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Long-Term Rates
of Denudation and Sediment Generation
Over Different Spatial Scales
Quantified Using In Situ Produced
Cosmogenic 10Be and 26Al
in Sediment and Rock
A Dissertation Presented
by
Erik Matthew Clapp
to
The Faculty of the Graduate College
Of The University of Vermont
Burlington Inquirer
Saturday
50 cents
March 29, 2003
Scientist predicts time for
world to crumble into the
sea, using strange particles
from outer space!
10Be
and 26Al were measured in bedrock and sediment
from three arid region drainage basins of different scales
and geologic complexities, to determine long-term, timeintegrated rates of sediment generation and bedrockequivalent lowering (denudation), identify sediment source
areas and mechanisms of sediment delivery, and evaluate
the effects of basin scale on the interpretation of
cosmogenic nuclide concentrations measured in sediment.
By measuring nuclide activities in individual geomorphic
features throughout each drainage basin, the assumptions
necessary for the interpretation of basin-wide erosion rates
from stream channel sediments were tested.
The results of the three studies suggest that for small
basins (<20km2), storage of sediment is generally small,
the nuclide concentration of bedrock surfaces, hillslope
colluvium, alluvial fans and terraces, and stream channel
sediments are similar, and the drainage network appears to
satisfactorily integrate sediment
and associated
cosmogenic nuclides from throughout a drainage basin.
Thus for small drainage basins, measuring nuclide
activities in stream channel sediments leaving the basin via
the trunk stream appears to provide reasonable estimates of
nuclide activities from throughout the basin and thus
provide a reasonable estimate of basin-wide erosion rates
calculated from the nuclide activities in the sediment.
However, at larger scales (>100km2), sediment storage
becomes significant, and the nuclide signature of the
stream channel sediments in the trunk stream are most
representative of the geomorphic features currently
yielding the greatest amount of sediment. currently
yielding the greatest amount of sediment. However, at
larger scales (>100km2), sediment storage becomes
significant, and the nuclide signature of the stream channel
sediments in the trunk streamrepresentative of the
geomorphic features currently yielding the greatest amount
of sediment. currently yielding the greatest amount of
sediment. However, at larger scales (>100km2), sediment
storage becomes significant, and the nuclide signature of
the stream channel sediments in the trunk stream
10Be
and 26Al were measured in bedrock and sediment from
three arid region drainage basins of different scales and
geologic complexities, to determine long-term, time-integrated
rates of sediment generation and bedrock-equivalent lowering
(denudation), identify sediment source areas and mechanisms
of sediment delivery, and evaluate the effects of basin scale on
the interpretation of cosmogenic nuclide concentrations
measured in sediment. By measuring nuclide activities in
individual geomorphic features throughout each drainage
basin, the assumptions necessary for the interpretation of
basin-wide erosion rates from stream channel sediments were
tested.
The results of the three studies suggest that for small basins
(<20km2), storage of sediment is generally small, the nuclide
concentration of bedrock surfaces, hillslope colluvium, alluvial
fans and terraces, and stream channel sediments are similar,
and the drainage network appears to satisfactorily integrate
sediment and associated cosmogenic nuclides from throughout
a drainage basin. Thus for small drainage basins, measuring
nuclide activities in stream channel sediments leaving the basin
via the trunk stream appears to provide reasonable estimates of
nuclide activities from throughout the basin and thus provide a
reasonable estimate of basin-wide erosion rates calculated from
the nuclide activities in the sediment. However, at larger
scales (>100km2), sediment storage becomes significant, and
the nuclide signature of the stream channel sediments in the
trunk stream are most representative of the geomorphic
features currently yielding the greatest amount of sediment.
However, at larger scales (>100km2), sediment storage
becomes significant, and the nuclide signature of the stream
channel sediments in the trunk stream currently yielding the
greatest amount of sediment. However, at larger scales
(>100km2), sediment storage becomes significant, and the
nuclide signature of the stream channel sediments in the trunk
streamgreatest amount of sediment. However, at larger scales
(>100km2), sediment storage becomes significant, and the
nuclide signature of the stream channel sediments in the trunk
streamgreatest amount of sediment. However, at larger scales
(>100km2), sediment storage becomes significant, and the
Were methods
learned from
psychic alien baby?
10Be
and 26Al were measured in bedrock and sediment from
three arid region drainage basins of different scales and
geologic complexities, to determine long-term, time-integrated
rates of sediment generation and bedrock-equivalent lowering
(denudation), identify sediment source areas and mechanisms of
sediment delivery, and evaluate the effects of basin scale on the
interpretation of cosmogenic nuclide concentrations measured
in sediment. By measuring nuclide activities in individual
geomorphic features throughout each drainage basin, the
assumptions necessary for the interpretation of basin-wide
erosion rates from stream channel sediments were tested.
The results of the three studies suggest that for small basins
(<20km2), storage of sediment is generally small, the nuclide
concentration of bedrock surfaces, hillslope colluvium, alluvial
The results of the three studies suggest that for small basins
(<20km2), storage of sediment is generally small, the nuclide
concentration of bedrock surfaces, hillslope colluvium, alluvial
(<20km2), storage of sediment is generally small, the nuclide
concentration of bedrock surfaces, hillslope colluvium, alluvial
The results of the three studies suggest that for small basins
(<20km2), storage of sediment is generally small, the nuclide
concentration of bedrock surfaces, hillslope colluvium, alluvial
Overall Hypothesis
(Bierman & Steig, 1996):
Measurements of 10Be and 26Al:
Can be used to calculate erosion rates
of individual boulders and bedrock outcrops.
N2
N1
Ni
N3
Nc
Nc=Avg(N1…Ni)
PRIMARY COSMIC RAYS
high energy protons (galactic)
(modulated by Earth’s magnetic field)
Collide with atmospheric
gases producing cascade of:
SECONDARY COSMIC RAYS
high energy neutrons
(modulated by atmospheric depth)
Distinct isotopes produced by
interaction of cosmic rays
with target atoms on Earth.
Nuclide Production
Spallation
n
n
3n
16
8O
10
4 Be
2n
28
Si
14
4p
16O
(n, 4p3n) 10Be
26
Al
13
p
28Si
(n, p2n) 26Al
Nuclides may also be produced by: -negative muon capture
-alpha particle interaction
-neutron activation
10Be
& 26Al Produced in Quartz
•by interactions with cosmic rays.
•at a “known” rate over time:
5.2 and 31.2 atoms g-1 yr-1 (a ratio of 1:6).
•at “known” relationships to:
altitude, latitude, and sample depth.
•have long half-lives:
1.5*106 and 0.75*106 yrs “STABLE”.
Depth
High P
Low P
Production Rate
Study Objectives
Using 10Be and 26Al...
•determine basin-wide erosion rates:
•from channel sediments.
•3 arid region basins.
•in basins of different scales & different
lithologies.
•compare results to rates from other techniques.
•determine D nuclide activities vs basin location.
•test for mixing of sediments by drainage network.
Study Objectives
Using 10Be and 26Al...
•determine if nuclides measurements can
identify sediment source areas.
•determine if nuclides measurements can
identify important erosion processes.
Field-Based Study Locations
Tel Aviv
Jerusalem
AZ
Yuma Wash
NM
(Sanoran Desert)
Arroyo Chavez
(Colorado Plateau)
Nahal Yael
A
B
(Negev Desert)
Arroyo Chavez Basin
107o06’52”
New Mexico
ECAC-6
site
ECAC-11(1-3)
ECAC-16
ECAC-14 (1-3)
ECAC-12
ECAC-1
ECAC-20 (A-E)
ECAC-19(A-G)
ECAC-10
ECAC-4
ECAC-9
1.1 km2
0
500
meters
contour interval = 20 ft
35o42’30”
High altitude
N
Arroyo Chavez sub-basin boundary
arroyo channel
shaded area = mesa top
Easily weathered rock
bedrock sample
sediment sample
depth profile samples
Semi-Arid (370 mm y-1)
Geomorphic Compartments
(sediment flow model)
exposed
bedrock
weathering
bedrock outcrop
exposed
bedrock
weathering
alluvial fan
hillslope colluvium
mesa top regolith
bedrock outcrop
arroyo
sub-colluvial bedrock
sub-colluvial bedrock
sub-colluvial
weathering
sub-colluvial
weathering
basin alluvium
export from
basin
Arroyo Chavez
10Be Summary
P
N=
mL-1+l
2.5
2.0
n=6
n=5
1.5
n=8
error bars = 1 s
n=4
5
-1
Be (10 atoms g )
n=3
Erosion Rate = 102 ± 24 mMy-1
10
1.0
0.5
A
B
C
D
D
Bedrock
Outcrop
Hillslope
Colluvium
Alluvial
Fan
Sediment
Basin
Alluvium
Channel
Sediment
0.0
Sediment Monitoring
(Gellis et al., 2000)
146 ± 25 m My-1
Overlap with 10Be results @ 1 sigma
(102 ± 24 mMy-1)
Labor and time intensive!
Arroyo Chavez
Nuclide-Sediment Deposition Models
Instantaneous Deposition Model
(all sediment deposited at once)
Depth Below Surface (cm)
Depth Below Surface (cm)
Steady-State Deposition Model
(sediment deposited steadily)
0
100
200
300
400
1.0
10Be
1.2 1.4
(105 atoms g-1)
A
0
100
Px=Poe-(x /L )
200
300
400
1.0
10Be
1.2 1.4
(105 atoms g-1)
B
Arroyo Chavez
10Be vs Sample Depth
Arroyo Chavez
Model Deposition Rates
10
0.0
0.5
1.0
Be (105 atoms g-1)
1.5
2.0
2.5
3.0
Depth Below Surface (cm)
0
50
error bars = 1 s
100
150
200
250
300
350
400
450
500
Deposition
Rate
and
Bedrock
Erosion
500 400 280 200
Rate
(296) (237) (165) (119)
(mMy-1)
100
(59)
3.5
Arroyo Chavez
Results
10Be/26Al
10Be/26Al
Hillslope
Channel Deposition Monitoring
Sediments
Model
(Gellis)
Regional
Rates
100
Erosion
(m My-1)
(Dethier)
102 ± 24
165 ± 52
146 ± 25
165
(Judson & Ritter)
83
(Holeman)
Sediment
Generation 275 ± 65
(g m-2 y-1)
446 ± 140
394 ± 68
17
Nahal Yael
Israel
Tel Aviv
160
Nahal Yael
Israel
Sediment
dam
N
To Nahal Roded
Jerusalem
NY8
NY20
0
20
NY5
NY4
0
NY6
Granite
(lower)
100
km
Nahal
Yael
NY7
Schist
(middle)
0
20
0
24
Long-Term Supply
vs
Short-Term Yield
240
NY19
280
NY17
NY12
NY9
NY10
NY11
240
Schist
(middle)
NY18
Amphibolite
(upper)
280
NY16
Sample Type
Bedrock
Colluvium
Terrace
Channel
280
Low altitude
Resistant rock
Hyper-arid (<20 mm y-1)
NY15
0.6 km2
Contour interval
20 m
NY14
Lithologic
Contact
NY13
0
29o30’N
200
34 56’E
o
m
400
Nahal Yael
10Be Summary
P
N=
mL-1+l
3
n=8
Erosion Rate = 29 ± 6 mMy-1
n=3
2
n=2
n=4
1
10
Be (105 atoms g-1)
error bars = 1 s
A
B
C
C
Bedrock
Colluvium
Channel
Terraces
0
Comparison
10Be &26Al vs 30-yr Sediment Budget
Basin-wide Erosion: (m My-1)
10Be
& 26 Al
Sediment Budget
(Schick & Lekach 1993)
29 + 6
42 to 51
Sediment Export: (tons km-2 yr-1) :
10Be
& 26 Al
Sediment Budget
(Schick & Lekach 1993)
78 + 16
113 to 138
Erosion Rates (m My-1)
Comparative Erosion Rates
160
140
error bars represent 1 s
120
100
80
Sediment
Budget
60
10Be
40
26Al
20
0
Yuma Wash
Yuma Proving Grounds
Arizona
Site
Yuma
N
0
100
km
B. Southwest Sub-basin
1.32
(24)
1.18
(10)
1.24
(14)
1.66
(25)
1.65
(11)
1.67
(13)
3.21
(7)
1.28
(15)
2.73
(9)
0
1000
187 km2
meters
1.35
(12)
2.16
(28)
1.53
(22)
bedrock
channel sediment
2.19
(21)
basin fill
hillslope colluvium
1.66
(27)
ate
oM
Mt
ts
s
1.92
(20)
1.81
(19)
Arizona
0.84
(16)
1.16
(3)
Ch
oco
l
1.56
(18)
Trig
8
1.20
(26)
1.16
(23)
2.25
(8)
km2
A. Yuma Wash
1.54
(17)
Rhyolite
site
1.28
(4)
1.36
(5)
Granite
1.28
(15)
10Be
(105 atoms g-1)
Low altitude
Resistant rock
Arid (<91 mm y-1)
N
N33o 03’
o
W114 35’
1.10
(2)
1.92
(20)
Sample YPG-20
0
Colorad
o
Rive
3000
meters
Yuma Wash
Southwest Sub-basin
B. Southwest Sub-basin
1.32
(24)
2.25
(8)
A. Y
1.20
(26)
1.16
(23)
1.18
(10)
1.24
(14)
1.66
(25)
1.65
(11)
1.67
(13)
3.21
(7)
1.28
(15)
2.73
(9)
0
1000
meters
1.35
(12)
bedrock
channel sediment
2.1
(28
1.53
(22)
2.1
(21
basin fill
hillslope colluvium
1.92
Yuma Wash SW Sub-Basin
10Be Summary
N=
0.35
Erosion Rate = 27 ± 3 mMy-1
n=3
10Be
Concentration
(106 atoms per gram)
0.30
0.25
error bars = 1 s
0.20
n=3
0.15
n=15
n=11
n=8
0.10
0.05
0.00
A
B
C
P
mL-1+l
B. Southwest Sub-basin
1.32
(24)
A. Yuma Wash
1.20
(26)
Yuma Wash
1.16
(23)
2.25
(8)
1.18
(10)
1.24
(14)
1.66
(25)
1.65
(11)
1.67
(13)
3.21
(7)
1.28
(15)
2.73
(9)
0
1000
meters
bedrock
channel sediment
basin fill
2.16
(28)
YPG-16
Al/Be=5.3
hillslope colluvium
1.53
(22)
2.19
(21)
1.66
(27)
1.92
(20)
ate
oM
Mt
ts
s
1.35
(12)
1.81
(19)
Arizona
0.84
(16)
1.16
(3)
Ch
oco
l
Trig
1.56
(18)
1.54
(17)
Southwest
Sub-basin
site
Rhyolite
1.28
(4)
1.36
(5)
Granite
1.28
(15)
10Be
(105 atoms g-1)
N
N33o 03’
o
W114 35’
1.10
(2)
1.92
(20)
Sample YPG-20
0
Colorad
o
Rive
3000
meters
1.9
mixing
model
Yuma Wash
Mixing Model Results
2.5
50
(YPG-21)
Be concentration
2
10
Be (10 5 atoms g -1)
(r = 0.98)
% Alluvium
2.0
40
2
(r = 0.96)
(YPG-19)
1.5
(YPG-17)
30
(YPG-5)
(YPG-2)
1.0
20
0.5
10
0.0
0
6
5
4
3
2
Distance Upstream (kilometers)
1
0
% Alluvium Contribution
10
Yuma Wash
Results
10Be/26Al
10Be/26Al
38 ± 4
27 ± 3
Average
Main Stem Southwest All SubSediments Sub-basin Basins
Erosion
(m My-1)
Sediment
Generation 101 ± 10
(g m-2 yr-1)
30 ± 2
Regional
Rates
10 to 150
(Judson & Ritter)
73 ± 8
81 ± 5
Erosion Rates (m My-1)
Comparative Erosion Rates
160
140
120
100
80
60
40
20
0
error bars = 1 s
Conclusions
•3 basins yield results similar to other methods.
•3 basins yield reasonable relative results.
•In small basins sediment storage appears to be less
significant resulting in representative stream
samples.
•In the larger, Yuma Wash drainage, as much as 40%
of the sediment leaving the drainage is recycled
basin alluvium.
Continued
Conclusions
• 3 basins suggest bedrock beneath a cover of colluvium
weathers more quickly than exposed rock.
• 3 basins suggest nuclides can be used as tracers
to identify sediment source areas.
•Method provides reasonable erosion rate estimates in
several weeks vs several years to decades.
•Measurement and interpretation of Cosmogenic Nuclides
is an evolving technology…..COSMO CALIBRATE.
Thanks To...
Paul Bierman
Al Cassell
Deane Wang
Andrea Lini
Rolfe Stanley
Asher Schick
Mike Abbott
Kyle Nichols
Sara Gran
Christine Massey
Kim Marsella
Susan Nies
Milan Pavich (USGS)
Mark Caffee (LLNL)
Russell Harmon (US DOD ARO)
John Sevee & Peter Maher (SME)
Yehouda Enzel
Judith Lekach
Val Morrill
UVM Geology
UVM SNR
And Especially:
Lynda & Henry! … (Sophie too!)
Chavez
Summary
•Channel 10Be & 26Al similar to other compartments
•Arroyo appears to a be good sediment mixer
•Rates determined from10Be & 26Al similar to:
•Long-term monitoring
•Deposition model
•Regional estimates
•Nuclides suggest important subtleties of basin dynamics
•Enough sediment is generated to support Arroyo cycling
Nahal Yael
Summary
•Channel seds representative of basin-wide 10Be & 26Al
•Erosion rates similar to 30-yr monitoring results…BUT
•Long-term generation < short-term export
•Nuclides suggest important subtleties of basin dynamics
Yuma Summary
Southwest sub-basin
Channel sediments representative of basin
Erosion rates calculated from channel sediments
Exposed rock weathering < sub colluvial weathering
Basin alluvium = Alluvial fans
Rapid deposition
Main stem
Nuclide measurements can be used to identify
sediment source areas
Nearly 40% of exported seds from long-term storage
Average erosion rate from upland basins gives most
representative basin-wide erosion rate
Erosion rates are low…
Consistent with others in similar arid climates
10Be
vs 26Al
All 3 Locations
slope = 6.02
R2 = 0.92
n=114
20
15
10
5
26
Al (10 5 atoms gram-1)
25
0
0
1
2
10
5
3
-1
Be (10 atoms gram )
4
Yuma Wash
10Be Depth Profiles
10
5
-1
Be Concentration (10 atoms g )
1.0
0
1.2
1.4
YPG-10
1.6
1.0
1.2
1.4
YPG-26
1
(YPG-26.1)
2
Depth Below Surface (m)
(YPG-10.3)
(YPG-26.2)
3
(YPG-26.3)
4
(YPG-10.5)
5
6
(YPG-10.7)
7
8
(YPG-10.9)
9
error bars = 1s
1.6
Arroyo Chavez
Yuma Wash
Nahal Yael
error bars = 1 standard error
3.0
2.0
1.0
10Be
(105 atoms g-1)
BEDROCK WEATHERING
OUTCROP vs SUB-COLLUVIAL
0.0
YAEL
YUMA
CHAVEZ
Nahal Yael
Sediment Grain-size vs 10Be
10
m = 1.41
s = 0.31
m = 1.35
s = 0.20
2.0
m = 1.45
s = 0.33
1.5
0.0
250-1000
1000-4000
>4000
Sediment Grain Size (mm)
NY20c
NY18c
NY19c
NY16c
NY17c
NY12c
NY15c
NY8c
NY19b
NY20b
NY15b
NY16b
NY17b
NY18b
NY8b
NY12b
NY20a
NY17a
NY18a
NY19a
NY16a
0.5
NY12a
1.0
NY8a
Be (105 atoms g -1)
2.5
Arroyo Chavez
Grain-size vs 10Be
10
Be (105 atoms g -1)
2.5
error bars = laboratory analytical error
2.0
grain-size (mm)
125-1000
1000-2000
>2000
1.5
1.0
0.5
0.0
ECAC11
ECAC14
ECAC19A
Sample ID
ECAC19D
Yuma Wash
Grainsize vs 10Be
2
10
Be Concentration
5
-1
(10 atoms g )
1.8
1.6
m =1.24
s = 0.07
m =1.29
s = 0.16
m =1.29
s = 0.23
1.4
1.2
1
0.8
0.6
0.4
0.2
0
250-1000
1000-4000
Sediment Grain-Size (mm)
error bars represent laboratory analytical error
>4000
Sediment Grain-Size (mm)
>4000
1000-4000
error bars = 1s
500-1000
250-500
>12,700
4000-12,700
2000-4000
Be Concentration
(105 atoms g-1)
1.5
1000-2000
500-1000
250-500
10
Yuma Wash
Grainsize vs 10Be
2.5
YPG-19
2.0
YPG-2
1.0
0.5
0.0
Nahal Yael
10Be Summary
3
Elevation (m)
4
300
Lower
Basin
250
Bedrock
Colluvium
Terrace
200
Channel
r2 = 0.90
150
0
2
10
5
4
-1
Be (10 atoms g )
error bars =
laboratory
analytical
error
2
10
Be (106 atoms g -1)
5
1
0
Lower Basin
Middle Basin
Upper Basin
(Granite)
(Schist)
(Amphibolite)
Overall Hypothesis
(Bierman & Steig, 1996):
Since:
Cosmogenic nuclides (10Be and 26Al)
have been shown to approximate erosion
rates of boulders and bedrock outcrops.
And, since:
Sediment particles in a drainage are derived from, &
therefore should be chemically representative of ...
Then, if:
A drainage network reasonably mixes particles
from throughout a basin,
cosmogenic nuclides in stream sediments should
give an integrated, average erosion rate for the basin.
Overall Hypothesis
(Bierman & Steig, 1996):
Since:
Cosmogenic nuclides (10Be and 26Al)
have been shown to approximate erosion
rates of boulders and bedrock outcrops.
And, since:
Sediment particles in a drainage are derived from, &
therefore should be chemically representative of ...
Then, if:
A drainage network reasonably mixes particles
from throughout a basin,
cosmogenic nuclides in stream sediments should
give an integrated, average erosion rate for the basin.
Laboratory Methods
Samples:
•prewashed in HCL to remove carbonate
•sieved to yield optimum grainsize
•heated and ultrasonically etched to isolate pure quartz
(once in 6N HCL and repeatedly in 1%HF & 1%HNO3)
•dissolved in HF
•250 mg of Be carrier added
•Be and Al isolated using ion chromatographic techniques
•10Be/9Be and 26Al/27Al ratios determined by accelerator
mass spectrometry at LLNL
•10Be determined from ratio and known 9Be (added as carrier)
•26Al determined from ratio and known 27Al (measured w/ICP)