Long-Term%20Rates

1
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
2
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, 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 (lt20km2),
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 (gt100km2),
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 (gt100km2), 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 (gt100km2),
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 (lt20km2),
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 (gt100km2),
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 (gt100km2), 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 (gt100km2),
sediment storage becomes significant, and the
nuclide signature of the stream channel sediments
in the trunk streamgreatest amount of sediment.
However, at larger scales (gt100km2), sediment
storage becomes significant, and the nuclide
signature of the stream channel sediments in the
trunk streamgreatest amount of sediment. However,
at larger scales (gt100km2), 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 (lt20km2),
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
(lt20km2), storage of sediment is generally small,
the nuclide concentration of bedrock surfaces,
hillslope colluvium, alluvial (lt20km2), 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 (lt20km2),
storage of sediment is generally small, the
nuclide concentration of bedrock surfaces,
hillslope colluvium, alluvial
3
Overall Hypothesis (Bierman Steig, 1996)
Measurements of 10Be and 26Al
Can be used to calculate erosion rates of
individual boulders and bedrock outcrops.
N2
Ni
N3
N1
Nc
NcAvg(N1Ni)
4
PRIMARY COSMIC RAYS high energy protons
(galactic) (modulated by Earths 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.
5
Nuclide Production
Spallation
n
2n
3n
Al
26 13
4p
p
16O (n, 4p3n) 10Be
28Si (n, p2n) 26Al
Nuclides may also be produced by
-negative muon capture -alpha particle
interaction -neutron activation
6

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 16).
• at known relationships to
• altitude, latitude, and sample depth.
• have long half-lives
• 1.5106 and 0.75106 yrs STABLE.

7
Depth
High P
Low P
Production Rate
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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.

9
Study Objectives
Using 10Be and 26Al...

• determine if nuclides measurements can
• identify sediment source areas.
• determine if nuclides measurements can
• identify important erosion processes.

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Field-Based Study Locations
Tel Aviv
Jerusalem
AZ
Yuma Wash (Sanoran Desert)
NM
Nahal Yael (Negev Desert)
Arroyo Chavez (Colorado Plateau)
B
A
11
Arroyo Chavez Basin
1.1 km2
High altitude Easily weathered rock
Semi-Arid (370 mm y-1)
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Geomorphic Compartments (sediment flow model)
exposed bedrock weathering
exposed bedrock weathering
mesa top regolith
hillslope colluvium
alluvial fan
bedrock outcrop
bedrock outcrop
arroyo
sub-colluvial bedrock
sub-colluvial bedrock
sub-colluvial weathering
sub-colluvial weathering
basin alluvium
export from basin
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Arroyo Chavez 10Be Summary
2.5
Erosion Rate 102 24 mMy-1
n3
n6
2.0
)
-1
n8
n5
atoms g
1.5
error bars 1 s
n4
5
1.0
Be (10
10
A
C
D
D
B
0.5
0.0
Bedrock
Hillslope
Alluvial
Basin
Channel
Outcrop
Colluvium
Fan
Alluvium
Sediment
Sediment
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Sediment Monitoring
(Gellis et al., 2000)
146 25 m My-1 Overlap with 10Be results _at_ 1
sigma
(102 24 mMy-1)
Labor and time intensive!
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Arroyo Chavez Nuclide-Sediment Deposition Models
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Arroyo Chavez 10Be vs Sample Depth
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Arroyo Chavez Model Deposition Rates
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Arroyo Chavez Results
Regional Rates
10Be/26Al Channel Sediments
10Be/26Al Deposition Model
Hillslope Monitoring (Gellis)
100 (Dethier) 165 (Judson Ritter) 83 (Holeman)
Erosion (m My-1)
102 24
165 52
146 25
Sediment Generation (g m-2 y-1)
275 65
446 140
394 68
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Nahal Yael Israel
Long-Term Supply vs Short-Term Yield
Low altitude Resistant rock Hyper-arid (lt20 mm
y-1)
0.6 km2
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Nahal Yael 10Be Summary
3
Erosion Rate 29 6 mMy-1
n8
error bars 1 s
)
n3
-1
2
n2
atoms g
n4
5
Be (10
1
A
B
C
C
10
0
Bedrock
Colluvium
Channel
Terraces
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Sediment Export (tons km-2 yr-1)
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
10Be 26 Al Sediment Budget
(Schick Lekach 1993)
78 16 113 to 138
22
Comparative Erosion Rates
160
error bars represent 1 s
140
120
Sediment Budget
100
Erosion Rates (m My-1)
80
10Be 26Al
60
40
20
0
Australia
Wind River
Nahal Yael
Puerto Rico
Nahal Yael
Chavez NM
Fort Sage Mts
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Yuma Wash Yuma Proving Grounds
24
8 km2
187 km2
Low altitude Resistant rock Arid (lt91 mm y-1)
25
Yuma Wash Southwest Sub-basin
26
Yuma Wash SW Sub-Basin 10Be Summary
0.35
Erosion Rate 27 3 mMy-1
0.30
n3
0.25
error bars 1 s
0.20
n15
n3
10Be Concentration (106 atoms per gram)
n11
n8
0.15
0.10
A
B
C
0.05
0.00
main channel
bedrock
hillslope
sub-basin channel
basin fill
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Yuma Wash
YPG-16 Al/Be5.3
1.9 mixing model
Southwest Sub-basin
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(No Transcript)
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Yuma Wash Results
10Be/26Al Main Stem Sediments
10Be/26Al Southwest Sub-basin
Average All Sub- Basins
Regional Rates
Erosion (m My-1)
38 4
27 3
30 2
10 to 150 (Judson Ritter)
Sediment Generation (g m-2 yr-1)
101 10
73 8
81 5
30
Comparative Erosion Rates
160
error bars 1 s
140
120
100
Erosion Rates (m My-1)
80
60
40
20
0
Australia
Wind River
Puerto Rico
Nahal Yael
Chavez NM
Fort Sage Mts
Yuma Wash
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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
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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.

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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!)
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(No Transcript)
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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

36
Nahal Yael Summary

• Channel seds representative of basin-wide 10Be
  26Al
• Erosion rates similar to 30-yr monitoring
  resultsBUT
• Long-term generation lt short-term export
• Nuclides suggest important subtleties of basin
  dynamics

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Yuma Summary
Southwest sub-basin
Main stem
38
10Be vs 26Al All 3 Locations
slope 6.02 R2 0.92 n114
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Yuma Wash 10Be Depth Profiles
40
Arroyo Chavez
Nahal Yael
Yuma Wash
41
BEDROCK WEATHERING OUTCROP vs SUB-COLLUVIAL

error bars 1 standard error
3.0
2.0
10Be (105 atoms g-1)
1.0
0.0
CHAVEZ
YUMA
YAEL
42
Nahal Yael Sediment Grain-size vs 10Be
43
Arroyo Chavez Grain-size vs 10Be
44
Yuma Wash Grainsize vs 10Be
error bars represent laboratory analytical error
45
Yuma Wash Grainsize vs 10Be
46
Nahal Yael 10Be Summary
error bars laboratory analytical error
47
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.
48
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.
49
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 1HF
  1HNO3)
• 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)