U.S. GEOLOGICAL SURVEY and the U.S. FOREST SERVICE—OUR VOLCANIC PUBLIC LANDS Boiling Water at Hot Creek—The Dangerous and Dynamic Thermal Springs in California’s Long Valley Caldera he beautiful blue pools and Timpressive boiling fountains along Hot Creek in east-central California have provided enjoyment to generations of visitors, but they have also been the cause of injury or death to some who disregarded warnings and fences. The springs and geysers in the stream bed and along its banks change location, temperature, and flow rates frequently and unpredictably. The hot springs and geysers of Hot Creek are visible signs of dynamic geologic processes in this volcanic region, where underground heat drives thermal spring activity. Hot Creek flows through the Long Valley Caldera in a volcanically active region of east-central California. This stretch of the creek, looking upstream to the southwest, has long been a popular recreation area because of the warm waters from its thermal springs. These springs, however, are In the Hot Creek Geologic Site, located unpredictable and can suddenly erupt with violence and at boiling temperature. Because of this danger, the U.S. Forest Service has had to close parts of the Hot Creek Geologic Site to visitors. in a narrow gorge 8 miles (12 km) east of (USGS photo by Chris Farrar.) the town of Mammoth Lakes, numerous hot springs flow into a snowmelt-fed stream. The has long monitored spring activity, water changes in the locations and vigor of springs area is managed by the U.S. Forest Service temperatures and chemistry, and stream can be sudden and dangerous to unprepared as a geologic interpretive site and has been a flow as part of a program that seeks to better visitors, especially if they stray beyond popular recreational area for fishing, swim- understand volcanic unrest and possible geo- walkways and fences. ming, hiking, bird watching, and photogra- logic hazards throughout the region. Since May 2006, springs in and near the phy. The U.S. Geological Survey (USGS) The attractions of Hot Creek, however, most popular swimming areas have been also harbor danger. The locations, dis- “geysering” or intermittently spurting very charge rates, and temperatures of springs hot, sediment-laden water as high as 6 feet often change. The larger and more vigorous (2 m) above the stream surface. At times springs flow from fractures in the volcanic this geysering activity is vigorous enough rock (altered rhyolite) in Hot Creek gorge. to produce “popping” sounds audible from When fractures become sealed by mineral hundreds of feet away. The geysering usually deposition, spring discharge and tempera- lasts a few seconds and occurs at irregular ture decline. When new fractures develop or intervals, with several minutes between erup- sealed fractures reopen, spring discharge and tions. The unpredictability of this hazardous temperatures can increase suddenly. Rock spring activity led the U.S. Forest Service to Conditions in Hot Creek can change very quickly. fracturing happens because the thermal area close parts of the Hot Creek Geologic Site in These fish—caught in a burst of high-temperature water—were cooked instantly. lies within a region of frequent earthquakes June 2006, and the closure has remained in (USGS photo by Chris Farrar.) and active ground uplift (deformation). The effect to date (June 2007). U.S. Department of the Interior USGS Fact Sheet 2007-3045 U.S. Geological Survey 2007 The thermal springs in Long Valley Cal- later wrote a paper describing hundreds of and pumice. A reservoir of partially molten dera have long been known to Native Amer- springs throughout California. rock (magma) beneath the caldera has pro- icans. Many of the hot springs have special duced subsequent volcanic eruptions. This status with Native American tribes and have Volcanic History of the Hot Creek Area activity formed many hills within the calde- been used for spiritual and medicinal pur- The Hot Creek Geologic Site lies within ra, such as the 300,000 year-old Hot Creek poses. Early written records of the springs the Long Valley Caldera, a large topograph- rhyolite flow, known locally as Doe Ridge. came from visits by pioneers and scien- ic depression formed 760,000 years ago The toe of that slow-moving lava entered a tists— USGS scientist G.A. Waring visited during a massive volcanic eruption that pro- lake, where interaction with water altered thermal springs in Long Valley in 1908 and duced extensive and thick deposits of ash the rhyolite and formed clay and perlite, a gray to black, glassy material with a pearly 119º 00' 118º 45' luster now exposed along the path from the parking area down into the gorge. After the 395 lake receded, a stream cut the steep-sided C Area a of gorge through the toe of the solidified lava. l I n i y f Map o o Glass r This stream, known here as Hot Creek, n C Mountain r i a a t begins its winding course some 11 miles º e 37 45' r s Lo ng (17 km) to the west as Mammoth Creek, a Va n River lle d Owens y C flowing through a series of small lakes west D a o ld m e of the town of Mammoth Lakes. The stream e e r Dom a s ent urg Hot Creek es Geologic Site water is derived primarily from melting R Well ek re snow as it leaves Twin Lakes, 8,500 feet 44-16 C t o (2,600 m) above sea level. It is quite cold, H Well CH-10B Casa Diablo rarely above 50°F (10°C). About 1.5 miles Geothermal Plant 203 (2.5 km) upstream from the thermal area, Mammoth Lakes CasaDoe Ridge Diablo Mammoth Creek is joined by warmer wa- reek Mammoth C 37º 37' 30" Fish hatchery ter from thermal springs in the Hot Creek Mammoth Airport S I Mountain Crowley State Fish Hatchery. From this point on, E R LakeLake R A the stream is named Hot Creek even though River Owens N E V 0 5 MILES water temperature seldom exceeds 68°F A D A 0 (20°C) until it reaches the main thermal 5 10 KILOMETERS 395 springs in the gorge. West East Why is Hot Creek Hot? In hydrothermal (“hot water”) systems the circulation of ground water is driven Long Valley Caldera by a combination of topography and heat Inyo sources. The system in Long Valley Cal- Sierra Nevada Craters Town of dera is recharged primarily from snowmelt and Casa Diablo Mammoth Geothermal Hot Creek Glass in the highlands around the western and Domes Mountain Lakes Plant Gorge southern rims of the caldera. The meltwater Resurgent infiltrates to considerable depths, where Well 44-16 Dome Well Hot Water CH-10B some is heated to at least 430°F (220°C) by 428ºF 338ºF 199ºF hot rock near cooling magma beneath the (220ºC) (170ºC) (93ºC) Inyo Craters and Domes, 10 miles (16 km) 2 Water west of Hot Creek. This volcanic chain ex- Cold Caldera fill deposits tends from the western part of Long Valley Magmatic Caldera northward to Mono Lake and has Intrusions Basement rocks DEPTH, IN KILOMETERS produced numerous eruptions over the past ***1997 Earthquake swarm 40,000 years, the latest only a few hundred 4 * * years ago. The heated water, kept from boiling by high pressure, still has lower Simplified geologic map (top) and diagrammatic cross section (bottom) of Long Valley Caldera. The resurgent dome, Doe Ridge, Mammoth Mountain, and the Inyo Craters and Domes all reflect volcanic density than cold water, and it rises along activity since 760,000 years ago, when a giant eruption formed the caldera. The thermal springs in Hot steeply inclined fractures to depths of 0.3- Creek are fed by Sierra Nevada snowmelt that seeps underground and migrates eastward, becom- 1.25 miles (0.5-2 km). It then flows east- ing heated to temperatures as high as 428°F (220°C) in the vicinity of partially molten rock (magma) beneath the western part of the caldera. The water cools as it migrates eastward beneath the ground ward through rock layers to discharge points (red arrows). The temperature at which water emerges in the springs at Hot Creek could be affected at the surface along Hot Creek and around by changes in seismic activity, heat extraction, mixing with cooler water, and other factors. Crowley Lake. The water temperature de- THERMAL WATER INPUT TO HOT CREEK DANGER COMES QUICKLY 300 Geysering begins 290 10:30:20 10:30:25 280 270 260 250 240 230 220 210 68ºF 86ºF 68ºF 199ºF 30ºC 20ºC 200 20ºC 93ºC THERMAL SPRING DISCHARGE, IN LITERS PER SECOND 1988 1997 2007 The temperature in Hot Creek can change in seconds. These photos were The U.S. Geological Survey monitors the thermal water discharge in Hot taken 5 seconds before and then during a violent geysering event, in which Creek gorge by measuring chloride concentration in the stream above boiling water (at 199°F or 93°C, the boiling point at this elevation) erupted and below the hot springs. The onset of geysering in 2006 was accompa- above the surface. Any swimmer caught in this part of the creek would have nied by a small spike in discharge. (1 liter = 0.264 gallon.) been severely scalded. (Photos courtesy of Alix Ginter.) creases eastward because of heat loss and Possible Causes of the Recent Changes 330 feet (100 m) deep and located 0.6 mile (1 mixing with cold water, and in the springs Geysering activity similar to that which start- km) south of the gorge.