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Hibok-Hibok Alert Signals
Wednesday, 10 August 2011 09:29

ALERT LEVEL

CRITERIA

INTERPRETATION

No alert 

Background, quiet

No eruption in foreseeable future

1

Low level seismic, fumarolic, other unrest.

Magmatic, tectonic or hydrothermal disturbance; no eruption imminent.

2

Low to moderate level of seismic, other unrest  with positive evidence for involvement of magma

Probable magmatic intrusion; could eventually lead to an eruption.

3

Relatively high and increasing unrest, including numerous b-type earthquakes, accelerating ground deformation and rockfalls, increased vigor of fumaroles, gas emission

Increasing likelihood of an eruption, possibly witin days to week.

4

Intense unrest, including harmonic tremor and/or may “long period” (=low frequency) earthquakes or quiet lava emissions and/or dome growth and/or small explosions

Magma close to or at earth’s surface.  Hazardous explosive eruption likely, possible within hours to days

5

Hazardous explosive eruption in progress, with pyroclastic flows, surges and/or eruption column rising at least  6 km or 20,000 feet above sea level

Explosive  eruption in progress.  Hazards in valleys and downwind

STAND-DOWN PROCEDURES:

In order to protect against “lull before the storm” phenomena, alert levels will be maintained for the following periods AFTER activity decreases to the next lower level:

From level 5 to level 4:

Wait 12 hours after level 5 activity stops

From level 4 to level 3 to 2:

Wait 2 weeks after activity drops below level 4

From level 3 to level 2:

Wait 2 weeks after activity drops below level 3

NOTE:

Ashfall will occur from secondary explosions for several years after eruption , whenever rainfall and lahars come in contact with still hot- pyroclastic deposits.  These secondary explosions will occur regardless of alert level.

 

PHILIPPINE STANDARD TIME

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