HR: 1330h
AN: V32B-1017    [PDF]
TI: The Submarine Flanks of Anatahan Volcano
AU: * Chadwick, W W
EM: william.w.chadwick@noaa.gov
AF: CIMRS, Oregon State University, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Embley, R W
EM:
AF: Pacific Marine Environmental Laboratory, NOAA, 2115 SE O.S.U. Dr., Newport,, OR 97365-5258 United States
AU: Johnson, P D
EM:
AF: SOEST, University of Hawaii, 1680 East-West Rd. POST 833, Honolulu, HI 96822 United States
AU: Merle, S G
EM:
AF: CIMRS, Oregon State University, 2115 SE O.S.U. Dr., Newport, OR 97365-5258 United States
AU: Ristau, S
EM:
AF: Pacific Marine Environmental Laboratory, NOAA, 2115 SE O.S.U. Dr., Newport,, OR 97365-5258 United States
AB: The submarine flanks of Anatahan volcano were surveyed with EM300 multibeam sonar and the MR1 sidescan sonar from the R/V Thomas G. Thompson in February 2003. This was part of a larger survey of over 50 submarine volcanoes within the Marianas volcanic arc between 13$\deg$10'N and 23$\deg$10'N (see Embley et al. and Baker et al. abstracts, this meeting). This work was part of a multi-year study of seafloor volcanism in diverse tectonic settings, funded by NOAA's Office of Ocean Exploration. (see: http://oceanexplorer.noaa.gov/explorations/03fire/). The island of Anatahan has a maximum elevation of 798 m, but its submarine flanks descend to depths of 2000-2600 m, so most of the volcano lies below sea level. The submarine part of the volcano is elongated in the east-west direction, like the island. Conspicuous in the bathymetry are numerous small parasitic cones and hummocky ridges on the southwest and east submarine flanks of the island that radiate outward (downslope) from the island. These features appear as areas of high reflectivity in the MR1 sidescan sonar and some have distinctly lobate outlines, suggesting that they are areas of relatively young lava flows. Some of these lava flows extend up to 15 km from the coastline of the island and to depths below 2000 m. The upslope sources of these lavas are often ambiguous, but we interpret that they were erupted underwater (as opposed to erupted on land and then flowing into the ocean) because they are associated with cones and ridges that may be vent areas. The other flanks of the island appear to be draped in volcaniclastic material that has been transported downslope from the shoreline, in some cases as distinct flows that radiate outward in braided channels that have slightly higher reflectivity than surrounding areas in the sidescan imagery. These fragmental flows also extend to depths below 2000 m, especially on the west and south flanks of the island. The most prominent feature in the bathymetry around Anatahan is a submarine volcano located about 10 km NE of the island, here named NE Anatahan volcano. The summit of NE Anatahan volcano reaches a depth of 459 m, and the depth of the saddle between NE Anatahan and the submarine flank of Anatahan is 1000 m. NE Anatahan volcano has a circular crater rim that is open to the west. The summit and northern flank of NE Anatahan volcano are cut by normal faults that trend north-south, possibly reflecting the orientation of the local tectonic stress field. Another submarine volcanic construction is located 5 miles north of the island and is a linear ridge aligned in the NNW-SSE direction. This ridge has a crest at a depth of 1000 m, and the most recent deposits from Anatahan and NE Anatahan volcanoes are deflected around it. There is no evidence of any landslide materials on the submarine flanks of Anatahan, except perhaps for a small area southeast of NE Anatahan volcano. Even though there appears to be evidence for relatively young submarine eruptions at Anatahan, there has been no reported evidence for submarine volcanic activity during the 2003 eruption.
DE: 3045 Seafloor morphology and bottom photography
DE: 8429 Lava rheology and morphology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting