HR: 1330h
AN: V22C-0603    [PDF]
TI: Obscure Subaerial Evidence for Landslides From West Maui Volcano and Haleakala, Island of Maui, Hawai`i
AU: * Sherrod, D R
EM: dsherrod@usgs.gov
AF: Hawaiian Volcano Observatory, U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718 United States
AU: Kauahikaua, J P
EM: jimk@usgs.gov
AF: Hawaiian Volcano Observatory, U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718 United States
AB: We propose two moderate-sized landslides from the Island of Maui. The submarine evidence for one is buried and for the other may be difficult to interpret in the narrow deep trough that contains it. On West Maui volcano, the herein-named Waikap\={u} landslide chopped off the volcano's east flank. Subaerial evidence is an 18-km-long, linear eastern mountain front defined by an eastward limit of lava-flow exposures owing to alluvial onlap. Microgravity profiles show no abrupt change across the sediment-lava flow contact; instead, the Bouguer-anomaly trend defines monotonically diminishing gravity values eastward away from the volcano's core. Therefore the alluvial onlap is interpreted as a depositional contact over east-dipping lava flows, not a headwall scarp at currently exposed altitudes. The Waikap\={u} landslide, comparable to or slightly larger than the Polol\={u} slump on the Island of Hawai`i, must have occurred during the shield-building stage prior to 1.4 Ma; its headwall subsequently was draped by tholeiitic lava late in the shield stage. Submarine evidence lies buried within the edifice of nearby Haleakal\={a} volcano, which became emergent through the surf zone soon after the landslide. On East Maui volcano, or Haleakal\={a}, the evidence for the herein-named P\={a}hihi landslide is found on the south flank, where the slopes are substantially steeper, 31-38%, than elsewhere on the volcano. The area of steepest slope coincides with the extent of a normal fault exposed in the south wall of the erosional summit valley, Haleakal\={a} Crater. At the 2300-m altitude, this south-side-down fault juxtaposes reversed-polarity 0.9-Ma transitional basalt (north) against postshield basanite (south) younger than 0.78 Ma. Postshield lava flows have subsequently draped the south flank, masking any truncation of older flows. Bouguer gravity contours along this flank of the volcano are similar in form to free-air data, owing to the overwhelming correlation of topography and mass. The P\={a}hihi landslide may have matched the Waikap\={u} in volume, depending on the extent of volcano sector involved, but direct comparison is difficult because their remnant subaerial geomorphic forms differ. P\={a}hihi debris presumably mantles the steep submarine south flank of Haleakal\={a} or lies in the 2-km-deep trough beneath the `Alenuih\={a}h\={a} Channel.
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting