Bulusan Volcano Alert Signals PDF Print
Saturday, 09 April 2011 02:10

BULUSAN VOLCANO ALERT LEVELS

ALERT LEVEL

CRITERIA

INTERPRETATION/

RECOMMENDATION

0

Quiet or No Alert

All monitored parameters within background levels. Unremarkable level of volcanic earthquakes occurring within the volcano area. Generally weak steam emission.

Quiescence; no magmatic eruption is foreseen. However, there are hazards 1 (explosions, rockfalls and landslides) that may suddenly occur within the four-kilometer radius Permanent Danger Zone (PDZ).

1

Low Level of Volcanic Unrest

Slight increase in volcanic earthquake and steam/gas activity. Sporadic explosions from existing or new vents. Notable increase in the temperature of hot springs. Slight inflation or swelling of the edifice.

Hydrothermal, magmatic, or tectonic disturbances. The source of activity is shallow, near crater or in the vicinity of Irosin Caldera. Entry into the PDZ must be prohibited.

2

Moderate Level of Volcanic Unrest

Elevated levels of any of the following: volcanic earthquake, steam/gas emission, ground deformation and hot spring temperature. Intermittent steam/ash explosion and above baseline Sulfur Dioxide2 (SO2) emission rates. Increased swelling of volcanic edifice.

Probable intrusion of magma at depth, which can lead to magmatic eruption. Entry within PDZ must be prohibited. Other areas within five (5) kilometers of the active vent may be included in the danger zone.

3

High Level of Volcanic Unrest

Sustained increases in the levels of volcanic earthquakes, some may be perceptible. Occurrence of low-frequency earthquakes, volcanic tremor, rumbling sounds. Forceful and voluminous steam/ash ejections. Sustained increases in SO2 emission rates, ground deformation/swelling of the edifice. Activity at the summit may involve dome growth and/or lava flow, resultant rockfall.

Magma is near or at the surface, and activity could lead to hazardous eruption in weeks. Danger zones may be expanded up to eight (8) kilometers from the active crater.

4

Hazardous Eruption Imminent

Intensifying unrest characterized by earthquake swarms and volcanic tremor, many perceptible. Frequent strong ash explosions. Sustained increase, or sudden drop, of SO2 emission. Increasing rates of ground deformation and swelling of the edifice. Lava dome growth and/or lava flow increases, with increased frequency and volume of rockfall.

Magmatic processes or effusive eruption underway, which can progress into highly hazardous eruption. Danger Zone may be extended up to nine (9) kilometers or more from the active crater.

5

Hazardous Eruption in Progress

Magmatic eruption characterized by explosive production of tall ash-laden eruption columns, or by massive collapses of summit lava dome. Generation of deadly pyroclastic flows, surges and/or lateral blasts and widespread ashfall.

Life-threatening eruption producing volcanic hazards that endanger communities. Additional danger areas may be declared as eruption progresses.

 

STAND-DOWN PROCEDURES
In order to minimize unnecessary changes in declaration of Alert Levels, the following periods shall be observed:
From Level 5 to Level 4: Wait at least 24 hours after hazardous activity stops
From Level 4 to Level 3 or 2: Wait at least 2 weeks after activity drops below Level 4
From Level 3 to Level 2: Wait 2 weeks after activity drops below Level 3
BULUSAN VOLCANO OBSERVATORY
Bgy. Cabid-an, Sorsogon City
Contact No: 09293006416
1 Lahars may be generated by intense rainfall over the volcano area and may affect riverside communities far down the PDZ.
2 Sulfur Dioxide is a major gas component of magma.
Revised 25 September 2014.