USGS Volcanic Activity Alert-Notification System
(Updated 14 March 07) The U.S. Geological Survey (USGS) Volcano Hazards Program has adopted an alert-notification system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. For information on the icons used to describe the alert levels, please see Icons for USGS Volcanic Activity Alert-Notification System.
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.
Volcano Alert Level
The four-tiered Volcano Alert Level uses the terms Normal, Advisory, Watch, and Warning (from background levels to highest threat - see Table 1). The Volcano Alert Levels are intended to inform people on the ground about a volcano's status and are issued in conjunction with the Aviation Color Code. Notifications are issued for both increasing and decreasing volcanic activity and are accompanied by text with details about the nature of the unrest or eruption and about potential or current hazards and likely outcomes.
|Table 1. SUMMARY OF VOLCANO ALERT LEVELS|
is in typical
background, noneruptive state
is exhibiting signs of
elevated unrest above
known background level
or escalating unrest
with increased potential
of eruption, timeframe
Hazardous eruption is imminent, underway, or suspected.
Aviation Color Code
The Aviation Color Code notifications are issued in conjunction with the Volcano Alert Levels. The color codes (Green, Yellow, Orange, Red - see Table 2) are used to provide succinct information about volcanic-ash hazards to the aviation sector. 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. SUMMARY OF AVIATION COLOR CODES|
in typical background, non-eruptive state
Volcano is exhibiting signs of elevated unrest above known background level
Volcano is exhibiting heightened or escalating unrest
with increased potential of eruption, timeframe uncertain,
Eruption is imminent with significant emmission of
volcanic ash into the atmosphere likely
Additional information on the alert-notification system can be found in the Fact Sheet U.S. Geological Survey's Alert-Notification System for Volcanic Activity.