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

Field Location andTectonic Setting

South Fork of

The Eel River

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

(Furlong et al., 2003)

Crustal Thickening

Mantle Flow& Buoyancy

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

N

Terrace Location Map n = 264(Note rotation from north axis)

Outlet to Mainstem Eel.

20 kilometers

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