10Be Analysis of Amalgamated Talus Pebbles to Investigate Alpine Erosion, Garnet Canyon, Teton Range, Wyoming GEOSPHERE; V

Research Paper THEMED ISSUE: Cenozoic Tectonics, Magmatism, and Stratigraphy of the Snake River Plain–Yellowstone Region and Adjacent Areas

GEOSPHERE 10Be analysis of amalgamated talus pebbles to investigate alpine erosion, Garnet Canyon, Teton Range, Wyoming GEOSPHERE; v. 13, no. 1 Lisa M. Tranel and Meredith L. Strow Department of Geography-Geology, Illinois State University, Campus Box 4400, Normal, Illinois 61790-4400, USA doi:10.1130/GES01297.1

8 figures; 2 tables ABSTRACT ments (Dussauge et al., 2003; Strunden et al., 2015). Hillslope erosion via rockfall occurs rapidly after glacial retreat (Arsenault and Meigs, 2005; Meigs et al., CORRESPONDENCE: ltranel@ilstu.edu Glaciers and subsequent mass wasting events create impressive mountain 2006; Sanders and Ostermann, 2011) because glaciation deeply scours canyons landscapes; however, the ruggedness that defines these beautiful landscapes to create steep valley walls (Hallet et al., 1996; Alley et al., 2003; Brocklehurst 10 CITATION: Tranel, L.M., and Strow, M.L., 2017, Be also makes it challenging to monitor erosion in the field. The result is that spa and Whipple, 2004; Foster et al., 2008). Low gradients of overdeepened valley analysis of amalgamated talus pebbles to investigate alpine erosion, Garnet Canyon, Teton Range, Wyo tial patterns and rates of erosion in alpine landscapes are understudied. Field floors reduce the efficiency of fluvial excavation; therefore, rockfall sediments ming: Geosphere, v. 13, no. 1, p. 36–48, doi:10 .1130 locations are steep and remote and hillslope processes, including rockfalls, accumulate to form talus fans that subsequently influence stream systems /GES01297.1. avalanches, and landslides, are stochastic and difficult to measure directly. (MacGregor et al., 2000; Dühnforth et al., 2008). If we can define spatial patterns This study uses talus fan sediments to deepen our understanding of individ of hillslope erosion and quantify when talus sediments were deposited, we can Received 23 November 2015 ual fan deposition and catchment averaged erosion processes in the alpine use talus deposits to investigate climate variability, individual tectonic events, Revision received 9 August 2016 Accepted 11 October 2016 setting of Garnet Canyon in the Teton Range, Wyoming, USA. We measured and connections between rock properties and erosion rates. Published online 10 November 2016 cosmogenic 10Be concentrations from bedrock and talus deposits to compare To date, talus fan volumes and glacial maximum ages are used to quantify them to volumetric estimates of erosion rates, lichen growth, and surface hillslope erosion rates to understand the role of mass wasting in mountain weathering on talus surfaces. Amalgamated pebbles from the talus depos landscape evolution (Olyphant, 1983; Sass and Wollny, 2001; Moore et al., its contained lower 10Be concentrations than any bedrock surfaces or stream 2009; O’Farrell et al., 2009; Tranel et al., 2015). In these estimates, the total sediments. The young talus surface exposure ages are all younger than 11 ka, volume of material accumulated on a valley floor is assumed to be derived reflecting the importance of continued rockfall activity long after glacial re from adjacent valley walls (Olyphant, 1983; Moore et al., 2009). Volume esti- treat. Only one talus fan corresponded to known seismic events. Talus depos mates require projecting the wall surface below the fan deposit unless subsur- its contribute sediments to stream systems; 10Be concentrations were lower in face images or intensive laser acquired wall images are obtained (Sass and amalgamated talus pebbles than in amalgamated stream sands. Lichen cover, Wollny, 2001; Stock et al., 2011; Strunden et al., 2015). Additional uncertainty volumetric estimates of erosion rates, and 10Be concentrations showed similar associated with evaluating rockfall extent and rates is due to the lack of detail spatial trends reflecting the migration of active rockfalls to higher elevations in the timing between events. The timing and size of rockfall events are often and validating the applicability of 10Be concentrations to quantify talus surface only recorded if they are directly observed or cause damage to anthropogenic ages. Distinct 10Be concentrations on various surfaces within Garnet Canyon structures. Repeat aerial imagery, laser scanning, or lichenometric dating indicate that future work with amalgamated samples from talus deposits can are methods used to determine the timing of mass movements; however, contribute to investigations about landscape evolution in alpine landscapes. environmental conditions, access to equipment, or data images may limit widespread use (Jomelli, 2013). Cosmogenic radionuclide analyses on amalgamated gravels or sands are increasingly used to constrain fluvial catch- INTRODUCTION ment averaged erosion rates (Anderson et al., 1996; Bierman and Steig, 1996; Granger et al., 1996, 2001; Cockburn et al., 2000; Balco et al., 2008; Portenga Mass movements in mountain environments shape hillslope topography and Bierman, 2011). Amalgamated sediments or pebble samples allow a and influence sediment flux in glacial and fluvial systems (Burbank et al., 1996; single sample to represent complex surfaces or events (Muzikar, 2009). Fewer Hales and Roering, 2009; Straumann and Korup, 2009; Stock and Uhrhammer, studies have also used amalgamated samples to study the timing of alluvial 2010; Ward and Anderson, 2011). The stochastic nature of mass movements, fan deposition in arid environments and valley wall retreat in glacial valleys however, makes quantifying erosion rates in remote high-altitude regions dif- (Repka et al., 1997; Heimsath and McGlynn, 2008; Ward and Anderson, 2011; ficult and introduces uncertainties in measurement techniques (Heimsath and Ivy-Ochs et al., 2013). For permission to copy, contact Copyright McGlynn, 2008). Observed rockfalls typically range from a few small blocks In this work we used cosmogenic in situ 10Be concentrations to study talus Permissions, GSA, or [email protected]. (<1 m) to large volumes of millions of cubic meters in various mountain environ- accumulation, the influence of rockfalls on alpine landscapes, and the applica

GEOSPHERE | Volume 13 | Number 1 Tranel and Strow | 10Be analysis of amalgamated talus pebbles Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/13/1/36/1000744/36.pdf 36 by guest on 30 September 2021 Research Paper

bility of amalgamating pebbles to date talus surfaces. We assess ridge bedrock N 120°W 100°W 80°W

and talus surface 10Be concentrations and compare them to talus volume ero- 50° A sion rates (by Tranel et al., 2015), lichen cover, and weathering on pebble surfaces. Then, we consider how well various talus observations help us under stand the evolution of Garnet Canyon, an alpine catchment in the Teton Range, N after glacial retreat. We use 10Be concentrations to evaluate relative age differ- 40° ences between bedrock surfaces and sediment deposits, spatial patterns of erosion, and relationships between concentrations previously studied erosion N rates and geologic events in the Teton Range (Wyoming, USA). 30°

GEOLOGIC SETTING AND PREVIOUS WORK

The Teton Range is located in northwestern Wyoming, south of the Yellow- stone volcanic high (Fig. 1). The collection and observation sites for this study were located in and around Garnet Canyon (Fig. 2), an east-draining water- B Yellowstone Lake shed adjacent to the central highest peak, the Grand Teton (elevation 4198 m). The bedrock in Garnet Canyon and neighboring Cascade Canyon to the north consists of Archean Webb Canyon Gneiss and Mount Owen Quartz Monzonite (Love et al., 1992; Zartman and Reed, 1998). Paleozoic strata unconformably

overlie the Archean igneous and metamorphic rocks (Love et al., 1992). Figure 1. (A) Area of the Teton Exhumation of the Teton Range began with development of thrust sheets Range in northwest Wyo during the Sevier-Laramide orogeny (Love, 1973; Craddock et al., 1988; Lage ming. (B) Aerial view of the study area. Gray line east son, 1992) and continued with Basin and Range extension and development of of the range represents the the Teton normal fault 11–9 Ma (Smith et al., 1993; Roberts and Burbank, 1993; Teton fault system. National Brown, 2010). Brown (2010) also completed three-dimensional volumetric esti- Agriculture Imagery Program mates of bedrock removed above the Paleozoic unconformity and calculated an aerial image is provided cour tesy of Grand Teton National exhumation rate of 0.18 mm/yr if uplift began ca. 10 Ma. Ongoing offset along Park. the Teton fault created scarps in Pinedale-age moraines, preserving evidence of displacement in the past 13 k.y.; the most recent displacement occurred between 8 and 4.8 ka (Smith et al., 1993; Byrd, 1995; Thackray and Staley, 2014). Intense glaciation during the Pleistocene carved a rugged landscape out of Jackson Lake the west-dipping uplifted fault block. Glaciers incised steep U-shaped canyons, created low-relief steps in the longitudinal canyon profiles, and deposited moraines extending into Jackson Hole to the east (Pierce and Good, 1992; Foster Moran, WY et al., 2010; Tranel et al., 2011). Glaciers most recently extended into Jackson Hole ca. 14 ka, and retreated by ca. 11.5 ka (Licciardi and Pierce, 2008; Larsen Jenny Lake et al., 2016). Several small glaciers remain at high elevation in the Teton Range. Bradley Lake Garnet Licciardi and Pierce (2008) dated boulders at the head of Cascade Canyon that tCanyon o n R a n g e were 13–10 ka (Lake Solitude) and bedrock surfaces that were ca. 13 ka. Ex- Moose, WY

posure ages of 12–11 ka on polished bedrock surfaces in central Garnet Can- T e yon were obtained (Tranel et al., 2015). The most recent retreat in the nearby Wind River Range was ca. 11 ka based on moraine exposure, although these ages may be older given recent advancements in cosmogenic dating methods (Gosse et al., 1995; Licciardi and Pierce, 2008). Although glaciers controlled the shape of the Teton landscape, rockfalls 015 020 also heavily influenced the landscape by rapidly eroding valley walls and de- Kilometers positing extensive talus fans on the valley floors (Foster et al., 2010; Tranel

A # TalusSample ! BedrockSample GlacierGulch TalusFan BedrockArea # Fan153:TTC-61 Drainage Basin TTC-03! Elevation(m) Cascade Canyon 1,810 –2,000 TTC-08! 2,001 –2,200 TTC-01! 2,201 –2,400 # Fan18:TTC-64 2,401 –2,600 TTC-07! Fan56:TTC-71 # 2,601 –2,800 Garnet Canyon # 2,801 –3,000 3,001 –3,200 Figure 2. Sample location map and rele 3,201 –3,400 Fan11:TTC-66 vant physiographic features of the study 3,401 –3,600 area. (A) Sample locations on talus fans 3,601 –3,800 and nearby contributing bedrock areas. 01 3,801 –4,000 (B) Slope map with Figure 8 profile loca AvalancheCanyon tions. (C) Aspect map. kilometers ¯ 4,001 –4,200

B C.

Wall 153

Wall 18 Wall 56

Profile Lines Wall 11 Slope 83° Aspect 0° Flat-Lakes East:45–135 West:225–315 North: 0–45 South: 135–225 North: 315–360

et al., 2011). In Tranel et al. (2015), the contribution of rockfalls to valley wall formly sized pebbles 5 cm thick or less to avoid variable accumulation of 10Be erosion was estimated with mapped talus deposits in Garnet, Avalanche, and due to size or rolling pebbles (Balco, 2011; Applegate et al., 2012; Mackey and Glacier Gulch Canyons; field surveys of talus volumes obtained erosion rates Lamb, 2013). We chose to sample sediment smaller than boulders to reduce ranging from 0.03 to 6 mm/yr and averaging 0.8 mm/yr. variability of inheritance, and larger than sand to reduce water, vegetation, or animal disturbance (Schmidt et al., 2011; Ivy-Ochs et al., 2013). We collected METHODS multiple pebbles from each fan to account for variable inheritance from degra dation of the fan surface and inputs from random locations on the valley walls Pebble and Bedrock 10Be (Matmon et al., 2006; Ward and Anderson, 2011; Applegate et al., 2010, 2012). Each pebble was gathered along a transect across the fan at the same ele- We collected samples of bedrock from two ridge locations and amalgam- vation and spaced 1–2 m apart, depending on fan width, for 3 of the 4 fans ated pebbles from four talus fans in and around Garnet Canyon. We chose (Fig. 3). Because the fourth fan (fan 18) was narrower, we collected the pebbles locations where we could access bedrock on the ridge almost directly above at equal intervals (1–2 m) from the top to the bottom of the fan (Fig. 3). The a talus deposit. Bedrock from the ridges was sampled from relatively flat and difference in collection methods could potentially influence mixing along the stable surfaces where shielding due to the surface slope would be minimal surface of the fan if materials rolled downslope along a similar path. However, (Figs. 2 and 3). We collected samples from fans that faced east, west, north, our observations of a recent rockfall deposit suggest that pebbles and materi- and south around Garnet Canyon. On each of 4 fans, we collected 16–20 uni- als of all sizes are scattered across a wide area on the fan surface (Fig. 4).

Bedrock TTC-01 Sample TTC-71/ Fan 56

0.5 m

Bedrock TTC-03 Sample TTC-61 / Fan 13

Figure 3. Photos of ridge (left column) and 2 m talus (right column) sample collection sites. Yellow dashed lines indicate exam Bedrock TTC-08 Sample TTC-64 / Fan 18 ples of the sampling strategy along tran sects for fans 13 and 18.

2 m

Bedrock TTC-07 Sample TTC-66 / Fan 11

2 m

A B

Figure 4. Photo of a rockfall deposit north west of the South Teton in Cascade Can yon in July 2011. (A) Most of the deposit below part of the bedrock source area. (B) Closer view of cobbles, pebbles, and dust particles deposited by the rockfall. Yellow circles indicate ~5 cm pebbles simi lar to those that were collected for this study. The total length of the recent rock fall was approximately 50 m.

We crushed and sieved samples to 0.25–1 mm at Illinois State University and locations in Jackson Hole. We multiplied the snow correction factor (0.94) and sent samples to the Purdue University Rare Isotope Measurement Laboratory the shielding correction factor (see Table 1) and used the combined value as (PRIME Lab, West Lafayette, Indiana) for digestion, beryllium separation, and the input for the shielding correction element in the CRONUS online calculator. accelerator mass spectrometry (Kohl and Nishiizumi, 1992). Exposure age cal- culations for all samples used the CRONUS online calculator (version 2.2; Balco Pebble Weathering et al., 2008). All results listed in Table 1 used the time-varying production rate from Dunai (2001) for comparison to results in Tranel et al. (2015). The elevation, We described weathering features on each pebble composing the amalga latitude, and longitude of each talus fan and bedrock area were estimated using mated samples before crushing for quartz extraction and dissolution. First we the centroid of each polygon plotted with the Feature to Point tool in ArcGIS. studied physical weathering with Krumbein (1941) roundness and Zingg (1935) We determined the shielding factor for talus surfaces using 3D Analyst shapes to characterize if corners were broken down either through chemical tools in ArcGIS and a 10 m U.S. Geological Survey digital elevation model weathering and dissolution of minerals or abrasion from rolling or washing (http://data .geocomm .com /catalog /US /61051 /322 /group4 -3 .html). We used the down the talus slope after initial deposition. We assume that all materials start ArcGIS Skyline tool to create polygons including all of the areas visible from out very angular because they break apart on impact with the hillslope walls the sample points on the talus surface. Then we used the Create Lines tool or on other rock debris as they fall. If pebbles are weathering, the corners will (ArcGIS) to draw lines extending from each sample point to the outer limit of become more rounded over time (Birkeland, 1973). the skyline polygon (the horizon). Usually a line was created approximately We also used the color or percentage of lichen cover to compare relative dif- every 3° (100 m), although some distances were greater or smaller. We se- ferences in exposure on fan surfaces. Pebbles deposited earlier were exposed lected the lines with a positive angle to the horizon, and calculated the topo- to chemical weathering longer, and would possibly display more surficial color

graphic shielding factor (CT) for each point (Dunne et al., 1999; Codilean, 2006; change in comparison to the unweathered interior of the pebble (Birkeland,

Norton and Vanacker, 2009). We averaged CT values for each sample point to 1973; Whitehouse and McSaveney, 1983). Each pebble was therefore sawed obtain the final shielding correction factor for each amalgamated sample. or broken to record any gradations in color compared to the Munsell color Because snow also shields the exposed surfaces and reduces 10Be produc- chart (www.munsell.com). We also observed the lichen cover on each side tion, we incorporated a correction factor to account for snow cover based on of the collected pebbles, assuming that pebbles showing more lichen cover modern snowfall estimates. Gosse and Phillips (2001) provided a calculation to would indicate longer residence and no renewed movement along the surface quantify snow shielding based on the density of snow, the depth of snowfall (Bradwell, 2009). The exposed surface was marked on each pebble during field each month, and attenuation length (Binnie, 2004). We applied the formulation collection. We estimated the percentage of lichen cover on each pebble face, using the average snowfall recorded by Dirks and Martner (1982) at stations in and averaged the values for each face to produce a whole pebble percent. Moran and Moose, Wyoming (elevation ~2000 m; Fig. 1). These values allowed To use lichen as a quantitative measurement of surface age requires exten- us to calculate a minimum shielding correction because the talus locations were sive work to determine the lichen growth rate curve for the specific environ- likely to receive higher snowfall at higher elevations than the weather station ments where the lichen are observed or calibrate the size to the age of known

TABLE 1. BERYLLIUM DATA FOR BEDROCK AND TALUS SAMPLES Sample Sample Elevation* Quartz Strike, dip† Thickness Sample density 10Be ± σ Shielding Exposure age± σ AMS ID type Lat, long (m) (g) (°) (cm) (g/cm3) (104 atm/g) correction§ (k.y.)** TTC-01†† ridge 43.7279 304246.325073 42.7 119.7 ± 2.70.9428 ± 3 b3448v –110.7823 24 NW TTC-03 ridge 43.7323 297026.632064 52.7 181.4 ± 5.60.9743 ± 5 201204297 –110.7803 32 NW TTC-07†† ridge 43.7258 349347.842151 32.7 139.9 ± 3.30.9829 ± 3 b3453 –110.8180 24 NE TTC-08 ridge 43.7299 371533.724ﬂat-lying5 2.751.53 ± 1.58 0.99 7 ± 1 201204298 –110.8116 surface TTC-61 talus 43.7336 282517.213– 5.42.7 4.01 ± 0.54 0.33 3.5 ± 0.6 201204299 fan 153 –110.7799 2987 TTC-64 talus 43.7272 298719.546– 5.22.7 5.19 ± 1.80 0.60 2.1 ± 0.8 201204300 fan 18 –110.7975 3223 TTC-66 talus 43.7235 326934.056– 4.12.7 2.50 ± 0.24 0.74 0.6 ± 0.1 201204301 fan 11 –110.8266 3521 TTC-71 talus 43.7249 2721 22.596 –5.4 2.713.78 ± 0.79 0.50 7.9 ± 1.0 201204302 fan 56 –110.7815 2978 *Regular font elevation is the average elevation of the pebble samples. Bold elevation value is the average elevation of the contributing bedrock area. †Strike and dip measured on bedrock surfaces. §Topographic shielding for bedrock samples was calculated with CRONUS calculator based on strike, dip, and angle and azimuth to high features on the skyline. Topographic shielding values for talus samples was calculated using the angle to features on the landscape from digital elevation model in ArcGIS at a central pebble location on the talus fan (Dunne et al., 1999; Codilean, 2006; Norton and Vanacker, 2009). **Exposure age values calculated with CRONUS calculator based on Dunai (2001). Be standardization used for samples TTC-1 and TTC-7 was NIST_27900. All other samples used 07KNSTD for Be standardization. ††Previously published in Tranel et al. (2015).

surfaces (Hanson, 2008; Armstrong and Bradwell, 2010). We chose to look at the Additional weathering observations were collected and listed in Table 2 overall coverage on the pebbles rather than measuring the maximum or aver- because differences in vegetation on talus surfaces indicated varying degrees age lichen size because the total surface area of the pebbles was too small for of soil development from low to high elevation. Weathering rinds were not other quantitative estimates. Competition between lichen and elevation could developed in our samples, although surface colors were different from inte- also influence growth (Kodros, 1997). We assume that the percentage of lichen rior colors. We observed red discoloration on samples from three talus fans cover increases with exposure time (Grab et al., 2005; Bradwell, 2009); there- throughout the pebbles, possibly related to weathered iron-bearing minerals fore, fans containing rocks with higher percentages of lichen cover are rela (Birkeland, 1973), but it occurred throughout the sample rather than concentric tively older than talus fans where few samples demonstrated lichen growth. to the surface. The most common Munsell rock colors for each talus fan are listed in Table 2. The most common color differed for each fan. Roundness was RESULTS similar for most of the samples. Krumbein values were uniform, and all samples had a high number of bladed pebbles with a little variation in the number Pebble Weathering of oblate or prolate pebbles (Table 2).

Lichen cover showed the most variability in the qualitative observations Pebble and Bedrock 10Be Concentrations on the amalgamated pebble samples (Table 2). The highest elevation talus fan (fan 11) was the only fan with no lichen growth on any of the pebbles (Figs. 2 We expected ridge bedrock samples to have the highest 10Be concentra- and 3). Lichen covered a maximum of 31% of the clasts on fan 153 (sample tions and represent the oldest surfaces around Garnet Canyon because they TTC-61), which faced north. The clast with the highest percentage of lichen were collected from stable surfaces. All ridge samples except one matched our cover (44%) was sampled from the lowest elevation and south-facing fan (fan assumption (Table 1). The exception was sample TTC-08 (5.15 × 105 10Be atm/g), 56, sample TTC-71). collected near the top of Middle Teton, which had a concentration closer to the

TABLE 2. SUMMARY OF PEBBLE OBSERVATIONS AND VOLUMETRIC EROSION RATES Max. Mean Average Most frequent Clasts per sample Volumetric Number of bedrock slope bedrock slope Krumbein Average Munsell with lichen Lichen cover* erosion rate ± σ Sample, talus fan pebbles (°) (°) roundness Zingg shape rock color (%) (maximum %) (mm/yr)† TTC-61, fan 153 16 75 47 0.4bladed, oblateN7318.3 2.4± 0.3 TTC-64, fan 18 20 72 48 0.4bladed, oblateN8102.5 1.1± 0.1 TTC-66, fan 11 20 67 45 0.3bladed10 YR 8/20 02.6 ± 1.8 TTC-71, fan 56 15 77 58 0.3bladed, prolate5 YR 8/420440.14± 0.03 *Describes the percent of area covered by lichen on a single pebble. †Calculated with 13.5 ka moraine age in Tranel et al. (2015).

glaciated floor surfaces (Fig. 5; 59.6 × 104 atm/g in TTC-11; Tranel et al., 2015). Instead, we compare 10Be concentrations between different surfaces and de- Concentrations in all other bedrock samples were >1.00 × 106 atm/g. Although posits in the landscape to consider the relative ages of geomorphic features, sample TTC-08 was taken from a flat surface (Fig. 3), we assumed that shield- incorporation into stream sediments, and spatial patterns of erosion. Then ing by snow cover would be minimal due to the high wind exposure near a we consider how the features we observed relate to the geologic history of peak at an elevation of 3903 m. the Teton Range. We expected the talus concentrations to be less than all the floor bedrock concentrations because we assume that the rockfalls accumulated after glaciers retreated from the canyon. Our results are consistent with this ex- Relative Ages of Geomorphic Features pectation. Concentrations of 10Be in the amalgamated pebbles were similar in three of the talus fans (2.00–5.00 × 104 atm/g), but much higher in sample In Figure 6 we divide the catchment features into four surface classes: TTC-71 (1.30 × 105 atm/g). Sample TTC-71 was collected from talus fan 56, bedrock ridges, bedrock hillslopes, talus deposits, and exposed bedrock on which was the largest fan. The fan size and 10Be concentration both suggest the valley floor. The areas were mapped and classified from field observa- that fan 56 is older than the other fans. Trends between concentrations and elevation were similar between talus deposits and bedrock surfaces. The lowest elevation talus fan (fan 56, sample TTC-71) had the highest 10Be con- 4000 centration, and the highest elevation talus fan (fan 11, sample TTC-66) had the lowest 10Be concentration. The average 10Be concentration on the valley floor (41.4 × 104 atm/g) reported in Tranel et al. (2015) was six times greater 4 than the average concentration in the talus deposits (6.4 × 10 atm/g). To put 3500 our results in the context of the geologic history of the Teton Range, we used concentrations of 10Be from the amalgamated talus samples to calculate ex-

posure ages of the talus surfaces. Talus surface exposure ages ranged from Figure 5. Concentrations of cosmo 0.6 to 7.9 k.y. (Table 1). 3000 genic 10Be plotted at collection ele vations. Stream and floor concen trations are from Tranel et al. (2015). Elevaon (m) Error bars represent concentration DISCUSSION uncertainties and are less than the symbol width for floor, ridge, and 2500 Studies using concentrations of 10Be to estimate erosion rates or exposure stream points. ages assume that erosion rates have been constant for a sufficiently long time and that sediment deposits represent an average of multiple processes

across a catchment area (Bierman and Steig, 1996; Cockburn et al., 2000; 2000 Niemi et al., 2005; Binnie et al., 2008; Balco et al., 2008; Yanites et al., 2009; 1 10 100 1000 Balco, 2011; Applegate et al., 2012). Because alpine postglacial landscapes 10Be concentraon (104 atoms/g) are rapidly changing from recent glacial retreat and stochastic processes, the assumptions commonly applied to cosmogenic nuclide rates do not fit well. talus ridge ﬂoor stream

110°48′W110°47′W110°46′W tions and geographic information system maps of elevation, slope, bedrock, A and Quaternary deposits. Each surface class is subjected to different combi- nations of geomorphic processes that influence10 Be concentrations. Ridges are high-elevation surfaces between catchments with low slopes near the drainage divide or in close proximity to peaks. Higher 10Be concentrations in ridge samples reflect relatively little erosion and exposure during glaciation,

N making them the oldest surfaces. Bedrock floors are low-elevation surfaces demonstrating evidence of glacial scour, striations, and chatter marks along

43°44′ the valley bottom near ice, lakes, and between talus deposits (Fig. 6). Concen- trations (from Tranel et al., 2015) reflect postglacial exposure, with little erosion since glacial retreat. Talus deposits are Quaternary colluvium (mapped by Love et al., 1992; Tranel et al., 2015). Talus concentrations are potentially a composite of high concentration material from near the ridges, steep bedrock hillslopes (either similar in age to ridges or to glacially scoured floors), and fresh rock fragments from boulders several meters thick. Talus samples contained the lowest 10Be concentration, and therefore are the youngest geomorphic features. Although older source material from bedrock hillslopes is incorporated in the deposit, it does not have a noticeable impact on the talus N 10Be concentration. Bedrock hillslopes are valley walls without talus cover, and are the most 43°43′ complex surface to evaluate for 10Be concentrations (Fig. 6). We did not collect samples from bedrock hillslopes, but we would expect that the 10Be concentration would be less than ridge values and greater or equal to valley floor values because many wall areas were probably covered by glacial ice at some time. Other surfaces on the bedrock hillslopes, however, were possibly exposed be- 2 Ridge area: 0.6 km cause observations and models suggest the valley was not completely filled B 10 4 Be concentrations: 51-181x10 atoms/g with ice during the last ice age (Foster et al., 2010). In addition, random lo-

2 cations on the bedrock hillslopes may have very low concentrations where Hillslope bedrock area: 2.9 km 10Be concentrations: 2-181x104 atoms/g boulders recently fell from the slope. White: Hillslope areas with low concentrations recently exposed by rockfall Purple: Areas with concentrations similar to ridges Green: Areas with concentrations similar to floors Comparison of Bedrock and Talus Surfaces to Stream Sediments

In the ideal setting, stream 10Be concentrations reflect combined inputs Talus area: 2.4 km2 10Be concentrations: 2-14x104 atoms/g from all surfaces in a catchment (bedrock ridges, bedrock hillslopes, talus, White: Clasts on talus with low concentrations and floor bedrock) eroding and contributing sediment equally. Weighting the recently deposited by rockfall concentrations of each surface class in Figure 6 by the corresponding con- Purple: Clasts with concentrations similar to ridges Gray: Clasts with concentrations similar to tributing area should equal the stream sediment concentration. The result of hillslopes the weighted average of talus, bedrock, and floor concentrations (~40 × 104 Green: Clasts with concentrations similar to floors atm/g) was almost 3 times greater than the average observed concentration of 14.5 × 104 atm/g in stream sand-sized sediments from Tranel et al. (2015). 2 Floor area: 0.9 km The difference between the stream and weighted concentrations indicates 10 4 Be concentrations: 32-60x10 atoms/g that talus contributes disproportionate sediment amounts to the relative sur- (Tranel et al., 2015) face area covered in Garnet Canyon. Although the grain sizes vary between the talus and stream deposits, the low concentrations in both indicate that Figure 6. Classification of bedrock and geomorphic surfaces in Garnet Canyon. (A) Map of four surface classes. (B) Photo hillslope processes interact with the stream system to make stream concen- illustrating the mapped surfaces and the potential mixing of material and 10Be concentrations. trations much lower than bedrock surface concentrations. This is consistent

with models and other field studies that predict that hillslope processes cause catchment averaged stream erosion rates to be higher than bedrock erosion A rates (Niemi et al., 2005). 5.0 The talus deposits are not the only sediment source to the stream system. 4.0 If the talus deposits were the only contributor, we would expect similar talus 3.0 and stream concentrations. One talus concentration (TTC-71; 13.78 × 104 atm/g) was similar to the stream concentrations (11–19 × 104 atm/g in 3 stream sand 2.0 samples; Tranel et al., 2015; Table 2); however, the rest were lower (<6 × 104 1.0 atm/g). The average of these stream 10Be concentrations is approximately two 0.0 Figure 7. Relationships between 10 times greater than the average of concentrations in the talus. Although bed- 0510 15 20 Be concentrations and rela 10Be concentraon (104 atoms/gram) tive age methods. (A) Talus rock weathering in Garnet Canyon is slow, some sediment from the valley floor Volumetric erosion rate (mm/yr ) volumetric erosion rate (Tranel or bedrock wall must enter the stream channel. As discussed in more detail et al., 2015) and talus 10Be con in the following, Garnet Canyon demonstrates spatial variability in erosion. If centrations. (B) Lichen cover on B % clasts with lichen Max % lichen cover per cobble pebbles and amalgamated talus sediments are well mixed, catchment averaged erosion rates can still repre- 10Be concentrations. Max—maxi 50 sent a long-term average (Foster and Anderson, 2016, and references within). mum. However, small catchments tend to be poorly mixed due to variable storage 40 and incision along the stream length (Yanites et al., 2009). Garnet Canyon ap- 30 pears poorly mixed because stream sediment concentrations are similar to 20 the concentration of sample TTC-71 from fan 56. Because we are comparing 10

pebbles to sands, however, our observations may instead reflect differences in Lichen percentages 0 concentrations recorded by distinct grain size classes (Lukens et al., 2016). Sand 0510 15 20 may be eroded from lower elevation sources. If we were to sample pebbles at 10Be concentraon (104 atoms/gram) the mouth as well, they might be similar to higher elevation talus fan sources (Riebe et al., 2015).

Implications for Inherited 10Be Uncertainty Estimates Spatial Patterns of Erosion Concentrations are sufficiently different between the surface types that To understand how well 10Be concentrations reflect ages or rates of pro- inheritance does not limit a study of differential erosion across a catchment. cesses, we compare results to other qualitative and quantitative measures of Inheritance is more problematic when comparing individual ages of talus fans, age and erosion rates. Talus 10Be concentrations, talus volume erosion rates but to address this problem we consider a number of factors that influence (Tranel et al., 2015), and lichen cover all support erosion activity increase or 10Be accumulation. In addition to sediment mixing and snow shielding, uncer- surface age decline with increasing elevation. Talus deposits exhibited lower tainties can include inheritance in bedrock and sediment deposits, as well as 10Be concentrations at higher elevations (Fig. 5). Talus volume erosion rate degradation of geomorphic features. estimates were faster at higher elevations, as expected from 10Be concen- We accounted for snow shielding as described herein using standard trations (Fig. 7A; data from Tranel et al., 2015). Lichen cover was reduced at methods (Gosse and Phillips, 2001). Corrections accounted for a 5% differ- higher elevations (Fig. 7B). The fan with the highest 10Be concentration (fan ence in results. Temperatures influenced by elevation could affect the amount 56, sample TTC-71) also held the single clast with the most lichen cover. The of snow cover across the catchment. For example, the length of snow cover spatial trends from our results suggest that as glaciers retreated from the can- (shielding) per year would increase with elevation because temperatures de- yon, new deposits covered surfaces previously covered by ice. Deposition on crease with elevation. If all talus fell at the same time with close to zero in- lower elevation fans became stagnant, but continued at higher elevations. heritance, then a reduction in concentration with elevation is expected. With These patterns imply that a catchment averaged erosion rate represents an the historic climate variability since 11 ka (Larsen et al., 2016), it would be average of processes in this complex alpine system, but that erosion is varia challenging to account for more complex shielding at individual talus loca- ble and dependent on factors affected by elevation (Riebe et al., 2015). To tions. Another problem is the inheritance from a complex exposure history understand overall landscape changes we need to separate the catchment of the bedrock source. Materials accumulated on talus fans were produced into zones defined by elevation, local climates, and dominant geomorphic from large blocks falling away from the valley wall and breaking apart in the processes in each area. fall. Outer surfaces of those blocks would contain 10Be accumulated when

the original block was in place; therefore, some pebbles might contain inher- mate controlled by north or south aspects and rock strength (Marston et al., ited 10Be from the parent material. 2011). Based on their observations of channel asymmetry, we would expect to Several methods have been proposed in the literature to account for inheri see lower 10Be concentrations and less lichen cover on the sides with steeper tance in geomorphic deposits. Studies using amalgamated cobble samples to slopes. The 10Be concentrations, weathering, and lichen cover in our study do date alluvial terraces sampled subsurface cobbles in at least one location to not capture significant differences in slope stability or effective erosion re- create a vertical profile of 10Be concentrations and quantify the exact amount lated to aspect in Garnet Canyon. Samples TTC-71 and TTC-61 were collected of inheritance in the sediments (Anderson et al., 1996; Repka et al., 1997). The from fans at similar elevations. The average and maximum slopes calculated nature of talus deposits in our study area precluded us collecting samples to for the contributing bedrock wall areas were similar (Table 2). The slopes of create a vertical profile. Large boulders would make the profile difficult to col- bedrock wall profiles were 45° above all talus fans except fan 153, where the lect and skew the profile concentrations. Given that all the talus surface ages angle was 37° (Fig. 8). The south-facing fan surface (TTC-71, fan 56) had a in our study are younger than valley floor ages estimated with 10Be (youngest higher 10Be concentration than the north-facing fan surface (TTC-61, fan 153). 11 ka; Tranel et al., 2015) and that the relationships between talus volume, More frequent lichen growth was observed on pebbles on the north-facing lichen cover, and 10Be concentrations described here were positive, none of talus fan (31% of the clasts showed evidence of lichen growth on TTC-61), but our results seem anomalously old due to significant inheritance. the single pebble with the greatest lichen cover (44%) was on the south-facing talus fan (TTC-71).

Talus Ages in Relation to Climate and Tectonics in the Teton Range CONCLUSION The parallels between maximum lichen cover, talus volumes, and 10Be concentrations support our use of the 10Be concentrations to estimate talus surface Talus surface features and 10Be concentrations have strong potential to ages. With ages for the talus deposits (Table 1), we can evaluate how rockfall help us understand geomorphic process interactions, as well as geologic and timing relates to climate and tectonic events in the Teton Range. In Tranel et al. climatic events. Ages from talus 10Be concentrations capture the significantly (2015) it was observed that the Garnet Canyon valley floor was exposed be- younger age of the deposits relative to bedrock surfaces. Rockfalls distribute tween 12 and 11 ka, and Larsen et al. (2016) observed nonglacial sediments a significant volume of sediment with little to no inheritance despite compli- began to dominate in Jenny Lake at about the same time. After glacial retreat, cated exposure histories on the source bedrock. The equivalent spatial pat- lake sediments preserved records of a warm period between 10 and 6.5 ka terns observed between 10Be concentrations, volumetric erosion rates, and and considerable climate variability after 6 ka (Larsen et al., 2016). At least one lichen cover validate the use of these methods to quantify hillslope processes. earthquake with a magnitude sufficient to displace surficial deposits occurred The overall low concentrations of 10Be in the talus deposits confirm that between 8 and 4.8 ka (Byrd, 1995). hillslope erosion is a significant and active geomorphic process contributing The age results in Garnet Canyon indicate that talus accumulation is not to the shape of the Teton landscape. Rockfall activity is closely linked to chang- a one-time event where all deposits formed immediately after deglaciation. ing climate conditions following glacial retreat, and only loosely connected All talus surfaces are younger than bedrock on the valley floor. As we would expect in a setting with rockfall mass wasting, those sediments accumulate over time as more rocks fall onto the surfaces. The oldest talus fan formed 3700 within a window of time where climate was warm and a magnitude 7 earthquake occurred in the Teton Range. If talus fan 56 (sample TTC-71) formed 3500 from an earthquake-triggered rockfall, perhaps that one event was sufficient to stabilize the slope above the fan so that few rockfalls have occurred since. Figure 8. Bedrock wall profiles The rest of the talus fans, however, are much younger. Major events are not 3300 above the corresponding talus de required to cause failures on steep rock slopes, and recent studies in Yosemite posits. Profiles were drawn along Elevation (m) Valley, California, observed that warm temperatures can propagate fracture 3100 the bedrock wall to intersect the expansion to trigger rockfalls (Collins and Stock, 2016). Fluctuations in climate apex of the corresponding talus deposit. likely influenced daily and monthly temperatures, precipitation, and water flow 2900 in bedrock joints to propagate the already fractured bedrock around Garnet 0 200 400 Canyon and eventually led to failures that produced talus fans over time. Distance from ridge (m) A study of cross-valley profiles throughout the Teton Range described Wall 56 Wall 18 valley shapes as asymmetric, reflecting variable erosion related to local cli- Wall 11 Wall 153

to earthquake events. Combined observations of 10Be concentrations in talus Binnie, S.A., 2004, Deriving Basin-Wide Denudation Rates from Cosmogenic Radionuclides, San pebbles, lichen cover, and volumetric erosion rates support a progression of Bernardino Mountains, California [Ph.D. thesis]: Edinburgh, UK, University of Edinburgh, 328 p. rockfall activity from low to high elevations. In addition, those high-elevation, Binnie, S.A., Phillips, W.M., Summerfield, M.A., Fifield, L.K., and Spotila, J.A., 2008, Patterns low-concentration sediments are incorporated into fluvial sands. Only one of denudation through time in the San Bernardino Mountains, California: Implications for talus deposit age correlated with a documented earthquake event. Most de- early-stage orogenesis: Earth and Planetary Science Letters, v. 276, p. 62–72, doi:10.1016/j .epsl.2008.09.008. posits likely occurred randomly through failures related to temperature and Birkeland, P.W., 1973, Use of relative age-dating methods in a stratigraphic study of rock glacier precipitation conditions contributing to joint fracture propagation. deposits, Mt. Sopris, Colorado: Arctic and Alpine Research, v. 5, p. 401–416, doi:10 .2307 Amalgamated pebble 10Be concentrations can provide valuable insight into /1550131. Bradwell, T., 2009, Lichenometric dating: A commentary in the light of some recent statistical the geomorphic mechanisms that shape alpine landscapes and contribute studies: Geografiska Annaler, ser. A, Physical Geography, v. 91A, p. 61–69. sediments to larger downstream systems. Pebble concentrations highlight the Brocklehurst, S.H., and Whipple, K.X., 2004, Hypsometry of glaciated landscapes: Earth Surface variability of erosion processes even within the limited area of a single small Processes and Landforms, v. 29, p. 907–926, doi:10.1002/esp.1083. catchment. To fully understand how mountain landscapes evolve, we need Brown, S.J., 2010, Integrating Apatite (U-Th)/He and Fission-Track Dating for a Comprehensive Thermochronological Analysis: Refining the Uplift History of the Teton Range [M.S. thesis]: to consider how local conditions within individual catchments influence the Blacksburg, Virginia Polytechnic Institute and State University, 84 p. system as a whole. Future work to investigate rockfall processes should in- Burbank, D.W., Leland, J., Fielding, E., Anderson, R.S., Brozovic, N., Reid, M.R., and Duncan, C., clude models and further field studies of sediment mixing and transport along 1996, Bedrock incision, rock uplift and threshold hillslopes in the northwestern Himalayas: Nature, v. 379, p. 505–510, doi:10.1038/379505a0. the talus surfaces and within stream channels, calibration of lichen growth, Byrd, J.O.D., 1995, Neotectonics of the Teton Fault, Wyoming [Ph.D. thesis]: Salt Lake City, Uni- and more intensive sample collection within talus deposits or across bedrock versity of Utah, 214 p. hillslopes for 10Be analyses. Cockburn, H.A.P., Brown, R.W., Summerfield, M.A., and Seidl, M.A., 2000, Quantifying passive margin denudation and landscape development using a combined fission-track thermochronology and cosmogenic isotope analysis approach: Earth and Planetary Science Let- ACKNOWLEDGMENTS ters, v. 179, p. 429–435, doi:10.1016/S0012-821X(00)00144-8. We thank Graham Andrews, Shanaka de Silva, and anonymous reviewers for valuable feedback Codilean, A.T., 2006, Calculation of the cosmogenic nuclide production topographic shielding on this manuscript. We also thank Audrey Happel, Amber Ritchie, Jill Tranel, and Anthony Abra- scaling factor for large areas using DEMs: Earth Surface Processes and Landforms, v. 31, ham for help in the field with sample collection. Funding to travel to the field to collect samples p. 785–794, doi:10.1002/esp.1336. was available through the Illinois State University College of Arts and Sciences New Faculty Ini- Collins, B.D., and Stock, G.M., 2016, Rockfall triggering by cyclic thermal stressing of exfoliation tiative Grant. We also thank Tom Clifton and others at the Purdue Rare Isotope Measurement fractures: Nature Geoscience, v. 9, p. 395–400, doi:10.1038/ngeo2686. Laboratory (PRIME Lab, West Lafayette, Indiana) for help with sample preparation and analyses. Craddock, J.P., Kopania, A.A., and Wiltschko, D.V., 1988, Interaction between the northern Idaho-Wyoming thrust belt and bounding basement blocks, central western Wyoming, in Schmidt, C.J., and Perry, W.J., Jr., eds., Interaction of the Rocky Mountain Foreland and the REFERENCES CITED Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 333–352, doi:10 .1130 Alley, R.B., Lawson, D.E., Larson, G.J., Evenson, E.B., and Baker, G.S., 2003, Stabilizing feed- /MEM171-p333. backs in glacier-bed erosion: Nature, v. 424, p. 758–760, doi:10.1038/nature01839. Dirks, R.A., and Martner, B.E., 1982, The Climate of Yellowstone and Grand Teton National Parks: Anderson, R.S., Repka, J.L., and Dick, G.S., 1996, Explicit treatment of inheritance in dating depo National Park Service Occasional Paper 6, 26 p. sitional surfaces using in situ 10Be and 26Al: Geology, v. 24, p. 47–51, doi:10.1130/0091-7613 Dühnforth, M., Densmore, A.L., Ivy-Ochs, S., and Allen, P.A., 2008, Controls on sediment evacua- (1996)024<0047:ETOIID>2.3.CO;2. tion from glacially modified and unmodified catchments in the eastern Sierra Nevada, Cali Applegate, P.J., Urban, N.M., Laabs, B.J.C., Keller, K., and Alley, R.B., 2010, Modeling the statisti- fornia: Earth Surface Processes and Landforms, v. 33, p. 1602–1613, doi:10.1002/esp.1694. cal distributions of cosmogenic exposure dates from moraines: Geoscientific Model Devel- Dunai, T.J., 2001, Influence of secular variation of the geomagnetic field on production rates of in opment, v. 3, p. 293–307, doi:10.5194/gmd-3-293-2010. situ produced cosmogenic nuclides: Earth and Planetary Science Letters, v. 193, p. 197–212, Applegate, P.J., Urban, N.M., Keller, K., Lowell, T.V., Laabs, B.J.C., Kelly, M.A., and Alley, R.B., doi:10.1016/S0012-821X(01)00503-9. 2012, Improved moraine age interpretations through explicit matching of geomorphic pro- Dunne, J., Elmore, D., and Muzikar, P., 1999, Scaling factors for the rates of production of cosmo- cess models to cosmogenic nuclide measurements from single landforms: Quaternary Re- genic nuclides for geometric shielding and attenuation at depth on sloped surfaces: Geo- search, v. 77, p. 293–304, doi:10.1016/j.yqres.2011.12.002. morphology, v. 27, p. 3–11, doi:10.1016/S0169-555X(98)00086-5. Armstrong, R., and Bradwell, T., 2010, Growth of crustose lichens: A review: Geografiska Annaler, Dussauge, C., Grasso, J.R., and Helmstetter, A.S., 2003, Statistical analysis of rockfall volume ser. A, Physical Geography, v. 92A, p. 3–17. distributions: Implications for rockfall dynamics: Journal of Geophysical Research, v. 108, Arsenault, A.M., and Meigs, A.J., 2005, Contribution of deep-seated bedrock landslides to ero- 2286, doi:10.1029/2001JB000650. sion of a glaciated basin in southern Alaska: Earth Surface Processes and Landforms, v. 30, Foster, D., Brocklehurst, S.H., and Gawthorpe, R.L., 2008, Small valley glaciers and the effective- p. 1111–1125, doi:10.1002/esp.1265. ness of the glacial buzzsaw in the northern Basin and Range, USA: Geomorphology, v. 102, Balco, G., 2011, Contributions and unrealized potential contributions of cosmogenic-nuclide ex- p. 624–639, doi:10.1016/j.geomorph.2008.06.009. posure dating to glacier chronology, 1990–2010: Quaternary Science Reviews, v. 30, p. 3–27, Foster, D., Brocklehurst, S.H., and Gawthorpe, R.L., 2010, Glacial-topographic interactions in doi:10.1016/j.quascirev.2010.11.003. the Teton Range, Wyoming: Journal of Geophysical Research, v. 115, F01007, doi:10 .1029 Balco, G., Stone, J.O., Lifton, N.A., and Dunai, T.J., 2008, A complete and easily accessible means /2008JF001135. of calculating surface exposure ages or erosion rates from 10Be and 26Al measurements: Foster, M.A., and Anderson, R.S., 2016, Assessing the effect of a major storm on 10Be concen- Quaternary Geochronology, v. 3, p. 174–195, doi:10.1016/j.quageo.2007.12.001. trations and inferred basin-averaged denudation rates: Quaternary Geochronology, v. 34, Bierman, P.R., and Steig, E.J., 1996, Estimating rates of denudation using cosmogenic isotope p. 58–68, doi:10.1016/j.quageo.2016.03.006. abundances in sediment: Earth Surface Processes and Landforms, v. 21, p. 125–139, doi:10 Gosse, J.C., and Phillips, F.M., 2001, Terrestrial in situ cosmogenic nuclides: Theory and applica- .1002/(SICI)1096-9837(199602)21:2<125::AID-ESP511>3.0.CO;2-8. tion: Quaternary Science Reviews, v. 20, p. 1475–1560, doi:10.1016/S0277-3791(00)00171-2.

Gosse, J.C., Evenson, E.B., Klein, J., Lawn, B., and Middleton, R., 1995, Precise cosmogenic Mackey, B.H., and Lamb, M.P., 2013, Deciphering boulder mobility and erosion from cosmogenic 10Be measurements in western North America: Support for a global Younger Dryas cooling nuclide exposure dating: Journal of Geophysical Research, v. 118, p. 184–197, doi:10.1002 event: Geology, v. 23, no. 10, p. 877–880, doi:10.1130/0091-7613(1995)023<0877:PCBMIW>2 /jgrf.20035. .3.CO;2. Marston, R.A., Weihs, B.J., and Butler, W.D., 2011, Slope Failures and Cross-Valley Profiles, Grand Grab, S., van Zyl, C., and Mulder, N., 2005, Controls on basalt terrace formation in the eastern Teton National Park, Wyoming: University of Wyoming National Park Service Research Cen- Lesotho highlands: Geomorphology, v. 67, p. 473–485, doi:10.1016/j.geomorph.2004.11.010. ter Annual Report, v. 33, article 7, p. 61–74. Granger, D.E., Kirchner, J.W., and Finkel, R.C., 1996, Spatially averaged long-term erosion rates Matmon, A., Nichols, K., and Finkel, R., 2006, Isotopic insights into smoothening of abandoned measured from in situ-produced cosmogenic nuclides in alluvial sediment: Journal of Geol- fan surfaces, southern California: Quaternary Research, v. 66, p. 109–118, doi:10.1016/j .yqres ogy, v. 104, p. 249–257, doi:10.1086/629823. .2006.02.010. Granger, D.E., Riebe, C.S., Kirchner, J.W., and Finkel, R.C., 2001, Modulation of erosion on steep Meigs, A., Krugh, W.C., Davis, K., and Bank, G., 2006, Ultra-rapid landscape response and sedi- granitic slopes by boulder armoring, as revealed by cosmogenic26Al and 10Be: Earth and ment yield following glacier retreat, Icy Bay, southern Alaska: Geomorphology, v. 78, p. 207– Planetary Science Letters, v. 186, p. 269–281, doi:10.1016/S0012-821X(01)00236-9. 221, doi:10.1016/j.geomorph.2006.01.029. Hales, T.C., and Roering, J.J., 2009, A frost “buzzsaw” mechanism for erosion of the eastern Moore, J.R., Sanders, J.W., Dietrich, W.E., and Glaser, S.D., 2009, Influence of rock mass strength Southern Alps, New Zealand: Geomorphology, v. 107, p. 241–253, doi:10.1016/j.geomorph on the erosion rate of alpine cliffs: Earth Surface Processes and Landforms, v. 34, p. 1339– .2008.12.012. 1352, doi:10.1002/esp.1821. Hallet, B., Hunter, L., and Bogen, J., 1996, Rates of erosion and sediment evacuation by glaciers: Muzikar, P., 2009, General models for episodic surface denudation and its measurement by A review of field data and their implications: Global and Planetary Change, v. 12, p. 213–235, cosmogenic nuclides: Quaternary Geochronology, v. 4, p. 50–55, doi:10.1016/j.quageo.2008 doi:10.1016/0921-8181(95)00021-6. .06.004. Hansen, E.S., 2008, The application of lichenometry in dating of glacier deposits: Geografisk Niemi, N.A., Oskin, M., Burbank, D.W., Heimsath, A.M., and Gabet, E.J., 2005, Effects of bedrock Tidsskrift, v. 108, p. 143–151, doi:10.1080/00167223.2008.10649580. landslides on cosmogenically determined erosion rates: Earth and Planetary Science Let- Heimsath, A.M., and McGlynn, R., 2008, Quantifying periglacial erosion in the Nepal high Hima- ters, v. 237, p. 480–498, doi:10.1016/j.epsl.2005.07.009. laya: Geomorphology, v. 97, p. 5–23, doi:10.1016/j.geomorph.2007.02.046. Norton, K.P., and Vanacker, V., 2009, Effects of terrain smoothing on topographic shielding cor- Ivy-Ochs, S., Dühnforth, M., Densmore, A., and Alfimov, V., 2013, Dating fan deposits with cos- rection factors for cosmogenic nuclide-derived estimates of basin-averaged denudation rates: Earth Surface Processes and Landforms, v. 34, p. 145–154, doi:10.1002/esp.1700. mogenic nuclides, in Schneuwly-Bollschweiler, M., et al., eds., Dating Torrential Processes O’Farrell, C.R., Heimsath, A.M., Lawson, D.E., Jorgensen, L.M., Evenson, E.B., Larson, G., and on Fans and Cones: Advances in Global Change Research Volume 47: Dordrecht, Nether- Denner, J., 2009, Quantifying periglacial erosion: Insights on a glacial sediment budget, lands, Springer, p. 243–263, doi:10.1007/978-94-007-4336-6_16. Matanuska Glacier, Alaska: Earth Surface Processes and Landforms, v. 34, p. 2008–2022, Jomelli, V., 2013, Lichenometric dating of debris avalanche deposits with an example from the doi:10.1002/esp.1885. French Alps, in Schneuwly-Bollschweiler, M., et al., eds., Dating Torrential Processes on Olyphant, G.A., 1983, Analysis of the factors controlling cliff burial by talus within Blanca Massif, Fans and Cones: Advances in Global Change Research Volume 47: Dordrecht, Netherlands, southern Colorado, U.S.A.: Arctic and Alpine Research, v. 15, p. 65–75, doi:10 .2307/1550982 . Springer, p. 211–224, doi:10.1007/978-94-007-4336-6_14. Pierce, K.L., and Good, J.D., 1992, Field guide to the Quaternary geology of Jackson Hole, Wyo- Kodros, C., 1997, Lichen dating methods and applications in northern California: Society for Cali ming: U.S. Geological Survey Open-File Report 92-0504, 54 p. fornia Archaeology Proceedings, v. 11, p. 141–147. Portenga, E.W., and Bierman, P.R., 2011, Understanding Earth’s eroding surface with 10Be: GSA Kohl, C.P., and Nishiizumi, K., 1992, Chemical isolation of quartz for measurement of in-situ-pro- Today, v. 21, no. 8, p. 4–10, doi:10.1130/G111A.1. duced cosmogenic nuclides: Geochimica et Cosmochimica Acta, v. 56, p. 3583–3587, doi:10 Repka, J.L., Anderson, R.S., and Finkel, R.C., 1997, Cosmogenic dating of fluvial terraces, Fre- .1016/0016-7037(92)90401-4. mont River, Utah: Earth and Planetary Science Letters, v. 152, p. 59–73, doi:10.1016/S0012 Krumbein, W.C., 1941, Measurement and geological significance of shape and roundness of sedi -821X(97)00149-0. mentary particles: Journal of Sedimentary Petrology, v. 11, p. 64–72, doi:10 .1306/D42690F3 Riebe, C.S., Sklar, L.S., Lukens, C.E., and Shuster, D.L., 2015, Climate and topography control -2B26-11D7-8648000102C1865D. the size and flux of sediment produced on steep mountain slopes: National Academy of Lageson, D.R., 1992, Possible Laramide influence on the Teton normal fault, western Wyoming, Sciences Proceedings, v. 112, p. 15,574–15,579, doi:10.1073/pnas.1503567112. in Link, P.K., et al., eds., Regional Geology of Eastern Idaho and Western Wyoming: Geologi- Roberts, S.V., and Burbank, D.W., 1993, Uplift and thermal history of the Teton Range (northwest- cal Society of America Memoir 179, p. 183–196, doi:10.1130/MEM179-p183. ern Wyoming) defined by apatite fission-track dating: Earth and Planetary Science Letters, Larsen, D.J., Finkenbinder, M.S., Abbott, M.B., and Ofstun, A.R., 2016, Deglaciation and post- v. 118, p. 295–309, doi:10.1016/0012-821X(93)90174-8. glacial environmental changes in the Teton Mountain Range recorded at Jenny Lake, Sanders, D., and Ostermann, M., 2011, Post-last glacial alluvial fan and talus slope associa- Grand Teton National Park, WY: Quaternary Science Reviews, v. 138, p. 62–75, doi:10.1016/j tions (Northern Calcareous Alps, Austria): A proxy for late Pleistocene to Holocene climate .quascirev.2016.02.024. change: Geomorphology, v. 131, p. 85–97, doi:10.1016/j.geomorph.2011.04.029. Licciardi, J.M., and Pierce, K.L., 2008, Cosmogenic exposure-age chronologies of Pinedale and Sass, O., and Wollny, K., 2001, Investigations regarding Alpine talus slopes using ground-pene- Bull Lake glaciations in greater Yellowstone and the Teton Range, USA: Quaternary Science trating radar (GPR) in the Bavarian Alps, Germany: Earth Surface Processes and Landforms, Reviews, v. 27, p. 814–831, doi:10.1016/j.quascirev.2007.12.005. v. 26, p. 1071–1086, doi:10.1002/esp.254. Love, J.D., 1973, Harebell Formation (Upper Cretaceous) and Pinyon Conglomerate (uppermost Schmidt, S., Hetzel, R., Kuhlmann, J., Mingorance, F., and Ramos, V.A., 2011, A note of caution Cretaceous and Paleocene), northwestern Wyoming: U.S. Geological Survey Professional on the use of boulders for exposure dating of depositional surfaces: Earth and Planetary Paper 734-4, 53 p. Science Letters, v. 302, p. 60–70, doi:10.1016/j.epsl.2010.11.039. Love, J.D., Reed, J.C., Jr., and Christiansen, A.C., 1992, Geologic Map of Grand Teton National Smith, R.B., Byrd, J.O.D., and Susong, D.D., 1993, The Teton fault, Wyoming: Seismotectonics, Park, Teton County, Wyoming: U.S. Geological Survey Miscellaneous Investigations Series Quaternary history, and earthquake hazards, in Snoke, A.W., et al., eds., Geology of Wyo- Map I-2031, scale 1:62,500. ming: Geological Survey of Wyoming Memoir 5, p. 628–667. Lukens, C.E., Riebe, C.S., Sklar, L.S., and Shuster, D.L., 2016, Grain size bias in cosmogenic nu- Stock, G.M., and Uhrhammer, R.A., 2010, Catastrophic rock avalanche 3600 years BP from El clide studies of stream sediment in steep terrain: Journal of Geophysical Research, v. 121, Capitan, Yosemite Valley, California: Earth Surface Processes and Landforms, v. 35, p. 941– p. 978–999, doi:10.1002/2016JF003859. 951, doi:10.1002/esp.1982. MacGregor, K.R., Anderson, R.S., Anderson, S.P., and Waddington, E.D., 2000, Numerical simu Stock, G.M., Bawden, G.W., Green, J.K., Hanson, E., Downing, G., Collins, B.D., Bond, S., and lations of glacial-valley longitudinal profile evolution: Geology, v. 28, p. 1031–1034, doi:10 Leslar, M., 2011, High-resolution three-dimensional imaging and analysis of rock falls in .1130/0091-7613(2000)28<1031:NSOGLP>2.0.CO;2. Yosemite Valley, California: Geosphere, v. 7, p. 573–581, doi:10.1130/GES00617.1.

Straumann, R.K., and Korup, O., 2009, Quantifying postglacial sediment storage at the moun- Ward, D.J., and Anderson, R.S., 2011, The use of ablation-dominated medial moraines as sam- tain-belt scale: Geology, v. 37, p. 1079–1082, doi:10.1130/G30113A.1. plers for 10Be-derived erosion rates of glacier valley walls, Kichatna Mountains, AK: Earth Strunden, J., Ehlers, T.A., Brehm, D., and Nettesheim, M., 2015, Spatial and temporal variations Surface Processes and Landforms, v. 36, p. 495–512, doi:10.1002/esp.2068. in rockfall determined from TLS measurements in a deglaciated valley, Switzerland: Journal Whitehouse, I.E., and McSaveney, M.J., 1983, Diachronous talus surfaces in the Southern Alps, of Geophysical Research, v. 120, p. 1251–1273, doi:10.1002/2014JF003274. New Zealand, and their implications to talus accumulation: Arctic and Alpine Research, Thackray, G.D., and Staley, A.E., 2014, Extensive glaciation during MIS 4 and 3 in the Teton v. 15, p. 53–64, doi:10.2307/1550981. range, Wyoming: Geological Society of America Abstracts with Programs, v. 46, no. 5, Yanites, B.J., Tucker, G.E., and Anderson, R.S., 2009, Numerical and analytical models of cosmo- p. 81. genic radionuclide dynamics in landslide-dominated drainage basins: Journal of Geophysi- Tranel, L.M., Spotila, J.A., Kowalewski, M., and Waller, C.M., 2011, Spatial variation of erosion in cal Research, v. 114, F01007, doi:10.1029/2008JF001088. a small, glaciated basin in the Teton Range, Wyoming, based on detrital apatite (U-Th)/He Zartman, R.E., and Reed, J.C., Jr., 1998, Zircon geochronology of the Webb Canyon Gneiss and thermochronology: Basin Research, v. 23, p. 571–590, doi:10.1111/j.1365-2117.2011.00502.x. Mount Owen Quartz Monzonite, Teton Range, Wyoming: Significance to dating late Archean Tranel, L.M., Spotila, J.A., Binnie, S.A., and Freeman, S.P.H.T., 2015, Quantifying variable erosion metamorphism in the Wyoming Craton: Mountain Geologist, v. 35, p. 71–77. rates to understand the coupling of surface processes in the Teton Range, Wyoming: Geo- Zingg, T., 1935, Beitrage zur Schotteranalyse: Schweizerische Mineralogische und Petrographische morphology, v. 228, p. 409–420, doi:10.1016/j.geomorph.2014.08.018. Mitteilungen, v. 15, p. 21–29.