Editing Long Valley Caldera (section)

===Hydrothermal system===
[[File:Hot Creek Fish Hatchery with Resurgent Dome in background-1200px.jpg|right|thumb|upright=1.5|Hot Creek Fish Hatchery at base of Resurgent Dome]]

The Long Valley Caldera hosts an active hydrothermal system that includes hot springs, [[fumarole]]s (steam vents), and mineral deposits. Hot springs exist primarily in the eastern half of the [[caldera]] where land-surface elevations are relatively low; fumaroles exist primarily in the western half where elevations are higher. Mineral deposits from thermal activity are found on an uplifted area called the resurgent dome, at [[Little Hot Creek]] springs, [[Hot Creek Gorge]], and other locations in the south and east [[moat]]s of the caldera.<ref name="usgshydro">{{USGS |url= http://volcanoes.usgs.gov/lvo/activity/monitoring/hydrology/ |title= Hydrologic Studies in Long Valley Caldera}}</ref>

Hot springs discharge primarily in Hot Creek Gorge, along [[Little Hot Creek]], and in the [[Alkali Lakes]] area. The largest springs are in Hot Creek Gorge where about {{convert|250|L|gal}} per second of thermal water discharge and account for about 80% of the total thermal water discharge in the caldera. At the other extreme are springs at [[Hot Creek Fish Hatchery]] which contain a small component (2–5%) of thermal water that raises water temperatures about {{convert|5|C-change|F-change|abbr=on}} higher than background temperatures. Use of the warm spring water in the [[hatchery]] has increased fish production because [[trout]] growth rates are faster in the warm water than in ambient stream temperatures in Long Valley.<ref name="usgshydro"/>

[[File:Mammoth Hot Creek Panorama.jpg|left|thumb|Hot Creek in the summer]]

In hydrothermal systems, the circulation of [[groundwater]] is driven by a combination of [[topography]] and [[heat]] sources. In Long Valley Caldera, the system is recharged primarily from [[snowmelt]] in the highlands around the western and southern rims of the caldera. The water from snowmelt and rainfall infiltrates to depths of a few kilometers, where it is heated to at least {{cvt|220|C|F|abbr=on}} by hot rock near geologically young intrusions. Upflow occurs in the west moat where the heated water with lower density rises along steeply inclined fractures to depths of {{cvt|1|-|2|km|abbr=on}}. This hydrothermal fluid flows laterally, down the hydraulic gradient, from the west to the southeast around the resurgent dome and then eastward to discharge points along Hot Creek and around [[Crowley Lake]]. Reservoir temperatures in the volcanic fill decline from {{cvt|220|C|F|abbr=on}} near the Inyo Craters to {{cvt|50|C|F|abbr=on}} near Crowley Lake due to a combination of heat loss and mixing with cold water.<ref name="usgshydro"/>

Hot Creek has been a popular swimming hole for decades. Over a dozen people have died in Hot Creek since the late 1960s, but most of these deaths happened to people who ignored the numerous warning signs and attempted to use the hydrothermal pools as [[hot tub]]s (like the stream portion of the creek, these pools alternate in temperature, but the eruptions in the pools are of super-heated water in already very hot water).{{Citation needed|date=April 2022}} Recent geothermal instability has led to its temporary closure for swimming. Officials are unsure of when (if ever) Hot Creek will officially reopen for swimming.

Hydrothermal activity has altered many rocks in the caldera, transforming them into [[travertine]] and [[clay]]. At the [[Huntley clay mine]], white chalky clay called [[kaolinite]] is mined; the kaolinite is exposed on the resurgent dome and appears as a brilliant white band.