Join the Mazama Research Committee for a series of presentations from the past recipients of a Mazama research grant.


SPEAKER: Dr. Allan Lerner, Univ. of Oregon & USGS Cascades Volcano Observatory

TITLE: The Prevalence and Significance of Offset Magma Reservoirs at Arc Volcanoes

ABSTRACT: Magma reservoirs are commonly assumed to be located directly beneath their associated volcanic edifices. This “central reservoir” idea dominates volcano modeling and monitoring. However, the actual geometries linking volcanoes and underlying magma reservoirs are poorly known. We compile a database of geophysical studies at subduction zone volcanoes where magma reservoirs were detected through the modeling of seismic waves, electrical conductivity, and ground deformation. We then map volcano shapes and compare their center locations with associated magma reservoirs. We find that while the majority of volcanoes are indeed located directly above their source reservoirs, a substantial number of magma reservoirs are laterally offset multiple kilometers from their volcano's centers. Approximately 20% of magma reservoirs are located beyond the “footprints” of their volcanoes. Additionally, magma reservoirs are more offset at small volcanoes but are more centrally-aligned at large volcanoes. Our work suggests that the central reservoir view of volcanic systems should be revised to account for magma focusing as volcanoes grow. Recognizing the global prevalence of laterally offset magmatic systems may better help design volcano monitoring networks.

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