The U.S. Geological Survey response plan for volcanic unrest in the Long Valley area is designed to improve communication about significant scientific information derived from monitoring measurements to local, state, and Federal civil authorities. The table shows a graded measure of the U.S. Geological Survey's concern about the possibility that a given level of unrest might threaten local communities with a volcanic eruption from within Long Valley caldera or along the Mono-Inyo Craters volcanic chain (it does not apply to regional earthquakes occurring in the tectonic regime outside the caldera or away from the Mono-Inyo Craters volcanic chain). This ranking offers civil authorities a framework they can use to gauge and coordinate their response to a developing seismic or volcanic crisis. Effective communication and coordination with emergency management officials are particularly important because the USGS has neither the authority nor the expertise to make decisions regarding the civil response to an evolving crisis.

The 4-level color-coded notification system below was developed in 1997 to replace a 5-level system devised in 1991 then modified in 2002 (see references below). 

Color-Code Conditions and Associated USGS Response
Long Valley Caldera and Mono-Inyo Craters Region, California

CONDITION	USGS RESPONSE1	ACTIVITY LEVEL	RECURRENCE INTERVAL2
GREEN—No immediate risk	Normal operations plus information calls to local and other authorities for weak through strong unrest as appropriate	Background or quiescence	Most of the time
		Weak Unrest	Days to weeks
		Minor Unrest	Weeks to months
		Moderate-to-Strong Unrest	Months to years
YELLOW (WATCH)	Full calldown and EVENT RESPONSE3	Intense Unrest	Years to decades
ORANGE (WARNING)	Full and calldown and EVENT RESPONSE3 (if not already in place under YELLOW)	Accelerating intense unrest: eruption likely within hours to days	Decades to centuries
RED (ERUPTION IN PROGRESS)	Full and calldown and EVENT RESPONSE3 (if not already in place under YELLOW OR ORANGE) Daily or more frequent updates on eruption levels	LEVEL 1: Minor eruption	Centuries
		LEVEL 2: Moderate explosive eruption	Centuries
		LEVEL 3: Strong explosive eruption	Centuries
		LEVEL 4: Massive explosive eruption	Centuries to millennia

¹USGS response for a given condition will include the responses specified for all lower conditions.

²Estimated recurrence intervals for a given condition are based primarily on the recurrence of episodes of unrest in Long Valley Caldera since 1980, the record of M>4 earthquakes activity in the region since the 1930's, and the geologic record of volcanic eruptions in the region over the past 5,000 years.

³ Event Response involves staffing the USGS field office in Mammoth Lakes for enhanced, on-site monitoring as well as staffing a field office in Bridgeport. See full description in USGS Bulletin 2185.

Standdown Rules for Color-Code Conditions

CONDITION	EXPIRES AFTER*	SUBSEQUENT CONDITION
GREEN (No immediate risk)   Weak Unrest   Minor Unrest   Moderate-to-Strong Unrest	1 day 2 days 3 days	GREEN Background Weak Unrest Minor Unrest
YELLOW (Watch)	14 days	GREEN (to appropriate Unrest level under green)
ORANGE (Warning)	7 days	YELLOW
RED (Alert: Eruption in progress)	1 day	ORANGE

*Number of days after the activity level falls below the threshold for a given CONDITION

Hill, D.P., Johnston, M.J., Langbein, J.O., McNutt, S.R., Miller, C.D., Mortensen, C.E., Pitt, A.M., and Rojstaczer, S., 1991, Response Plans for Volcanic Hazards in the Long Valley Caldera and Mono Craters Area, California: U.S. Geological Survey Open-File Report 91-270, 64 p.