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Long-Term Rates of Denudation and Sediment Generation Over Different Spatial Scales

Long-Term Rates of Denudation and Sediment Generation Over Different Spatial Scales Quantified Using In Situ Produced Cosmogenic 10 Be and 26 Al in Sediment and Rock. A Dissertation Presented by Erik Matthew Clapp to The Faculty of the Graduate College Of The University of Vermont.

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Long-Term Rates of Denudation and Sediment Generation Over Different Spatial Scales

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  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 (<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

  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 Nc=Avg(N1…Ni)

  4. 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.

  5. n 10 4 Be 28 14 Si 16 8 O Nuclide Production Spallation n 2n 3n 26 13 Al 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 1:6). • at “known” relationships to: • altitude, latitude, and sample depth. • have long half-lives: • 1.5*106 and 0.75*106 yrs “STABLE”.

  7. Depth High P Low P Production Rate

  8. 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.

  10. Field-Based Study Locations Tel Aviv Jerusalem AZ Yuma Wash (Sanoran Desert) NM Nahal Yael (Negev Desert) Arroyo Chavez (Colorado Plateau) A B

  11. New Mexico 107o06’52” ECAC-6 site ECAC-11(1-3) ECAC-16 ECAC-14 (1-3) ECAC-12 ECAC-1 6600 ECAC-20 (A-E) ECAC-19(A-G) ECAC-10 ECAC-4 6500 6400 ECAC-9 0 500 N meters contour interval = 20 ft bedrock sample 35o42’30” sediment sample Arroyo Chavez sub-basin boundary depth profile samples arroyo channel shaded area = mesa top Arroyo Chavez Basin 1.1 km2 High altitude Easily weathered rock Semi-Arid (370 mm y-1)

  12. 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

  13. P N= mL-1+l Arroyo Chavez 10Be Summary 2.5 Erosion Rate = 102 ± 24 mMy-1 n=3 n=6 2.0 ) -1 n=8 n=5 atoms g 1.5 error bars = 1 s n=4 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

  14. 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!

  15. Arroyo Chavez Nuclide-Sediment Deposition Models Instantaneous Deposition Model (all sediment deposited at once) Steady-State Deposition Model (sediment deposited steadily) 0 0 100 100 Px=Poe-(x / ) Depth Below Surface (cm) Depth Below Surface (cm) 200 200 300 300 400 400 1.0 1.2 1.4 1.0 1.2 1.4 A B 10Be (105 atoms g-1) 10Be (105 atoms g-1)

  16. Arroyo Chavez 10Be vs Sample Depth

  17. Arroyo Chavez Model Deposition Rates

  18. 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

  19. Nahal Yael Israel Long-Term Supply vs Short-Term Yield Low altitude Resistant rock Hyper-arid (<20 mm y-1) 0.6 km2

  20. P N= mL-1+l Nahal Yael 10Be Summary 3 Erosion Rate = 29 ± 6 mMy-1 n=8 error bars = 1 s ) n=3 -1 2 n=2 atoms g n=4 5 Be (10 1 A B C C 10 0 Bedrock Colluvium Channel Terraces

  21. Comparison 10Be &26Al vs 30-yr Sediment Budget Sediment Export: (tons km-2 yr-1) : 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

  23. Arizona Site Yuma 0 100 N km Yuma Wash Yuma Proving Grounds

  24. 8 km2 187 km2 Low altitude Resistant rock Arid (<91 mm y-1)

  25. Yuma Wash Southwest Sub-basin

  26. Yuma Wash SW Sub-Basin 10Be Summary P N= mL-1+l 0.35 Erosion Rate = 27 ± 3 mMy-1 0.30 n=3 0.25 error bars = 1 s 0.20 n=15 n=3 10BeConcentration (106 atoms per gram) n=11 n=8 0.15 0.10 A B C 0.05 0.00 main channel bedrock hillslope sub-basin channel basin fill

  27. Yuma Wash YPG-16 Al/Be=5.3 1.9 mixing model Southwest Sub-basin

  28. Yuma Wash Mixing Model Results 2.5 50 10 Be concentration (YPG-21) 2 ) (r = 0.98) % Alluvium -1 2.0 40 2 (r = 0.96) (YPG-19) atoms g 1.5 30 (YPG-5) (YPG-17) % Alluvium Contribution 5 1.0 (YPG-2) 20 Be (10 0.5 10 10 0.0 0 6 5 4 3 2 1 0 Distance Upstream (kilometers)

  29. 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

  31. 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

  32. 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.

  33. 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!)

  34. 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

  35. 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

  36. Channel sediments representative of basin • Erosion rates calculated from channel sediments • Exposed rock weathering < sub colluvial weathering • Basin alluvium = Alluvial fans Rapid deposition • 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 Yuma Summary Southwest sub-basin Main stem

  37. 10Be vs 26Al All 3 Locations slope = 6.02 R2 = 0.92 n=114

  38. Yuma Wash 10Be Depth Profiles

  39. Arroyo Chavez Nahal Yael Yuma Wash

  40. BEDROCK WEATHERING OUTCROP vs SUB-COLLUVIAL error bars = 1 standard error 3.0 2.0 10Be (105 atoms g-1) 1.0 0.0 YAEL YUMA CHAVEZ

  41. Nahal Yael Sediment Grain-size vs 10Be

  42. Arroyo Chavez Grain-size vs 10Be

  43. Yuma Wash Grainsize vs 10Be error bars represent laboratory analytical error

  44. Yuma Wash Grainsize vs 10Be

  45. Nahal Yael 10Be Summary error bars = laboratory analytical error

  46. 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.

  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. 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)

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