HR: 0800h
AN: H51E-0805    [Abstracts]
TI: Amphitheater-Headed Valleys: Unique or Non-Unique Origin? The Hawaiian Laboratory
AU: * Pederson, D T
EM: dpederson2@unl.edu
AF: University of Nebraska-Lincoln, Department of Geosciences, Lincoln, NE 68588-0340, United States
AU: Blay, C
EM: teok@aloha.net
AF: TEOK Investigations, PO BOX 549, Koloa, HI 96756, United States
AB: While the formation and migration of amphitheaters (knickpoints) in unconsolidated sediment is fairly well understood the same cannot be said for amphitheaters formed in a variety of bedrock types, climate settings, and even planetary location. The question remains, is there a single knickpoint forming process at work or do multiple landscape forming processes have a convergence tendency because of cybernetic feedback? A simple example would be a waterfall creating a micro-environment that enhances and focuses specific landscape forming processes like weathering, microbial action, and vegetation growth aiding in the continuation of the knickpoint form. It should be noted that weathering, microbial growth and vegetation growth would have cybernetic feedback among them. In fact it may be difficult to determine the controlling process, if any. If one considers that knickpoints likely intercept the regional groundwater flow system there is an additional focused source of water supply which further contributes to the micro-environment of the knickpoint. Groundwater discharge has significant cybernetic feedbacks with landscape forming processes. The nature and composition of the bedrock and climatic factors may determine rates of knickpoint migration but the resulting morphologic features in different settings would likely be similar with cybernetic feedback. It should be noted that cybernetic feedback can either be damping or amplifying. Amphitheater-headed valleys have developed in many locations on the Hawaiian Islands. The islands have formed in a time sequence as the supporting oceanic plate moves over a focused mantle source for the basalts. The amphitheaters of Hawaii occur in "fresh" and "older" basaltic rock depending on island location. Weathering processes have acted longer on some islands. Because of the topography and its affect on trade winds the main islands have focused rainfall, significant recharge, and active groundwater flow systems. While climate is uniform overall, the wet and dry sides of the islands coupled with topography represent multiple climatic zones. This affords the opportunity to use the Hawaiian Islands as a laboratory to study the cybernetic feedbacks among knickpoint forming processes. Feedback examples will be presented for several Hawaiian knickpoints.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1815 Erosion
DE: 1824 Geomorphology: general (1625)
DE: 1886 Weathering (0790, 1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting