HR: 13:35h
AN: V13C-01 INVITED     [Abstracts]
TI: The Ultimate Hydrologic Sponge: Hydrology and Dynamics of a Young Volcanic Arc in a Mediterranean Climate
AU: * Grant, G E
EM: gordon.grant@oregonstate.edu
AF: USDA Forest Service, Pacific Northwest Research Station, 3200 Jefferson Way, Corvallis, OR 97331 United States
AU: Tague, C
EM: ctague@mail.sdsu.edu
AF: Dept. of Geography, San Diego State University, 5500 Camanile Drive, San Diego, CA 92182 United States
AU: Jefferson, A
EM: jeffersa@geo.orst.edu
AF: Dept. of Geosciences, Oregon State University, Corvallis, OR 97331 United States
AB: Young basaltic landscapes in wet geographic settings can store prodigious quantities of water. Factors contributing to their behavior as vast hydrologic sponges include extremely high porosities and permeabilities due to large interstitial spaces, cracks, cavities, and tubes, along with the intrinsically high permeability of basalt. In addition, relatively flat hydraulic gradients result in long residence times and slow release of water. Volumes of water stored as groundwater in even relatively small areas can be on the same order as large continental lakes or ice sheets or total global volumes of streamflow. This groundwater hydrology dominates the flow, stream temperature, sediment transport, and landscape evolution of young volcanic landscapes. For example, our research has revealed that streamflow, sediment transport, and temperature regimes in the Cascade Mountains of Oregon vary dramatically between the geologically distinct Western and High Cascade regions. A key control on streamflow response between these two regions is the partitioning of water input between a fast-draining shallow subsurface flow network (Western Cascades) versus a slow-draining deeper groundwater system (High Cascades). These differences result from the extremely high contrasts in rock permeability and porosity and drainage density between landscapes dominated by old versus young volcanic rocks. Along with controlling streamflow regimes, such geologically-based differences in groundwater storage capacity can significantly alter streamflow response to climatic warming. In particular, we expect that for the young volcanic terrains comprising the High Cascade Range of Oregon and Northern California, ground water storage is of sufficient magnitude to buffer potential changes in snowpack volume, hence summer streamflow, due to changing climate. Older volcanic and granitic landscapes in the Oregon Western Cascades and California Sierras, in contrast, will be much more sensitive to diminished snowpacks and summer streamflow changes. Even within the Sierras, local variations in bedrock geology and associated differences in volume and seasonal fluxes of subsurface water will likely result in significant spatial variability in sensitivity to climate forcing. Taken together, these results imply that current models linking climate and streamflow changes need to account for differences in groundwater storage as a first-order control in volcanic terrain.
UR: http://www.fsl.orst.edu/wpg
DE: 1829 Groundwater hydrology
DE: 1833 Hydroclimatology
DE: 1860 Runoff and streamflow
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly