HR: 1330h
AN: V32B-1009    [PDF]
TI: The First Historical Eruption of Anatahan Volcano, Mariana Islands
AU: * Fischer, T P
EM: fischer@unm.edu
AF: Dep. of Earth & Planet. Sci., University of New Mexico, Albuquerque, NM 87131-1116 United States
AU: Hilton, D R
EM: drhilton@ucsd.edu
AF: Geosci. Res. Division, Scripps Inst. Oceanography, La Jolla, CA 92093-0244 United States
AU: DeMoor, J
EM: maarten@unm.edu
AF: Dep. of Earth & Planet. Sci., University of New Mexico, Albuquerque, NM 87131-1116 United States
AU: Jaffe, L
EM: ljaffe@ucsd.edu
AF: Geosci. Res. Division, Scripps Inst. Oceanography, La Jolla, CA 92093-0244 United States
AU: Spilde, M N
EM: mspilde@unm.edu
AF: Dep. of Earth & Planet. Sci., University of New Mexico, Albuquerque, NM 87131-1116 United States
AU: Counce, D
EM: counce@lanl.gov
AF: Earth & Env. Sci., Los Alamos Nta. Lab., Los Alamos, NM 87545 United States
AU: Camacho, J T
EM: juantcamacho@hotmail.com
AF: CNMI EMO, P.O. Box 10007, Saipan, MP 96950 Northern Mariana Islands
AB: The first historical eruption of Anatahan volcano occurred on May 10, 2003. The MARGINS office responded by authorizing helicopter surveillance and ship deployment to visit the volcano. The helicopter flight on May 19 allowed visual observations and identification of the east crater as the source of the eruption. The top of the plume was estimated to be at 10,000 ft - significantly less than the 30,000 ft of the initial blast. No bombs were ejected out of the east crater at this time but were falling back into the crater. The bombs looked irregular in shape, massive and were estimated to be a few m in diameter. Bombs and tephra samples were collected from the eastern side of the island when blasts were occurring at a rate of approx. 1 per 5min. The ship visit followed on May 21 to the western side of the island for collection of samples and SO$_{2}$ flux measurements, along with maintenance of a previously deployed seismometer.\\ Volcanic samples collected on Anatahan consisted of bombs, ash and scoria from the present eruption and old lavas (age unknown). The ash section on the western shore was 25 cm thick and consisted of the following sequence (bottom to top): 0-5 cm: grey/tan layer fine ash coarsening upward to sand size, 5-8 cm: well sorted accretionary lapilli (2-3 mm), 8-20cm: inversely? graded dark ash with scoria and pumice clasts (1-2 cm), 20-25 cm: well sorted clast-supported scoria (max 2 cm) with some fine ash. The maximum total thickness measured at a site 6 km from the east crater was approximately 45 cm. The sequence is interpreted as 1) initial blast 2) interaction of magma with water (from pre-existing hydrothermal system) as evidenced by accretionary lapilli 3) magmatic phase of the eruption producing juvenile material. Electron microprobe analyses of the pumice and scoria show uniform compositions of ~ 60wt% SiO$_{2}$ in the glass; zoned plagioclase with average composition of 61% An, 37.7% Ab, 1.2% Or; pyroxenes (19.4% Wo, 53.4% En, 26.7% Fs) and Fe-Ti oxides. Sulfur and Cl contents are approx. 100 and 1500 ppm, respectively. Water content of the glass may be several wt% based on analytical totals.\\ Volatile emissions from the volcano were measured by traversing under the plume with a ship-based COSPEC. Using wind speed data from NOAA (10-15 knots on May 21), we estimate the daily SO$_{2}$ flux to be 3000 - 4500 tons. Our observations are consistent with the idea that the initial phreatic eruption evolved rapidly into a magmatic phase producing juvenile (and vesicular) material accompanied by a high SO$_{2}$ flux. Details on the eruption products, chemical analyses, seismic measurements, and current monitoring efforts can be found in accompanying posters.
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting