Volcano warning schemes of the United States


In October 2006, the United States Geological Survey adopted a nationwide alert system for characterizing the level of unrest and eruptive activity at volcanoes. The system is now used by the Alaska Volcano Observatory, the California Volcano Observatory, the Cascades Volcano Observatory, the Hawaiian Volcano Observatory and the Yellowstone Volcano Observatory.
Under this 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 an eruption underway that poses limited hazards; and, "warning", if a highly hazardous eruption is underway or imminent. 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.

Summary of Volcanic Activity Alert Notification System

NormalTypical 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.
AdvisoryElevated 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.
    • WatchHeightened/escalating unrest with increased potential for eruptive activity OR a minor eruption underway that poses limited hazards.
    WarningHighly hazardous eruption underway or imminent.

    Aviation color codes

    Earlier volcano warning schemes for the United States

    Prior to October 2006, three parallel Volcano warning schemes were used by the United States Geological Survey and the volcano observatories for different volcano ranges in the United States. They each have a base level for dormant-quiescent states and three grades of alert.

    Color Code Conditions, Long Valley Caldera and Mono-Inyo Craters Region, California

    Developed in 1997 to replace a previous 5-level system devised in 1991.
    CodeNarrativeLevels
    GreenNo immediate riskLevels from Quiescent to Strong Unrest
    YellowWatchIntense Unrest
    OrangeWarningAccelerating intense unrest: eruption likely within hours to days
    RedEruption in progressLevels 1 to 4

    Level of Concern Color Codes for volcanoes in Alaska

    The Alaska Volcano Observatory used the following color-coded system to rate volcanic activity. It was originally established during the 1989-90 eruption of Redoubt Volcano.
    ClassDescription
    GreenVolcano is in its normal "dormant" state.
    YellowVolcano is restless. Seismic activity is elevated. Potential for eruptive activity is increased.
    OrangeSmall ash eruption expected or confirmed. Plume not likely to rise above 25,000 feet above sea level.
    RedLarge ash eruptions expected or confirmed. Plume likely to rise above 25,000 feet above sea level.

    All five classifications are spelled as proper nouns, i.e., Level of Concern Color Code Orange not Level of concern color code Orange or any other variation. On its website the AVO spells the alert color in all capitals, but this is not otherwise necessary outside their system.

    Warning system for Cascade Range volcanoes in Washington and Oregon

    Introduced following the May 18, 1980, eruption of Mount St. Helens.