When people think of the term supervolcano,
they tend to think of the Yellowstone caldera in wyoming. However, yellowstone
is not the only supervolcano in the United States which is still geologically active.
There is also the Valles caldera in New Mexico, and the long valley caldera in California.
This supervolcano last erupted 16,000 years ago, and its lava is likely to erupt again.
This video will discuss this supervolcano in detail, and mention what its future hazards are.
The Long Valley caldera supervolcano can be found in eastern central California. Specifically, it
is 20 miles west of the Nevada border. The town of Mammoth Lakes is located within this vast caldera.
Volcanic activity in the vicinity of the Long Valley caldera began around 3.1 million years ago.
The initial eruptions deposited a volcanic rock known as rhyodacite. This rock type contains a
little less than half of its weight in quartz and generally has a light gray color. It represents a
series of highly explosive eruptions eruptions which continued until 2.5 million years ago.
Then, 2.1 million years ago, eruptions became slightly more explosive as the composition of lava
changed from rhyodacite to rhyolite. One of the features formed during this period is glass
mountain, which got its name from the abundance of volcanic glass known as obsidian on its slopes.
During these eruptions, the shallow magma chamber which fed glass mountain was slowly getting
larger. Eventually, the magma chamber contained more than 100 cubic miles of lava.
Then, 767,000 years ago, a massive eruption began on the surface. As the eruption continued, several
cubic miles of lava erupted onto the surface in an explosive manner. Additional vents began to
erupt and the eruption escalated. A plume of ash carried volcanic material more than 25 miles into
the atmosphere. Over the next 6 days, 150 cubic miles of lava was erupted. During this eruption,
massive pyroclastic flows swept over a vast area, traveling perhaps 100 or more miles
away . These pyroclastic flows covered a vast area with several thousand feet of volcanic rock.
Near the eruption's center, the the ash beds were measured at 4600 feet thick. Areas as far
away as Oklahoma City, which is more than 1000 miles from the eruption, received a discernable
layer of ash which coated the ground. Due to the sheer volume of magma erupted,
a large part of the magma chamber emptied. This caused the overlying rock to collapse
more than a mile downwards and fill this empty space, which formed a 20 mile wide caldera.
This caldera stretches from Mammoth mountain in the west to glass mountain in the east.
17,000 years later, the first of many post caldera eruptions began near the center of the caldera.
These eruptions resulted from uplift in the center of the caldera, which is termed resurgent doming.
One of these eruptions 690,000 years ago created lookout mountain along with a vast lava flow.
During this period, the caldera was slowly filled with a lake from the Owens River.
By 600,000 years ago, this lake reached a depth of 980 feet. The lake covered
everything below 7500 feet in elevation. Over the next several hundred thousand years,
additional eruptions occurred between the center of the caldera and the crater walls. One of
these eruptions 333,000 years ago created a vast lava flow near the modern whitmore hot springs.
Since then, recent eruptions have been centered near the town of Mammoth Lakes.
One eruption 175,000 years ago created a cinder cone at the base of what is now
Mammoth Mountain. Lavas from this vent traveled more than 5 miles away.
Several thousand years after this eruption, the existing caldera lake drained away.
The most recent eruption from the long valley caldera created a series of small basalt lavas
flows near deadman pass 16,000 years ago. Today, the caldera lies dormant. However,
there is an increased likelihood of eruptions in the next few decades. From 1980 to 1982,
an intrusion of magma began reaching towards the surface just north of Mammoth Mountain.
This resulted in high emissions of carbon dioxide from the mountain, which has resulted in areas of
dead trees. Although the levels of carbon dioxide have since subsided slightly, this area represents
the most likely site of a future eruption from the caldera. A future eruption could either
form a large rhyolite lava dome OR erupt a basalt cinder cone. A lava dome eruption would be highly
explosive, and create pyroclastic flows, thick ashfall, and lahars. A cinder cone eruption would
be less destructive, as the main hazard from this eruption type is its long distance lava flows.
Overall, the odds of a future eruption within long valley are about 1 in 12,000 each year.
In two recent videos, I covered portions of the 30 mile volcanic chain which stretch from Mammoth
Mountain to Mono Lake. Click on these video links if you want to learn more. I hope that you
enjoyed this video. If you would like to request a specific topic, please leave a comment below!