Multimedia

Tuffisite veins form during eruptions, when a mix of hot volcanic gas and rock fragments are forced through fractures in cooled lava. USGS photo by J. Crozier.

Mono Craters consists of a series of high-silica rhyolite lava domes, many erupted within the last 10,000 years. The domes are often steep, glassy, and contain very few phenocrysts.

Main hydrothermal features of the new (2016) 3-D model of the subsurface at Long Valley Caldera. This schematic is based on a survey of the electrical properties of the earth (magnetotellurics) below. Arrows show subsurface water flow, with colors keyed to changing water temperature, from blue (cold) to red (hot). Purple arrows show an extinct hot water pathway.

This is a simplified diagram of regional range front faults as they intersect the Long Valley Caldera.

C1 and C3 are granitic crystal-melt mush (partially crystallized magma) columns that fed the most recent Mono Craters eruptions. The connection from C1 to South Coulée (SC) is older and colder than the connection from C3 to North Coulée (NC) and Panum Crater (PC), which carries hydrothermal fluid to the surface.

Hydrothermal system and water flow in the subsurface beneath Long Valley Caldera, California. Cartoon Illustration from USGS FS 2007-3045.