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America's Volcanic Past
Long Valley Vicinity, California

"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994
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Volcanic Highlights and Features:
[NOTE: This list is just a sample of various Long Valley features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Long Valley.]

  • Long Valley Vicinity
  • Bishop Tuff
  • Black Point
  • Devil's Punchbowl
  • Inyo Craters and Domes
  • Long Valley Caldera
  • Mammoth Mountain
  • Mono Basin and Craters
  • Negit Island
  • Obsidian Dome
  • Panum Crater
  • Paoha Island
  • Red Cones

Long Valley Vicinity

About 760,000 years ago a cataclysmic volcanic eruption in the Long Valley, California area blew out 150 cubic miles of magma (molten rock) from a depth of about 4 miles beneath the Earth's surface. Rapidly moving flows of glowing hot ash covered much of east-central California, and airborne ash fell as far east as Nebraska. The Earth's surface sank more than 1 mile into the space once occupied by the erupted magma, forming a large volcanic depression that geologists call a caldera. The massive Long Valley eruption was followed by hundreds of smaller eruptions over the next few hundred thousand years. These eruptions of lava flows, domes, and pyroclastic flows were concentrated in the central and western parts of the caldera. Volcanic activity then moved northward to the Mono Lake area about 35,000 years ago to build the Mono Craters. The most recent eruptions in the area occurred from the Mono and Inyo Craters about 600 years ago, and from Negit Island in Mono Lake about 250 years ago.




Excerpts from: Hill, et.al., 1996, Living With a Restless Caldera -- Long Valley, California: USGS Fact Sheet 196-96
   


Bishop Tuff

Bishop Tuff:4
Fallout from the Long Valley eruption blanketed most of the western states with ash as far east as Nebraska, and covered the Mono Basin, Owens Valley, and parts of the Sierras in 600-3,000 feet of 1300 degrees F. burning ash. This ash solidified into a pinkish igneous rock known as the Bishop Tuff, a layer of which covers 580 square miles of California and Nevada and is especially exposed along the highways of the Mono Basin and Owens River Valley region.




Black Point

Black Point:4
Black Point is the low, black, mesa-like hill that lies on Mono Lake's northwestern shore. Black Point is a basaltic volcano that erupted approximately 13,000 years ago, in the middle of the last ice age. At the time, glacially-inundated Mono Lake was 900 feet deeper than it is today, and completely submerged Black Point's eruption. The weight of hundreds of feet of water is responsible for its flat top, and for the intriguing fissures on its southwestern face. These fissures -- some as deep as 80 feet and as narrow as four or five across -- are presumed to be cooling fissures, although geologic debate over their origins continues. Now exposed by Mono's receded lakeline, Black Point makes an excellent specimen of an exposed underwater-volcano for scientific study.




Devil's Punchbowl

Devil's Punchbowl:4
In the Mono Basin, a great example of a smaller explosion pit is the Devil's Punchbowl, located at the south end of the Mono Craters.


Inyo Craters and Domes

Mono-Inyo Craters Volcanic Chain:1
The Long Valley Caldera is only one part of a large volcanic system in eastern California that also includes the Mono-Inyo Craters volcanic chain. This chain extends from Mammoth Mountain at the southwest rim of the caldera northward 25 miles to Mono Lake. Eruptions along this chain began 400,000 years ago, and Mammoth Mountain itself was formed by a series of eruptions ending 50,000 years ago. The volcanic system is still active. Scientists have determined that eruptions occurred in both the Inyo Craters and Mono Craters parts of the volcanic chain as recently as 600 years ago and that small eruptions occurred in Mono Lake sometime between the mid-1700's and mid-1800's.


Long Valley Caldera

Long Valley Caldera:2
Long Valley, from the headwaters of Owens River to Lake Crowley, is a giant 10-mile-wide, 20-mile-long volcanic caldera. Long Valley occupies the eastern half of this caldera. Magma still underlies the caldera and heats underground water. The heated water feeds local hot springs and natural steam vents and drives three geothermal power plants, producing a combined 40 megawatts of electricity.

Resurgent Dome:2
The resurgent dome is a broad area of the central caldera floor that was pushed upward within 100,000 years or less of the caldera-forming eruption 730,000 years ago. This uplift was caused by upward pressure related to the intrusion of molten rock into the magma reservoir beneath the caldera. The resurgent dome is made of layers of lava flows, tephra, and pyroclastic flows that were erupted onto the caldera floor soon after the caldera formed. The uplift arched and faulted these volcanic rocks to form a central highland area about 10 kilometers in diameter and as high as 500 meters above the surrounding caldera floor.


Mammoth Mountain

Mammoth Mountain:2,3
Mammoth Mountain - a massive volcanic dome - has grown on the Long Valley caldera margin. Mammoth Mountain was built by eruptions between about 200,000 and 50,000 years ago. Mammoth Mountain was built by the eruption of at least 12 different steep domes and thick lava flows. These eruptions occurred between about 200,000 and 50,000 years ago. Volcanic activity then moved northward to the Mono Lake area about 35,000 years ago to build the Mono Craters, a collection of more than 30 overlapping lava flows, domes, cones, and craters. The most recent eruptions in the area occurred from the Mono Craters and Inyo Craters about 600 years ago, and from Negit Island in Mono Lake about 250 years ago.




Mono Basin and Craters

Mono-Inyo Craters Volcanic Chain:1
The Long Valley Caldera is only one part of a large volcanic system in eastern California that also includes the Mono-Inyo Craters volcanic chain. This chain extends from Mammoth Mountain at the southwest rim of the caldera northward 25 miles to Mono Lake. Eruptions along this chain began 400,000 years ago, and Mammoth Mountain itself was formed by a series of eruptions ending 50,000 years ago. The volcanic system is still active. Scientists have determined that eruptions occurred in both the Inyo Craters and Mono Craters parts of the volcanic chain as recently as 600 years ago and that small eruptions occurred in Mono Lake sometime between the mid-1700's and mid-1800's.

Mono Basin:4
The Mono Basin lies in one of the most geologically active areas on the planet. Its eventful history of volcanic activity is evident in both the extinct volcanic ranges of the Bodie and Anchorite Hills to the north and east and the dormant Mono Craters to the south. While the rolling Bodie and Anchorite hills were last active over hundreds of millions of years ago, the Mono Craters are the youngest mountain range in North America--the oldest of its 9,000' peaks is only 40,000 years old. Panum Crater, the northernmost and youngest of the Craters, erupted only 640 years ago. Panum, a textbook example of a rhyolitic plug-dome volcano, is easily reached from Hwy. 120, three miles east of Hwy. 395.

Mono Craters:2
The Mono Craters is a 17-kilometer-long chain of rhyolite domes and flows that were erupted from 35,000 to about 600 years ago. All but four of the 24 exposed domes and flows of the Mono Craters are less than 10,000 years old. The most recent eruptive episode occurred between A.D. 1325 and 1365, during which time there were several explosive eruptions and five separate lava flows that oozed onto the surface, including Panun Dome and North Coulee flow.




Negit Island

Negit Island:4
In addition to the volcanoes surrounding Mono Lake, the two islands that rise above Mono's surface are also volcanic. Negit, a classic black cinder cone poking out of the water, first erupted some 1,600 years ago and most recently flowed 270 years ago. Paoha Island, the large white island in the center, is less than 300 years old.




Obsidian Dome

Obsidian Dome:4
Obsidian Dome, of the nearby Inyo Craters, is an example of a dome that has completely overrun its debris ring.




Panum Crater

Panum Crater:4
The twenty-one volcanic cones to the south of Mono Lake form the youngest mountain range in North America, the Mono Craters. While the earliest eruptions occurred about 35,000 years ago, the most recent activity dates back merely 600 years. The most accessible cone is Panum Crater, located three miles east of Highway 395 on Highway 120. This 600 year-old volcano exhibits all of the characteristics of the textbook rhyolitic, plug-dome volcano.




Paoha Island

Paoha Island:4
The youngest member of the Mono Basin volcanic family is Paoha, the white island in the middle of the lake, which formed only 300 years ago. An unusual volcanic formation, Paoha looks very different from the classic cinder cone of Negit Island. White and rolling, it resembles more the sediment that covers that bottom of Mono Lake. And with good reason! Paoha is, indeed, exposed lake-bottom sediment, pushed up over the surface of the lake in a volcanic upheaval that lacked the momentum to fully erupt. Although there have been a few small lava flows on the north end of the island, Paoha has yet to let go in a full-scale eruption. Still, steam vents and fumaroles on the island indicate its potential for future activity!


Red Cones

Red Cones:2
Several small cinder cones are located on the floor and rim of Long Valley caldera. The youngest cones in the area include Red Cones 5 kilometers south of Mammoth Mountain and Black Point on the north shore of Mono Lake. Geologists estimate that Red Cones may have erupted as recently as about 5,000 years ago and Black Point about 13,000 years ago. The other cones on the caldera floor and along the rim range in age from 228,000 to 64,000 years.






Excerpts from:
1) Hill, et.al., 1996, Living With a Restless Caldera -- Long Valley, California: USGS Fact Sheet 196-96;
2) USGS California Volcano Observatory Website, 2000, 2001
3) USGS/NPS Geology in the Parks Website, August 2001
4)U. S. Forest Service Website, Region 5, August 2001


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11/09/01, Lyn Topinka