Relatore: Prof. Richard Aster, New Mexico Institute of Mining and Technology, USA - 12.00, aula Caianiello del Dipartimento Scienze Fisiche, Complesso Universitario di Monte S.Angelo - Via Cinthia, Napoli.
Abstract
Mount Erebus is an approximately 1 My old polygenic stratovolcano lying within the Terror rift region (local crustal thickness of approximately 18 km) near the boundary between between cratonic east and extended
West Antarctica. The persistently active summit region hosts a long-lived convecting lava lake and erupts a highly chemically evolved tephriphonolite from a diverse set of vents. An incessantly convecting lava lake, eruptive, and lava flow activity are all confined to a multiple vent inner crater with a diameter of just several hundred m that can be readily observed with diverse instrumentation across a wide range of azimuths and at ranges as short as a few hundred m. A combination of high public interest in Antarctica science and volcanology has facilitated significant education and outreach activities, ranging from mass media productions to hosting undergraduate students and Earth science teachers on the volcano.
Due to an unusually stable upper conduit system geometry and self-reconstructing pre-eruptive conditions, Erebus lava lake eruptions are remarkably characteristic, producing highly repeatable signals across a bandwidth spanning many 10's of s to 10's of Hz. Broadband seismic observations of lava lake eruptions also show oscillatory and highly repeatable very-long-period (30-5 s) energy associated with eruptive gas and magmatic mass transport within the upper conduit system. VLP signals both precede and accompany eruptions, during which the upper portion of the lava lake system is removed, and furthermore persist for several minutes through the lava lake refill phase as the system is recharged from a deeper magma reservoir by magmatic flow. Moment tensor inversion indicates a VLP centroid region that is offset from the lava lake by several hundred m, and resides at least several hundred m below the lava lake surface.
Geodetic observations and a lack of internal seismicity show substantial stability in the upper volcano, despite variability in eruptive and other inner crater activity and eruptive frequency. This is consistent with an open conduit system that is unable to accrue significant internal volumetric stress changes, but has enough geometric complexity to change its ability to sequester gas in response to subtle changes. Subtle changes in VLP timing with respect to eruptions is also suggestive of upper conduit changes that may be caused by progressive assimilation/collapse of the inner crater system during the past decade. Recent geochemical observations suggest that the various inner crater vents may be complexly linked at significant depth, rather than coalescing in a simple manner to a single shallow magma chamber.
High-frequency coda signals are sufficiently similar between eruptions that they can be processed to investigate subtle structure and temporal changes in the near-summit/conduit structure, extracted via multicomponent coda crosscorrelation. These scattering images complement recent tomographic images from an active shot program, and illuminate a complex near-summit magmatic system that may simplify by 1 km depth below the summit. Doppler radar measurements of eruptions, combined with seismic, video, and infrasonic measurements, have facilitated the calculation of a complete energy budget for the key components of Erebus eruptions.