Decades of swelling
A caldera can swell and shake for forty years without erupting.
Long Valley has risen by the better part of a metre and produced repeated earthquake swarms since the 1980s. One leading interpretation is that much of the recent unrest is driven by deep fluids escaping an old, cooling magma body - not fresh magma racing to erupt.
What is happening at Long Valley Caldera
Long Valley is a large caldera next to the resort town of Mammoth Lakes. It has been in a state of on-and-off unrest for over four decades, with ground uplift along the caldera鈥檚 central resurgent dome.
The unrest shows up as earthquake swarms along the ring-fault zone and steady swelling. Research links a good part of the recent activity to fluids and gas released as an ancient magma chamber slowly cools and crystallises.
The hazard record here
THE RECORD HERE
A magnitude 6.5 earthquake struck here in 2020.
Epicentre: Monte Cristo Range, NV Earthquake.
Live figures from the QuakeMate hazard API - USGS earthquake catalog, NOAA tsunami database and published recurrence estimates. Some fields are blank where there is no record.
Recent earthquakes at Long Valley Caldera
- 0.79 km E of Mammoth Lakes, CA1 week ago 路 19/07/2026, 08:44:32 路 6 km deep
- 1.19 km E of Mammoth Lakes, CA1 week ago 路 19/07/2026, 08:43:11 路 6 km deep
- 0.77 km E of Mammoth Lakes, CA6 days ago 路 25/07/2026, 13:13:48 路 2 km deep
- 0.310 km E of Mammoth Lakes, CA1 week ago 路 19/07/2026, 14:55:14 路 8 km deep
- 0.17 km E of Mammoth Lakes, CA2 weeks ago 路 16/07/2026, 08:49:41 路 4 km deep
- 1.79 km E of Mammoth Lakes, CA1 week ago 路 19/07/2026, 08:43:42 路 7 km deep
84 more earthquakes at Long Valley Caldera
Open the QuakeMate app to see every quake here, sorted and mapped - plus real-time alerts when a new one strikes.
Notable events
1980
Four M6 quakes in two days marked the start of the modern unrest.
1989
A swarm under Mammoth Mountain was tied to magma movement and gas release.
1997
One of the strongest swarms of the era shook the caldera.
What scientists watch
The USGS tracks uplift, swarm depth and CO2 emissions - including the tree-kill areas at Mammoth Mountain where volcanic gas seeps up.
Staying ahead of it
Swarms here can escalate over hours - real-time alerts keep residents and visitors ahead of the shaking.
Get QuakeMate freeGet warned before the next one at Long Valley Caldera.
QuakeMate sends a push the instant the ground moves - plus tsunami and volcano alerts. Free to download.
Long Valley Caldera: common questions
Is Long Valley going to erupt?
There is no indication of an imminent eruption. Decades of uplift and swarms may be driven largely by deep fluids from a cooling magma system rather than new magma - which is why it can stay restless so long without erupting.
Why does the ground at Long Valley keep rising?
Pressure changes beneath the resurgent dome push the surface up. The caldera has risen substantially since persistent unrest began, in pulses rather than steadily.
Related hazard zones
Earthquake data via the QuakeMate API (USGS, EMSC and regional agencies). Historical notes summarise well-established events; magnitudes and dates follow the published record. Live figures may be revised.