Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 1, January 1995
Bulusan (Philippines) Phreatic ash eruptions continue with low
seismicity and deformation
Bulusan
Luzon, Philippines
12.77 N, 124.05 E; summit elev. 1,565 m
All times are local (= GMT + 8 hours)
Phreatic activity that started in November (Bulletin v. 19, nos.
11-12) continued through December and January (table 2). 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 eruption
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 approaching within 4 km of the summit. This warning of
heightened activity was non-committal about the timing of future
volcanic events because seismicity and deformation have not changed
prior to these short-lived ash eruptions.
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: Ray Punongbayan (Director) and Ernesto Corpuz
(Monitoring), Philippine Institute of Volcanology & Seismology
(PHIVOLCS), 6th Floor, Hizon Bldg., 29 Quezon Avenue, Quezon City,
Philippines.
Table 2. Summary of recent phreatic eruption at Bulusan, 27
November 1994 to 28 January 1995. Data courtesy of PHIVOLCS, see
Bulletin v. 19, nos. 11-12 for additional details.
Date Ashfall Comments
27 Nov In villages W & SW 14 minutes felt tremor;
1.5-km-high plume
3 Dec -- Rumbling;
heavy cloud cover
4 Dec Traces 7 km away --
5 Dec In villages 5 km WSW 1.5-km-high plume
12 Dec As far as 16 km SW Cauliflower-shaped
column 3 km high
18 Dec In five villages SW Small explosion;
cloud cover
20 Dec ~7 km SW Small explosion;
cloud cover
23 Dec Light ashfall in six villages SW Four minutes long
24 Dec Light ashfall ~7 km away Three minutes long
27 Dec Nine villages Seven minutes; largest
since 12 Dec
31 Dec Ash ejection Rumbling & lightning
flashes
7 Jan Light ashfall 5-6 km away --
10 Jan Very light ashfall 7 km SW Plume 1 km above
summit
21 Jan Light ashfall 5 km SW Lightning flashes
over summit
28 Jan <=3 mm of ash up to 15 km away Plume 2 km high