New Caltech Imaging Penetrates 10 Kilometers into California's Long Valley Caldera, Revealing Solidified Magma Chamber

California's Long Valley Caldera, a vast volcanic depression partly underlying the popular ski town of Mammoth Lakes, is drawing renewed attention following advanced imaging by Caltech researchers. This geological feature, formed by a colossal eruption 760,000 years ago, has been the subject of intensive monitoring due to its active history. Recent studies, utilizing fiber optic cables, have provided unprecedented views up to 10 kilometers beneath the surface, revealing a largely solidified magma chamber.

The Long Valley Caldera, measuring approximately 20 miles long and 11 miles wide, is classified as a supervolcano, a designation for volcanoes capable of eruptions exceeding 1,000 cubic kilometers of material. Its formation resulted from a massive eruption that emptied a magma chamber, leading to collapse. While its past activity was immense, scientists emphasize that future eruptions are likely to be small to moderate in scale, not on the catastrophic level of its initial formation.

Since 1980, the caldera has experienced episodic unrest, characterized by earthquake swarms and the uplift of its central resurgent dome. The U.S. Geological Survey (USGS) maintains a dense network of sensors to track these changes, including seismic activity and ground deformation. Notable periods of unrest include strong earthquake swarms in May 1980, which caused a 10-inch uplift of the caldera floor, and renewed inflation that began in 2011 and continued for several years.

The latest breakthrough in understanding the caldera comes from Caltech researchers, who published their findings in October. Their innovative technique involved using fiber optic cables, typically used for internet services, to conduct seismic measurements through distributed acoustic sensing (DAS). This allowed them to capture the most detailed underground images ever, penetrating up to 10 kilometers and confirming that the ancient magma chamber is now largely covered by a solidified lid of crystallized rock.

Beyond seismic activity, the caldera remains thermally active with numerous hot springs and fumaroles. Diffuse carbon dioxide (CO2) emissions, particularly around Mammoth Mountain, have been monitored, notably after a 2006 incident where three ski patrol members died from CO2 asphyxiation in a snow cave formed by a fumarole. Authorities have since implemented stricter fencing and warnings around such hazards.

Despite its designation as a supervolcano and its history of unrest, the Long Valley Caldera's current hazard status remains 'Green,' indicating no immediate threat. Scientists continuously analyze data, suggesting that while future volcanic activity is possible, it is expected to be localized and significantly less powerful than the caldera-forming event, primarily involving lava fountaining or explosive but small-to-moderate eruptions.