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Hydrology and geomorphic evolution of basaltic landscapes, High Cascades, Oregon

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dc.contributor.advisor Grant, Gordon
dc.contributor.advisor Lancaster, Stephen
dc.creator Jefferson, Anne (Anne Jarvis)
dc.date.accessioned 2006-10-13T20:00:22Z
dc.date.available 2006-10-13T20:00:22Z
dc.date.copyright 2006-09-20 en
dc.date.issued 2006-10-13T20:00:22Z
dc.identifier.uri http://hdl.handle.net/1957/3140
dc.description Graduation date: 2007 en
dc.description.abstract The basaltic landscapes of the Oregon High Cascades form a natural laboratory for examining how geologic setting and history influence groundwater flowpaths, streamflow sensitivity to climate, and landscape evolution. In the High Cascades, highly permeable young basaltic lavas form extensive aquifers. These aquifers are the dominant sources of summer streamflow for the Willamette River and its tributary, the McKenzie River, whose watershed forms the study area. Groundwater is discharged at large volume, cold springs, and discharge, temperature, and isotopic measurements at seven springs were used to constrain groundwater patterns. Lava flow geometries have a significant influence on groundwater recharge areas and flowpaths, sometimes superseding topographic controls. Transit times to springs are ~3-14 years, and flowpaths are generally shallow and have limited contact with deeper geothermal systems, except at fault zones. Time-series analyses of historical discharge, precipitation, snow, and temperature records reveal that the distribution of permeable rocks and resultant groundwater systems strongly influence streamflow response to climatic forcing. The annual hydrograph is shaped by groundwater storage and release, but inter-annual streamflow variability is largely the result of climatic forcing. Over the past 60 years, warmer winters and earlier snowmelt have lengthened the summer recession period and decreased autumn minimum discharges in a groundwater-dominated watershed. A chronosequence of dated rock units, combined with field observations and measurements of slopes, contributing areas, and drainage densities, shows that the geologic history of a watershed controls the stage of drainage development. Groundwater flowpaths remain the dominant drainage mechanism for up to one million years, but as chemical weathering, glaciation, and other processes reduce the land surface permeability, channel networks grow up-slope of the springs. Within three million years, water is carried via a fully developed runoff-dominated stream network, groundwater discharge is insubstantial, and the landscape is shaped by fluvial and mass-wasting processes. The geology of a landscape is important for understanding hydrological processes at time scales ranging from a single season to several million years. en
dc.format.extent 6279678 bytes
dc.format.mimetype application/pdf
dc.language.iso en_US en
dc.subject hydrology en
dc.subject geomorphology en
dc.subject groundwater en
dc.subject springs en
dc.subject High Cascades en
dc.subject McKenzie River en
dc.subject.lcsh Hydrogeology -- Oregon -- McKenzie River Watershed en
dc.subject.lcsh Geomorphology -- Oregon -- McKenzie River Watershed en
dc.title Hydrology and geomorphic evolution of basaltic landscapes, High Cascades, Oregon en
dc.type Thesis en
dc.degree.name Doctor of Philosophy (Ph. D.) in Geology en
dc.degree.level Doctoral en
dc.degree.discipline Graduate School en
dc.degree.grantor Oregon State University en
dc.contributor.committeemember Haggerty, Roy
dc.contributor.committeemember McDonnell, Jeffrey
dc.contributor.committeemember Huber, Wayne

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