"Under the Stafford Act (Public Law 93-288), the U.S. Geological Survey (USGS) has the Federal responsibility to issue timely and effective warnings of potential volcanic disasters. The USGS, through its five volcano observatories, determines the alert levels for a given volcano and notifies the appropriate Federal and State (and in some cases local) emergency management agencies of notable unrest and eruptive activity. Those agencies then start a process of disseminating information outward to other government and public organizations. Information is communicated to the public primarily through local and national news outlets and the Internet. The USGS has now standardized the alert-notification system used at its volcano observatories. The goals of this alert-notification system are to (1) communicate a volcano's status clearly to nonvolcanologists, (2) help emergency-response organizations determine proper mitigation measures, and (3) prompt people and businesses at risk to seek additional information and take appropriate actions. A key benefit of a standardized, nationwide alert system […] is that it minimizes confusion for those needing information about current threats from volcanic activity."
USGS Fact Sheet 2006-3139
U.S. Geological Survey: http://www.usgs.gov/