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

Burlington Inquirer Saturday 50 cents March 29, Be and 26 Al 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 ( 100km 2 ), 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 (>100km 2 ), 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 (>100km 2 ), sediment storage becomes significant, and the nuclide signature of the stream channel sediments in the trunk stream Scientist predicts time for world to crumble into the sea, using strange particles from outer space! Were methods learned from psychic alien baby? 10 Be and 26 Al 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 (<20km 2 ), 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 (<20km 2 ), storage of sediment is generally small, the nuclide concentration of bedrock surfaces, hillslope colluvium, alluvial (<20km 2 ), 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 (<20km 2 ), storage of sediment is generally small, the nuclide concentration of bedrock surfaces, hillslope colluvium, alluvial 10 Be and 26 Al 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 ( 100km 2 ), 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 (>100km 2 ), 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 (>100km 2 ), sediment storage becomes significant, and the nuclide signature of the stream channel sediments in the trunk streamgreatest amount of sediment. However, at larger scales (>100km 2 ), sediment storage becomes significant, and the nuclide signature of the stream channel sediments in the trunk streamgreatest amount of sediment. However, at larger scales (>100km 2 ), sediment storage becomes significant, and the

Overall Hypothesis (Bierman & Steig, 1996): Measurements of 10 Be and 26 Al: Can be used to calculate erosion rates of individual boulders and bedrock outcrops. N1N1N1N1 N2N2N2N2 N3N3N3N3 N c =Avg(N 1 …N i ) NcNcNcNc NiNiNiNi

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.

Spallation Nuclide Production O 16 8 Be p 3n n Al Si n p 16 O (n, 4p3n) 10 Be 28 Si (n, p2n) 26 Al Nuclides may also be produced by:-negative muon capture -alpha particle interaction -neutron activation 2n

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*10 6 and 0.75*10 6 yrs “STABLE”. 10 Be & 26 Al Produced in Quartz

High P Depth Production Rate Low P

Study Objectives Using 10 Be and 26 Al... determine basin-wide erosion rates: determine basin-wide erosion rates: from channel sediments. from channel sediments. 3 arid region basins. 3 arid region basins. in basins of different scales & different in basins of different scales & different lithologies. lithologies. compare results to rates from other techniques. compare results to rates from other techniques. determine  nuclide activities vs basin location. determine  nuclide activities vs basin location. test for mixing of sediments by drainage network. test for mixing of sediments by drainage network.

determine if nuclides measurements can determine if nuclides measurements can identify sediment source areas. identify sediment source areas. determine if nuclides measurements can determine if nuclides measurements can identify important erosion processes. Study Objectives Using 10 Be and 26 Al...

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

ECAC-6 ECAC-11(1-3) ECAC-16 ECAC-14 (1-3) ECAC-12 ECAC-20 (A-E) ECAC-19(A-G) ECAC-4 ECAC-1 ECAC-10 ECAC o 06’52” 35 o 42’30” meters N Arroyo Chavez sub-basin boundary arroyo channel shaded area = mesa top bedrock sample sediment sample depth profile samples contour interval = 20 ft New Mexico site 6600 Arroyo Chavez Basin 1.1 km 2 High altitude Easily weathered rock Semi-Arid (370 mm y -1 )

sub-colluvial bedrock bedrock outcrop hillslope colluvium arroyo alluvial fan basin alluvium sub-colluvial weathering exposed bedrock weathering export from basin mesa top regolith Geomorphic Compartments (sediment flow model)

Bedrock Outcrop Hillslope Colluvium Alluvial Fan Sediment Basin Alluvium Channel Sediment 10 Be (10 5 atoms g atoms g ) error bars = 1  Arroyo Chavez 10 Be Summary n=3 n=5 n=4 n=8 n=6 Erosion Rate = 102 ± 24 mMy -1 ACDD B N=P m  -1 + m  -1 +

146 ± 25 m My -1 Overlap with 10 Be 1 sigma (Gellis et al., 2000) Sediment Monitoring Labor and time intensive! (102 ± 24 mMy -1 )

Arroyo Chavez Nuclide-Sediment Deposition Models

Arroyo Chavez 10 Be vs Sample Depth

Arroyo Chavez Model Deposition Rates

Arroyo Chavez Results 10 Be/ 26 Al ChannelSediments DepositionModelHillslopeMonitoring(Gellis) RegionalRates Erosion (m My -1 ) 102 ± ± ± (Dethier)165 (Judson & Ritter) 83(Holeman) SedimentGeneration (g m -2 y -1 ) 275 ± ± ± 68

Nahal Yael Israel Long-Term Supply vs Short-Term Yield 0.6 km 2 Low altitude Resistant rock Hyper-arid (<20 mm y -1 )

BedrockColluviumChannelTerraces 10 Be (10 5 atoms g atoms g ) Nahal Yael 10 Be Summary n=8 n=3 n=4 n=2 error bars = 1  ABCC N=P m  -1 + m  -1 + Erosion Rate = 29 ± 6 mMy -1

Sediment Export: (tons km -2 yr -1 ) : Comparison 10 Be & 26 Al vs 30-yr Sediment Budget 10 Be & 26 Al Sediment Budget to to 51 Basin-wide Erosion: (m My -1 ) to Be & 26 Al Sediment Budget (Schick & Lekach 1993)

Australia Nahal Yael Puerto Rico Fort Sage Mts Chavez NM Comparative Erosion Rates Erosion Rates (m My -1 ) error bars represent 1  Wind River SedimentBudget 10 Be 26 Al

Yuma Arizona N km Site Yuma Wash Yuma Proving Grounds

187 km 2 8 km 2 Low altitude Resistant rock Arid (<91 mm y -1 )

Yuma Wash Southwest Sub-basin

Yuma Wash SW Sub-Basin 10 Be Summary bedrock hillslope basin fill sub-basinchannel mainchannel 10 Be Concentration (10 6 atoms per gram) error bars = 1  n=3 n=3 n=11 n=15 n=8 A B C Erosion Rate = 27 ± 3 mMy -1 N=P m  -1 + m  -1 +

YPG-16Al/Be=5.3 Yuma Wash Southwest Sub-basin 1.9mixingmodel

Distance Upstream (kilometers) 10 Be (10 5 atoms g ) % Alluvium Contribution % Alluvium (r 2 = 0.96) 10 Be concentration (r 2 = 0.98) (YPG-21) (YPG-19) (YPG-17) (YPG-5) (YPG-2) Yuma Wash Mixing Model Results

Yuma Wash Results 10 Be/ 26 Al Main Stem Sediments 10 Be/ 26 Al SouthwestSub-basinAverage All Sub- BasinsRegionalRates Erosion (m My -1 ) 38 ± 4 27 ± 3 30 ± 2 10 to 150 (Judson & Ritter) SedimentGeneration (g m -2 yr -1 ) 101 ± ± 8 81 ± 5

Australia Nahal Yael Yuma Wash Puerto Rico Fort Sage Mts Chavez NM Comparative Erosion Rates Erosion Rates (m My -1 ) error bars = 1  Wind River

Conclusions 3 basins yield results similar to other methods. 3 basins yield results similar to other methods. 3 basins yield reasonable relative results. 3 basins yield reasonable relative results. In small basins sediment storage appears to be less 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% In the larger, Yuma Wash drainage, as much as 40% of the sediment leaving the drainage is recycled basin alluvium. Continued

3 basins suggest bedrock beneath a cover of colluvium 3 basins suggest bedrock beneath a cover of colluvium weathers more quickly than exposed rock. 3 basins suggest nuclides can be used as tracers 3 basins suggest nuclides can be used as tracers to identify sediment source areas. Conclusions Method provides reasonable erosion rate estimates in Method provides reasonable erosion rate estimates in several weeks vs several years to decades. Measurement and interpretation of Cosmogenic Nuclides 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!)

ChavezSummary Channel 10 Be & 26 Al similar to other compartments Channel 10 Be & 26 Al similar to other compartments Arroyo appears to a be good sediment mixer Arroyo appears to a be good sediment mixer Rates determined from 10 Be & 26 Al similar to: Rates determined from 10 Be & 26 Al similar to: Long-term monitoring Long-term monitoring Deposition model Deposition model Regional estimates Regional estimates Nuclides suggest important subtleties of basin dynamics Nuclides suggest important subtleties of basin dynamics Enough sediment is generated to support Arroyo cycling Enough sediment is generated to support Arroyo cycling

Nahal Yael Summary Channel seds representative of basin-wide 10 Be & 26 Al Channel seds representative of basin-wide 10 Be & 26 Al Erosion rates similar to 30-yr monitoring results…BUT Erosion rates similar to 30-yr monitoring results…BUT Long-term generation < short-term export Long-term generation < short-term export Nuclides suggest important subtleties of basin dynamics Nuclides suggest important subtleties of basin dynamics

Yuma Summary   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 Southwest sub-basin Main stem

slope = 6.02 R 2 = 0.92 n= Be vs 26 Al All 3 Locations

Yuma Wash 10 Be Depth Profiles

Yuma Wash Nahal Yael Arroyo Chavez

BEDROCK WEATHERING OUTCROP vs SUB-COLLUVIAL CHAVEZYUMAYAEL error bars = 1 standard error 10 Be (10 5 atoms g -1 )

Nahal Yael Sediment Grain-size vs 10 Be

Arroyo Chavez Grain-size vs 10 Be

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

Yuma Wash Grainsize vs 10 Be

Nahal Yael 10 Be Summary error bars = laboratoryanalyticalerror

Overall Hypothesis (Bierman & Steig, 1996): Since: Cosmogenic nuclides ( 10 Be and 26 Al) 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 ( 10 Be and 26 Al) 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 prewashed in HCL to remove carbonate sieved to yield optimum grainsize sieved to yield optimum grainsize heated and ultrasonically etched to isolate pure quartz heated and ultrasonically etched to isolate pure quartz (once in 6N HCL and repeatedly in 1%HF & 1%HNO 3 ) (once in 6N HCL and repeatedly in 1%HF & 1%HNO 3 ) dissolved in HF dissolved in HF 250  g of Be carrier added 250  g of Be carrier added Be and Al isolated using ion chromatographic techniques Be and Al isolated using ion chromatographic techniques 10 Be/ 9 Be and 26 Al/ 27 Al ratios determined by accelerator 10 Be/ 9 Be and 26 Al/ 27 Al ratios determined by accelerator mass spectrometry at LLNL 10 Be determined from ratio and known 9 Be (added as carrier) 10 Be determined from ratio and known 9 Be (added as carrier) 26 Al determined from ratio and known 27 Al (measured w/ICP) 26 Al determined from ratio and known 27 Al (measured w/ICP)