felt at intensity II. Steam emission from the upper fissure remained white with the plume varying from wispy to weak. Thermal measurements showed no anomalous change.

Information Contacts: PHIVOLCS.

February 1988 (SEAN 13:02) Cite this Report

Small ash ejections and seismicity

A mild ash ejection began on 20 February at 1945. Lightning flashes were observed near the summit during the activity, and hissing and rumbling were faintly audible from 2010 until 0600 the next morning on the W side of the volcano. A field investigation revealed traces of ash on W flank villages (Gulanggulang, 7 km SW of the summit; Bolos, 7 km W; and Sangkayon). No clear precursors were observed. Local seismicity had varied from 0 to 3 volcanic events/day, temperatures and chemistry of monitored hot springs showed no anomalous changes, and results of the latest EDM survey, in October, were within background levels.

After the eruption, a white steam plume emerged from the vent under some pressure; during quiescent periods, only a wispy plume is usually emitted. Vapor emission from the upper end of a fissure was about half that of the steaming vent. Temperatures of hot springs remained stable. The single nearby PHIVOLCS seismograph (at San Benon, 5.1 km SW of the crater) recorded an indistinct explosion signal with the onset of ash ejection. An increase in local seismicity followed, as 29 low-frequency volcanic earthquakes (LFVE), 19 tremor episodes, and five explosion shocks were recorded during the remainder of the day. Only one LFVE was detected the next day (21 February), but a sulfurous odor was noted at Gulanggulang. Local seismicity increased again on 22 February, with 6 high-frequency volcanic earthquakes (HFVE) and 12 LFVEs. Amplitudes of the HFVEs were larger, but none were felt.

A magnitude 6.9 regional earthquake was centered 80 km NE of Bulusan on 24 February and felt at Rossi-Forel intensity V in the Bulusan area; several aftershocks were also felt there. At about the time of the regional earthquake, a landslide was observed to have recently occurred on the volcano's middle to lower flank. The number of recorded local earthquakes reached a maximum the same day (80 events), and seismicity remained vigorous through the end of the month. Steaming from the upper end of the fissure varied from weak to moderate. Sulfurous odors and hissing sounds were often evident (at Gulanggulang; Angas, 2 km W; San Benon; and Cogon, 5 km SW).

Small ash emissions occurred on 1 March, at 0502, 0552, 1458, 1510, 1523, 1528, and 1547, accompanied by rumbling sounds, explosion earthquakes, and several minutes of harmonic tremor. The ash plume ejected at 1458 reached 1 km above the crater; summit weather clouds obscured the morning plumes. Ash emitted in the morning was carried west by prevailing winds (to the villages of Gulanggulang, Sangkayon, and Puting Sapa). Afternoon ashfall was more extensive, and included the NW flank (reaching Aniog, 5.5 km NW; Rangas, 7 km NW; Bacolod, 6.5 km WNW; Puting Sapa; Buran-Buran; Sangkayon; Bolos, 7 km W; Guruyan, 9 km WSW; and Cogon). A small mudflow was observed at Cogon at 0700, consisting partly of ash ejected earlier that day. Some low-frequency harmonic tremor was detected after the 1 March explosions.

Ash ejections resumed 6-8 March. On 6 March, a 1,500-m column was emitted at 1504, depositing ash to the W and SW (on the villages of Cogon; San Benon; Mt. Jormajan, 6 km WSW; Puting-Sapa; Gulanggulang; Monbon, 6 km SW; Gabao, 9.5 km WSW; and Tinampo). Additional ejections at 1521, 1525, 1536, 1606, 1649, and 2050 were recorded as explosion earthquakes. On 7 March at 1107, a 1,430-m-high ash cloud was observed from the SE flank village of Salvacion. Ejections continued that evening at 2013 and 2016 and early the next morning at 0030, 0249, and 0414. Ash again fell on the S and SW flanks (at Monbon, Gulang, Cogon, and Tinampo). Rumbling sounds accompanied all of the episodes except those on 7 March at 2013 and 8 March at 0030, when distinct explosions were heard by volcanologists at San Benon. Frequent seismicity continued, with a maximum of 58 tectonic earthquakes and 43 volcanic events on 7 March.

PHIVOLCS noted that Bulusan's 1988 behavior remains similar to the 1980 activity, which lasted for 9 months, and more mild ash ejections are expected.

Information Contacts: PHIVOLCS.

June 1988 (SEAN 13:06) Cite this Report

Strong seismicity

High levels of seismicity have persisted at Bulusan for the past 2 months. Volcanic earthquakes averaged 70/day with peak numbers of events reported on 26 April and 9 June. Seismic activity has not been as high since 24 February when one large event of Rossi-Forel intensity V and 80 smaller events were recorded at Bulusan (13:2).

On 26 April, 535 high-frequency and 37 low-frequency volcanic earthquakes, and one harmonic tremor episode were recorded by the San Benon Observatory (5.1 km SW of the crater). Three of these large-amplitude events were felt at intensity I (San Benon) and two events at intensity II (Bulusan Lake, 5.9 km SE of the crater). Several strong pulses of seismicity were noted in May and June: 1-11 May, 12-22 May, 25 May-1 June, and 5 June to July. These pulses may be attributed to fracturing within the caldera or within defined faults along the SE caldera rim. Epicentral plots clustered in two areas; one 6 km SE of the crater and the other 3 km NW of the crater. Depths ranged from 3 to 5 km. The seismic network recorded 233 volcanic earthquakes on 9 June. On 16 June, one of the day's 42 recorded volcanic events was felt at intensity I at San Benon, and on 17 June a tectonic earthquake was felt at intensity II at the Bulusan Lake Station.

Steam emission generally was profuse. The latest EDM data (19 June) suggest a slight inflationary trend for Bulusan.

Information Contacts: PHIVOLCS.

August 1988 (SEAN 13:08) Cite this Report

Vigorous seismicity continues; inflation

The high levels of seismicity that have persisted at Bulusan since April continued with seismic swarms on 22-23 June, 15-17 July, and 27-28 July. High-frequency tremor with a maximum double amplitude of 2.5 mm was recorded during the 27-28 July swarm. During an 8-day period from 16 to 23 August, 804 volcanic events were detected by the seismic network. Hypocenters followed a general NW-SE trend with average depths of 7 km. Small-amplitude (1.5-2.5 mm) events were also recorded on 6 days in August, most recently on the 22nd. Steam emission remained moderate to profuse, rising to about 150 m above the active vent. The latest EDM measurements, on 17 August, indicated an inflationary trend.

Further Reference. Bautista, L.P., 1988, The 1988 Bulusan Volcano Activity: PHIVOLCS Observer, v. 4, no. 1, p. 1, 3-4.

Information Contacts: PHIVOLCS.

November 1994 (BGVN 19:11) Cite this Report

Phreatic explosions cause ashfall in local villages and up to 16 km away

A phreatic eruption at 2043 on 27 November sent an ash plume 1.5 km high that drifted W and SW, causing ashfall in six villages, and was accompanied by 14 minutes of felt tremor. Following this event, PHIVOLCS declared the area within 4 km of the crater off-limits. A second ash explosion on 3 December at 2348 was accompanied by rumbling, but details are sketchy owing to heavy cloud cover. The third ash ejection, on 4 December, deposited traces of ash ~7 km downwind; no other observations were possible. The next day, another explosion at 1227 sent ash 1.5 km high that caused ashfall 5 km WSW and was noticed in two villages.

A phreatic explosion at 0650 on 12 December was also the strongest so far. The cauliflower-shaped eruption column, accompanied by a loud "pop," rose 3 km and deposited ash as far as 16 km SW. The main eruption column, light gray in color, rose vertically, and a smaller dark-gray surge cloud seemed to emanate from the base of the main eruption cloud. However, the runout was still within 4 km of the vent and no evacuation was recommended.

Five additional small explosions occurred through 28 December. Observations of an ash explosion at 0155 on 18 December was hampered by clouds, but was inferred from the seismogram and ash deposits at 5 villages, all SW of the volcano. A minor ash explosion at 0807 on 20 December produced an ash cloud not directly observed due to rain clouds, but ash fell ~7 km SW of the vent. A brief cloud break enabled volcanologists to make a COSPEC measurement of ~370 metric tons/day. At 1525 on 23 December, a slightly stronger ash ejection lasted 4 minutes, causing light ashfall in 6 villages, also in the SW. Light ashfall 7 km from the summit was noted again the next day following a 3-minute ash ejection at 2153 on 24 December. Ash output from a 7-minute eruption at 1253 on 27 December seemed to be larger than other events and spread to a wider area, despite calmer winds, depositing small amounts of ash in nine villages.

The onset of all ash emissions had a corresponding explosion-type earthquake recorded on the seismogram. This became diagnostic during heavy cloud cover when ash plumes could not be observed directly. Based on the earthquake amplitudes, the 27 November and 12 December events were the biggest explosions, although ash emission was greater on 27 December. In nearly each case, the ash deposit was <=2 mm thick at ~7 km downwind. Hazard maps had been prepared before the 27 November event. PHIVOLCS is planning to pull the telemetered seismic network installed on Mindoro for aftershock monitoring, and move it to Bulusan.

Information Contacts: R. Punongbayan, E. Corpuz, and E. Listanco, PHIVOLCS; Reuters.

December 1994 (BGVN 19:12) Cite this Report

Phreatic eruptions continue, but at a slower rate

The phreatic eruptions that started in late November seem to have slowed down, as evident from an apparent increase in intervals between ash explosions. There has been no great change in seismic character, with only a few daily earthquakes plus a few episodes of low-frequency tremor, some of which were probably related to steam jetting. An explosion at 2213 on 31 December ejected ash and was accompanied by rumbling and lightning flashes observed at Salvacion Monitoring Station (South). Areas affected were Cogon, Tinampo, Monbon, Bagsanga. Another ash explosion at 0008 on 7 January caused light ashfall at Barangay Cogon, Irosin (5-6 km from summit). At 1344 on 10 January, an ash explosion sent a plume 1 km above summit (1.5 km elevation) that drifted SSW. Very light ashfall was reported in villages up to 7 km SW.

Information Contacts: R. Punongbayan and E. Corpuz, PHIVOLCS.

January 1995 (BGVN 20:01) Cite this Report

Phreatic ash eruptions continue with low seismicity and deformation

Phreatic activity that started in November continued through December and January (table 1). Another eruption on 21 January at 2237 generated rumbling noises, lightning flashes over the summit, and light ashfall at the San Benon Observatory, ~5 km SW. Based on the seismic record, this event was fairly strong, but ash deposits measured later that day (1-2 mm, 7 km downwind) were similar in amount to previous ash emissions. COSPEC measurements could not be undertaken because of heavy cloud cover. The interval between this ash eruption and the previous had increased, which, along with very low seismicity and ground deformation, may be taken as an indicative of decreasing activity. Alert Level 2 was maintained, which advises against anyone visiting within 4 km of the summit. This warning of heightened volcanic activity was non-committal about the timing of future events because seismicity and deformation have not changed prior to these short-lived ash eruptions.

Table 1. Summary of recent phreatic eruption at Bulusan, 27 November 1994 to 28 January 1995. Data courtesy of PHIVOLCS.

Another explosion on 28 January at 1433 produced a 2-km-high ash cloud above the summit craters and deposited andesitic ash (<=3 mm) on villages up to 15 km downwind. This event, recorded by the local seismic network as an explosion-type earthquake, was again preceded by low and unremarkable local seismicity; most earthquakes and short-duration tremor have occurred after each explosion. Ground deformation was also at background levels. Because no escalating activity has been detected, as of 1 February there was no change in 4-km-radius danger zone and no evacuation was recommended. No damage to crops or villages have been reported nor have there been any injuries as a result of these eruptions.

Information Contacts: R. Punongbayan and E. Corpuz, PHIVOLCS.

April 2006 (BGVN 31:04) Cite this Report

Eruptions and earthquakes in March and April 2006 after years of little activity

Bulusan, after remaining relatively quiet since 1995, erupted multiple times during March and April 2006. There were no casualties or damage from these eruptions. On 21 March at 1044 the summit crater erupted, sending a column of ash 1.5 km into the sky accompanied by lightning and rumbling noises. Ash drifted N, W, and SW of the volcano and an hour after the event light ash fell on neighborhoods such as Barangays Cogon, Tinampo, Gulang-Gulang, and Bolos in the town of Irosin, as well as Barangays Puting Sapa and Bura-Buran in the town of Juban.

Ash ejected at 1058 on 22 March coincided with an explosion-type earthquake. Three other earthquakes were recorded at 2330, 2332, and 2337. The hazard status had been raised to Alert Level 1; the area within a 4 km radius of the summit is a Permanent Danger Zone.

On 29 April the volcano erupted in a similar fashion, emitting ash nearly 1.6 km into the air. There was no sign of lava and no reports of rumbling noises. It was reported that ash rained on nearby communities.

Information Contacts: R.U. Solidum and E. Corpuz, Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, PHIVOLCS Building, C.P. Garcia Avenue, Univ. of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Inq7.net, a venture between The Philippine Daily Inquirer Inc., and GMANetwork Inc. (URL: http://news.inq7.net/).

May 2006 (BGVN 31:05) Cite this Report

Explosive activity continues

Bulusan erupted at 2258 on 21 March 2006, continuing into April 2006 (BGVN 31:04). Figure 2 shows the location of Bulusan volcano on the SE tip of Luzon. Figure 3 gives satellite measurements of SO₂ one day after the eruption.

Figure 2. Map of the Philippines showing the PHIVOLCS earthquake and volcano monitoring network, and Bulusan's location. Smaller inset focuses on the Bulusan region and indicates some settlements. The smaller map is from Encarta Maps; the larger map, courtesy of PHIVOLCS.

Figure 3. Sulfur dioxide (SO2) emissions at 1345-1347 (local) on 22 March 2006 from Bulusan. The eruption was measured by the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite [OMI detects the total column amount of SO2 between the sensor and the Earth's surface]. This cloud appeared quite significant (estimated total mass ~ 1,000 metric tons) considering that the event was reported as phreatic and that the image was collected about 15 hours after the eruption. Courtesy of Simon Carn.

An ash eruption on 29 April did not cause any damage, but authorities asked people to avoid the region near the crater (figure 4). The current report stems in large part from information coming from The Philippine Institute of Volcanology and Seismology (PHIVOLCS). Table 2 provides a brief summary of 2006 activity and resulting plumes.

Figure 4. Image of a light ash plume snaking W from Bulusan acquired at 1250 on 29 April 2006. The image was made by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the U.S. National Aeronautics and Space Administration (NASA) Terra satellite. Courtesy of NASA Earth Observatory.

Table 2. Bulusan explosive plumes recorded during 2006. Courtesy of PHIVOLCS.

A phreatic ash explosion was recorded by the seismograph network at Bulusan between 2117 and 2130 on 25 May 2006. Light ashfall ranging from trace amounts to deposits 2 mm thick was reported from the W and SW villages of Bacolod, Sankayon, Puting Sapa, Rangas, Mapili, Caladgao, and Buraburan in the municipality of Juban, and Bolos in the municipality of Irosin, province of Sorsogon. PHIVOLCS reported that the ash explosion was more-or-less typical of activity at Bulusan during its current eruptive phase, and they expect more explosions to occur. Bulusan was at Alert Level 1, with a Permanent Danger Zone of 4 kilometers around the summit. The PHIVOLCS volcano alert signals range from Alert Level 1 (low-level unrest, no eruption imminent) through Alert Level 5 (hazardous explosive eruption in progress).

An ash-and-steam cloud emitted from the volcano on 31 May 2006 (figure 5) resulted in light ashfall, from trace amounts to 1.5 mm thickness, in areas W and NW of the volcano. An ash-and-steam cloud from Bulusan on 7 June 2006 resulted in light ashfall 5 km N and trace amounts as far as 20 km N. The Alert Level was raised to 2, which means restricted entry within 4 km of the summit. On 10 June, an ash-and-steam cloud reached a height of ~ 1 km above the summit and drifted N and NE. The Manila Standard Today reported one death caused by an asthma condition aggravated by exposure to ash.

Figure 5. A Bulusan ash explosion seen at 1617 on 31 May 2006. The event was photographed from the foot of the volcano, 5- 6 km from the summit, in the town of Irosin. Courtesy of PHIVOLCS.

On 13 June 2006 at 1904, an explosion lasting ~13 minutes issued from a fissure W of the summit vent of Bulusan. It produced an ash-and-steam cloud (table 2). Ashfall up to 7 mm thick accumulated at the foot of the volcano in neighborhoods in the municipality of Juban.

On 18 June at 1556 , an explosion lasted ~11 minutes; it produced an ash-and-steam cloud (figure 6). This was the 8th explosion since Bulusan reactivated in March. Ash up to 5 mm thick fell on a W-flank village.

Figure 6. Mount Bulusan spews ash on 18 June 2006. Courtesy of Associated Press.

On 20 June, a mild ash-and-steam explosion lasted approximately 17 minutes. The seismic network around the volcano recorded only one high frequency volcanic earthquake prior to the explosion. The ash and steam emission coincided with heavy rains that generated some lahars and torrential flows. The sulfur dioxide (SO₂) emission rate that morning was 469 tons per day (t/d).

At 0800 on 26 June 2006, PHIVOLCS reported that the Bulusan seismic network had recorded four volcanic earthquakes during the past 24 hours. Steaming activity was wispy to moderate and reached an approximate height of 50 m above the summit before drifting WNW. On 28 June 2006, PHIVOLCS reported at 0800 that continuous seismic observation at Bulusan disclosed one small explosion-type earthquake and two volcanic earthquakes for the past 24 hours. The explosion occurred at 0206 on 28 June and lasted for about 4 minutes. However, the event was not observed because the summit was cloud covered all of 27 June until early in the morning of 28 June. No ashfall was reported following the explosion, and no lahar occurred at Gulang-gulang River in Cogon, Irosin. Sulfur dioxide (SO₂) emission rates of the volcanic plume measured on 27 June decreased slightly, to 597 tons per day (t/d) in comparison to the 26 June 2006 rate of 942 t/d.

PHIVOLCS summarized the current 2006 activity as follows. In general, the character of explosions evolved only slightly, apparently becoming a little stronger later. The explosions in June were also somewhat longer in duration than earlier ash ejections, based on instrumental records and general visual monitoring. However, the absence of earthquakes, tremor, and generally low SO₂ emission rates prior to each explosion suggested an absence of a large or active magmatic intrusion into shallow depths. Instead, they interpreted the sequence of explosions since March 2006 as pointing to interaction of small volumes of magma with an overlying water-saturated zone beneath the summit. These were thought to develop overpressures released during each explosion. It remains to be seen if the recent explosions would provide an "uncorking effect" and induce a major hazardous eruption. The very low earthquake activity was taken to suggests otherwise.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), PHIVOLCS Building, C.P. Garcia Avenue, U.P. Campus, Diliman, Quezon City, PHILIPPINES (URL: http://www.phivolcs.dost.gov.ph/); Earth Observatory, National Aeronautics and Space Administration (NASA) (URL: http://earthobservatory.nasa.gov/NaturalHarards/); The Manila Standard Today (URL: http://manilastandard.net/); Simon Carn, Joint Center for Earth Systems Technology (JCET), University of Maryland Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250.

September 2006 (BGVN 31:09) Cite this Report

Ten explosions recorded seismically between 21 March and 28 June 2006

On 19 March 2006, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the status of Bulusan from Zero Alert (no alert) to Alert Level 1 to reflect elevated seismic, fumarolic, and other unrest (BGVN 31:05). From that date until an ash explosion on 28 June 2006, 10 explosions were recorded (see table 3).

Table 3. Summary of significant events through late July 2006 at Bulusan . Numbering of explosion-type (E-type) quakes began 21 March 2006. Courtesy of Philippine Institute of Volcanology and Seismology (PHIVOLCS).

After the ash explosion of 28 June 2006, Bulusan's monitored parameters gradually decreased to near baseline levels. The daily count of volcanic earthquakes was very low, and SO₂ emission rates and ground-deformation data revealed the volcano's deflated condition, indicating the absence of active magma ascent. Ash emission stopped and steaming from the active vents and fissures gradually returned to normal levels. Due to the decline in activity, on 29 July PHIVOLCS lowered the status of Bulusan from Alert Level 2 to 1.

On 10 October 2006 at 1256 UTC, the Tokyo Volcanic Ash Advisory Center announced that an eruption plume from Bulusan was visible on satellite imagery reaching altitudes of 3 km and drifting SW and SSE.

Unlike nearby Mayon volcano (~ 70 km NW) (see BGVN 31:08), no thermal anomalies were detected at Bulusan by satellite or recorded by the Hawai'i Institute of Geophysics and Planetology (HIGP) MODIS/ MODVOLC web site from the beginning of 2006 to 10 October 2006.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph); Tokyo Volcanic Ash Advisory Center (VAAC) (URL: http://www.jma.go.jp/jma/jma-eng/jma-center/vaac/index/html); HIGP MODIS Thermal Alert System, Hawai'i Institute of Geophysics and Planetology (HIGP), University of Hawaii at Manoa, 168 East-West Road, Post 602, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

April 2007 (BGVN 32:04) Cite this Report

Continued explosive eruptions and ashfall during October 2006 through May 2007

Activity declined at Bulusan in late June 2006 after a series of 10 explosions that began on 19 March 2006 (BGVN 31:09). Between 30 August and 1 September steam plumes reached up to 350 m above the summit; the plumes drifted NW and SE. This report summarizes Bulusan's activity from 10 October 2006 through 12 May 2007 (table 4). Hazard maps created by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) illustrate the risks to the large numbers of cummunities in the vicinity of the volcano (figure 7). Review of the available MODIS data indicates no thermal alerts during the year prior to 31 May 2007.

Table 4. An overview of Bulusan's activity, as noted by PHIVOLCS during 10 October 2006 through 12 May 2007. Courtesy of PHIVOLCS.

Figure 7. Hazards maps for Bulusan showing susceptibility to pyroclastic flows and surges (left), and lava flows and lahars (right). Courtesy of PHIVOLCS.

PHIVOLCS reported an explosion from Bulusan on 10 October that produced an ash-and-steam plume that rose to 4.5 km altitude and drifted mainly SE and SSW. Light ashfall (1.5-5.0 mm thick) was reported in neighboring towns downwind. Based on seismic data, the activity lasted for 9 minutes. On 11 and 12 October, steam plumes drifted SW and SSW. Another explosion occurred on 19 October. The following day, steam plumes drifted W and WSW. On 23 October, an explosion produced a brownish ash plume that rose to about 2.6 km and drifted SE and SW. Light ashfall (trace to 0.5 mm thick) from the 19 and 23 Cctober explosions was reported from neighborhoods in the municipality of Irosin, about 7 km S of the summit.

During 25-26 October, PHIVOLCS reported a lahar that deposited sediments 15 cm thick along a tributary leading to the Gulang-gulang River. According to news articles, the lahar mobilized boulders as large as trucks and caused at least 96 people to evacuate. During 30-31 October, ash explosions generated a light gray ash-and-steam plume that rose to 2.3 km and drifted NNE. Later field inspection revealed ashfall (trace to 1 mm) N of the volcano, as well as in the municipalities of Casiguran and Gubat, about 12 km SSE and 18 km NNE, respectively, from the summit. Two explosion-type earthquakes recorded late on 31 October were followed by ashfall in Casiguran, Malapatan, and Irosin.

News articles and wire services reported that Bulusan emitted ash accompanied by rumbling noises and lightning flashes on 20 December. Clouds hindered a view of the summit. Ash deposits up to 4 mm thick were noted in several villages in the foothills. A news report in News Balita noted a plume of gas and "white ash" on 22 December.

In January 2007, PHIVOLCS reported that an explosion from the summit on 24 January lasted about 10 minutes, based on seismic interpretation. Observation was inhibited due to cloud cover. Ashfall was reported SW of the volcano.

On 15 March, news media reported that ash fell on Bulusan's SW slopes and nearby villages. A resident volcanologist stated that ashfall was caused by voluminous steaming during 12-15 March, not explosions. Other news articles stated that eruptions on 8 April produced ash plumes that rose to altitudes of 3.1-6.6 km.

PHIVOLCS reported another ash explosion on 12 May 2007 with an eruption column reaching a maximum height of 4 km above the summit before drifting to the WSW and WNW. The activity was accompanied by rumbling sounds and was recorded by the seismic network as an explosion type earthquake that lasted for about 35 minutes. Prior to the explosion, during 9-12 May, an increase in the daily number of volcanic earthquakes was noticed, with 42, 65 and 97 events recorded.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph); Tokyo Volcanic Ash Advisory Center, Tokyo, Japan (URL: http://www.jma.go.jp/jma/jma-eng/jma-center/vaac/index/html); Inquirer.net, Philippines (URL: http://www.inquirer.net/); Associated Press (URL: http://www.ap.org/); News Balita, Philippines (URL: http://news.balita.ph/).

February 2008 (BGVN 33:02) Cite this Report

Ash ejections continued to at least late 2007

Our last report on Bulusan described explosive eruptions and ashfall during 10 October 2006 to 12 May 2007 (BGVN 32:04). This current report will cover the events from late May 2007 to January 2008. There were ash-bearing eruptions on 31 July and 4 October 2007. Hazard concerns also included steam-driven explosions, lahars, and related flooding.

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported on 20 May 2007 that seismicity remained high following an explosion on 12 May (BGVN 32:04). The seismic network detected 673 volcanic earthquakes during five days. The epicenters were located along a NW-SE trend. Ground deformation measurements conducted on 17 May on the NE flank revealed 4 mm of inflation since 7 April, measurements in a series which have shown continued inflation since June 2006. Sulfur dioxide flux measurements were 165-315 tons per day (t/d), below a baseline level of 500 t/d. The Alert Level was raised in mid-May from 1 to 2 (out of 5) due to the increased seismicity and inflation. On 22 May, heavy rain triggered lahars, but they were confined and did not affect populated areas. On 25 May 2007 sulfur emission reached 500 t/d.

During mid-2007, scientists from PHIVOLCS conducting an aerial investigation discovered lahar deposits and three steaming fissures. Scientists also observed steam plumes that rose to altitudes of 1.6-1.7 km and drifted NW and NE. The S flank had inflated by 3 mm. Residents near the base of the volcano noted the odor of sulfur dioxide.

No significant activity was reported during June 2007. Steaming from the active vents and fissures generally consisted of weak to moderate emissions of steam. On 13 July 2007, PHIVOLCS lowered the Alert Level to 1 due to a decline in activity including decreased seismicity, and lower than baseline sulfur dioxide emissions. On 19-21 June the NE and SE flanks were deflated when compared to previous surveys. Sulfur dioxide emission rates were 50-400 t/d.

On the morning of 31 July 2007 an explosion produced an ash plume that rose to an altitude of 6.6 km and drifted WSW and WNW. Initial field reports indicated that light ashfalls were experienced in Cogon, Gulang-gulang, Puting Sapa, Bolos, Monbon and Gabao in Irosin, and Sangkayon and Buraburan in Juban. Small to moderate sized earthquakes and ash explosions continued. On 2 August, white steam plumes rose from active craters and fissures.

On 28 September 2007 the number of volcanic earthquakes increased and PHIVOLCS noted a possible eruption. Explosions at 0134 and 0139 on 4 October 2007 caused a blanket of thick ashfall in sixteen villages that resulted in minor injuries and damage. Instruments recorded 40 volcanic earthquakes and eight short harmonic tremors during a 24 hour interval ending at 0526 that day. Moderate steaming from fissures were found on the SW flank.

According to the news source Southen Luzon Bureau, on 15 October 2007 PHIVOLCS found an additional six points of emission around the volcano, three each on the NW and SE slopes. Several other emission points had stopped on the N, SSW, and SW slopes. Overall, nine emission points were active. News reports also mentioned that residents in the village of San Rogue noted bulging of the ground. A deformation survey was allegedly conducted, but results were not available in PHIVOLCS reports.

In the 24 hours from 0800 on 6 January 2008, at least seven minor earthquakes were recorded, but no steaming was noted. Although the Alert Level remained at 1, authorities began to enforce a no-entry policy in a 4-km radius.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph); Southern Luzon Bureau, Philippine Daily Inquirer, PO Box 2353, Makati Central Post Office, 1263 Makati City, Philippines (URL: http://newsinfo.inquirer.net/).

March 2011 (BGVN 36:03) Cite this Report

Earthquakes and explosions during 6 November 2010-early March 2011

The current report describes activity at Bulusan during 2008 through early March 2011, an interval punctuated by seismic signals indicative of explosions and occasional cases where ash fell up to 70 km away. During 2007, there were explosions, ash and steam plumes, and some ground inflation (BGVN 33:02).

Quiet during 2008 through October 2010. According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), seismic events were infrequent after the middle of 2008 through 2009. In addition, ground deformation surveys in 2009 showed deflation of the volcanic edifice. These observations were indicative of a decline in the overall activity of the volcano. Thus, the Alert Level was lowered from 1 to 0 (out of 5) on 15 May 2009. Maps appear below (figures 8 and 9).

Figure 8. Index map of Bulusan, a large stratovolcano located on the S portion of Luzon Island (Philippines). Courtesy of PHIVOLCS.

Figure 9. Map showing monitoring network at Bulusan. Equipment includes seismic instruments (4 stations), EDM surveying instruments and reflectors, and benchmarks for precise leveling traverses (N and S flanks of volcano). Courtesy of PHIVOLCS.

Quiet ends in November 2010. A volcanic, explosion-type earthquake occurred on 6 November 2010 coincident with a steam-and-ash plume that rose 600 m above the crater. Trace amounts of ashfall were reported in multiple areas 6-10 km NW. The Alert Level was raised from 0 to 1, and PHIVOLCS reminded the public not to enter the permanent danger zone, defined as a 4-km radius around the volcano.

After 6 November and during late 2010 to early 2011, Bullusan experienced a number of earthquakes (table 5), and steam was often observed rising from the crater and known thermal vents, especially after an explosion. However, cloud cover frequently obscured the summit area. The Tokyo Volcanic Ash Advisory Center (VAAC) occasionally reported the presence of ash plumes (table 6).

Table 5. Earthquakes at Bulusan recorded by the seismic network between 1 November 2010-8 March 2011. Based on reports from PHIVOLCS.

Table 6. Volcanic ash emissions from Bulusan during 6 November 2010-26 March 2011. Based on reports from the Tokyo VAAC. The line indicated by "x" refers to an ash plume that was reported to authorities but not identifiable on imagery.

On 7 November, PHIVOLCS noted that seismic activity had increased during the previous 24 hours. A phreatic explosion on 8 November produced a brownish-to-light-gray plume that rose 700 m above the crater. Several neighborhoods to the NW, W, and WSW reported ashfall. Steam rose from the crater after the explosion. On 9 November two consecutive ash explosions, accompanied by rumbling sounds, produced ash plumes that rose as high as 1 km above the crater and drifted SW. Ashfall up to 2 mm thick was reported in areas to the SW and WNW.

On 11 November 2010, white steam plumes rose 150 m above the crater and drifted ENE. An aerial survey noted that recent explosions resulted in the joining of two of the 2006-2007 craters into one. PHIVOLCS scientists also found that deposits from an explosion on 9 November did not contain juvenile material. On 12 November an ash explosion produced an ash-and-steam plume that rose 700 m above the crater and drifted SW. Multiple neighborhoods to the W and SW reported light ashfall. During 12-14 November, some steaming from the crater was observed. An explosion late at night on 15 November was followed by ashfall in nearby neighborhoods.

An explosion earthquake on 21 November 2010 was coincident with rumbling sounds and an ash plume that rose 2 km above the crater. Ashfall up to 3 mm thick was reported in multiple areas. According to news reports (Philippine Daily Inquirer), about 500 families evacuated and some local roads were impassable.

On 24 November 2010, PHIVOLCS reported that an explosion, recorded for almost six minutes by seismographs, produced an ash plume that rose 1 km above the crater, drifted SW, and dissipated. Ashfall was not observed outside of the permanent danger zone, defined as a 4-km radius from the summit, suggesting that ashfall was confined to the upper flanks. On 26 November, an explosion-type earthquake was recorded.

On 17 December 2010, PHIVOLCS reported that an explosion, recorded for about 3 minutes by seismographs, produced an ash-and-steam plume that rose 500 m above the crater and drifted SW. Another explosion on 23 December followed tremor that lasted for almost 31 minutes. A grayish steam-and-ash plume rose to about 500 m above the crater rim and drifted S-SW.

Seismic activity continued into 2011 with volcanic earthquakes, frequent steam emissions, and an occasional explosion. Tokyo VAAC reported ash plumes from Bulusan, although cloud cover frequently obscured the summit area.

An explosion on 18 January 2011 was accompanied by a rumbling sound audible in Monbon, a barangay (neighborhood) in the municipality of Irosin, 6 km to the SW. Trace amounts of ashfall were observed in Monbon. A deformation survey conducted during 25-29 January showed slight deflation relative to a December 2010 survey.

An explosion on 21 February 2011 produced a gray ash plume that rose ~3 km above the crater and drifted SW. Rumbling sounds were heard up to 10 km away in the town of Juban (NW). The event was recorded by the seismic network as an explosion-type earthquake lasting for about 19 minutes. Field investigations confirmed ash deposits in the towns of Irosin (up to 5 mm) 8 km SSW, and Bulan (up to 3 mm) 22 km SW. Traces of ashfall were also reported in the municipalities of Juban and Magallanes (24 km WNW), and in Masbate City, Masbate (70 km SW). According to news articles (Xinhua), about 2,000 people evacuated.

There were 13 lahar-related seismic signals detected during 27-28 February 2011. Continuous heavy rain caused small lahars on the flanks and in river channels, including the Cogon and Monbon rivers to the SW. A map showing the susceptible lahar areas appeared in BGVN 32:04.

Based on notices from the Manila airport and satellite image observations, the Tokyo VAAC reported that ash plumes were detected occasionally during and after the explosion of 6 November 2010.

Table 6 denotes the substantial ash plumes reported by the Tokyo Volcanic Ash Advisory Center (VAAC) through 26 March 2011.

During the reporting period, there were no thermal alerts derived from the Hawai'i Institute of Geophysics and Planetology Thermal Alerts System (MODVOLC).

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Southern Luzon Bureau; Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Philippine Daily Inquirer (URL: http://www.inquirer.net/); Xinhua (URL: http://www.xinhuanet.com/english2010/).

March 2016 (BGVN 41:03) Cite this Report

Phreatic eruptions May 2011, May-July 2015, and February 2016

This report summarizes activity at Bulusan from March 2011 through May 2016. Eruptive activity that began on 6 November 2010 with ash explosions was continuing in late March 2011 (BGVN 36:03), and ended on 16 May 2011. The volcano was quiet until renewed activity during 1 May-17 July 2015. Another brief eruption was noted on 22 February 2016. Activity typically includes phreatic explosions from the summit crater and flank vents, ash-and-steam plumes, and minor ashfall in surrounding villages. Information was provided by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the Tokyo Volcanic Ash Advisory Center (VAAC).

Activity during March-May 2011. Following lahars in late February 2011, the number of daily volcanic earthquakes dropped to six or fewer in the first week of March. This small daily number of events continued through early May, except for nine earthquakes reported on 26 April.

During March through early May 2011, weak steaming from the SE and NW vents was only intermittently observed when cloud cover did not obscure the view. Steam emissions seen in late April from the NW and SE vents reached an approximate height of 50 m before drifting WSW. During six days in March and eight days in April the Manilla airport reported to the Tokyo Volcanic Ash Advisory Center (VAAC) that volcanic ash had been observed, but the VAAC could not identify ash in satellite data.

A phreatic eruption occurred at the cloud-covered summit crater of Bulusan on 13 May 2011 at 0025 local time. Rumbling sounds from the explosion were reported up to 5 km away from the volcano. The explosion earthquake associated with this event lasted for 10 minutes. The seismic network had detected only 10 earthquakes in the preceding 24 hours. Field investigations conducted immediately after the explosion confirmed the presence of thin (0.5-2.5 mm) ash deposits reaching approximately 9 km away from the crater to the NW and SW. Eight barangays in the municipality of Juban NW of the volcano (Caladgaw, Rangas, Puting- Sapa, Sangkayon, Bacolod, Buraburan, Gurayan, and Aniog) and four in the municipality of Irosin SSW of the volcano (Cogon, Bolos, Umagom, and Gulang-gulang) reported light ashfall after the event. Eleven volcanic earthquakes were recorded in the 24 hours after the explosion, but only four more in each of the next 24-hour periods.

A significant increase in the seismic activity occurred during the morning of 16 May when 80 volcanic earthquakes were detected. This number increased to 144 volcanic earthquakes for the next 24-hour period. Only weak to moderate steaming from the active vents was reported following the explosion through 16 May. After this, the frequency of volcanic earthquakes declined to baseline levels of 0-2 events per day.

Short-lived swarms of 9-21 events were reported on 25 May, 10 August, 11 September, and 20-26 December 2011, and 22 January 2012. In April 2012 ground deformation surveys indicated that the edifice had deflated since late November 2011. This overall decline in activity led PHIVOLCS to lower the hazard status in April 2012 from Alert Level 1 to Alert Level 0 (on a 0-5 level scale), meaning no eruption was foreseen for the immediate future.

Activity during May-July 2015. Bulusan remained quiet following the 13 May 2011 explosion until 1 May 2015, except for a single episode of increased seismicity (13 volcanic earthquakes over 24 hours) and minor inflation in mid-July 2014. A series of explosions during 1 May-17 July 2015 originated from the NW vent, generally sending ash plumes to heights of 150-250 m above the summit, with larger plumes rising 1-1.5 km on 16 and 19 June.

A five-minute-long steam-and-ash explosion erupted from the cloud-covered summit in the morning of 1 May 2015 and was followed by strong to moderate steaming from the NW vent that reached 200 m high and drifted WNW. The explosion distributed traces of ash in the areas W and WNW of the volcano, affecting the barangays of Bolos, Cogon, Gulang-Gulang, Sangkayon, Tinampo, and Umagom up to 7 km to the SW, and barangay Putting Sapa up to 12 km to the NW. Only five volcanic earthquakes were detected during the week prior to the eruption by the seismic network, but 62 were recorded in the eight hours following the explosion. A second 3.5-minute-long steam-driven explosion occurred on 6 May at 2146 that sent an ash plume approximately 250 m high before it drifted W. Traces of ash were observed about 8 km SW in Sitio Tulay, Cogon, Monbon, and Tinampo.

As a result of these two explosions, PHIVOLCS raised the hazard status from Alert Level 0 to 1. Between 6 May and 16 June the volcano was quiet with very few volcanic earthquakes and weak emissions of steam from the NW and SW vents that drifted SW or WNW. Precise Leveling surveys conducted in early May indicated very slight inflation relative to March surveys.

Activity resumed with two steam-driven explosions on 16 June at 1102 and 1120. The first event lasted approximately 10 minutes and produced a 1 km high steam-and-ash plume which drifted WSW. Rumbling from the explosion was heard by residents of Cogon on the WSW slopes of the volcano. The second explosion lasted for about one minute. A two-minute explosion was reported during 18-19 June, but dense clouds obscured visual observations of the summit. A seven-minute-long phreatic explosion occurred at 1455 on 19 June, and produced a 1.5-km high ash plume that drifted WSW. A low-level ash cloud on the upper NW flank, possibly from a short pyroclastic flow, was also observed. Minor amounts of ash fell in the neighborhoods of Bacolod, Buraburan, Mapili, Puting Sapa, and Juban 11 km to the NW. The eruption was followed by a voluminous steam emission, rising 250 m before drifting SW. A smaller explosion on 21 June lasting 111 seconds generated a 150 m high steam-and-ash plume that drifted E. Trace amounts of ash fell up to 8 km east of the volcano in San Jose, San Francisco, Bulusan Proper, Sapngan, San Rafael, and Dapdap. In late June, weak to moderate steam plumes up to 100 m high were observed drifting from the WNW and SW vents. Precise leveling surveys in late June 2015 indicated very slight inflation of the volcano's edifice relative to May 2015.

PHIVOLCS reported that at 1310 on 17 July a phreatic eruption from the active vent on its upper NW slopes was detected by the seismic network for 11 minutes and generated an ash plume that rose 200 m above the vent that drifted WNW before drifting further N and NE. Ashfall was reported in areas up to 18 km to the N and NE in the Sorsogon Province, including Inlagadian (municipality of Casiguran), Tigkiw, Tugawe, Nazareno, Bugtong and Rizal (municipality of Gubat), and Fabrica, San Isidro, Sta. Cruz, and San Ramon (municipality of Barcelona). The rumbling from the eruptions was audible up to 6 km from the summit.

Activity during July 2015-February 2016. Following the 17 July 2015 explosive activity, seismic activity decreased to background levels of 0-5 daily events with intermittent spikes a few times a month to a maximum of 24 earthquakes. Precise Leveling surveys and continuous GPS data between August 2015 and December 2015 indicated slight inflationary changes of the volcano's edifice during that time.

On 21 February 2016 the seismic network recorded 15 earthquakes, followed by two minor eruptions at 1501 on 22 February that generated a short steam-and-ash column approximately 500 m high from the WNW fissure vent. The eruption signal consisted of two earthquake events, a rock fracturing event, recorded as a high-frequency earthquake, followed by an explosion-type (low frequency) earthquake with a total duration of just over four minutes. Explosions were accompanied by a rumbling sound heard at Puting Sapa, Juban and Bolos, 12 km NW. Traces of volcanic ash were reported in barangays Putting Sapa, Sagkayon and Caladgao in Juban (12 km NW), and barangay Bolos in Irosin (8 km SW).

Precise leveling survey results from 23-28 February 2016 indicated slight deflationary changes of the edifice relative to December 2015, consistent with ground deformation measurements from continuous GPS data through February 2016.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

February 2017 (BGVN 42:02) Cite this Report

Phreatic explosions with minor ashfall continue during June-December 2016

Recent eruptive activity at Bulusan included episodes during 6 November 2010-16 May 2011, 1 May-17 July 2015, and 22 February 2016; activity typically included phreatic explosions from the summit crater and flank vents, ash-and-steam plumes, and minor ashfall in nearby villages (BGVN 41:03). The most recent eruption began 10 June 2016 and continued through the end of the year. Information was provided by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the Tokyo Volcanic Ash Advisory Center (VAAC).

During the reporting period of June-December 2016, the Alert Level remained at 1 (on a scale of 0-5), indicating abnormal conditions and a 4-km radius Permanent Danger Zone (PDZ). Activity consisted of intermittent phreatic explosions generating emissions of ash and steam that typically rose 70-2,500 m above the summit crater (table 7). Minor ashfall in nearby municipalities often accompanied the explosions.

In October 2016, PHIVOLCS extended the danger zone an additional 2 km as a result of a fissure that extended 2 km down the upper S flank; PHIVOLCS was concerned that active vents along the upper part of the SE flank could pose a greater risk to the populated barangays (neighborhoods) of Mapaso (Irosin), Patag (Irosin), and San Roque (Bulusan). The municipalities of Irosin and Bulusan are about 8 km SSW and 7 km ESE, respectively, of the volcano.

Table 7. Summary of volcanic activity at Bulusan, June-December 2016.

Ashfall. On 23 June 2016, minor amounts of ash fell in the barangays (neighborhoods) of Poblacion (11 km NW), Añog (12 km NW), and Bacolod (13 km NW), all in the municipality of Juban (about 12 km NW), and the municipality of Mabini (12 km NNW). A sulfur odor was detected in the neighborhoods of Mabini, Bacolod (Irosin), Añog (Juban), and Puting Sapa (Juban).

On 16 September there was ashfall in the municipalities of Casiguran (11 km NNW), Gubat (18 km NNE), and Barcelona (14 km NE). Minor amounts of ash fell during 1 October in the barangays of San Rafael, San Roque, and San Jose, all in the municipality of Bulusan. A minor explosion on 6 October caused ashfall in some areas of the municipality of Gubat, and rumbling was noted in San Roque.

A phreatic explosion on 21 October generated a plume that resulted in a thin layer of ash in Casiguran and Gubat, and trace amounts in barangays in Barcelona, Casiguran, and Gubat. On 23 October, a phreatic explosion produced trace ashfall in multiple barangays in Irosin; the most ash, 1 mm-thick deposits, were found in Puting Sapa (Juban).

On 29 December, a phreatic explosion generated an ash plume that resulted in minor amounts of ashfall in areas downwind, including several Irosin barangays (Cogon, Tinampo, Bolos, Umagom, Gulang-gulang, and Monbon) and two Juban barangays (Caladgao and Guruyan). Residents of Guruyan, Monbon, and Tinampo noted a sulfur odor.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Tokyo Volcanic Ash Advisory Center (VAAC), Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

August 2017 (BGVN 42:08) Cite this Report

Weak phreatic explosions on 2 March and 5 June 2017

Activity at Bulusan typically has included phreatic explosions from the summit crater and flank vents, ash-and-steam plumes, and minor ashfall in nearby villages (BGVN 41:03, 42:02). The danger zone was expanded in October 2016 when a fissure extended 2 km down the upper S flank that was the source of multiple phreatic explosions (figure 10, and see BGVN 42:02). During the first eight months of 2017, eruptive activity included similar episodes on 2 March and 5 June. Information was provided by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). Throughout the reporting period of 1 January-8 September 2017 the Alert Level remained at 1, indicating a low level of volcanic unrest and a 4-km-radius Permanent Danger Zone (PDZ).

Figure 10. A phreatic ash explosion from the SE vent at Bulusan on 17 October 2016 lasted 24 minutes. White steam plumes can be seen rising from other vents. Photo by Drew Zuñiga and provided by 2D Albay, as published in The Philippine Star (18 October 2016).

According to PHIVOLCS, a weak phreatic eruption occurred at 1357 on 2 March 2017. The event was recorded by the seismic network as an explosion-type earthquake followed by short-duration tremor that lasted approximately 26 minutes. Visual observations were obscured by weather clouds, although a small steam plume rising from the SE vent was recorded by a webcam.

On 5 June 2017 another weak phreatic eruption was recorded at 1029 by the seismic network for 12 minutes. The eruption again could not be visually observed due to dense weather clouds covering the summit. Minor ashfall, a sulfuric odor, and a rumbling sound were reported in the barangays (neighborhoods) of Monbon and Cogon, while sulfuric odor was noted in the barangay of Bolos. These three neighborhoods are within the municipality of Irosin, about 8 km SSW of the volcano.

According to a news account (Manila Bulletin), precise leveling data obtained during 29 January to 3 February 2017 indicated deflationary changes since October 2016. PHIVOLCS reported that precise leveling data obtained during 14-23 June 2017 indicated inflation since February 2017. According to PHIVOLCS, continuous GPS measurements have indicated an inflationary trend since July 2016.

Sulfur dioxide emissions on 31 July and 20 August, reported by PHIVOLCS, averaged 82 tonnes/day, which according to a news account (Manila Bulletin) was the same as measured on 29 April 2017. The seismic monitoring network recorded three volcanic earthquakes on 7-8 September. Weak steam plumes from the active vents rose to 50 meters and drifted SW.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Manila Bulletin (URL: http://mb.com.ph/); Philippine Star (URL: http://www.philstar.com/).

July 2022 (BGVN 47:07) Cite this Report

Phreatic activity during 5-12 June 2022

Bulusan lies at the SE end of the Bicol volcanic arc in the Philippines. It is flanked by several other large intra-caldera lava domes and cones and its summit contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Moderate explosive eruptions have been recorded since the mid-19th century. The previous eruption period, during June 2017, consisted of weak phreatic explosions and produced minor ashfall in nearby villages (BGVN 42:08). This reporting period covers a new eruption period during June 2022, characterized by similar phreatic explosions, based on information from the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

Summary of activity during January 2020-May 2022. Activity since the last eruption in June 2017 mainly consisted of occasional volcanic earthquakes and weak gas-and-steam emissions, sulfur dioxide emissions were below detectable levels since 2018, and the frequency of volcanic earthquakes had been at baseline levels of 0-2 earthquakes/day since May 2019. During 3-7 July 2020 a total of 72 volcanic earthquakes were detected, which included 43 low-frequency events. Diffuse white gas-and-steam plumes rose from the lower SE vent. Ground deformation data from continuous GPS measurements indicated short-term inflation of the edifice since late February 2020. On 6 July the Volcano Alert Level (VAL) was raised to 1, but activity remained relatively low, and on 26 October the VAL was lowered to 0 (normal conditions). Diffuse white gas-and-steam plumes continued to rise from the summit vents.

Unrest increased again during 7-10 May 2021, according to PHIVOLCS. There was a total of 186 volcanic earthquakes detected during 7-11 May. Inflation that was first recorded on the upper flanks on 6 March had continued. Sulfur dioxide emissions peaked at 48 tons/day on 20 May 2021, which was still within baseline levels. The VAL was raised to 1 on 11 May. During 12 June a total of 95 weak volcanic earthquakes were detected, in addition to diffuse white gas-and-steam plumes rising from the SW vent. Seismicity declined to the baseline level of 2-3 volcanic earthquakes per day during 1 July-17 August 2021, during which a total of 109 weak events were recorded. Short-term inflation had been detected since July 2020.

Activity during June 2022. During 4-5 June, PHIVOLCS reported 77 volcanic earthquakes. Ground deformation data from continuous GPS monitoring indicated short-term inflation, and electronic tilt data recorded an inflation event on the SE lower slopes beginning in April 2022. A phreatic eruption occurred at 1037 on 5 June 2022 and lasted approximately 17 minutes, based on seismic and infrasound monitoring by the Bulusan Volcano Network (BVN). Though cloud cover obscured most visual observations, a gray ash plume seen from Juban (Sorsogon Province) rose at least 1 km high and drifted W. Ashfall was reported to the NW in Puting Sapa, Añog, Guruyan, Catanusan, Buraburan, Bacolod, and Sangkayon in Juban, and Bolos in Irosin, Sorsogon Province. Residents of Añog, Guruyan, and Catanusan also reported rumbling sounds and a sulfur odor. As a result, the VAL was raised to 1. After this event, gas-and-steam emissions rose from the main crater, as well as the NW summit vent. A total of 27 weak volcanic earthquakes were recorded until 1600 by the BVN.

Increased seismicity began at 0500 on 9 June, which included a total of 45 volcanic earthquakes, including two low-frequency events. Most of these events were low magnitude and shallow. Another phreatic explosion was detected by the BVN at 0337 on 12 June, which lasted 18 minutes, based on seismic records. The eruption plume was not visible in webcams, but residents of Inlagadian (Casiguran municipality) briefly saw incandescence at the base of a plume. An explosion was felt by residents within 5 km, including in the barangays of Añog (Juban) and Inlagadian. Rumbling was heard in Sitio Bagong Barrio, and in the barangays of Santa Lourdes (Barcelona), Inlagadian and San Juan (Casiguran), Bentuco (Gubat), and Añog, Calateo, and Puting Sapa (Juban). Sporadic ash emissions were detected starting at 0430; ash emissions were visible rising from six vents: Blackbird Crater (the main crater), three explosion pits in the summit crater, and two vents on the NW and N sides of the summit. Gas-and-steam and ash plumes rose 400-750 m above the summit and drifted several kilometers NW. Ashfall was reported in areas as far as 50 km NW in Sorsogon City and Palanas, Pilar, Sorsogon Province, across Sorsogon Bay, and as far as Anislag (Daraga, Albay). Minor ashfall was detected in several barangays in the municipalities of Casiguran, Juban, and Magallanes. Sulfur dioxide emissions averaged 1,900 tons/day during 5-12 June. According to a Rappler news article, more than 11,000 people (at least 2,800 families) in Juban evacuated, and flights in and out of the Bicol International Airport were cancelled.

Unrest persisted through the rest of June. Gas-and-steam emissions rose 100-500 m above the summit and drifted NW, WSW, SW, and W. Daily sulfur dioxide emissions were 559-1,255 tons/day. Seismicity increased on 20 June; during 0500-1145 a total of 65 volcanic earthquakes were detected, including one low-frequency volcanic earthquake, though most were weak shallow events. During 24-29 June the BVN detected a total of 213 volcanic earthquakes, the strongest of which was an Mw 3.5 that occurred at 2327 on 24 June. Residents of Irosin and Bulusan in the Sorsogon Province felt the earthquake. A small-volume lahar began approximately at 1904 on 26 June during a thunderstorm, based on seismic and infrasound data. The event lasted 54 minutes and the Bulusan Volcano Observatory (BVO) confirmed thin, channel-confined lahar deposits along the Calang Creek on the SW flank, in the Cogon barangay.

Seismicity decreased to background levels during the third week of July. During 25 July-6 August sulfur dioxide emissions were 230 tons/day. On 21 August PHIVOLCS lowered the Alert Level to 0, reporting that unrest continued to decline to background levels.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Rappler, Unit B, 3/F, North Wing Estancia Offices, Capitol Commons, Ortigas Center, Pasig City 1605, Bulusan Volcano erupts again, ash spreads to more areas, (URL: https://www.rappler.com/nation/phivolcs-bulusan-volcano-phreatic-eruption-advisory-june-12-2022-420am/).