Caldera Unrest

at a Glance

‘85 ‘90 ‘95 ‘00 ‘05 ‘10

0.05

0.10

0.00 0.00

0.05

0.10

shallow inflation source (6 km)

deep inflation source (12 km)

Deep reservoir

relative volume (km3

)

Year

Shallow reservoir

relative volume (km3

)

Langbein, 2003

Summary of Earthquake Activity and Deformation

Inflation of the resurgent dome from 1975 through August 2014 and earthquake activity plotted in terms of the cumulative 

number of M>2 earthquakes within the Long Valley Caldera and the Sierra Nevada block to the south. Deformation of the 

resurgent dome is shown from leveling survey lines and EDM through 1997 and frequent measurements with the two-color 

EDM instrument and GNSS data after 1997. Inset shows modeled volume change of the two reservoirs over time. 

References:

Ewert, J.W., Harpel, C.J., Brooks, S.K., and Marcaida, M., 

2010, Bibliography of Literature Pertaining to Long Valley 

Caldera and Associated Volcanic Fields: U.S. Geological 

Survey Open-File Report 2010–1320, 146 p., and database.

Hill, D.P., Dzurisin, D., Ellsworth, W.L., Endo, E.T., Galloway, 

D.L., Gerlach, T.M., Johnston, M.J.S., Langbein, J.O., McGee, 

K., Miller, C.D., Oppenheimer, D., and Sorey, M.L., 2002, 

Response plan for volcano hazards in the Long Valley caldera 

and Mono Craters region California: U.S. Geological Survey 

Bulletin 2185, 57 p.

Langbein, J.O., 2003, Deformation of the Long Valley Caldera, 

California; inferences from measurements form 1988 to 

2001: Journal of Volcanology and Geothermal Research, v. 

127, no. 3-4, p. 247–267.

Savage, J.C., 1988, Principal component analysis of 

geodetically measured deformation in Long Valley Caldera, 

eastern California, 1983–1987: Journal of Geophysical 

Research, v. 93, no. B11, p. 13297–13305.

Savage, J.C., and Cockerham, R.S., 1984, Earthquake swarm in 

Long Valley Caldera, California, January 1983; evidence for 

dike inflation: Journal of Geophysical Research, v. 89, no. 10, 

p. 8315–8324.

1975 1980 1985 1990 1995 2000 2005 2010 2015

0

600

1200

1800

2400

3000

3600

4200

4800

5400

6000

Cumulative Earthquake Count

Year

1975 1980 1985 1990 1995 2000 2005 2010 2015

0

100

200

300

400

500

600

700

800

Cumulative Uplift, Resurgent Dome (mm)

Resurgent Dome Uplift (Casa-Krak Baseline)

Caldera Earthquakes (M>2) Sierra Nevada Earthquakes (M>2)

Casa Diablo Geothermal Plant

Mammoth Mountain

Resurgent Dome

South Moat Seismic Zone

Town of Mammoth Lakes

SW caldera rim

USGS photo by Margaret Mangan

0 2 KM

0 0

0

0

0

0

20

20

20

20

20

40

40

40

60

resurgent dome margin

X

X

X

X

X

X

X

X

X X

X

EXPLANATION

10 mm

0

Leveling monuments

Observed EDM displacement

Subsidence contours in 

millimeters

X

Basalt 

Canyon

Casa Diablo 

Geothermal Field

Geothermal power production began in 1985 at the Casa Diablo plant located at the southern margin of 

the resurgent dome. Presently ~40 MW is generated using a counter flow heat exchanger. Hot water at 

~170  ̊C is pumped from the shallow thermal aquifer at 150 m depth to heat isobutane which is used to 

drive turbines. The cooled water at 80  ̊C is then reinjected into a deeper thermal aquifer at ~600 m 

depth. Water throughput is ~900 kg/s—much larger than the natural ~370 kg/s flow of the shallow 

thermal aquifer, causing a large impact on caldera hydrology. Thermal contraction at reinjection sites 

and depressurization at extraction sites give rise to localized subsidence and changes in magmatic gas 

and heat emission. No strong evidence exists for production-induced seismicity. Potential plant expansion with as many as 8 new wells is under consideration. The photo below shows view of Casa Diablo 

plant observed from resurgent dome looking westward across the caldera toward Mammoth Mountain.

The influence of geothermal production on volcano monitoring: deformation, geochemical, and thermal monitoring of 

LVC are locally obfuscated by short-term and long-term changes in the shallow hydrothermal system under the caldera.

Displacements observed from two-color EDM sites for the interval 

1999–2001 show shallow, localized subsidence due to geothermal production. The contours are the estimated collapse in millimeters modeled 

assuming a 200 m deformation source (known depth of hydrothermal 

reservoir). Langbein and others, 2003.

Deformation was flat from 2004 through 2010, and SMSZ seismicity held steady at 

about 10 M1–M2 events per month. Seismicity continued in the Sierra Block south of 

the caldera with many M>3 and M>4 events. In 2011, after ~8 years of little deformation, the resurgent dome began to inflate at a rate of 2–3 cm/year with little change in 

SMSZ seismicity. The rate of inflation is similar to that of 2002–2003, on the order of 

2–3 cm/yr, and as in 2002–2003, SMSZ seismicity continues at background levels of 

~10 M1–M2 events per month. Preliminary time-dependent modeling of EDM and 

GNSS suggests a ~0.1 km3

 cumulative volume increase in both deformation sources 

from 1983 to the present, with negligible contributions since the unrest of 1997-1998, 

despite the modest inflationary signals of 2002–2003 and 2011–2012. A seismic swarm 

in June 2013 in the SMSZ included 100 small events with a maximun M3.0. Between 

February 3–18, 2014, a seismic swarm occurred under Mammoth Mountain that 

included M>1 events with a maximum M3.1 on February 5. Seismicity in June 2014 

included 73 M>1 events within a brisk swarm with a maximum M2.41.

Recent Unrest: 2004–2014

Modest uplift without swarms.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 2004–2014 with 

95% confidence ellipse

Inflation sources

Text labels are GNSS 

sites.

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

2004–2014

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

2002–2003

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

2002–2003: Renewed inflation without swarms. 

The resurgent dome started a modest inflationary period in early 

2002, ending ~3 years of quiescence. About 3 cm of uplift was 

added over the year, but SMSZ seismicity stayed at background 

levels, with the exception of distantly-triggered earthquakes following Alaska’s M7.9 Denali earthquake on November 3, 2002. Approximately 7 years of relative quiet followed. 

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 2002–2003 with 

95% confidence ellipse

Inflation sources

Text labels are GNSS 

sites.

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

1999–2001

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

1999–2001: M>5 events in Sierra Block but LVC remains calm. 

A M5.6 earthquake and numerous aftershocks rattled the Sierra 

Block in May of 1999. The 1999 event, as well as the 2 M>4 (both 

4.9) events in 1998, had b values typical of tectonic earthquakes, and 

none were followed by increased seismicity or deformation in the 

caldera. Caldera seismicity remained at background levels with 

virtually no further inflation of the resurgent dome. In fact, minor 

deflation was observed.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 1999–2001 with 

95% confidence ellipse

Center of deflation

Text labels are GNSS 

sites.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 1997–1998 with 

95% confidence ellipse

Inflation sources

Text labels are GNSS 

sites.

1997–1998: Rapid escalation of caldera unrest. 

With the exception of 2 M>4 Sierra Block earthquakes in February, 

relative quiet prevailed through the first half of 1997, giving way to 

accelerated uplift and SMSZ swarms in the second half of the year. 

Unrest peaked in late 1997, and then declined through early 1998. 

Swarms included ~12,000 earthquakes over 7 months, including 

120 M>3 and 8 M>4 events. Peak extension rates up to 2 mm/day 

ultimately resulted in an additional 10 cm of uplift by mid-1998 

before rates declined. In the second half of 1998, seismicity focused 

in the Sierra Block with 2 M>4 earthquakes.

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

1997–1998

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

1993–1996

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

1993–1996: Unusual deformation and seismicity in 1996. 

Levels of SMSZ and Sierra Block seismicity and resurgent dome 

uplift held relatively steady through 1995. In early 1996, an intense 

swarm of SMSZ earthquakes occurred without a sympathetic uptick 

in inflation, breaking the pattern of seismicity and deformation rates 

acting in tandem. The swarm peaked in the spring of 1996 with 

>1,600 earthquakes over 2 months, including 3 M>4 and 21 M>3 

events.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 1993–1996 with 

95% confidence ellipse

Inflation sources

Text labels are GNSS 

sites.

1988–1992: Rapid inflation and 1992 Landers M7.3 triggering. 

Resurgent dome uplift increased in 1989 to ~7 cm/year followed by 

an increase in SMSZ seismicity. Inflation slowed to ~2 cm/year by 

1990, but SMSZ seismicity continued, peaking with a swarm of 

>1,000 earthquakes over 4 days in 1991, including 22 M>3 events. 

The deformation sources were located ~6 km and ~12 km below the

dome. In 1992, seismic swarms in the SMSZ and Sierra Block were 

triggered within seconds of the June 28, 1992 M7.3 Landers earthquake located ~400 km south of LVC in the Mojave Desert. The 

distantly triggered swarms included several M>3 events.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

tilla

5 cm

EXPLANATION

Observed displacement 

from 1988–1992 with 

95% confidence ellipse

Inflation sources

Text labels are GNSS 

sites.

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

1988–1992

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

1978–1983: Dramatic seismicity and uplift, then calm. 

Intermittent M3–M4 earthquakes in the South Moat Seismic Zone (SMSZ) in 

1978 were followed by an intense seismic swarm in May 1980 that included 4 

M>6 earthquakes in the SMSZ and Sierra Block. Focal mechanisms for 2 of the 

4 earthquakes suggest they were caused by magma or hydrothermal fluid injection. The swarm coincided with 25 cm of resurgent dome uplift. New fumaroles 

in the Casa Diablo area appeared in 1982. Another SMSZ swarm occurred in 

1983 with 2 M>5 earthquakes and an additional 7-cm uplift, modeled as a dike 

intruding to within 4 km depth beneath the resurgent dome. Seismicity declined 

thereafter and the uplift rate dropped to less than 1 cm/year.

10 km

casa

krak

saw

lookout

bald

crater

119°0'W

37°50'N

After Savage and Cockerham,1984,

and Savage, 1988

tilla

5 cm

EXPLANATION

Observed displacement from 

1982–1983 and 1983–1987

with 95% confidence ellipse

Text labels are GNSS 

sites.

M6 earthquake

EXPLANATION

M5 earthquake

M4 earthquake

M3 earthquake

M2 earthquake

1978–1987

Caldera Rim 

Hilton Creek Fault

Hartley Springs Fault

Bald Mountain

Mono Craters

Glass Mountain

Mammoth

Mountain

Mammoth

Lakes

Lake

Crowley

Highway 395

SIERRA NEVADA

BLOCK

Resurgent Dome

SMSZ

119°0'W 118°50'W

37°50'N

37°40'N

37°30'N

0

0

5 10 KILOMETERS

5 10 MILES

Modified from Hill and others, 2002

pressure center of

inflating magma body

volcanic vent

vertical fault zones

major range front

normal faults

EXPLANATION

dike under 

Mammoth Mountain

10 km

Resurgent Dome

Caldera Rim

SIERRA NEVADA 

BLOCK

Hilton Creek

Hartley Springs

Lake

Crowley Mammoth

Mountain Inyo Domes

regional E-NE extension

depth ~6 km

depth

~12 km

SMSZ

Sources of Caldera Unrest

High precision deformation measurements evolved from labor intensive leveling and 

2-color Electronic Distance Measurement (EDM) techniques to automated measurements from continually operating GNSS receivers. While both the older and newer 

technologies have the same precision, the new instruments allow for real-time recording at a 1-second interval of deformation. The LVC seismic network consists of 

30 telemetered sites, including 8 broadband stations. The tiltmeter network includes 

2 borehole tiltmeters, and one long baseline tiltmeter capable of resolving changes 

of 0.1 microradian over a week and 1.0 microradian over a year. The strain network 

consists of 3 dilatometers capable of detecting 0.02 ppm changes over days and 0.01 

ppm over hours.

The U.S. Geological Survey (USGS) California Volcano Observatory monitors Long Valley Caldera and vicinity with 

continuous Global Navigation Satellite System (GNSS), seismometers, tiltmeters, and strainmeters.

Locations of inferred sources contributing to the 

1978–1999 unrest in Long Valley Caldera and vicinity.

Red circles indicate centers of inflating magma bodies. The dashed 

black line indicates a dike intruded beneath Mammoth Mountain in 

1989. Thick red dashed lines indicate near-vertical fault zones. 

Double-barbed arrows indicate sense of slip across fault systems. 

Large arrows indicate regional east-northeast extension. Major 

range-front normal fault systems are indicated by solid lines with ball 

on the down-dropped block. SMSZ: south moat seismic zone.

Mammoth

Mountain

Mammoth Lakes 

Highway 395

Bald Mountain

Glass Mountain

Resurgent Dome

SMSZ

SIERRA NEVADA

BLOCK

Lake

Crowley

Mono Craters

USGS tiltmeters

USGS strainmeters

USGS broadband seismic sites

USGS GNSS sites

USGS seismic sites

Caltech broadband seismic site

UNAVCO GNSS sites

EXPLANATION

Hilton Creek Fault

Hartley Springs Fault

Long Valley Caldera 

0

0

5 10 KILOMETERS

5 10 MILES

View of Long Valley Caldera (LVC) looking eastward from Mammoth Mountain. 

LVC is located in California along the eastern escarpment of the Sierra Nevada Range. The caldera formed about 760,000 years ago as the eruption of 600 

km3 of rhyolite magma (Bishop Tuff) resulted in collapse of the partially evacuated magma chamber. Resurgent doming in the central part of the caldera occurred shortly afterwards, and the most recent eruptions inside the caldera occurred about 50,000 years ago. The caldera remains thermally active, with many 

hot springs and fumaroles, and has had significant deformation and seismicity since at least 1978. Periods of intense unrest in the 1980s to early 2000s are 

well documented in the literature (Hill and others, 2002; Ewert and others, 2010). In this poster, we extend the timeline forward, documenting seismicity and 

deformation over the past decade.

Resurgent Dome

Casa Geothermal Power Plant

South Moat Seismic Zone

Town of Mammoth Lakes

Glass Mountain White Mountains

SIERRA NEVADA BLOCK

Mammoth Mountain

Lake Crowley

Round Mountain

Bald Mountain

Long Valley Caldera—California’s Restless Giant Unrest in Long Valley Caldera and vicinity from 1978 to 2003

Long Valley Caldera 2003 through 2014: Overview of Low Level Unrest in the Past Decade

By

Stuart Wilkinson, David P. Hill, John O. Langbein, Mike Lisowski, and Margaret Mangan

2014

U.S. Departyment of the Interior

U.S. Geological Survey

October 2014

California Volcano Observatory

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to 

reproduce copyrighted items must be secured from the copyright owner.

Suggested Citation: Wilkinson, S., Hill, D.P., Langbein, J.O., Lisowski, M., and Mangan, M., 2014, Long Valley Caldera 2003 through 2014—Overview of 

low level unrest in the past decade: U.S. Geological Survey Open-File Report 2014–1222, 1 sheet, http://dx.doi.org/10.3133/ofr20141222.

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141222