The contribution of G.E. Grant to this article was prepared as part of his official duties as a United States Federal Government employee.
Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA
Version of Record online: 28 JAN 2010
Copyright © 2010 John Wiley & Sons, Ltd.
Earth Surface Processes and Landforms
Volume 35, Issue 7, pages 803–816, 15 June 2010
How to Cite
Jefferson, A., Grant, G.E., Lewis, S.L. and Lancaster, S.T. (2010), Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA. Earth Surf. Process. Landforms, 35: 803–816. doi: 10.1002/esp.1976
- Issue online: 26 MAY 2010
- Version of Record online: 28 JAN 2010
- Manuscript Accepted: 17 NOV 2009
- Manuscript Revised: 11 NOV 2009
- Manuscript Received: 17 JUL 2009
- landscape evolution;
- Cascade Range
Young basalt terrains offer an exceptional opportunity to study landscape and hydrologic evolution through time, since the age of the landscape itself can be determined by dating lava flows. These constructional terrains are also highly permeable, allowing one to examine timescales and process of geomorphic evolution as they relate to the partitioning of hydrologic flowpaths between surface and sub-surface flow. The western slopes of the Cascade Range in Oregon, USA are composed of a thick sequence of lava flows ranging from Holocene to Oligocene in age, and the landscape receives abundant precipitation of between 2000 and 3500 mm per year. On Holocene and late Pleistocene lava landscapes, groundwater systems transmit most of the recharge to large springs (≥0·85 m3 s−1) with very steady hydrographs. In watersheds >1 million years old, springs are absent, and well-developed drainage networks fed by shallow subsurface stormflow produce flashy hydrographs. Drainage density slowly increases with time in this basalt landscape, requiring a million years to double in density. Progressive hillslope steepening and fluvial incision also occur on this timescale. Springs and groundwater-fed streams transport little sediment and hence are largely ineffective in incising river valleys, so fluvial landscape dissection appears to occur only after springs are replaced by shallow subsurface stormflow as the dominant streamflow generation mechanism. It is proposed that landscape evolution in basalt terrains is constrained by the time required for permeability to be reduced sufficiently for surface flow to replace groundwater flow. Copyright © 2010 John Wiley & Sons, Ltd.