Background, quiet

No eruption in foreseeable future

Low level seismic, fumarolic, other unrest

Magmatic, tectonic, or hydrothermal disturbance; no eruption imminent

Moderate level of seismic, other unrest with positive evidence for involvement of magma

Probable magma intrusion; could eventually lead to an eruption

Relatively high and increasing unrest, including numerous low frequency volcanic earthquakes, accelerating ground deformation, increasing fumarolic activity

Increasing likelihood of an eruption, possibly explosive, probably within days to weeks.

Intense unrest, including harmonic tremor and/or many “long-period” (i.e., low frequency) earthquakes and/or dome growth and/or small explosions

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

Hazardous 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 actually 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 or 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