Ground deformation associated with the precursory unrest and early phases of the January 2006 eruption of Augustine Volcano, Alaska

Abstract

On January 11, 2006 Augustine Volcano erupted after nearly 20 years of quiescence. Global Positioning System (GPS) instrumentation at Augustine, consisting of six continuously recording, telemetered receivers, measured clear precursory deformation consistent with a source of inflation or pressurization beneath the volcano's summit at a depth of around sea level. Deformation began in early summer 2005, and was preceded by a subtle, but distinct, increase in seismicity, which began in May 2005. After remaining more or less constant, deformation rates accelerated on at least three stations beginning in late November 2005. After this date, GPS data suggest the upward propagation of a small dike into the edifice, which, based on the style of deformation and high levels of gas emission, appears to have ascended to shallow levels by mid‐December 2005, about four weeks before the eruption began.

Pyroclastic Flow Deposits and InSAR: Analysis of Long-Term Subsidence at Augustine Volcano, Alaska

“…An exception to this general behavior was a deformation episode that started immediately before and lasted through the initial phases of the 2006 eruption [36]. While this deformation was significant, it occurred at a time not covered by our SAR data and had almost entirely ceased at the time of our first SAR acquisition after the 2006 eruption.…”

“…Each of these eruptions were similar in nature and composition, beginning with an initial explosive phase (VEI~3), followed by a period of decreasing intensity, and finally, an effusive, dome building phase [34][35][36]. Although Augustine has had four eruptions in the past 50 years, this paper examines the two most recent eruptions in 1986 and 2006.…”

The Augustine magmatic system as revealed by seismic tomography and relocated earthquake hypocenters from 1994 through 2009

“…From late April through October 2005, the seismicity rate gradually increased, from 16 relocated earthquakes in April to 99 in October, and the rate continued to increase until a ∼14 h long seismic swarm on 11 January, ending at the onset of explosive activity [ Power and Lalla , 2010], when 672 earthquakes were located by AVO. GPS data indicate a period of inflation beginning in roughly July 2005 [ Cervelli et al , 2006; Mattia et al , 2008; Cervelli et al , 2010]. Previous work has noted increased clustering in this time period and grouped some of the pre‐eruptive seismicity into a number of earthquake families based on waveform similarity [ DeShon et al , 2010].…”

“…It is a dacitic stratovolcano that erupted most recently in 2006, following previous major eruptions in 1986, 1976, 1963–1964, 1935, and 1885. The January 2006 eruption was preceded by increased seismicity beginning in late April 2005 and surface deformation indicating inflation beginning in November 2005 [ Cervelli et al , 2006]. In early to mid‐December 2005, activity escalated with a series of phreatic explosions.…”

The reawakening of Alaska's Augustine volcano

“…Geodetic data suggest that magma began to ascend from sea level as many as 50 days prior to the eruption of juvenile material, likely coincident with the onset of phreatic explosions. Modeling suggests that this intru sion may have progressively slowed as it ascended the final kilometer to the surface [Cervelli et al, 2006]. Continued analysis of this eruption should enable a better defini tion of the physical processes responsible for the accumulation, ascent, and eruption of high-silica andesites and dacites during the explosive as well as effusive periods.…”