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MMEIRS

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Philippine Institute of Volcanology and Seismology, Powered by Joomla!
Pinatubo Volcano Alert Signals PDF Print
Wednesday, 10 August 2011 09:25

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, 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 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 the 1991 Plinian (calderagenic) eruption, whenever rainfall and lahars come in contact with still hot-hot 1991 pyroclastic flow deposits.  These secondary explosions will occur regardless of alert level.