The Salton Buttes are a group of volcanoes in Southern California, on the Salton Sea. They consist of a 7-kilometer-long (4.3 mi) row of five lava domes, named Mullet Island, North Red Hill, Obsidian Butte, Rock Hill, and South Red Hill. They are closely associated with a fumarolic field and a geothermal field, and there is evidence of buried volcanoes underground. In pre-modern times, Obsidian Butte was an important regional source of obsidian. The Salton Buttes lie within the Salton Trough, a tectonic depression formed by the San Andreas Fault and the San Jacinto Faults. The depression forms the northward extension of the Gulf of California, and is separated from it by the Colorado River Delta. A number of geothermal and volcanic features are located in the area, which is a region of active seafloor spreading. While the Salton Buttes were formerly considered to be of the late Pleistocene epoch (which ended with the end of the Last Glacial Maximum), newer dating efforts have determined that all of them formed more recently, during the current Holocene epoch, mostly through effusive eruptions. Future eruptions are possible and could endanger the surroundings.
Geomorphology and geography
The Salton Buttes lie on the southeastern shores of the Salton Sea, with their peaks at an elevation of −40 m (−130 ft), in Imperial County, California. The towns of Niland and Calipatria lie northeast and southeast of the Salton Buttes, respectively, and Palm Springs is 140 kilometers (90 mi) northwest. The Alamo River enters the Salton Sea between the Salton Buttes. The name "Niland Field" has also been applied to the system.
The Salton Buttes are five lava domes that rise 30–40 m (98–131 ft) above the surrounding terrain. Each peak is no wider than 1 km (0.62 mi), but together they form a chain 7 km (4.3 mi) long. From north to south, they are named Mullet Island (33°13′32″N 115°36′30″W), North Red Hill (33°12′0″N 115°36′43″W), South Red Hill (33°11′46″N 115°36′42″W), Rock Hill (33°11′1″N 115°37′24″W), and Obsidian Butte (33°10′17″N 115°38′16″W). Of the buttes, the Red Hills and Obsidian Butte are the largest. The Red Hills are a paired volcano, connected through pyroclastic deposits. The Red Hills are also known collectively as Red Island; Red Island and Mullet Island were both islands in 2005. As of 2018, Mullet Island is a peninsula. The other domes have also been islands at times, and waves have cut erosional terraces along the former shorelines. The Salton Buttes are lava domes. They formed from viscous lava rising in a volcanic vent 250 m (820 ft) wide. Obsidian Butte is surrounded by a lava flow, and Mullet Island has a characteristic "onion-skin" foliation. On Red Hill, there is a quarry, a marina, and a trailer park, and Obsidian Butte has been extensively quarried, to the point that it has lost most of its original appearance. There are hot springs and mofettes on Mullet Island. A fumarole field is associated with the Salton Buttes. The field is characterized by gryphons and salses. These exhale carbon dioxide and steam, as well as ammonia and hydrogen sulfide. Some of these fumarolic vents reach heights of 2 m (6.6 ft), and resemble the lava-erupting vents. Mud pots are also found. Parts of the field have recently emerged from the Salton Sea, due to dropping water levels, which have also caused the fumarolic vents to develop and grow noticeably, including an increased number of gryphons. There is a geothermal field associated with the Salton Buttes. It is one of the largest and warmest on Earth, with temperatures of 360 °C (680 °F) at 1.5–2.5 km (0.93–1.55 mi) depth. Various volcanic rocks have been found in drill cores at the Salton Buttes. Rocks found include andesite, basalt, dacite, diabase, gabbro, and rhyolite. Some of these volcanic rocks bear traces of hydrothermal alteration. In some places the layers of volcanic rocks are as thick as 100 m (330 ft). There may be other volcanoes buried in the sediment pile; at least four separate aeromagnetic anomalies have been found at the Salton Buttes, and these may be signs of buried volcanoes. The field has been prospected for geothermal power generation, and presently eleven geothermal power plants in the Imperial Valley Geothermal Project have capacity to produce 432 megawatts of power.
Geology Since the Pliocene, the Salton Trough and the Gulf of California have formed an active rift zone south of the San Andreas Fault. In a rift zone, seafloor spreading is underway, accompanied by volcanic and geothermal activity, active faulting, a thinned crust and rapid sedimentation. Since five million years ago, the buildup of sediments in the Colorado River Delta separated the Salton Trough area from the actual Gulf of California, forming a large depression that currently reaches a depth of 40 m (130 ft) below sea level. This depression is a pull-apart basin. It has formed between various branches of the San Andreas Fault and the San Jacinto Fault (which are connected by the Brawley Seismic Zone) The Salton Trough is still actively subsiding at rates of 3 mm/a (0.12 in/year), increasing to 4–8 mm/a (0.16–0.31 in/year) in the central area of the Trough. A number of Quaternary volcanic centers have formed in the region, including Cerro Prieto, Consag Rock, Isla San Luis, Isla Tortuga, the Salton Buttes, and Sierra Pinacate, which is the largest of these volcanoes. Strong geothermal activity has been observed as well, with the Salton Trough alone hosting five geothermal fields (Brawley-Mesquite, Cerro Prieto, East Mesa, Heber, and Salton Sea). These five fields have a total heat output of 1–10 GW. Part of this heat output is used to generate geothermal power, with annual production of 1–3 TWh/a (110–340 MW).
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