|
BULUSAN VOLCANO |
Alert Level |
Monitoring Network |
|
Hazard Map |
Volcano Observatory |
LOCATION:
SORSOGON PROVINCE, 250 km SE of Manila; 70 km SE of Mayon Volcano (12°46,2'N - 124°03'E)
PHYSICAL CHARACTERISTICS:
Height: 1.559 m above sea level (asl)
Base Area: 400 kmē
Craters: Four (4) craters
aligned along N 70° W
Crater #1 - Blackbird Lake, 20 m diameter; 15 m deep
Crater #2 - Oval in shape; 60 m by 30 m; 15 m deep
Crater #3 - 90 m diameter; 20 m deep
Crater #4 - NW tip of the volcano; 60 m by 30 m by 20 m
Type of Volcano: Stratovolcano formed inside a
caldera
Predominant Rock:
Two pyroxene andesite in Bulusan, dacite associated with caldera
Irosin Caldera:
200 m depth; 11 km dia.; age greater than 40,000 years
(C-14 dating&method)
Cones: Mt.
Homahan, Mt. Binicatan, Mt. Batuan, Mt. Calungalan,
Mt. Calaunan,
Mt. Tabon-Tabon,
Mt. Juban, Mt. Jormajan
Lakes:
Bulusan Lake - SE at elevation 635 m asl; 33 m deep; 16.5 hectares
(area);
2 km circumference, formed by damming of a river by lava flows
Lake Aguingay - Between the trough of Mt. Bulusan and Sharp Peak;
1100 m asl
HISTORICAL ERUPTIONS:
No. of Recorded Eruptions: 18 eruptions since 1852
Destructive Eruption:
Calderagenic eruption which occured 40,000 years before present (YBP)
Latest Eruption:
27 November 1994
Type of Eruptions:
Phreatic - explosion driven by steam produced by heat and expansion
of ground water
due to an underlying hot source (e.g. 1918-1922, 1980 eruptions)
Strombolian - quiet effusion of lava
(1918-1919 eruptions) Caldear-forming eruption (40,000 YBP)
Eruption Precursors:
Increase in frequency of quakes with rumbling sounds Increased
steaming activity
Noticeable increase in the extent of drying up of vegetation around
the volcano's uppper slopes
Phenomena Associated
with Eruption: Lava flows, Pyroclastic flows,
Lahars
MONITORING TECHNIQUES:
Monitoring Methods:
A. Geophysical Method
Seismic Monitoring - 2-component Hosaka seismograph at San Benon
Thermal measurement of San Benon hot springs (5 km SSW of the
crater)
B. Geodetic methods - ground deformation
Electronic Distance Measurement (EDM)
Precise leveling
Tilt measurement (wet and dry)
C. Visual Ibservation
Monitoring Station:
Bulusan Volcano Observatory at San Benon, Irosin, Sorsogon;
1.5
km SSWof the crater.
HAZARD ZONES:
Permanent Danger Zone - 4 km radius from the
summit
Probable Danger Zone - 4 to 10 km
from the summit
Areas within 5-km High Rsk Zone:
Bgy. Cogon, Puting Sapa, Mapaso and San Roque
Areas frequently affected by ash
fallout (barangays on the NW-W-SW side of the volcano):
Sangkayon
Puting Sapa
Gulang-gulang
Kaladgaw
Bolos
Mombon
Aniog
Bacolod
Kalian
Buran-buran
Cogon
Bagsangan
Rangas
Tinampo