Joanna M. Reuter - University of Vermont · •Tectonics –Susquehanna River Basin erosion rates...

Erosion rates & patterns

inferred from

cosmogenic 10Be in the

Susquehanna River Basin

Joanna M. ReuterThesis Defense

March 11, 2005

Paul Bierman, advisor

Motivation:• Applied questions

–Chesapeake Bay sedimentation

• Basic science questions

–Topographic change over time

–Relationships between erosion rate and landscape characteristics

Cosmogenic 10Be in fluvial sediment

Sediment yield

Erosion rates Landscape characteristics

• Tectonics

• Climate

• Vegetation

• Topography

• Bedrock geology

Geographic information

systems (GIS)

Cosmic ray bombardment

produces 10Be in quartz.

O 10Be

Quartz

Cosmic Rays

0

1

2

3

0 50 100% % %

Depth

(meters)

Production Rate

10Be is a proxy for erosion rate.

Time scale:

104-105 years

Virtual Tour

of the

Susquehanna

River Basin

EXPLANATION

Forested

Agricultural

Developed

Barren

EXPLANATION

Cities & towns

Coal fields

EXPLANATION

Major dams

EXPLANATION

Basin Selection

and

Sampling Approach

Advantage:

Sediment yield

Disadvantage:

Complex basins

EXPLANATION

Glaciated

Part glaciated

Non-glaciated

USGS Basins

GIS-selected

basins

EXPLANATION

GIS-selected

Basins

GIS-selected Basins

mean

slope:

3.4º mean

slope:

8.0º

GIS-selected Basins:

Nested Basins

Bedrock Samples

Summary of Groups of

Samples

• USGS Basins

–mostly large, complex

• GIS-selected Basins

–small, simple

• Bedrock Samples

10Be Concentrations

and

Inferred Erosion Rates

0.001

0.01

0.1

1

10

1000 1 2 3 4 5 6 7

REG_ID_NUMBER

10

BeN

orm

__

__

___

___

___

___

AK

all

RP

YU

SR

CA

ID

LL

SQ

SM

OC

PR

PN

VZ

BO

WU

LO

RG

NC

ME

NM

BH

HM

SL

NY

WP

TR

Expon. (all)Region

No

rmali

zed

10B

e (

10

5ato

ms g

-1q

uart

z)

Great

Smoky

Mountains

Namibia Australia

Europe

Bolivia

Himalayas

Data sources:

Matmon et al., 2003; Bierman and Caffee, 2001; Schaller et al., 2001; Morel et

al., 2003; Safran et al., in press; Vance et al., 2003; Duncan, unpublished data

Susquehanna

Results for USGS Basins

if assumptions have been met

xx

0

10

20

30

40

50

60

70

0.1 10 1000 100000

Basin area (km2)

10 B

e e

rosio

n r

ate

allAP SSVR SSVR SHPD SCAppalachian PlateausValley and RidgePiedmontSeries1Series9

10Be

erosion

rate

(meters/

million

years)

16 ± 1014 ± 4

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

Erosion

rate

(meters/

million

years)

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

Slope

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

R2 = 0.72

no correlation0

10

20

30

40

50

60

70

0 5 10 15 20 25

Mean slope of basin (degrees)

R2 = 0.37

R2 = 0.51

10Be Erosion of the Appalachians

0

10

20

30

40

50

60

0 5 10 15 20 25 30

Mean slope of basin (degrees)

Susquehanna

Great Smoky Mountains

Erosion

rate

(meters/

million

years)

R2 = 0.54

Smokies data from Matmon et al., 2003

60

50

40

30

20

10

0

Bedrock Samples

4.0

2.5 m/My

4.0

4.9 m/My

Bedrock samples

from Namibia:

Source:

Bierman and Caffee, 2001

Summary of Results

• Erosion rate correlates positively with

basin slope

• No discernible relationship exists between

lithology and erosion rate

• Results for non-glaciated USGS basins are

robust

• For basins impacted by glaciation, 10Be

results cannot be directly interpreted as

erosion rates

• Bedrock outcrops are eroding slowly

10Be Erosion Rates

Compared to

Sediment Yield

10Be vs.

• Sediment

generation

• Time scale: 104-105

years

• Representative of

full rock erosion

• Export of sediment

from the basin

• Period of record, 2

to 29 years

• Suspended load

only; does not

include dissolved

load or bedload

Source of sediment yield data:

Gellis et al. (2005), Williams and Reed (1972), and unpublished data from A. Gellis

Sediment

Yield

For comparison, present both as erosion rates (m/My)

R2 = 0.32

1

10

100

1000

0 20 40 60 80 100

Cleared land (% of basin area)

1

10

100

1000

0 20 40 60 80 100

Cleared land

(% of basin area)

Erosion

rate

(m/My)

Erosion

rate

(m/My)

10Be

Sediment yield

Appalachian Plateaus

Valley and Ridge

Piedmont

• Davis’s Geographical Cycle

• Hack’s Dynamic Equilibrium

• Statistical Steady State

• Perturbations

Testing

Geomorphic Models

of Topographic

Change

Geographical Cycle (Davis)

Image sources:

http://www.staff.amu.edu.pl/~sgp/gw/wmd/wmd.html

http://epswww.unm.edu/facstaff/gmeyer/eps481/481tectclimateveg_files/frame.htm#slide0032.htm

“Youth”

“Maturity”

“Old Age”

xImage source:

http://epswww.unm.edu/facstaff/gmeyer/eps481/481tectclimateveg_files/frame.htm#slide0032.htm

Dynamic Equilibrium (Hack)

“It is assumed that within a single erosional system all

elements of the topography are mutually adjusted so

that they are downwasting at the same rate.”

slope

ero

sio

n r

ate

lithologic resistance

slo

pe

lithologic resistance

Dynamic Equilibrium (Hack)

ero

sio

n r

ate

Image source:

Hack (1960)

Dynamic Equilibrium (Hack)

Statistical Steady State

x

Statistical Steady State

Geographical Cycle

Peneplain

Dynamic Equilibrium

Uniformly eroding

topography

Statistical Steady State

Changing topography,

constant relief

Mountains

Perturbation

More stableLess stable

x

Hack’s Equilibrium?

0

5

10

15

20

25

30

35

0 10 20Mean slope of basin (degrees)

10B

e e

rosio

n r

ate

(m

/My)

Series1

VR sandstone

VR shale

Linear (Series1)

slope

ero

sio

n r

ate

lithologic resistance

slo

pe

lithologic resistance

ero

sio

n r

ate

0

5

10

15

20

25

30

35

1.502.503.50

10B

e e

rosio

n r

ate

(m

/My)

VR

shale

VR

sandstone

0

5

10

15

20

25

1

Mean s

lope o

f basin

(degre

es)

shale sandstone

Basin lithologyBasin lithology

Geographical Cycle

Peneplain

Dynamic Equilibrium

Uniformly eroding

topography

Statistical Steady State

Changing topography,

constant relief

Mountains

Perturbation

More stableLess stable

x

x

Is Relief Changing?

• Slow erosion of

ridges:

– Bedrock samples

– High elevation, low

slope sandstone

basins

• Capacity for rapid

stream incision:

– Holtwood Gorge

7 m/My

9 m/My

13 m/My

Mechanism for

reduction

of relief:

Slope retreat

Geographical Cycle

Peneplain

Dynamic Equilibrium

Uniformly eroding

topography

Statistical Steady State

Changing topography,

constant relief

Mountains

Perturbation

More stableLess stable

x

x?

Perturbation?

Background:10Be data from the Sierra Nevada

Riebe et al. (2001)

No base level fall,

no correlation with slope:

Base level fall,

correlation with slope:

0

10

20

30

40

50

60

0 5 10 15 20 25

R2 = 0

R2 = 0.37

0

10

20

30

40

50

60

0 5 10 15 20 25

R2 = 0.72

0

10

20

30

40

50

60

0 5 10 15 20 25

10Be

erosion

rate

(m/My)

Slope (degrees)

10Be

erosion

rate

(m/My)

10Be

erosion

rate

(m/My)

average: 22

average: 13

average: 9Gradient in erosion rates across basin would have to be maintained by differential rock uplift

for statistical steady

state to apply

Geographical Cycle

Peneplain

Dynamic Equilibrium

Uniformly eroding

topography

Statistical Steady State

Changing topography,

constant relief

Mountains

Perturbation

More stableLess stable

x

x

x

Evidence for a Miocene Perturbation• Offshore sedimentary record: increased sediment

delivery (Poag and Sevon, 1989; Pazzaglia and

Brandon, 1996)

• Fission track: period of rapid exhumation

beginning in the Miocene (Blackmer et al., 2001)

• Detrital chert and detrital fission track data

suggest stream capture and drainage

reorganization in the central Appalachians (Naeser

et al., 2004)

Rates and patterns of erosion in the

Susquehanna River Basin may reflect ongoing

adjustment to Miocene stream capture and base-

level fall.

0

10

20

30

40

50

60

0 5 10 15 20 25

R2 = 0

R2 = 0.37

0

10

20

30

40

50

60

0 5 10 15 20 25

R2 = 0.72

0

10

20

30

40

50

60

0 5 10 15 20 25

10Be

erosion

rate

(m/My)

Slope (degrees)

10Be

erosion

rate

(m/My)

10Be

erosion

rate

(m/My)

average: 22

average: 13

average: 9

Global Compilation of10Be Data from

Fluvial Sediment:

A Brief Overview

Regions with 10Be erosion rate data from sedimentPublished data from:Bierman and Caffee, 2001; Brown et al., 1995; Brown et al., 1998; Clapp et al., 2000;

Clapp et al., 2002; Granger et al., 1996; Heimsath et al., 1997; Heimsath et al., 2001;

Hewawasam et al., 2003; Kirchner et al., 2001; Matmon et al., 2003; Morel et al., 2003;

Riebe et al., 2000; Riebe et al., 2003; Schaller et al., 2001; Vance et al., 2003

In press, in preparation, and unpublished data from:Bierman, Duncan, Johnsson, Nichols, Reuter, Safran

Topography

Tectonics

Climate

Vegetation

Topography

Tectonics

Climate

Vegetation

Lithology

1

10

100

1000

10000

0 20 40 60 80 100TRCVMEAN

ero

s_re

p________________

SQ

Mean tree cover in basin (percent)10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Vegetation

Susquehanna

Mean tree cover in basin (percent)10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Vegetation

n = 454

Mean annual precipitation in basin (millimeters)10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Climate

n = 454

Precipitation of 3 driest months/total precipitation10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Climate

uniformseasonal

n = 454

R2 = 0.37

p < 0.001

Mean slope of basin (degrees)10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Topography

n = 454

R2 = 0.39

p < 0.001

10B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

)

Mean basin elevation (meters)

Topography

n = 454

R2 = 0.44

p < 0.001

Peak ground acceleration (m/s2) with 10% probability of exceedance in 50 years1

0B

e e

ros

ion

ra

te (

me

ters

per

mil

lio

n y

ears

) Tectonics

n = 454

R2 = 0.50

p < 0.001

• Tectonics– Susquehanna River Basin erosion rates are relatively

low and similar to other passive margin and tectonically quiescent settings

• Topography– Slope matters

– Elevation and erosion rate are not correlated within the region

• Climate– Relatively uniform intra-annual distribution of

precipitation, and correspondingly low erosion rates

– Glaciation disrupts isotopic steady state and precludes simple interpretation of erosion rates from 10Be

Conclusions

• Vegetation and land use– 10Be results are robust to land use impacts

– Contemporary sediment yields for the Piedmont are high relative to background 10Be sediment generation rates

• Lithology– No clear impact of lithology on erosion rate in the

Susquehanna River Basin

• History– Rates and patterns of erosion may reflect ongoing

adjustment to Miocene stream capture and base-level fall

Conclusions

• Funding: NSF, USGS, UVM

• Paul Bierman

• Jen Larsen, Megan McGee, Bob Finkel

• Milan Pavich, Allen Gellis

• Donna Rizzo, Beverley Wemple, Cully Hession

• Luke Reusser, Matt Jungers, and all the other Geo grads, faculty, & staff

• Eric Butler

Acknowledgments

Erosion rates

– Sediment yield

Landscape characteristics

• Topography

– Relief

from Ahnert, 1970Mean relief h (m)

Mean

den

ud

ati

on

rate

d (

m/1

,000 y

ears

)

For example:

Erosion rates

– 10Be in fluvial sediment

Landscape characteristics

• Topography

– Relief

from Vance et al., 2003

For example:

Results for

non-glaciated

USGS basins

are robust

within a factor

of 2

0

10

20

30

40

50

60

70

0.1 10 1000 100000Basin area (km

2)

0

10

20

30

40

50

60

70

0 10 1000 100000

Basin area (km2)

180 260

Erosion

rate

(m/My)

from

sediment

yield

Erosion

rate

(m/My)

from10Be

0

10

20

30

40

50

60

70

0.1 10 1000 100000

Basin area (km2)

10 B

e e

rosio

n r

ate

all

AP SS

VR SS

VR SH

PD SC

Appalachian Plateaus

Valley and Ridge

Piedmont

10Be

erosion

rate

(meters/

million

years)

Factors of possible importance for

understanding sediment dynamics

and/or interpreting 10Be data

• Multiple lithologies, varying quartz content

• Glaciation

• Human impact

– Agriculture

– Logging

– Development

– Coal mining

– Dams

Results for USGS Basins

if assumptions have been met

0

10

20

30

40

50

60

70

0.1 10 1000 100000

Basin area (km2)

10 B

e e

rosio

n r

ate

all

AP SS

VR SS

VR SH

PD SC

Appalachian Plateaus

Valley and Ridge

Piedmont

10Be

erosion

rate

(meters/

million

years)

Summary

LithologyRock Type (Susquehanna)

Erodibility metric (Rio Puerco)

No

Yes

Vegetation Tree cover No

Climate Mean annual precipitation

Seasonality of precipitation

No

Yes

Topography

Slope

Relief

Elevation

Yes

Yes

Yes

Tectonics Seismic hazard assessment Yes

Relates to 10Be erosion rate?

Landscape

characteristic Metric

0.001

0.01

0.1

1

10

1000 1 2 3 4 5 6 7

REG_ID_NUMBER

10

BeN

orm

__

__

___

___

___

___

AK

all

RP

YU

SR

CA

ID

LL

SQ

SM

OC

PR

PN

VZ

BO

WU

LO

RG

NC

ME

NM

BH

HM

SL

NY

WP

TR

Expon. (all)Region

No

rmali

zed

10B

e (

10

5ato

ms g

-1q

uart

z)

Great

Smoky

Mountains

Namibia Australia

Europe

Bolivia

Himalayas

Susquehanna

Data sources:

Matmon et al., 2003; Bierman and Caffee, 2001; Schaller et al., 2001; Morel et

al., 2003; Safran et al., in press; Vance et al., 2003; Duncan, unpublished data

Summary: 10Be and Sediment Yield

• Sediment yield is out of equilibrium with 10Be in the Piedmont