Coso Volcanic Field facts for kids
Quick facts for kids Coso Volcanic Field |
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A basaltic lava flow that is typical of the process that created the stepped terraces of Coso as it flowed across the landscape, producing a more or less flat surface eroding to a sheer front.
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| Highest point | |
| Elevation | 7,874 ft (2,400 m) |
| Geography | |
| Location | Inyo County, California, US |
| Parent range | Coso Range |
| Topo map | USGS Cactus Pk (CA) |
| Geology | |
| Age of rock | Pliocene to Quaternary |
| Mountain type | Monogenetic volcanic field and Lava domes |
| Last eruption | 39,000 yrs |
The Coso Volcanic Field is a cool area in Inyo County, California. It sits on the western edge of the Basin and Range region and the northern part of the Mojave Desert. You can find the Fossil Falls here, which were formed by the ancient Owens River. This field is located inside the Naval Air Weapons Station China Lake, northeast of Little Lake and U.S. Route 395.
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What is the Coso Volcanic Field?
The Coso Volcanic Field is a place where volcanoes have been active for a very long time. It's known for its many lava domes made of a rock called rhyolite. These domes are like big, rounded hills formed by thick, sticky lava.
How the Coso Volcanoes Formed
Volcanic activity at Coso started before the land began to stretch and pull apart. This stretching created the "Basin and Range" landscape we see today.
The first period of eruptions laid down basalt lava flows. These flows spread out over flat land. Over the next 1.5 million years, more complex rocks erupted as the land became more uneven.
After a long break, a new period of eruptions began. This time, both basalt lava flows and rhyolite lava domes formed. Many of the newer basalt flows filled up existing valleys.
Understanding Rhyolite Domes
The Coso Volcanic Field is famous for its rhyolite domes from the Pleistocene era. There are 38 of these domes. They form a long line on top of a raised block of older rock.
Many domes look fresh and untouched by erosion. Some are found inside bowl-shaped craters called tuff rings. A few domes even overflowed their craters, sending lava flows a kilometer or two long.
Most of the rhyolite here is very high in silica (about 77 percent). This makes the lava very thick. You can often find obsidian (volcanic glass) on these domes.
Ancient History of Coso
Native American groups, especially the Coso people, used the obsidian from the Coso Volcanic Fields a lot. They made tools like knives and arrowheads from this sharp volcanic glass.
The busiest time for obsidian mining was between 3,000 and 1,000 years ago. People dug deep pits and cut into hillsides to get the raw material.
Obsidian from Coso was traded far and wide. It traveled all the way to the California coast in San Diego, San Luis Obispo County, and Santa Barbara, California. It also went across the Mojave Desert and even further east.
Archaeologists have found that the obsidian came from at least four different spots within the field. These spots include Sugarloaf and West Sugarloaf, which were the most popular sources for tools.
Coso Geothermal Power Project
| Coso Geothermal Power Project | |
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The Navy 1 geothermal power plant of the Coso Geothermal Power Project
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| Country | United States |
| Location | NAWS China Lake Inyo County, California |
| Coordinates | 36°02′00″N 117°49′00″W / 36.03333°N 117.81667°W |
| Status | Operational |
| Commission date | Navy I: May 1987 Navy II: 1988 BLM East: 1989 BLM West: 1989 |
| Operator(s) | Coso Operating Company |
| Website Coso Operating Company |
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The Coso Volcanic Field is also famous for its geothermal energy. This means there's a lot of heat underground. You can see fumaroles, which are vents that release steam and gases from the Earth.
Scientists studied the area in the 1970s. They found enough heat to produce 650 megawatts of electricity for 30 years! This heat likely comes from a magma body deep below the ground.
Commercial power plants started operating here in the 1980s. The Coso Geothermal Power Project is located within the Naval Air Weapons Station China Lake near Ridgecrest, California.
Today, it produces 270 megawatts of electricity from four power plants. Over 100 wells have been drilled, reaching depths of 2,000 to 12,000 feet (610 to 3,700 meters). The temperatures underground can reach 200° to 350°C (392° to 662°F). Coso began making electricity in 1987 and has become more efficient over time.
Earthquakes in Coso
The Coso Volcanic Field is one of the most active earthquake areas in the United States. It experiences dozens of small tremors (Magnitude 1 and 2) every week.
- Magnitude 3 quakes happen about 2 to 6 times a month.
- Magnitude 4 quakes occur two or three times a year.
Bigger quakes (Magnitude 5) happened in 1996 and 1998. Several quakes over M5 occurred within a day of each other. These were recorded about 15 miles (24 km) east of the Coso Volcanic Field.
From September 30 to October 6, 2009, there were 429 earthquakes! They ranged from 0.1 to 5.2 in magnitude. Some days had a tremor almost every minute. On October 2, 2009, three strong quakes (5.2, 4.7, and 4.9) happened within one hour.
The 2019 Ridgecrest Earthquakes
On July 4th and 5th, 2019, two very large earthquakes shook the area around the Coso Volcanic Field. The first big quake on July 4 was Magnitude 6.4. The largest one on July 5 was Magnitude 7.1.
Within a week, more than 8,000 smaller earthquakes followed. These were mostly M1.0 to M4.5. Only 27 quakes larger than M4.5 happened after the main events. Luckily, no one died in California.
Residents in Ridgecrest and the nearby town of Trona saw moderate to severe property damage. There were two structure fires, and some areas lost power for up to 24 hours. Trona was even without water. Highway 178, a key road to Trona, was blocked by rockslides and damaged sections. Ridgecrest declared a state of emergency.
Why So Many Earthquakes?
Earthquake swarms are common in the Coso Range area. They often produce hundreds of tremors in just a few days. This active earthquake behavior is typical in volcanic regions. Other examples include Long Valley Caldera near Mammoth Lakes and Yellowstone Caldera at Yellowstone.
The Coso Volcanic Field last showed signs of volcanic activity about 30,000 to 40,000 years ago. However, some ash eruptions and small cone formations might have happened more recently, within the last 10,000 years.
