USGS Volcanic Activity Alert-Notification System

The U.S. Geological Survey (USGS) Volcano Hazards Program(Updated 14 March 07) has adopted an alert-notification system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. The volcano alert-notification system is used by the Alaska Volcano Observatory, the Cascades Volcano Observatory, the Hawaiian Volcano Observatory, the Long Valley Observatory, and the Yellowstone Volcano Observatory.The standardized USGS alert-notification system for volcanic activity was designed to be useful to people on the ground and to those in aviation. To meet these goals, the alert-notification system has two parts - a four-tiered Volcano Alert Level and a four-tiered Aviation Color Code. Volcano observatory scientists determine alert levels for a volcano by using monitoring data and their knowledge of the expected or ongoing hazardous activity. Details about the volcanic activity accompany any notifications of changes in alert levels.
For more information on the icons used to describe the alert levels, please see Icons for USGS Volcanic Activity Alert-Notification System.

http://volcano.wr.usgs.gov/activity/alertsystem/index.php

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