Alert Level

Criteria

Interpretation

0

Background, quiet

No eruption in foreseeable future.

1

Low level seismicity, fumarolic, other activity

Magmatic, tectonic or hydrothermal disturbance; no eruption imminent.

2

Low to moderate level of seismicity, persistence of local but unfelt earthquakes. Ground deformation measurements above baseline levels. Increased water and/or ground probe hole temperatures, increased bubbling at Crater Lake.

A) Probable magmatic intrusion; could eventually lead to an eruption.

B) If trend declines, volcano may soon go to level 1

3

Relatively high unrest manifested by seismic swarms including increasing occurrence of low frequency earthquakes and/or harmonic tremor (some events felt). Sudden or increasing changes in temperature or bubbling activity or radon gas emission or crater lake pH. Bulging of the edifice and fissuring may accompany seismicity

A) If trend is one of increasing unrest, eruption is possible within days to a few weeks.

B) If trend is one of decreasing unrest, volcano may soon go to level 2

4

Intense unrest, continuing seismic swarms, including harmonic tremor and/or “low frequency earthquakes” which are usually felt, profuse steaming along existing and perhaps new vents and fissures.

Hazardous explosive eruption is possible within days.

5

Base surges accompanied by eruption columns or lava fountaining or lava flows.

Hazardous eruption in progress. Extreme hazards to communities west of the volcano and ashfalls on downwind sectors.