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Volcanic History: Evidence of Recent Eruptions
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Volcanic History
Evidence of Recent Eruptions

...there is a range of volcanic cones that attract the eye, not only on account of their height and the symmetry of their curving slopes of light gray lapilli, but also because they form so striking an exception to the prevailing mountain forms in view. These are the Mono Craters. So perfect are their shapes and so fresh is their appearance that the eye lingers about their summits in half expectation of seeing wreaths of vapor or the lurid light of molten lava ascending from their throats.

Israel C. Russell
19th century geologist

 

VOLCANOVILLE

The Negit Islands volcanic complex is less than 2000 years old.Except for the Sierra Nevada immediately to the west, Mono Lake is surrounded by a volcanic landscape. The Bodie Hills to the north and the Cowtrack Mountains to the East of the lake do not look much like volcanoes today, but they are remnants of an earlier volcanic era that predated the existence of Mono Lake hundreds of thousands to millions of years ago. The Mono Craters, stretching to the south of Mono erupted recently in geologic time and are the some of the more obvious volcanic features at Mono Lake along with Black Point and the Negit Island volcanoes.

THE MONO CRATERS

The Mono CratersThis volcanic chain stretching ten miles north to south and topping 9,000 ft. may be the youngest volcanic mountain range in North America. The last eruption in the Mono Craters chain occurred less than 700 years ago at Panum Crater. Panum Crater, located just above the south shore of Mono Lake, is not a true crater. It is more accurately a plug-dome volcano, where cooled lava has created a massive dome-like structure that now "plugs" the volcanic vent at the bottom of the crater. The entire Mono Craters chain is actually a series of plug dome volcanoes that erupted into existence within the last 40,000 years. Odds are the Mono Craters will erupt again.

A RARE EVENT

Imagine a volcanic eruption 2,500 times greater than the Mt. St. Helens blast of 1980! Twenty miles south of present-day Mono lies the northern edge of Long Valley Caldera. Seven hundred sixty thousand years ago the Long Valley eruption blasted more than 150 cubic miles of earth and ash skyward, burying much of the region in hundreds of feet of volcanic debris. Ash fell as far east as Nebraska. The earth's surface collapsed more than one mile deep following the eruption, forming a 200 square mile depression, called Long Valley Caldera. Today, Long Valley Caldera is part of a large volcanic complex that stretches from Mammoth Mountain to Mono Lake. Click here to go to the USGS Long Valley Observatory.

AN ANCIENT LAKE

Magma pushed lake bottom sediments above the surface of Mono Lake approximately 340 years ago forming the large gray island, Paoha.Geologists have determined the age of Mono Lake from the Long Valley eruption. In 1908, oil prospectors, drilling for oil on Paoha Island, discovered an ash layer from the Long Valley eruption beneath hundreds of feet of lake sediment. Beyond the ash layer was more lake sediment. The unlucky prospectors did not find oil, but they did inadvertently discover the secret to Mono Lake's age. Geologists determined that Mono Lake has held water since the Long Valley eruption 760,000 years ago, and lake sediments below the ash layer hint that Mono Lake could be much older, among the oldest lakes in North America.

Click here to see a USGS gallery of Mono Basin volcanic images.

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