HR: 10:50h
AN: V52B-03    [Abstracts]
TI: Gravity Variations at a Dynamic Basaltic Caldera: Before and After the 2005 Eruption of Sierra Negra Volcano, Galapagos Islands
AU: Geist, D
EM: dgeist@uidaho.edu
AF: University of Idaho, Box 3022, Moscow, ID 83844,
AU: * Vigouroux, N
EM: nathalie.vigouroux@gmail.com
AF: Simon Fraser University, Earth Sciences, Burnaby, BC V5A1S6, Canada
AU: Williams-Jones, G
EM: glynwj@sfu.ca
AF: Simon Fraser University, Earth Sciences, Burnaby, BC V5A1S6, Canada
AU: Chadwick, W
EM: William.W.Chadwick@noaa.gov
AF: OSU/NOAA, 2115 SE OSU Drive, Newport, OR 97365, United States
AU: Johnson, D
EM: none
AF: University of Puget Sound, (deceased), Tacoma, WA 98416, United States
AB: Sierra Negra volcano, an active basaltic volcano in the western Galapagos, last erupted in October 2005 following a period of accelerated uplift of the central caldera floor that started in April 2003. Deformation data indicate that a shallow (~ 2 km) sill underlies the caldera floor, and an intrusion rate of 64 x 106 m3/y for the 6 months prior to eruption was calculated from a continuous GPS network installed in 2002. Micro-gravity measurements were conducted in 2005, 2006, and 2007 at three stations in the center of the caldera and one station on the outer flank of the volcano and referenced to a base station on the NE rim of the caldera. From June 2005 to June 2006, residual gravity measured in the caldera increased by 1500 microgals at the center of the caldera to 184 microgals halfway to the northern edge of the caldera. This increase in residual gravity (height corrected) was accompanied by an uplift rate of ~ 212 cm/y until February 2006 after which the uplift rate decreased to 73 cm/y in 2006 and 44 cm/y in 2007. Similarly, from June 2006 to June 2007 gravity increased less dramaticaly than in 2005-2006 with an average increase of 11 microgals at the center of the caldera and 132 microgals at the more northern part of the caldera. Interestingly, the center of maximum gravity change shifted from the center of the caldera to the northern part sometime between June 2006 and June 2007. Gravity measurements on the outer rim of the caldera showed a 300 and a 200 microgal decrease from June 2005 to June 2006 and June 2006 to June 2007, respectively accompanied by low rates of inflation (1.8 cm/y). The coupling of gravity and deformation change supports the hypothesis of significant mass increase in the central-northern part of the caldera.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 8419 Volcano monitoring (7280)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting