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Evaluating the Mendocino Crustal Conveyor Hypothesis An analysis of river terraces and channel profiles along the South Fork Eel River, Northern California.

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Presentation on theme: "Evaluating the Mendocino Crustal Conveyor Hypothesis An analysis of river terraces and channel profiles along the South Fork Eel River, Northern California."— Presentation transcript:

1 Evaluating the Mendocino Crustal Conveyor Hypothesis An analysis of river terraces and channel profiles along the South Fork Eel River, Northern California Benjamin Crosby Idaho State University Jane Willenbring Staiger Univ. Minnesota, NCED now at Leibniz Universität Hannover

2 Field Location and Tectonic Setting South Fork of The Eel River

3 S N (Furlong and Schwartz, 2004) The Mendocino Crustal Conveyor Crustal thickening at North End due to influx of upwelling material cooling against crust. Slab window exposes crust to asthenospheric upwelling. Everything migrates northward

4 (Furlong et al., 2003) Crustal Thickening Mantle Flow & Buoyancy

5 South Fork of The Eel River Expectation : Double-humped wave of rock uplift in wake of migrating Mendocino Triple Junction (Lock et al., 2006)

6 USGS 10 meter DEM Confluence with Mainstem Eel River Hypothesis Modern channel profiles and strath terraces from the Eel River reflect the northward propagating wave of thermal uplift

7 Terrace Mapping Procedure Identify “flat” areas adjacent to the channel. Create polygon shapefile of flat areas. Identify average elevation of each terrace Find the distance upstream of each polygon. Create terrace profiles

8 N Terrace Location Map n = 264 (Note rotation from north axis) Outlet to Mainstem Eel. 20 kilometers

9 Channel Profile From Junction with Mainstem Eel River To headwaters of the South Fork of the Eel River -using 10m USGS DEM-

10 Channel Profile From Junction with Mainstem Eel River To headwaters of the South Fork of the Eel River -using 10m USGS DEM-

11 Channel Profile From Junction with Mainstem Eel River To headwaters of the South Fork of the Eel River -using 10m USGS DEM-

12 Channel Profile From Junction with Mainstem Eel River To headwaters of the South Fork of the Eel River -using 10m USGS DEM-

13 Channel Profile From Junction with Mainstem Eel River To headwaters of the South Fork of the Eel River -using 10m USGS DEM-

14 Channel steepness Index

15 Channel steepness

16

17 N Detrital Cosmogenic Erosion Rates -modern samples collected from the mainstem -Erosion rates increase systematically downstream ( mm/yr) -Progressive dilution of low rate samples from headwaters? -Spatial gradient in uplift rate or transient response? 20 kilometers

18 Conclusions Division of basin into relict and adjusting regions Amount of incision decreases to the North Northward propagating welt of uplift produces both a downstream propagating knickpoint that is followed by an upstream propagating one Erosion rates derived from mainstem detrital cosmogenic sampling suggest increasing erosion rates downstream. The systematic increase could be due to the mixing of two distinct populations or a systematic change in erosion rate downstream. Tributary analysis pending! Tributary knickpoints, coincident with the height of mainstem terraces, provide the greatest measure of basin response to a rolling wave of uplift

19 New data eros mm/yuncert. sample nameUTM EUTM N ANG05SFE ANG05SFE ANG07SFE ANG07SFE ANG07SFE ANG07SFE ANG07SFE ANG07SFE ANG07SFE


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