Something Deep Beneath California Is Causing the Ground to Swell
Ground movement tied to volcano systems gets attention across the U.S. whenever scientists detect changes that could affect nearby communities. In eastern California, researchers say the Long Valley Caldera near Mammoth Lakes is still swelling as magma and underground fluids shift below the surface. The change has been measured for decades, and officials say it remains under close watch.
Scientists say the Long Valley area is still rising
The U.S. Geological Survey said on July 18, 2024, that parts of the Long Valley Caldera and the nearby resurgent dome have continued to uplift, based on GPS stations, satellite radar, and other ground measurements. The agency said the long-running deformation is centered in eastern California near Mammoth Lakes, about 300 miles north of Los Angeles. USGS monitoring has tracked changes there since the late 1970s.
According to the USGS, the total uplift in parts of the caldera has reached several feet since 1980, although the rate has changed over time. Scientists said the latest movement is not a sudden spike but part of a longer pattern that includes periods of faster and slower inflation. The California Volcano Observatory confirmed the area also sees earthquake swarms from time to time.
What is confirmed in California, and what is not
What is confirmed is that the ground in the Long Valley region has risen measurably and that the source is deep underground, according to USGS scientists. The monitored area includes Mammoth Lakes, the Long Valley Caldera, and surrounding parts of Mono County. Public data also show recurring seismic activity in the same region.
What is not confirmed is any immediate eruption timeline. The USGS has not stated that the current uplift means an eruption is imminent, and it has not announced any evacuation order or emergency warning tied to the recent measurements. Scientists have also not identified a single exact depth or one simple source for every part of the uplift pattern.
Why the ground is swelling and what residents should expect
USGS scientists said the swelling is most likely being driven by magma and hot fluids moving or pressurizing beneath the caldera. Long Valley formed about 760,000 years ago in a very large eruption, and the present-day system still contains heat, fluids, and active faults. Researchers have said those conditions can produce uplift without leading directly to an eruption.
For California residents and travelers, the practical takeaway is that the area remains an active volcanic system under routine monitoring. The USGS and the California Volcano Observatory continue to track earthquakes, gas emissions, and surface deformation in and around Mammoth Lakes. Officials have said ongoing unrest in Long Valley can last for years, and current monitoring is meant to detect any significant change quickly.
