In October 2006, the

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

(USGS) 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 Alaska Volcano Observatory (AVO) is a joint program of the United States Geological Survey, the Geophysical Institute of the University of Alaska Fairbanks, and the State of Alaska Division of Geological and Geophysical Surveys (ADGGS). AVO ...

, the

California Volcano Observatory The California Volcano Observatory (CalVO) is the volcano observatory that monitors the volcanic and geologic activity of California and Nevada. It is a part of the Volcano Hazards Program of the United States Geological Survey, a scientific agen ...

(California and Nevada), the

Cascades Volcano Observatory The David A. Johnston Cascades Volcano Observatory (CVO) is a volcano observatory in the US that monitors volcanoes in the northern Cascade Range. It was established in the summer of 1980, after the eruption of Mount St. Helens.Hawaiian Volcano Observatory The Hawaiian Volcano Observatory (HVO) is an agency of the U.S. Geological Survey (USGS) and one of five volcano observatories operating under the USGS Volcano Hazards Program. Based in Hilo, Hawaii, the observatory monitors six Hawaiian volcan ...

and the

Yellowstone Volcano Observatory The Yellowstone Volcano Observatory (YVO) is a volcano observatory that primarily monitors the Yellowstone Caldera in Yellowstone National Park in the United States. The observatory's jurisdiction also includes volcanic centers in the states of Col ...

(Montana, Wyoming, Colorado, Utah, New Mexico and Arizona). 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. Volcanic-alert icons

Summary of Volcanic Activity Alert Notification System

Aviation color codes

Earlier volcano warning schemes for the United States

Prior to October 2006, three parallel Volcano warning schemes were used by the

and the volcano observatories for different

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates ...

ranges in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. 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.

Level of Concern Color Codes for volcanoes in Alaska

The

(AVO) used the following color-coded system to rate volcanic activity. It was originally established during the 1989-90 eruption of Redoubt Volcano. All five classifications are spelled as

proper noun A proper noun is a noun that identifies a single entity and is used to refer to that entity (''Africa'', ''Jupiter'', '' Sarah'', ''Microsoft)'' as distinguished from a common noun, which is a noun that refers to a class of entities (''continent, ...

s, 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 Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often ...

of Mount St. Helens. {, class="wikitable" ! Code !! Narrative !! Levels , - !No Alert , colspan=2, "Information Statements" may be issued about unusual but non-threatening events , - !Alert Level One , Notice of Volcanic Unrest, , Significant anomalous conditions are recognized that could be indicative of an eventual hazardous volcanic event. , - !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. , - !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.

References

USGS Volcanic Activity Alert-Notification System pageAVO information release about new warning scheme
Volcanology Warning systems Color codes