World Organization of Volcanic Observatories

1203-14
Long Valley Caldera Monitoring, MS 977
United States Geological Survey
345 Middlefield Rd.,
Menlo Park, CA 94025
USA

PERSONNEL (All located at USGS Headquarters in Menlo Park, CA, unless otherwise noted. Most have major responsibilites in other projects under the Earthquake or Volcano Hazards Programs in addition to Long Valley caldera monitoring)

Chief Scientist: David P. Hill

email: hill@usgs.gov

Assistant Chief Scientist: William Ellsworth

Monitoring Team Leader: Malcolm Johnston

Hazards Team Leader: C. Dan Miller (Cascades Volcano Observatory)

Support Team Leader:

Scientific Advisory Team:

Peter Lipman (Team Leader)
Robert Christiansen
Robert Decker (Mariposa, CA; Kamuela, HI)
Jerry Eaton
Paul Segall (Stanford University)
Wayne Thatcher

Seismology:

David Hill
Mitch Pitt
Randy White
David Oppenheimer
Rick Lester

Geodesy:

Elliot Endo (Cascades Volcano Observatory)
Dan Dzurisin (Cascades Volcano Observatory)
John Langbein
Stuart Wilkinson (Mammoth Lakes, CA)
Elliot Endo (Cascades Volcano Observatory)
Dan Dzurisin (Cascades Volcano Observatory)
Ross Stein

Continuous strain:

Malcolm Johnston
Carl Mortensen
Roger Bilham (University of Colorado)
Bob Mueller
Doug Myren
Stan Silverman

Hydrology, Hot Spring Chemistry, and Gas Chemistry

Bill Evans
Chris Farrar (Carnelian Bay, CA)
Terry Gerlach (Cascades Volcano Observatory)
Ken McGee (Cascades Volcano Observatory)

BACKGROUND AND ORGANIZATION

In 1982, the U.S. Geological Survey under the Volcano Hazards Program began an intensive effort to monitor and study persistent unrest in Long Valley caldera that began with a swarm of four magnitude 6 earthquakes in May of 1980. The continuing unrest includes recurring earthquake swarms and dome-shaped uplift of the central section of the caldera accompainied by changes in thermal springs and gas emissions (see references for a selected list of papers and articles on Long Valley caldera). A principal objective of this monitoring effort is to provide residents and civil authorities in the area reliable information on the nature of the potential hazards posed by this unrest and timely warning of an impending volcanic eruption, should it develop.

The USGS regional center in Menlo Park, CA serves as headquarters for Long Valley Caldera Monitoring. Data from monitoring instruments located in and around the caldera are sent by radio and satellite telemetry to computers in Menlo Park where they are automatically processed in real time for immediate analysis by scientists. The computers include an automatic paging system that alerts scientists of significant changes in activity 24 hours a day. A communication protocol for notifying civil authorities and emergency response officials of the level of concern for a given level of unrest is based a four-color system ranging from green to red. The colors under this system have the following meaning:

GREEN : "typical" behavior posing no immediate risk

YELLOW : intense unrest (a WATCH and intensified on-site monitoring)

ORANGE : an eruption is likely with hours to days (WARNING)

RED : an eruption is underway (ALERT)

This color system is a modification of the original, 5-stage, alphabetic STATUS system described in the Long Valley caldera Response Plan (Hill and others, 1991). We are currently updating this response document to reflect both the new color-code for response levels as well as recent organizational changes within the U.S. Geological Survey.

The Chief Scientist for Long Valley Caldera is responsible for overseeing and coordinating the U.S. Geological Survey monitoring efforts in the caldera carried out by projects in both the Geologic and Water Resources Divisions. This person is also responsible for ensuring that accurate and timely hazards assessment and supporting scientific information are issued to all concerned parties, including local, state, and Federal officials and the public. The Chief Scientist is supported by an Assistant Chief Scientist and four Team Leaders.

Monitoring Team Leader serves as a consultant and advisor the Chief Scientist in determining monitoring requirements and in analyzing and interpreting the results.

Hazards Team Leader updates hazards assessments based on results of the monitoring data and geologic studies.

Support Team Leader provides liaison with other agencies and the press.This person also facilitates resource and logistic backup in case of a field response to a volcanic crisis in the Long Valley region.

Scientific Advisory Team Leader heads a team of five senior scientists with broad volcanological and geophysical knowledge that can provide the Chief Scientist a calm and objective analysis of an evolving crisis without being caught up in the operation esponsibilities of the USGS response.They also provide advice on long-term monitoring, hazard assessment, and scientific strategies.

MONITORING NETWORKS (Current data from these networks are displayed in the Long Valley Caldera WWW Home Page)

Seismic network

Earthquakes occurring in Long Valley caldera and vicinity are recorded by a network of 18 short-period (1 Hz natural period), vertical-component seismic stations within the caldera and an additional 20 stations within a distance of 50 km beyond the caldera boundary (two stations also have horizontal component seismometers).These stations comprise parts of both the Northern California Seismic Network (NCSN) operated by the U.S. Geological Survey in Menlo Park, CA (stations names ending in M), and the Nevada seismic network operated by the University of Nevada, Reno (station names ending in R). The signals from the combined stations are shared by both networks. The FM stations are shared by both networks. The FM analog signals from these stations are telemetered to USGS headquarters in Menlo Park and processed along with data from the rest of the Northern California Seismic Network. The resulting seismicity data are archived on a mass storage device at the University of California, Berkeley - USGS data center.

Geodetic networks

A two-color geodimeter is used to monitor line-length changes to a precision of several parts in 10^7 for a network of baselines that span the caldera and the southern part of the Inyo-Mono Craters volcanic chain. Measurements of the baselines extending from the CASA monument on the resurgent dome are made several time a week, weather permitting. The remaining baselines are measured less frequently (quarterly to annually), depending on the location and intensity of seismic activity and other indicators of unrest.

More than 30 GPS sites in the Long Valley-Mono Lake area provide control on regional strain. These sites are generally occupied on an annual basis. Three GPS sites within the caldera are operated in a continuous mode in a cooperative effort with the Jet Propulsion Laboratory (Pasadena, CA) and the University of Miami.

A network of level lines along the principal roads through Long Valley caldera provides ontrol on vertical deformation. These lines are re-sruveyed on an annual or bi-annual basis, depending on the general level of unrest.

Continuous strain networks

Data from instruments measuring continuous strain changes in Long Valley caldera are sampled every 10 minutes and telemetered to Menlo Park via the GEOS satellite. Initial on-line computer processing of these data provide scientists in Menlo Park near-real-time information on strain changes occurring in the caldera. The continuous strain instrumentation includes:

Two Sacks-Evertson borhole volumetric strain meters (dilatometers)

Seven shallow (2-10 m deep) borehole tiltmeters

One two-component, long-base (500 m) Michaelson interferometry tiltmeter

Hydrology and Gas Chemistry

Water levels in seven wells within the caldera are sampled at intervals from 30 seconds to 15 minutes as part of an effort to monitor the hydrologic and geochemical regime in Long Valley caldera. In addition, the chemistry and flow rates of hot springs and the gas chemistry of fumaroles in the caldera sampled several times a year. Soil gas concentrations and flux are also being monitored on Mammoth Mountain to assess the implications of anomalous magmatic gas discharge for future eruptive activity and public health.

SELECTED REFERENCES

Bailey, R.A., 1989, Geologic map of Long Valley caldera, Mono-Inyo Craters volcanic chain, and vicinity, Mono County, California. U.S. Geological Survey Miscellaneous Investigations Map I-1933, scale 1:62,500.

Bailey, R. A. , G. B. Dalrymple, M.A. Lanphere, 1976, Volcanism, structure, and geochronology of Long Valley caldera, Mono County, California. Jour. Geophys. Res., v. 81, pp. 725-744. (also see additional papers on Long Valley in this same volume.)

Farrar, C.D., M.L. Sorey, W.C. Evans, J.F. Howle, B.D. Kerr, B.M. Kennedy, C.-Y. King, and J.R. Southon, 1995, Forest-killing diffuse CO2 emissions at Mammoth Mountain as a sign of magmatic unrest. Nature, v. 376, pp. 675-678.

Hill, D.P., 1996, Earthquakes and carbon dioxide beneath Mammoth Mountain, California.Seismol. Research Lett., v. 67, pp. 8-15.

Hill, D.P., 1984, Monitoring unrest in a large silicic caldera, the Long Valley-Inyo craters olcanic complex in east-central California. Bull. Volcanol., v. 47., pp371-395.

Hill, D.P., R.A. Bailey, and A.S. Ryall, 1985, Active tectonic and magmatic processes beneath Long Valley caldera, eastern California: a summary. Jour. Geophys. Res., v. 90, pp. 11,111-11,120. (also see additional papers on Long Valley in this same volume).

Hill, D.P., M.J.S. Johnston, J.O. Langbein, S.R. McNutt, C.D. Miller, C.E. Mortensen, A.M. Pitt, and S. Rojstaczer, 1991, Response plans for volcanic hazards in the Long Valley caldera and Mono Craters area, California. U.S. Geological Survey Open File Report 91-270, 64 p.

Hill, D.P., R.E. Wallace, and R.S. Cockerham, 1985, Review of evidence on the potential for major earthquakes and volcanism in the Long Valley-Mono Craters-White Mountains region of eastern California. Earthquake Prediction Research, v. 3, pp. 571-594.

Langbein, J.O., D.P. Hill, T.N. Parker, and S.K. Wilkinson, 1993, An episode of reinflation of the Long Valley caldera, eastern California: 1989-1991. Jour. Geophys. Res., v. 98, pp. 15,851-15870.

Miller, C.D., D.R. Mullineaux, D.R. Crandell, and R.A. Bailey, 1982, Potential hazards from future volcanic eruptions in the Long Valley-Mono Lake area, east-central California and southwest Nevada - a preliminary assessment. U.S. Geological Survey Circular 887, 10 p.

Rundle, J.B., and D.P. Hill, 1988, The geophysics of a restless caldera - Long Valley, California. Ann. Rev. Earth Planet. Sci., v. 16, pp. 251-271.

Pitt, A.M., and D.P. Hill, 1994, Long-period earthquakes in the Long Valley caldera region, eastern California. Geophys. Res. Lett., v. 21, pp. 1679-1682.

Sorey, M.L., G.A. Suemnicht, N.C. Strurchio, and G.A. Nordquist, 1991, New evidence on the hydrothermal system in Long Valley caldera, California, from wells, fluid sampling, electrical geophysics and age determinations of hot-spring deposits, Jour. Volcan. Geoth. Res., v. 48, 229-263.

Sorey, M.L., B.M. Kennedy, W.C. Evans C.D. Farrar, and G.A. Suemnicht, 1993, Helium isotope and gas discharge variations associated with crustal unrest in Long Valley caldera, California, 1989-1992. Jour. Geophys. Res., v. 98, pp. 15,871-15,888.

Information submitted September 1997