Open AccessGround surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008
Author(s) -
Lu Zhong,
Dzurisin Daniel,
Biggs Juliet,
Wicks Charles,
McNutt Steve
Publication year - 2010
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009jb006969
Subject(s) - geology , lateral eruption , effusive eruption , magma , magma chamber , volcano , caldera , petrology , dense rock equivalent , seismology , subsidence , vulcanian eruption , interferometric synthetic aperture radar , volcanology , explosive eruption , geomorphology , synthetic aperture radar , remote sensing , structural basin
Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, magma accumulated in a storage zone centered ∼3.5 km beneath the caldera floor at a rate that varied with time. A Mogi‐type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time‐sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, magma storage increased by 3.2–4.5 × 10 7 m 3 , which corresponds to 75–85% of the magma volume erupted in 1997. Thereafter, the average magma supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, magma storage had increased by 3.7–5.2 × 10 7 m 3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region. Eventually the effects of continuing magma supply and vesiculation of stored magma caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of magma during the eruptions depressurized the shallow storage zone, causing significant volcano‐wide subsidence and initiating a new intereruption deformation cycle.