The LVO SIC will inform by telephone the duty officer of the California Office of Emergency Services (OES) communication center in Sacramento that a specific Color Code is in force according to the procedures outlined previously (see tables 1 and 2; section III). In the case of a condition YELLOW, ORANGE, or RED, the SIC, with concurrence of the Western Regional Geologist, will fax one of the following messages to the Director of OES. OES is responsible for relaying the message to county and city officials within twenty minutes of receipt from the USGS. After appropriate civil officials have been notified, the message will be released to the media and the public.
The U.S. Geological Survey (USGS) has initiated a field operation centered in Mammoth Lakes to closely monitor the (specify activity: earthquakes swarm activity, ground deformation, etc.) currently centered in (specify place: south moat of Long Valley Caldera, the Mono Craters, etc.) approximately (x) miles (direction) from (nearby towns). Activity of this sort is symptomatic of magma (molten rock) movement in the crust beneath volcanic areas throughout the world. Most likely the activity will decay to normal background levels over the next few weeks or months, as has been the case with previous episodes of heightened activity in the Long Valley region. There remains a small possibility, however, that the current activity may escalate and possibly evolve toward a volcanic eruption. In such a case, USGS scientists would expect the earthquake activity and ground deformation to intensify as magma moves upward to shallow depths in the crust. The expanded USGS monitoring efforts will focus on the early identification of any changes in the activity pattern that may be diagnostic of an impending eruption. The USGS will establish direct contact with California Office of Emergency Services (OES) and local civil authorities from the temporary USGS field center in Mammoth Lakes and will keep them informed of significant changes in activity and provide an assessment of its implication for possible volcanic hazards.
The intense activity (specify type) currently centered in (specify place) indicates that a volume of magma (molten rock) is being injected into the shallow crust with a strong possibility that the magma will reach the surface to produce a volcanic eruption in the coming hours to days. It is not possible to say precisely when magma might reach the surface, nor to specify the precise size, duration, or type of the eruption should one actually develop. Indeed, it is still possible that the magma may yet stop short of the surface and not result in an eruption.
Intensified USGS monitoring efforts from a temporary field center in Mammoth Lakes (or Bridgeport) will focus on the prompt identification of any changes in the activity pattern that may help specify the time and place magma may reach the surface to produce an eruption. The USGS will maintain direct contact with California Office of Emergency Services (OES) and local civil authorities from the temporary USGS field center in and will keep them informed of significant changes in activity and provide an assessment of its implication for possible volcanic hazards.
If an eruption does develop from this activity, it will most likely produce small to moderate volumes of rhyolitic (silica rich, explosive) lava similar the eruptions that occurred 650 years ago at the north end of the Mono Craters and 550 years ago at the Inyo Domes. In this case, any or all of the following may be expected: (1) phreatic (steam blast) eruptions as the magma interacts with shallow ground water, producing explosions that can throw large blocks of rock several hundred yards from the vent (the "eruption" could stop at this point, as it did with the phreatic blasts that formed the Inyo Craters), (2) an explosive magmatic phase during which hot pumice and ash would be ejected several miles into the air producing thick pumice accumulations near the vent, extensive deposits of fine ash hundreds of miles downwind, and destructive pyroclastic flows that may reach distances as great as 3 to 6 miles from the vent, and (3) a final phase that involves the slow extrusion of lava to form steepsided flows and domes. As with the eruptions 550 and 650 years ago, eruptions may occur fnrom several separate vents in succession, with the vents spaced over a distance as great as 6 miles. Individual eruptions may be separated in time by days to perhaps weeks. Larger, more destructive eruptions following the same basic pattern are possible but less likely.
Also possible, but less likely, is a small to moderate eruption of basaltic (Hawaii-like) lava similar to the eruptions that produced the Red Cones several thousand years ago. In this case, the following may be expected: (1) an initial series of phreatic eruptions as described above for the silicic eruption sequence, (2) the onset of magmatic eruptions with fluid basaltic lava fountaining several hundred yards into the air from a line of vents that may extend several miles. Both 1 and 2 would scatter ash and tephra over the surrounding region and feed the beginnings of slowmoving lava flows, and (3) consolidation of lava fountaining into a few vents feeding lava flows that move downslope at speeds ranging from a few yards per hour to several miles per hour. The resulting lava flows may extend 6 miles or more from the vents depending on the vigor and duration of eruption.
The specific wording for a condition-RED message will depend strongly on the actual nature, size, and location of eruptive activity. A condition-RED message should include the following elements:
Condition-RED messages will be updated as frequently as needed to describe the ongoing activity and any changes in the anticipated hazardous impacts. Sample condition-RED messages are given below.
A (specify intensity and type as appropriate: for example, minor phreatic, moderate effusive, strong explosive, etc.) eruption began at (specify local time) with the vent(s) centered near (specify place). The U.S. Geological Survey (USGS) has announced a condition RED, LEVEL (specify from table 2) indicating that a (specify intensity: weak, moderate, etc.) eruption is currently underway. Based on its location, type, and current intensity, the eruption can be expected to (specify expected impact on public and built infrastructure, including ash cloud hazards to aircraft, and ash fall hazards downwind). The map illustrates areas likely to be affected by eruptive activity (attach or refer to hazard-zonation map and hazard assessment for the vent that is active).
The USGS will closely monitor this eruptive activity and provide frequent updates as conditions evolve. For more information, visit the USGS web site for the Long Valley Observatory at http://lvo.wr.usgs.gov or call (specify telephone number for recorded updates). It is important to recognize that volcanic eruptions can wax and wane in intensity over extended periods. Changes in style and intensity can sometimes occur abruptly with little warning.
The following is a U.S. Geological Survey (USGS) update of the eruption at (specify place) as of (specify time). The condition is RED, LEVEL (specify level from table 2).
Specific wording for the remainder of a condition RED update message will depend strongly on the actual nature, size, and location of eruptive activity. In addition to the above, each update message must include at least the following:
The USGS will continue to closely monitor this eruptive activity and provide frequent updates as conditions evolve. It is important to recognize that volcanic eruptions can vary in intensity over extended periods of time. Changes in the character and intensity of eruptions can sometimes occur abruptly with little warning.
Maintained by: Michael Diggles
Last modified: May 18, 2005