Seismic Observations of the Redoubt Magmatic System: 1989 through 2009
Abstract
Seismic activity at Redoubt Volcano, Alaska, has been closely monitored since 1989 by a network of five to nine SP seismometers within 22 km of the volcano’s summit. Major eruptions occurred in 1989-90 and 2009 and were characterized large volcanic explosions, episodes of lava dome growth, pyroclastic flows, and lahars. The 1989-90 eruption was characterized seismically by 1) weak precursory tremor and a short (23-hour) intense swarm of repetitive shallow long-period (LP) events centered 1.4 km below the crater floor, 2) shallow volcano-tectonic (VT) and hybrid earthquakes that separated early episodes of dome growth, 3) 13 additional swarms of LP events at shallow depths proceeded many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity, and 4) a persistent cluster of VT earthquakes at 6 to 9 km depth. Based on the evolution of seismicity during the 1989-90 eruption the Redoubt magmatic system is envisioned to consist of a magma source region at roughly 6 to 9 km depth and a shallow system of cracks extending 1 to 2 km below the crater floor. In contrast the 2009 eruption was preceded by a pronounced increase in deep-LP (DLP) events at lower crustal depths (25 to 35 km) that began in mid-December 2008, three months before the eruption onset and episodes of strong shallow volcanic tremor that started on January 23, 2009. The 2009 eruption consisted of at least17 major explosions between March 15 and April 4, again accompanied by shallow VT earthquakes, several episodes of shallow repetitive LP events and dome growth continued until mid May. Increased VT earthquakes at 4 to 9 km depth slowly began in early April possibly defining a magma source zone. Magmatic processes associated with the 2009 eruption seismically activated the same portions of the Redoubt magmatic system as the 1989-90 eruption, although the time scales and intensity vary considerably amoung the two eruptions. The occurrence of precursory DLP events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.V51F..02P
- Keywords:
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- 7280 SEISMOLOGY / Volcano seismology;
- 8419 VOLCANOLOGY / Volcano monitoring;
- 8428 VOLCANOLOGY / Explosive volcanism