Evaluating the Mendocino Crustal Conveyor Hypothesis An analysis of river terraces and channel...
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Transcript of Evaluating the Mendocino Crustal Conveyor Hypothesis An analysis of river terraces and channel...
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 atLeibniz Universität Hannover
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
South Fork of
The Eel River
Expectation:
Double-humped wave ofrock uplift in wake of migratingMendocino Triple Junction
(Lock et al., 2006)
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
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
Channel Profile From Junction with Mainstem Eel RiverTo headwaters of the South Fork of the Eel River
-using 10m USGS DEM-
Channel Profile From Junction with Mainstem Eel RiverTo headwaters of the South Fork of the Eel River
-using 10m USGS DEM-
Channel Profile From Junction with Mainstem Eel RiverTo headwaters of the South Fork of the Eel River
-using 10m USGS DEM-
Channel Profile From Junction with Mainstem Eel RiverTo headwaters of the South Fork of the Eel River
-using 10m USGS DEM-
Channel Profile From Junction with Mainstem Eel RiverTo headwaters of the South Fork of the Eel River
-using 10m USGS DEM-
Legend
ks_points
ks
42.800000 - 133.800000
133.800001 - 211.500000
211.500001 - 276.500000
276.500001 - 329.400000
329.400001 - 369.400000
369.400001 - 404.100000
404.100001 - 433.500000
433.500001 - 461.600000
461.600001 - 491.500000
491.500001 - 521.800000
521.800001 - 557.000000
557.000001 - 589.500000
589.500001 - 634.000000
634.000001 - 707.300000
707.300001 - 783.300000
783.300001 - 865.900000
865.900001 - 1000.300000
1000.300001 - 1206.400000
1206.400001 - 1460.100000
1460.100001 - 1859.400000
40
1900
Channel steepnessIndex
Le
ge
nd
ks
_p
oin
ts
ks
42
.8
00
00
0 - 1
33
.8
00
00
0
13
3.8
00
00
1 - 2
11
.5
00
00
0
211
.5
00
00
1 - 2
76
.5
00
00
0
27
6.5
00
00
1 - 3
29
.4
00
00
0
32
9.4
00
00
1 - 3
69
.4
00
00
0
36
9.4
00
00
1 - 4
04
.1
00
00
0
40
4.1
00
00
1 - 4
33
.5
00
00
0
43
3.5
00
00
1 - 4
61
.6
00
00
0
46
1.6
00
00
1 - 4
91
.5
00
00
0
49
1.5
00
00
1 - 5
21
.8
00
00
0
52
1.8
00
00
1 - 5
57
.0
00
00
0
55
7.0
00
00
1 - 5
89
.5
00
00
0
58
9.5
00
00
1 - 6
34
.0
00
00
0
63
4.0
00
00
1 - 7
07
.3
00
00
0
70
7.3
00
00
1 - 7
83
.3
00
00
0
78
3.3
00
00
1 - 8
65
.9
00
00
0
86
5.9
00
00
1 - 1
00
0.3
00
00
0
10
00
.3
00
00
1 - 1
20
6.4
00
00
0
12
06
.4
00
00
1 - 1
46
0.1
00
00
0
14
60
.1
00
00
1 - 1
85
9.4
00
00
0
40 1900Channel steepness
N
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?
20 kilometers
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
New data
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10
downstream ->
ero
sio
n r
ate
(m
m/y
)
eros mm/y uncert. sample name UTM E UTM N0.22 0.02 ANG05SFE11 444750 43984000.17 0.02 ANG05SFE12 445912 44006360.34 0.03 ANG07SFE06 432395 44238510.29 0.02 ANG07SFE07 437381 44140920.32 0.02 ANG07SFE09 441830 44084280.41 0.03 ANG07SFE10 432664 44302800.49 0.05 ANG07SFE11 430997 44438750.48 0.03 ANG07SFE12 425220 44571030.52 0.04 ANG07SFE13 421188 4467460