USGS Volcano-Warning Scheme for the
Cascade Range Volcanoes

Alert-level notifications will be accompanied by brief explanatory text to clarify hazard implications as fully as possible. Updates may be issued to supplement any alert-level statement. Alert-level assignments depend upon observations and interpretations of changing phenomena. Some volcanic events may not be preceded by obvious changes, or the observed changes may not be well understood; thus, surprises are possible, and uncertainty about timing and nature of anticipated events is likely. Alert levels are not always followed sequentially.


Information Statement

Unusual events such as steam bursts (with or without minor ash fall), small avalanches, rock falls, minor mudflows, thunderstorms, and slash burning often attract media and public interest and inquiry. These events do not fit into any other information category. Most such volcano- related events are usually short-lived, and some may be hazardous. As this type of event almost always occurs without specifically recognized precursors, there is usually no opportunity to provide warning or arrange evacuation. Thus, persons in proximity to such an event are at some personal risk and will need to make their own safety decisions.

Information about a discrete natural event may come from any source. For example, a local outburst flood or rockfall may be observed and reported by hikers or US Forest Service personnel. Owing to frequent public and media inquiries that result from such events, USGS-CVO along with other involved agencies will attempt to verify the nature and extent of the event, issuing commentary as appropriate in "information statements."

"Information statements" may also be issued to provide commentary about notable events occurring within any staged alert level during volcanic unrest.

Notice of Volcanic Unrest - Alert Level ONE

This alert level is declared by USGS-CVO when significant anomalous conditions are recognized that could be indicative of an eventual hazardous volcanic event. The most likely such anomalous condition would be sustained, elevated seismicity. A "notice of volcanic unrest" expresses concern about the potential for hazardous volcanic activity but does not imply imminent hazard. Among the possible outcomes are: (1) anomalous condition is determined not symptomatic of an eventual hazardous volcanic event, leading to cancellation of "notice of volcanic unrest;" (2) symptomatic activity wanes, leading to cancellation of the "notice of volcanic unrest;" (3) conditions evolve so as to indicate progress toward hazardous volcanic activity, leading to issuance of a "volcano advisory" or "volcano alert."

Volcano Advisory - Alert Level TWO

This alert level is declared by USGS-CVO when 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. This alert level is used to emphasize heightened concern about potential hazard. Among the possible outcomes are: (1) precursory activity wanes, leading either to cancellation of the "volcano advisory" or to a downgrade of alert level to "notice of volcanic unrest;" (2) conditions evolve so as to indicate that a life-threatening volcanic or hydrologic event is imminent or underway, leading to issuance of a "volcano alert." "Volcano advisory" statements, supplemented as appropriate by "updated volcano advisory" statements will clarify as fully as possible USGS-CVO understanding of the hazard implications.

Volcano Alert - Alert Level THREE

This alert level is declared by USGS-CVO when 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. Depending upon further developments, a "volcano alert" will be maintained, updated, downgraded to a "volcano advisory," or canceled. A "volcano alert" statement will indicate, in as much detail as possible, the time window, place, and expected impact of an anticipated hazardous event. "Updated volcano alert" statements will amplify hazard information as dictated by evolving conditions.

• Link to: USGS Volcano Hazards Website, USGS Volcano-Warning Schemes in the United States