Pyroclastic Flow and Surge Hazard Zones in the Long Valley - Mono Lake Area, California

Areas as far as 15 km (10 mi) from an explosive eruption could be swept by hot, fast-moving pyroclastic flows and surges. A pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more. The temperature within a pyroclastic flow may be greater than 500° C, sufficient to burn and carbonize wood. Once deposited, the ash, pumice, and rock fragments may deform (flatten) and weld together because of the intense heat and the weight of the overlying material.

Scientists examine the distances that pyroclastic flows are known to have traveled in the past few thousand years to determine areas where they might occur in the future. The actual areas covered by pyroclastic flows or surges during a future explosive eruption depends primarily on the location of the vent(s), the surrounding topography, and volume of magma erupted.

Pyroclastic flows generated from vents on Mammoth Mountain could travel farther than 15 km (10 mi) because of the extra momentum that would be gained as the flows descend hundreds of meters down Mammoth's steep flanks and move across low-lying areas.

Potential hazards from pyroclastic flows and surges for small to moderate-sized eruptions from along the Mono-Inyo Craters volcanic chain or in the south moat of Long Valley Caldera, California

Map of potential pyroclastic-flow hazards in the Long Valley area, California

Map from C.D. Miller, modified by J. Johnson.

Map shows hazard zone for pyroclastic flows and surges around existing explosive vents along the Mono-Inyo Craters volcanic chain and from potential vents located in the south moat area of Long Valley Caldera.

This hazard zone is based on explosive eruptions from vents located along the chain in the past 10,000 years that are known to have that ejected <1 km3 of magma and generated pyroclastic flows or surges. Future pyroclastic flows and surges from a single eruption from along the Mono-Inyo chain or in the south moat would affect only a part of the total hazard zones shown on the map.

Large-sized map (345 KB; 600 x 824 pixels)

Pyroclastic-flow and -surge hazard zones

References

Miller, C.D., Mullineaux, D.R., Crandell, D.R., and Bailey, R.A., 1982, Potential hazards from future volcanic eruptions in the Long Valley-Mono Lake area, East-Central California and Southwest Nevada -- a preliminary assessment: U.S. Geological Survey Circular 877, 10 p.

Miller, C.D., 1989, Potential hazards from future volcanic eruptions in California: U.S. Geological Survey Bulletin 1847, 17 p.