U.S. Geological Survey, Volcano Hazards Program

Volcano Hazards Program

Volcano Observatories: Alaska / Cascades / Hawaii / Long Valley / Mariana Islands / Yellowstone /

USGS Volcano-Warning Scheme for the United States

The U.S. Geological Survey (USGS) has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. The new volcano alert-level system is now used by the Alaska Volcano Observatory, the Cascades Volcano Observatory, the Hawaiian Volcano Observatory, the Long Valley Observatory, and the Yellowstone Volcano Observatory.

Under the new system, the USGS ranks the level of activity at a U.S. volcano using the terms "Normal", for typical volcanic activity in a non-eruptive phase; "Advisory", for elevated unrest; "Watch", for escalating unrest or a minor eruption underway that poses limited hazards; and, "Warning", if a highly hazardous eruption is underway or imminent (Table 1). These levels reflect conditions at a volcano and the expected or ongoing hazardous volcanic phenomena. When an alert level is assigned by an observatory, accompanying text will give a fuller explanation of the observed phenomena and clarify hazard implications to affected groups.

Table 1. SUMMARY OF VOLCANIC-ALERT LEVELS
NORMAL	Typical background activity of a volcano in a non-eruptive state After a change from a higher level: Volcanic activity considered to have ceased, and volcano reverted to its normal, non-eruptive state.
ADVISORY	Elevated unrest above known background activity After a change from a higher level: Volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH	Heightened/escalating unrest with increased potential for eruptive activity (timeframe variable) OR a minor eruption underway that poses limited hazards.
WARNING	Highly hazardous eruption underway or imminent.

As part of the alert-level system, color codes (Green, Yellow, Orange, Red) are used to provide succinct information about volcanic-ash hazards to the aviation sector (Table 2). Volcanic activity threatens safe air travel when finely pulverized, glassy, abrasive volcanic material is explosively erupted into the atmosphere and dispersed as airborne clouds in flight paths of jet aircraft. The color codes are in accord with recommended ICAO (International Civil Aviation Organization) procedures to help pilots, dispatchers, and air-traffic controllers who are planning or executing flights over broad regions of the globe quickly ascertain the status of numerous volcanoes and determine if continued attention, re-routing, or extra fuel is warranted.

Table 2. AVIATION COLOR CODES
GREEN	Volcano is in normal, non-eruptive state. or, after a change from a higher level: Volcanic activity considered to have ceased, and volcano reverted to its normal, non-eruptive state.
YELLOW	Volcano is exhibiting signs of elevated unrest above known background levels. or, after a change from a higher level: Volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
ORANGE	Volcano is exhibiting heightened unrest with increased likelihood of eruption, or, Volcanic eruption underway with no or minor ash emission [specify ash-plume height if possible].
RED	Eruption is forecast to be imminent with significant emmission of ash into the atmosphere likely. or, Eruption is underway with significant emission of ash into the atmosphere [specify ash-plume height if possible].

Additional information on the alert-level system can be found in the pdf file USGS ALERT-LEVEL SYSTEM FOR COMMUNICATING THE STATUS OF ACTIVITY AT U.S. VOLCANOES.

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U.S. Department of the Interior | U.S. Geological Survey
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Page Last Modified: Thursday, January 04, 2007 (dyv)