Erosion rates & patterns
inferred from
cosmogenic 10Be in the
Susquehanna River Basin
Joanna M. Reuter
Thesis 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
Erosion rates
Cosmogenic 10Be in
fluvial sediment
Sediment yield
Landscape
characteristics
• Tectonics
• Climate
• Vegetation
• Topography
• Bedrock
geology
Geographic
information
systems
(GIS)
Cosmic ray bombardment
produces 10Be in quartz.
Cosmic Rays
O
Quartz
10Be
10Be
is a proxy for erosion rate.
Time scale:
104-105 years
0
Depth 1
(meters)
2
3
0%
50 %
Production Rate
100%
Virtual Tour
of the
Susquehanna
River Basin
EXPLANATION
Forested
Agricultural
Developed
Barren
EXPLANATION
Cities & towns
EXPLANATION
Coal fields
EXPLANATION
Major dams
Basin Selection
and
Sampling Approach
USGS Basins
EXPLANATION
Glaciated
Part glaciated
Non-glaciated
Advantage:
Sediment yield
Disadvantage:
Complex basins
GIS-selected
Basins
EXPLANATION
GIS-selected
basins
GIS-selected Basins
GIS-selected Basins:
Nested Basins
mean
slope:
3.4º
mean
slope:
8.0º
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
10BeNorm________________
Normalized 10Be (105 atoms g-1 quartz)
0.001
Himalayas
0.01
Bolivia
0.1
Great
Smoky
Mountains
Europe
Namibia
1
10
Australia
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al., 2003; Safran et al., in press; Vance et al., 2003; Duncan, unpublished data
100
0
1
2
3
4
Region
REG_ID_NUMBER
5
6
7
Results for USGS Basins
x x
if assumptions have been met
70
all
AP SS
VR SS
VR SH
PD SC
Appalachian Plateaus
Valley and Ridge
Piedmont
Series1
Series9
10Be
Be erosion rate
60
50
10
erosion 40
rate
(meters/ 30
million
years) 20
16 ± 10
14 ± 4
10
0
0.1
10
1000
Basin area (km2)
100000
Slope
70
60
R2 = 0.72
50
Erosion
rate
40
(meters/
million 30
years)
R2 = 0.51
20
R2 = 0.37
10
no correlation
0
0
5
10
15
Mean slope of basin (degrees)
20
25
10Be
Erosion of the Appalachians
60
60
Susquehanna
Great Smoky Mountains
50
50
R2 = 0.54
Erosion 40
40
rate
(meters/
30
million 30
years)
20
20
10
10
00
0
5
10
15
20
25
30
Mean slope of basin (degrees)
Smokies data from Matmon et al., 2003
Bedrock Samples
Bedrock samples
from Namibia:
4.9 m/My
4.0
4.0
2.5 m/My
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
Sediment
Yield
• Export of sediment
from the basin
• Period of record, 2
to 29 years
• Suspended load
only; does not
include dissolved
load or bedload
For comparison, present both as erosion rates (m/My)
Source of sediment yield data:
Gellis et al. (2005), Williams and Reed (1972), and unpublished data from A. Gellis
1000
10Be
Appalachian Plateaus
100
Valley and Ridge
Erosion
rate
(m/My)
Piedmont
10
1000
Sediment yield
1
0
20
40
60
Cleared land
(% of basin area)
80
100
100
2
R = 0.32
Erosion
rate
10
(m/My)
1
0
20
40
60
80
Cleared land (% of basin area)
100
Testing
Geomorphic Models
of Topographic
Change
• Davis’s Geographical Cycle
• Hack’s Dynamic Equilibrium
• Statistical Steady State
• Perturbations
Geographical Cycle (Davis)
“Youth”
“Maturity”
“Old Age”
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
Dynamic Equilibrium (Hack)
x
Image source:
http://epswww.unm.edu/facstaff/gmeyer/eps481/481tectclimateveg_files/frame.htm#slide0032.htm
Dynamic Equilibrium (Hack)
slope
Image source:
Hack (1960)
slope
erosion rate
erosion rate
“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.”
lithologic resistance
lithologic resistance
Dynamic Equilibrium (Hack)
Statistical Steady State
x
Statistical Steady State
Less stable
More stable
Geographical Cycle
Peneplain
x
Mountains
Perturbation
Dynamic Equilibrium
Uniformly eroding
topography
Statistical Steady State
Changing topography,
constant relief
15
10
5
0
0
10
20
Mean slope of basin (degrees)
Mean slope of basin (degrees)
20
Be erosion rate (m/My)
25
35
10
Be erosion rate (m/My)
10
30
Series1
VR sandstone
VR shale
Linear (Series1)
lithologic resistance
lithologic resistance
slope
35
slope
erosion rate
erosion rate
Hack’s Equilibrium?
30
25
20
15
10
5
0
3.50
VR
VR
2.50
shale
sandstone1.50
Basin lithology
25
20
15
10
5
0
1
shale
sandstone
Basin lithology
Less stable
More stable
Geographical Cycle
Peneplain
Mountains
Perturbation
x
x
Dynamic Equilibrium
Uniformly eroding
topography
Statistical Steady State
Changing topography,
constant relief
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
Mechanism for
reduction
of relief:
Slope retreat
9 m/My
13 m/My
Less stable
More stable
Geographical Cycle
Peneplain
Mountains
Perturbation
x
x
Dynamic Equilibrium
Uniformly eroding
topography
Statistical Steady State
Changing topography,
constant relief
?
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:
60
10Be
erosion
rate
(m/My)
R2 = 0.72
average: 22
50
40
30
20
10
0
60
0
erosion
rate
(m/My)
10
15
20
25
average: 13
50
10Be
5
R2 = 0.37
40
30
20
10
0
Gradient in erosion
rates across basin
would have to be
maintained by
differential rock uplift
for statistical steady
state to apply
60
0
erosion
rate
(m/My)
10
15
20
25
20
25
average: 9
50
10Be
5
40
30
20
R2 = 0
10
0
0
5
10
15
Slope (degrees)
Less stable
More stable
Geographical Cycle
Peneplain
Mountains
Perturbation
x
x
x
Dynamic Equilibrium
Uniformly eroding
topography
Statistical Steady State
Changing topography,
constant relief
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 baselevel fall.
60
10Be
erosion
rate
(m/My)
R2 = 0.72
average: 22
50
40
30
20
10
0
60
0
erosion
rate
(m/My)
10
15
20
25
average: 13
50
10Be
5
R2 = 0.37
40
30
20
10
0
60
0
erosion
rate
(m/My)
10
15
20
25
20
25
average: 9
50
10Be
5
40
30
20
R2 = 0
10
0
0
5
10
15
Slope (degrees)
Global Compilation of
10Be Data from
Fluvial Sediment:
A Brief Overview
Regions with 10Be erosion rate data from sediment
Published 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
per million years)
erosion rate (meters
eros_rep________________
10Be
Vegetation
10000
1000
100
Susquehanna
10
1
0
20
40
60
80
TRCVMEAN
Mean tree cover
in basin (percent)
100
erosion rate (meters per million years)
10Be
Vegetation
n = 454
Mean tree cover in basin (percent)
erosion rate (meters per million years)
10Be
Climate
n = 454
Mean annual precipitation in basin (millimeters)
erosion rate (meters per million years)
10Be
Climate
seasonal
uniform
n = 454
R2 = 0.37
p < 0.001
Precipitation of 3 driest months/total precipitation
erosion rate (meters per million years)
10Be
Topography
n = 454
R2 = 0.39
p < 0.001
Mean slope of basin (degrees)
erosion rate (meters per million years)
10Be
Topography
n = 454
R2 = 0.44
p < 0.001
Mean basin elevation (meters)
erosion rate (meters per million years)
10Be
Tectonics
n = 454
R2 = 0.50
p < 0.001
Peak ground acceleration (m/s2)
with 10% probability of exceedance in 50 years
• Tectonics
Conclusions
– 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
Acknowledgments
•
•
•
•
•
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
For example:
Erosion rates
Mean denudation rate d (m/1,000 years)
– Sediment yield
Landscape
characteristics
• Topography
– Relief
Mean relief h (m)
from Ahnert, 1970
For example:
Erosion rates
Landscape
– 10Be in fluvial sediment characteristics
• Topography
– Relief
from Vance et al., 2003
Results for
non-glaciated
USGS basins
are robust
within a factor
of 2
70
60
50
Erosion
40
rate
(m/My)
30
from
10Be
20
10
0
0.1
10
70
Basin area (km2)
180
1000
100000
260
60
50
Erosion 40
rate
(m/My) 30
from
20
sediment
yield 10
0
0
10
1000
2
Basin area (km )
100000
70
all
AP SS
VR SS
VR SH
PD SC
Appalachian Plateaus
Valley and Ridge
Piedmont
10Be
Be erosion rate
60
50
10
erosion 40
rate
(meters/ 30
million
years) 20
10
0
0.1
10
1000
2
Basin area (km )
100000
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
70
all
AP SS
VR SS
VR SH
PD SC
Appalachian Plateaus
Valley and Ridge
Piedmont
10Be
Be erosion rate
60
50
10
erosion 40
rate
(meters/ 30
million
years)
20
10
0
0.1
10
1000
Basin area (km2)
100000
Summary
Landscape
characteristic
Metric
Relates to
10Be erosion rate?
Lithology
Rock Type (Susquehanna)
Erodibility metric (Rio Puerco)
No
Vegetation
Tree cover
No
Mean annual precipitation
No
Seasonality of precipitation
Yes
Climate
Yes
Slope
Topography Relief
Elevation
Yes
Yes
Yes
Tectonics
Yes
Seismic hazard assessment
10BeNorm________________
Normalized 10Be (105 atoms g-1 quartz)
0.001
Himalayas
0.01
Bolivia
0.1
Great
Smoky
Mountains
1
Europe
Namibia
10
Australia
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
100
0
1
2
3
4
Region
REG_ID_NUMBER
5
6
7
Summary:
10Be and Sediment Yield
• Sediment yield is out of equilibrium with
10Be in the Piedmont