Volcano warning schemesThree parallel Volcano warning schemes are used by the United States Geological Survey for different volcano ranges in the United States. They each have a base level for dormant-quiescent states and three grades of alert.
Developed in 1997 to replace a previous 5-level system devised in 1991.
| Code | Narrative | Levels
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| Green | No immediate risk | Levels from Quiescent to Strong Unrest
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| Yellow | Watch | Intense Unrest
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| Orange | Warning | Accelerating intense unrest: eruption likely within hours to days
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| Red | Eruption in progress | Levels 1 (Minor eruption) - 4 (Massive explosive eruption)
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Level of Concern Color Codes for volcanoes in Alaska
Established during the 1989-90 eruption of Redoubt Volcano.
| Code | Narrative
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| Green | Volcano is in its normal "dormant" state
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| Yellow | Volcano is restless. Seismic activity is elevated. Potential for eruptive activity is increased.
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| Orange | Small ash eruption expected or confirmed. Plume(s) not likely to rise above 25,000 feet above sea level.
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| Red | Large ash eruptions expected or confirmed. Plume likely to rise above 25,000 feet above sea level.
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Introduced following the May 18, 1980, eruption of Mount St. Helens.
| Code | Narrative | Levels
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| No Alert | "Information Statements" may be issued about unusual but non-threatening events
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| Alert Level ONE | Notice of Volcanic Unrest | Significant anomalous conditions are recognized that could be indicative of an eventual hazardous volcanic event.
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| Alert Level TWO | Volcano Advisory | Monitoring and evaluation indicate that processes are underway that have significant likelihood of culminating in hazardous volcanic activity but when the evidence does not indicate that a life- or property-threatening event is imminent.
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| Alert Level THREE | Volcano Alert | Monitoring and evaluation indicate that precursory events have escalated to the point where a volcanic event with attendant volcanologic or hydrologic hazards threatening to life and property appears imminent or is underway.
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External link
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