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760,000 YEARS AFTER A SUPERVOLCANO EXPLODES


Volcanic rock as seen en route to Long Valley Caldera

SUPERVOLCANOES are among the most violent and complex eruptions of the volcanic world. Weighing in at a magnitude 8, which is the highest ranking number on the Volcanic Explosivity Index and ejecting over 240 cubic miles of debris, a supervolcanic eruption could conceivably wipe out large parts of the planet. Generating lava avalanches, temperatures that threaten the global climate, and ash that can travel thousands of miles, supervolcanoes are often characterized as the apocalyptic super villains of the geological world.

Currently, there are somewhere between 18 to 20 known supervolcanoes on Earth— including Phlegrean fields near Naples, Italy, Lake Toba in Indonesia, and Wyoming’s Yellowstone National Park— whose bubbling geysers and hot springs signal the churning activity stirring below the surface. While news of 18 existing supervolcanoes might incite terror, geologists are quick to explain that cataclysmic eruptions offer warning signs that are extremely hard to miss. The most recent eruption of a supervolcano is believed to have occurred at New Zealand’s Taupo volcano over 26,000 years ago— but science and technology have come a long way since then.

Unlike the composite volcanoes (cone-shaped mountains formed by a series of small eruptions) from our last blog, supervolcanoes typically form calderas, in which the top surface of the volcano completely collapses into itself and creates a hollow depression rather than a mountain. Today, geo enthusiasts can visit one of these volcanic craters on almost every continent. For residents and visitors of California, the closest supervolcano is less than a days drive away.

Eager to learn more about the geological landscapes that form in the aftermath of a volcanic eruption, my partner and I packed up the car and set out on a road trip to explore the Long Valley Caldera and neighboring Mammoth Mountain.

FOSSIL FALLS, CALIFORNIA— Located off Highway 395, three hours outside of metropolitan Los Angeles, is a waterless, wild area known as Fossil Falls. With only one place marker on each side of the highway, it would be easy to drive right past the falls without thinking much of it. But these impressive geological structures are not something you want to miss.

Presently, the area surrounding the falls is bone dry, making it hard to believe that just a few thousand years ago the thirsty desert landscape was flooded with water.  A stop at Fossil Falls offers neither fossils or waterfalls but rather an extraordinary composite of polished geological art.  Composed of two levels of basalt lava rock that formed around 400,000 years ago, the base of the falls were created when the once-flowing Owens River was dammed by an erupting volcano at the Coso Range.  During the last Ice Age, rushing water raged from the Sierra Nevada Mountains all the way to Death Valley, flowing over the hardened lava rock. The result is the surreal, complex canyon of sculpted black lava you see below.


Nature’s handiwork— Basalt lava rock carved during the last Ice Age.
Exploring the second layer of the falls. Note: The climb down to this area can be dangerous and should only be done if you are an experienced hiker.

12,000 years ago, Native American tribes like the Coso People lived by the water that once flowed from Fossil Falls.  Though the area is a protected region and artifacts cannot be removed, we encountered several chips of obsidian (used for making tools) at the base of the falls.


Small cave and potential shelter alongside the falls.

THE LONG VALLEY CALDERA—Among the 4-million-year-old eastern Sierra Mountains are the remnants of a supervolcano that erupted nearly 760,000 years ago creating one of the earth’s largest craters, the Long Valley Caldera. Geologists studying this region have discovered 240 cubic miles of semi-molten magma below the 10-mile wide and 20-mile-long caldera, which gives this California crater its status as a supervolcano. If Long Valley were ever to erupt, it would eject over 800 times the volume of magma, gas, and ash than we saw in the 1980 eruption of Mount Saint Helen’s—the largest and most destructive volcanic eruption in U.S. history. While there is no suggested threat in our lifetime, scientists are heavily monitoring the activity happening beneath the crust.

Visitors to Long Valley can hike 2.3 miles up to Glass mountain and walk along the caldera’s rim. The hike is strenuous and takes anywhere from 3.5-5 hours, but for some, standing on the edge of a supervolcano is worth the trip.

MAMMOTH MOUNTAIN— Formed by a series of violent eruptions that spanned from 220,000 and 50,000 years ago, Mammoth Mountain chronicles an era of geologic turmoil in the Eastern Sierra. The young volcano on the rim of Long Valley Caldera was built by 25 separate eruptive events that occurred and persisted until the final eruption completed the development of Mammoth Mountain. Today, the 12 overlapping volcanic domes of Mammoth are increasingly popular among skiers, snowboarders, and hikers (when the weather permits) and while the volcano itself is no longer considered active, the mountain is still alive with evidence of an explosive past.  Thermal vents (or fumaroles) are still discharging volcanic gases from the fissures in the mountain. Since 1994, scientists have been aware of high concentrations of CO2 gas in the soil on Mammoth Mountain. This invisible gas, seeping from beneath the volcano, has been killing trees and forests around Mammoth’s Horseshoe Lake for over two decades.



Our time in Mammoth was marked by a bitter chill, snowy skies, and a lot of snow. Though we did find time to explore the nearby terrain, residents and landscapes were still reeling from a recent snowstorm which deposited over ten feet of snow on the mountain and the snow piles were too high to capture any decent footage of our surrounding.

Since 80% of the Earth’s surface was formed by volcanic activity, anyone can get outside and explore the rocks and geological sediments near you. Who knows what amazing things are waiting for you in your own back yard!

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