HR: 1330h
AN: V32B-1022    [PDF]
TI: Anatahan, Northern Mariana Islands: Reconniassance Geological Observations During and After the Volcanic Crisis of Spring 1990, and Monitoring Prior to the May 2003 Eruption
AU: * Rowland, S K
EM: scott@higp.hawaii.edu
AF: Hawaii Institute of Geophysics & Planetology University of Hawaii, 2525 Correa Rd., Honolulu, HI 96822 United States
AU: Lockwood, J P
EM: geohaz@aloha.net
AF: Geohazards Consultants, Inc., P.O. Box 479, Volcano, HI 96785 United States
AU: Trusdell, F A
EM: trusdell@usgs.gov
AF: U.S. Geological Survey Hawaiian Volcano Observatory, P.O. Box 51, HVNP, HI 96718 United States
AU: Maurice, S
AF: U.S. Geological Survey Hawaiian Volcano Observatory, P.O. Box 51, HVNP, HI 96718 United States
AU: Koyanagi, R
AF: U.S. Geological Survey Hawaiian Volcano Observatory, P.O. Box 51, HVNP, HI 96718 United States
AU: Moore, R B
EM: rbmoore@usgs.gov
AF: U.S. Geological Survey, 520 N Park Ave., Tucson, AZ 85719 United States
AU: Kojima, G
AF: U.S. Geological Survey Hawaiian Volcano Observatory, P.O. Box 51, HVNP, HI 96718 United States
AB: Anatahan island is an elongate strato volcano 9.5 km east-west by 3.5 km north-south. It is truncated by an elongate caldera (5 km east-west by 2.5 km north-south). The oldest rocks are andesitic and dacitic lavas and pyroclastics exposed on the outer flanks and caldera walls. These comprise the bulk of Anatahan, and include thick ($\sim$10 m) and thin (2-3 m) plagioclase-porphyritic flows, well-indurated tuffs, and scoria units. On the steep north and south flanks of the volcano these rocks are cut by numerous $\sim$east-west oriented lineations of undetermined origin. Indurated breccias and a few lavas unconformably overlie scarps low on the flanks. Intermediate-age eruptive units include caldera-filling lavas and pyroclastics, and on the outer flanks eruptive vents and lava flows that filled erosional gullies. The youngest pre-2003 volcanic unit is a series of hydromagmatic pyroclastic surge and fall deposits. This unit is found over almost the entire island and in many places original depositional surfaces are preserved, often in high-energy environments, indicating a young (but undetermined) age. In March of 1990 increased local seismicity, a regional earthquake and reported increased fumarolic activity in the caldera prompted evacuation of Anatahan village, located at the W end of the island. Field investigations by the authors in April of 1990 to collect samples of rocks and fumarolic waters and to set up a geophysical monitoring network were inconclusive with respect to determining whether the activity was anomalous. Water samples were collected from bubbling muddy hot springs within the $\sim$1 km-diameter by $\sim$200 m-deep crater in the Eastern part of the caldera. Temperatures of near boiling and pH values as low as 0.75 were recorded in the field. A brief return visit in June of 1990 revealed that most of the water within the Eastern crater was gone although minor bubbling pools were observed. In the decade of the 1990s a more extensive seismic monitoring system was installed on the Northern Mariana Islands. Unfortunately, it had fallen into disrepair by the time of the May 2003 eruption and no precursory geophysical (or geological) data were available to indicate pre-eruption unrest.
DE: 8404 Ash deposits
DE: 8419 Eruption monitoring (7280)
DE: 8424 Hydrothermal systems (8135)
DE: 9355 Pacific Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting