Beneath the seemingly calm and serene landscape of Eastern California lies one of the planet’s most explosive features — a volcanic giant that has been slumbering for thousands of years. It’s the Long Valley Caldera, a vast geological structure that stands as a testament to one of the most violent volcanic eruptions in Earth’s recent history.
The Owens Valley, located in eastern California, is renowned globally for its volcanic history. Situated about 200 miles east of San Francisco, the Long Valley Caldera was born around 760,000 years ago during a cataclysmic eruption that ejected an estimated 150 cubic miles of material. To put this into perspective, the 1980 eruption of Mount St. Helens released just about 0.3 cubic miles of material, indicating the colossal magnitude of the Long Valley eruption.
The aftermath of this gigantic eruption formed a vast depression, or caldera, measuring about 10 miles wide and 20 miles long. This is not a unique event in Earth’s history, as there are many similar calderas worldwide. What makes the Long Valley Caldera distinctive is the incredible geothermal activity that continues beneath the surface, reminding us of the latent power it holds.
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Inside the caldera, one discovers a geological wonderland that resembles a surreal moonscape, with its otherworldly terrain, bizarre formations, and strikingly barren features. Hot springs and fumaroles, areas where volcanic gases escape from the ground, are scattered across the area. This dynamic geology is further expressed by Mammoth Mountain itself, a lava dome complex located on the caldera’s rim. The area also holds an intricate hydrothermal system, with ground temperatures at depth reaching boiling point and more. On April 6, 2006, three members of the Mammoth Mountain ski patrol tragically lost their lives after falling into a volcanic fumarole near the summit. The incident happened while they were conducting safety operations to secure a snow-covered geothermal vent following an unprecedented snowfall.
Over the next several hundred thousand years, the Long Valley Caldera experienced a series of volcanic eruptions, including the formation of several domes and lava flows. The most recent eruption occurred about 600 years ago, creating the Inyo Craters, a group of small cinder cones located on the western edge of the caldera.
One of the most notable features of the Long Valley Caldera is the presence of a magma chamber beneath the caldera floor. The magma chamber is responsible for the ongoing geothermal activity in the area, including hot springs and geysers, such as the famous Mono Lake Tufa State Natural Reserve.
Here, the Owens River flows through it, winding south through Owens Valley.(Erik Olsen)
Volcanism in the region is relatively recent, and it remains extremely active today. Upon entering the town of Mammoth Lakes, there is a small, but steep rise to the East. This area, called the Resurgent Dome, has also uplifted about 80 cm (about 2.5 feet) since 1980.
The current tranquillity of the Long Valley Caldera might deceive the casual observer into thinking that it poses no danger. This assumption is not entirely true. The United States Geological Survey (USGS) closely monitors the caldera due to its high volcanic risk.
In 1980, the region experienced a swarm of strong earthquakes, arousing concern among geologists about possible renewed volcanic activity. Since then, seismic activities have been routinely observed, along with ground deformation — indications that magma might be accumulating underneath. Scientists recently tried to take the temperature of that lava. Here is a more detailed discussion of Long Valley Caldera’s deep and shallow hydrothermal systems.
The Long Valley Caldera and Mammoth Mountain are classified as “High Threat” volcanoes by the USGS. The primary concerns are volcanic eruptions and the release of harmful gases, such as carbon dioxide, from the ground. Such an eruption could disrupt local communities, cause significant economic impact due to damaged infrastructure and affect air travel by releasing ash clouds.
The scenario might seem dire, but it’s crucial to understand that the chances of a massive eruption like the one 760,000 years ago are extremely low. Most potential future eruptions are likely to be smaller events, possibly similar to those experienced at the Mammoth Mountain area.
In addition to its volcanic history, Owens Valley also played an important role in the history of California. In the late 19th and early 20th centuries, the valley was the site of a major water rights dispute between the city of Los Angeles and local farmers and ranchers. The city ultimately won the dispute, and the water from the Owens River was used to fuel the growth of Los Angeles, leading to the displacement of many local residents.
The Long Valley Caldera continues to be a focal point for scientific research and natural wonder. Ongoing studies are uncovering new details about its volcanic past, current geothermal activity, and future potential. As we deepen our understanding of this dynamic landscape, we also gain valuable insights into the natural processes that shape our world and the potential impacts of climate change. Whether through scientific discovery or personal exploration, the Long Valley Caldera offers a unique window into the powerful forces that govern our planet.
