Evaluating the Mendocino Crustal Conveyor Hypothesis

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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
Benjamin Crosby Idaho State University Jane
Willenbring Staiger Univ. Minnesota, NCED now
at Leibniz Universität Hannover
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Field Location and Tectonic Setting
South Fork of The Eel River
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• 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

(Furlong and Schwartz, 2004)
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Crustal Thickening
Mantle Flow Buoyancy
(Furlong et al., 2003)
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Expectation Double-humped wave of rock uplift
in wake of migrating Mendocino Triple Junction
South Fork of The Eel River
(Lock et al., 2006)
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Confluence with Mainstem Eel River
Hypothesis Modern channel profiles and
strath terraces from the Eel River reflect
the northward propagating wave of thermal uplift
USGS 10 meter DEM
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• 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

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Terrace Location Map n 264 (Note rotation from
north axis)
Outlet to Mainstem Eel.
N
20 kilometers
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Channel Profile From Junction with Mainstem Eel
River To headwaters of the South Fork of the Eel
River -using 10m USGS DEM-
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Channel Profile From Junction with Mainstem Eel
River To headwaters of the South Fork of the Eel
River -using 10m USGS DEM-
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Channel Profile From Junction with Mainstem Eel
River To headwaters of the South Fork of the Eel
River -using 10m USGS DEM-
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Channel Profile From Junction with Mainstem Eel
River To headwaters of the South Fork of the Eel
River -using 10m USGS DEM-
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Channel Profile From Junction with Mainstem Eel
River To headwaters of the South Fork of the Eel
River -using 10m USGS DEM-
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1900
Channel steepness Index
40
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Channel steepness
40
1900
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(No Transcript)
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Detrital Cosmogenic Erosion Rates -modern
samples collected from the mainstem -Erosion
rates increase systematically downstream (0.1-0.5
mm/yr) -Progressive dilution of low rate samples
from headwaters? -Spatial gradient in uplift
rate or transient response?
N
20 kilometers
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• 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

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eros mm/y uncert. sample name UTM E UTM
N 0.22 0.02 ANG05SFE11 444750 4398400 0.17 0.02
ANG05SFE12 445912 4400636 0.34 0.03 ANG07SFE06 43
2395 4423851 0.29 0.02 ANG07SFE07 437381 4414092
0.32 0.02 ANG07SFE09 441830 4408428 0.41 0.03 AN
G07SFE10 432664 4430280 0.49 0.05 ANG07SFE11 4309
97 4443875 0.48 0.03 ANG07SFE12 425220 4457103 0.
52 0.04 ANG07SFE13 421188 4467460
New data