Active tectonic and magmatic processes beneath Long Valley Caldera, eastern California: An overview

Geological, chronological, and structural studies of the Long Valley-Mono/Inyo Craters area document a long history of related volcanic eruptions and earthquakes controlled by regional extensional tectonics of the Basin and Range province. This activity has persisted for hundreds of thousands of years and is likely to continue. The Long Valley magma chamber had a volume approaching 3000 km3 prior to its climatic caldera-forming eruption 0.7 m.y. ago but has been reduced to less than a third of this volume by cooling, eruption, and crystallization. Seismic evidence indicates that the main mass of the present Long Valley magma chamber is about 10 km in diameter and that its roof is 8–10 km deep with smaller cupolas as shallow as 4–5 km. Although a chamber of this size is probably capable of producing an eruption approaching 30 km3 of lava, the record over the past 0.5 m.y. suggests that eruptions of 1 km3 or less are far more likely. Models proposed for the current ground uplift and seismicity within the caldera require inflation of 0.1–0.2 km3 by additional magma since mid-1979, and some models suggest that inflation was accompanied by injection of a thin dike or dikes (probably of silicic magma) into the ring fracture zone beneath the south moat. Several of the M 5.8–6.2 earthquakes that occurred in the region beginning in 1978 had non-double-couple focal mechanisms. Whether these unusual mechanisms indicate injection of mafic (low-viscosity) magma at midcrustal depths in the Sierra Nevada block south of the caldera remains debatable. Studies of calderas of various ages throughout the world indicate that episodes of unrest are relatively common and do not invariably culminate in eruptions. Although current unrest is concentrated in the south moat of Long Valley caldera, the Inyo/Mono Craters probably hold a greater potential for producing an eruption in the foreseeable future. The Inyo/Mono Craters have erupted at 500-year intervals over the past 2000–3000 years, whereas the Long Valley magma chamber has erupted at about 200,000-year intervals over the past 700,000 years. In either case, a major earthquake near the caldera could strongly influence the course of volcanic activity.

[1]  D. Hill.  Structure of Long Valley Caldera, California, from a seismic refraction experiment , 1976 .

[2]  A. Ryall,et al.  Spatial-temporal variations in seismicity preceding the May 1980, Mammoth Lakes, California, earthquakes , 1981 .

[3]  J. Liddicoat,et al.  Core KM-3, a surface-to-bedrock record of late Cenozoic sedimentation in Searles Valley, California , 1983 .

[4]  R. E. Wallace,et al.  Review of Evidence on the Potential for Major Earthquakes and Volcanism in the Long Valley-Mono Craters-White Mountains Regions of Eastern California , 1985 .

[5]  A. Ryall,et al.  Sierra Nevada-Great Basin boundary zone: Earthquake hazard related to structure, active tectonic processes, and anomalous patterns of earthquake occurrence , 1980 .

[6]  M. L. Sorey.  Evolution and present state of the hydrothermal system in Long Valley Caldera , 1985 .

[7]  A. Ryall,et al.  Systematic change of focal mechanism with depth in the Western Great Basin , 1983 .

[8]  R. Wood,et al.  The geology of the angareb ring dike complex, northwestern ethiopia , 1976 .

[9]  R. A. Bailey,et al.  Potential hazards from future volcanic eruptions in the Long Valley-Mono Lake area, east-central California and southwest Nevada; a preliminary assessment , 1982 .

[10]  H. R. Shaw.  Links between magma‐tectonic rate balances, plutonism, and volcanism , 1985 .

[11]  A. Lachenbruch,et al.  9: Models of an extending lithosphere and heat flow in the Basin and Range province , 1978 .

[12]  Tony Reichhardt.  Comet rendezvous mission , 1984 .

[13]  K. Kellogg.  Root zone of the Late Proterozoic Salma Caldera, northeastern Arabian Shield, Kingdom of Saudi Arabia , 1985 .

[14]  G. Neumann,et al.  The Long Valley/Mono Basin Volcanic Complex: A preliminary magnetotelluric and magnetic variation interpretation , 1984 .

[15]  S. Sipkin,et al.  Earthquake processes in the Long Valley Caldera Area, California , 1985 .

[16]  C. W. Roberts,et al.  Temporal and areal gravity investigations at Long Valley Caldera , 1985 .

[17]  A. Ryall,et al.  Spasmodic Tremor and Possible Magma Injection in Long Valley Caldera, Eastern California , 1983, Science.

[18]  W. Hildreth.  The Bishop Tuff: Evidence for the origin of compositional zonation in silicic magma chambers , 1979 .

[19]  T. Wallace.  A reexamination of the moment tensor solutions of the 1980 Mammoth Lakes Earthquakes , 1985 .

[20]  J. C. Savage,et al.  Magmatic Resurgence in Long Valley Caldera, California: Possible Cause of the 1980 Mammoth Lakes Earthquakes , 1982, Science.

[21]  D. Williams.  Geothermal investigations of the U.S. Geological Survey in Long Valley , 1976 .

[22]  D. Hill.  A model for earthquake swarms , 1977 .

[23]  K. Aki.  Evidence for magma intrusion during the Mammoth Lakes Earthquakes of May 1980 and implications of the absence of volcanic (harmonic) tremor , 1984 .

[24]  S. Self,et al.  Introduction to Calderas Special Issue , 1984 .

[25]  J. Rundle,et al.  A model for deformation in Long Valley, California, 1980–1983 , 1984 .

[26]  P. Lipman.  The roots of ash flow calderas in western North America: Windows into the tops of granitic batholiths , 1984 .

[27]  W. Mooney,et al.  Crustal refraction profile of the Long Valley caldera, California, from the January 1983 Mammoth Lakes earthquake swarm , 1985 .

[28]  J. C. Savage,et al.  Earthquake Swarm in Long Valley Caldera, California, January 1983: Evidence for Dike Inflation , 1984 .

[29]  P. Lysne,et al.  Research drilling at Inyo Domes, Long Valley Caldera, California , 1984 .

[30]  Giovanna Berrino,et al.  Ground deformation and gravity changes accompanying the 1982 Pozzuoli uplift , 1984 .

[31]  G. Mahood,et al.  Precursors to the Bishop Tuff Eruption: Glass Mountain, Long Valley, California , 1985 .

[32]  C. Miller,et al.  Holocene eruptions at the Inyo volcanic chain, California: Implications for possible eruptions in Long Valley caldera , 1985 .

[33]  Geometry of magma bodies beneath Long Valley, California determined from anomalous earthquake signals , 1983 .

[34]  L. Cordell,et al.  Geophysical expression of the batholith beneath Questa Caldera, New Mexico , 1985 .

[35]  A. Ryall,et al.  Attenuation of P and S waves in a magma chamber in Long Valley Caldera, California , 1981 .

[36]  F. Innocenti,et al.  The phlegraean fields: Magma evolution within a shallow chamber , 1983 .

[37]  R. A. Bailey,et al.  Volcanism, structure, and geochronology of Long Valley Caldera, Mono County, California , 1976 .

[38]  R. Denlinger,et al.  Deformation of Long Valley Caldera, Mono County, California, from 1975 to 1982 , 1984 .

[39]  D. Blackwell.  A transient model of the geothermal system of the Long Valley Caldera, California , 1985 .

[40]  D. Hill.  Monitoring unrest in a large silicic caldera, the long Valley-inyo craters volcanic complex in east-central California , 1984 .

[41]  F. Innocenti,et al.  Phlegraean Fields 1982–1984: Brief chronicle of a volcano emergency in a densely populated area , 1984 .

[42]  D. Pollard,et al.  Igneous Dikes at Long Valley, CA: Emplacement Mechanisms and Associated Geologic Structures , 1984 .

[43]  B. Julian.  Evidence for dyke intrusion earthquake mechanisms near Long Valley caldera, California , 1983, Nature.

[44]  C. Sanders,et al.  Location and configuration of magma bodies beneath Long Valley, California, determined from anomalous earthquake signals , 1984 .

[45]  D. Hill,et al.  Constraints on the upper crustal structure of the Long Valley‐Mono Craters Volcanic Complex, eastern California, from seismic refraction measurements , 1985 .

[46]  C. Bacon,et al.  Implications of silicic vent patterns for the presence of large crustal magma chambers , 1985 .

[47]  K. Priestley,et al.  Surface wave excitation and source mechanisms of the Mammoth Lakes Earthquake Sequence , 1985 .

[48]  A. Ryall,et al.  Aftershock distribution related to the controversy regarding mechanisms of the May 1980, Mammoth Lakes, California, earthquakes , 1985 .

[49]  J. C. Savage,et al.  Uplift across Long Valley Caldera, California , 1984 .

[50]  Robert B. Smith.  6: Seismicity, crustal structure, and intraplate tectonics of the interior of the western Cordillera , 1978 .

[51]  S. Wood.  Chronology of Late Pleistocene and Holocene Volcanics, Long Valley and Mono Basin Geothermal Areas, Eastern California , 1983 .

[52]  J. Fink.  Geometry of silicic dikes beneath the Inyo Domes, California , 1985 .

[53]  B. Chouet,et al.  Dynamics of an expanding fluid-filled crack , 1985 .

[54]  R. E. Wallace.  Patterns and timing of Late Quaternary faulting in the Great Basin Province and relation to some regional tectonic features , 1984 .

[55]  G. Luongo,et al.  Inflation and microearthquake activity of phlegraean fields, Italy , 1977 .

[56]  R. Denlinger,et al.  Deformation of Long Valley Caldera between August 1982 and August 1983 , 1985 .