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Magma reservoirs from the upper crust to the Moho inferred from high-resolution Vp and Vs models beneath Mount St. Helens, Washington State, USA

Eric Kiser, Imma Palomeras, Alan Levander, Colin Zelt, Steven Harder, Brandon Schmandt, Steven Hansen, Kenneth Creager and Carl Ulberg
Magma reservoirs from the upper crust to the Moho inferred from high-resolution Vp and Vs models beneath Mount St. Helens, Washington State, USA
Geology (Boulder) (April 2016) 44 (6): 411-414

Abstract

The size, frequency, and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust. Several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath Mount St. Helens (Washington State, USA), currently the most active volcano in the Cascade Range. Data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir, as well as its connection to deeper zones of magma accumulation in the crust. The inversion of P and S wave traveltime data collected during the active-source component of the iMUSH (Imaging Magma Under St. Helens) project reveals a high P-wave (Vp)/S-wave (Vs) velocity anomaly beneath Mount St. Helens between depths of 4 and 13 km, which we interpret as the primary upper-middle crustal magma reservoir. Beneath and southeast of this shallow reservoir, a low Vp velocity column extends from 15 km depth to the Moho. Deep long-period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids. Southeast of Mount St. Helens, an upper-middle crustal high Vp/Vs body beneath the Indian Heaven Volcanic Field may also have a magmatic origin. Both of these high Vp/Vs bodies are at the boundaries of the low Vp middle-lower crustal column and both are directly above high Vp middle-lower crustal regions that may represent cumulates associated with recent Quaternary or Paleogene-Neogene Cascade magmatism. Seismicity immediately following the 18 May 1980 eruption terminates near the top of the inferred middle-lower crustal cumulates and directly adjacent to the inferred middle-lower crustal magma reservoir. These spatial relationships suggest that the boundaries of these high-density cumulates play an important role in both vertical and lateral transport of magma through the crust.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 44
Serial Issue: 6
Title: Magma reservoirs from the upper crust to the Moho inferred from high-resolution Vp and Vs models beneath Mount St. Helens, Washington State, USA
Affiliation: Rice University, Department of Earth Science, Houston, TX, United States
Pages: 411-414
Published: 20160428
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 33
Accession Number: 2016-054097
Categories: Quaternary geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016134
Illustration Description: illus. incl. sketch map
N46°12'00" - N46°12'00", W122°10'60" - W122°10'60"
Secondary Affiliation: University of Texas at El Paso, USA, United StatesUniversity of New Mexico, USA, United StatesUniversity of Washington, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201626
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