Mount Bulusan

From Wikipedia

Mount Bulusan, or Bulusan Volcano, is the southernmost volcano on Luzon Island in the Philippines. It is found in the province of Sorsogon in the Bicol region (12°46.2'N, 124°03'E), 70 km southeast of Mayon Volcano and approximately 250 km southeast of the Philippine capital of Manila.

Bulusan is classified by volcanologists as a stratovolcano (composite volcano) inside a caldera that was formed about 40,000 before the present. It has an elevation of 1,565 meters above sea level and a base diameter of 15 km.

It has four craters and four hot springs. Crater No. 1, called Blackbird Lake, is 20 m in diameter and 15 m deep. The oval Crater No. 2 is 60 m by 30 m and 15 m deep. Crater No. 3 is about 90 m in diameter and 20 m deep and Crater No. 4, which is near the northeastern, rim opened during the 1981 eruption. There is also a 100-meter fissure measuring 5 to 8 m wide below Crater No. 4.

Its hot springs are San Benon Springs, Mapaso Springs, San Vicente Springs, Masacrot Springs

Its adjacent volcanic edifices are Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban and Mt. Jormajan.

Bulusan has erupted 15 times since 1886.

The Philippine Institute of Volcanology and Seismology (Phivolcs) declared Alert Level 1 on March 19, 2006 after it recorded increased seismic unrest. On June 8, 2006, volcanologists raised Alert Level 2 (moderate level of seismic unrest) after it spewed ash. On June 9, the resulting ash cloud damaged a number of houses in the nearby town of Casiguran, 5 kms north of the volcano, and reached Sorsogon City, about 20 kilometers north of Bulusan.

Bulusan is generally known for its sudden steam-driven or phreatic explosions and is one of the 22 active volcanoes in the Philippines, part of the so-called "Pacific ring of fire" made up of islands created by volcanic activity on the Western Pacific.




From Phivolcs

PHYSICAL FEATURES
Elevation: 1.559 km
Base Diameter: 15 km
Type of Volcano: Stratovolcano formed inside a caldera
Hotsprings: San Benon Springs, Mapaso Springs, San Vicente Springs, Masacrot Springs
Craters and Fissure:
1. Crater No. 1 or Blackbird Lake - 20 m in diameter and 15 m deep
2. Crater No. 2 - roughly oval in shape, 60 m by 30 m and 15 m deep
3. Crater No. 3 - approximately 90 m in diameter and 20 m deep
4. Crater No. 4 - near the NE rim, opened during the 1981 eruption

Fissure - located below Crater No. 4, measuring 5 to 8 m wide and about 100 m long
Adjacent Volcanic Edifice: Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban and Mt. Jormajan

GEOLOGICAL FEATURES
Rock Type: Two-pyroxene andesite in Bulusan, dacite associated with caldera
Tectonic Setting: Bicol Volcanic Chain
Age of Deposits:
a) 1500±300 years ( located at 12°45'N, 124°04'E)
b) 5,480±150 years ( located at Mapaso Stream Valley, 12°45'N, 124°04'E)
c) 5,800±100 years (located at a trail leading to Inlagadian, Casiguran, 12°49'N, 124°03'E)
d) 33,500±1,500 years (located at Magallanes Road, Juban, NW of Bulusan Volcano, 12°49'N, 123°58'E, sample taken from 30-40 m thick Irosin Caldera ashflow sheet)
SOURCE: Newhall, C. and Cruz, J. (Unpublished data)

VOLCANIC ACTIVITY
Number of Historical Eruptions: 15
Latest Eruption/Activity: 1994 November 27 - 1995 January

Eruption Type:
1. Phreatic (e.g. 1918-1922, 1980)
2. Strombolian (e.g. 1918-1919)
3. Caldera-forming (e.g. 40,000 YBP)

Precursors to Eruption:
1. Increase in the frequency of volcanic quakes with rumbling sounds
2. Increased steaming activity
3. Noticeable increase in the extent of drying up of vegetation around the volcano's upper slopes
4. Variation in the temperature of hot springs at San Benon
5. Rumbling sound
6. Increased amount of whitish to yellowish deposits of sulfur sublimates at NNW portion of the crater

VOLCANIC HAZARDS
Type of Hazards:
1. Pyroclastic flows (hot blasts, hot avalanche)
2. Lava flows
3. Lahars
4. Ashfall
Permanent Danger Zone: Four (4) km radius from the summit
Other Buffer Zones: 4 to 10 km from the summit (Probable Danger Zone)

MONITORING ACTIVITY
Volcano Observatory: Bulusan Volcano Observatory, Cabid-an, Sorsogon City
Monitored Methods:
1. Seismic
2. Ground deformation – precise leveling, electronic distance measurement (EDM), tilt
3. Hotspring temperature and flow rate measurements
4. Visual observations – steaming activity and other visually observed phenomena

Monitoring Stations:
A - Seismic Network
· Bulusan Volcano Observatory, Sorsogon City (VBN)
· Upper Inlagadian Hill Seismic Station (VBIH)
· Upper Mayong Payong Hill Seismic Station (VBMH)
· Mt. Jormajan Repeater Site (VBRJJ)
· Upper San Roque Seismic Station (VBSR)
· Salvacion Slope Repeater Site (VBSS)

B - Ground Deformation Network
· EDM : Survey lines at Salvacion-Hinde and Aniog-Lower Slope
· PRECISE LEVELING: Survey line at Mapaso
· TILT MEASUREMENT (wet) - San Benon