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Cosmogenic 10Be and 26Al exposure ages from 20 erratic samples collected from Cadair Idris (893 m), a mountain in southern Snowdonia, Wales, provide evidence for the timing of deglaciation from summits to cirques at the end of the Late Pleistocene. The summit of the mountain is characterised by intensely modified frost-shattered surfaces that have long been identified as a representing a former nunatak. Numerous glacially-transported quartz boulders on the highest ground indicate that ice overran the summit at some point in the Pleistocene. Two quartz boulders, one with preserved striations, sampled at c. 856 m near the summit of Cadair Idris yielded consistent 10Be and 26Al paired exposure ages of 75 ka to 60 ka (using a high-latitude sea level 10Be spallation production rate of 4.20 at/g/y, scaled by the Lal/Stone scheme). A glacially polished bedrock quartzite outcrop at 735 m gave an age of 17.5 ka. Immediately below this, cirque and down-valley recessional moraine ages, covering an elevation of 480 m to 350 m ranged from 10 to 15 ka respectively.These results confirm that Cadair Idris was overridden by the Welsh Ice Cap during marine isotope stage (MIS) 4, when ice was thicker than at the global last glacial maximum (LGM) in MIS 2. This is consistent with findings from northern Snowdonia. The highest Welsh summits, including Cadair Idris, emerged above a thinning Welsh Ice Cap (British Irish Ice Sheet) during the transition from MIS 4 to 3. The summit area above ~800 m then stood as nunataks above the LGM ice sheet surface in MIS 2. The Welsh Ice Cap then rapidly thinned over Cadair Idris at ~20-17 ka based on ages from high-level ice-moulded bedrockThis is supported by more new ages from high-level paired erratics and bedrock samples on several other mountains throughout Snowdonia, leading to a phase of alpine-style deglaciation. Valley glaciers initiated their retreat up-valley from ~17 to 14 ka after Heinrich Event 1. A later phase of glacier stabilisation or still stand formation produced classic cirque moraines near the rim of a present cirque lake basin (480 m elevation) yielding 10Be ages of 13-10 ka during the Younger Dryas.

Reworking of old sediment in the Murray-Darling implies alteration of environmental signals traveling from source to sink., Understanding how sediment transport and storage will delay, attenuate, and even erase the erosional signal of tectonic and climatic forcings has bearing on our ability to read and interpret the geologic record effectively. Here, we estimate sediment transit times in Australia’s largest river system, the Murray-Darling basin, by measuring downstream changes in cosmogenic 26Al/10Be/14C ratios in modern river sediment. Results show that the sediments have experienced multiple episodes of burial and reexposure, with cumulative lag times exceeding 1 Ma in the downstream reaches of the Murray and Darling rivers. Combined with low sediment supply rates and old sediment blanketing the landscape, we posit that sediment recycling in the Murray-Darling is an important and ongoing process that will substantially delay and alter signals of external environmental forcing transmitted from the sediment’s hinterland.

The eastern seaboard of Australia is characterized by a passive margin and a continental divide that separates the inland-draining rivers from those that drain to the Coral and Tasman seas. Seaward of this divide lies the Great Escarpment (GE) of Australia that separates a moderate relief coastal plain from a low relief, high elevation plateau. Quantifying the spatial variation of erosion rates from temperate New England (NE), NSW and tropical Bellenden Ker (BK), Queensland, two regions with distinctly different climates and escarpment embayment, could help constrain erosional controls that contribute to escarpment form. In this study, we compared forty detrital 10Be samples collected from sediments in the main trunk and tributaries of five major rivers: the Macleay, Bellinger, and Clarence in NE and the Russel-Mulgrave and North Johnstone in BK. We then traced the escarpment position in ARCGIS and calculated a sinuosity ratio to better compare the degree of embayment in each region. Across both datasets we found that for NE, which has deep gorges cutting into the plateau, the degree of embayment was twice that of BK, where the escarpment position is significantly less embayed and erosion rates significantly more variable (ratio of .18 vs .38). Erosion rates in low slope areas, such as on the plateau, were universally low with no other significant controlling factors. There was no correlation between erosion rates and catchment area, and that our data echo previous studies that find that once mean rainfall passes an approximate threshold (around 2000mm/yr) basin characteristics that are known to control erosion rates, such as slope and lithology, are subdued. In temperate NE, where rainfall ranges from approximately 800-1200mm/yr, there was a moderate linear correlation with mean catchment rainfall and erosion rates (R2 .50), which is likely due to a strong orographic effect due to the escarpment. Erosion rates from tributaries below the plateau were highly variable and ranged from 5m/Ma up to 60m/Ma and correlated strongly with mean catchment slope (R2 .86). In addition, there were moderate inverse linear correlations between erosion rate and the catchment total percent granite and sedimentary rock (R2 .53 and .63 respectively) and a moderate correlation between erosion rate and catchment total percent metamorphic rock (R2 .57). Similar to previous studies, these data suggest that in temperate climates with moderate amounts of annual rainfall, individual basin characteristics play a significant role in controlling basin wide erosion rates.In contrast, data from tropical BK, where mean rainfall amounts are in excess of 2000mm/yr, erosion rates from tributaries below the plateau were significantly less variable than NE. Rates had a mean of 37m/Ma ± 9 (standard deviation 5m/Ma, N=10) and were not significantly correlated with mean catchment slope nor catchment lithology. The mean erosion rate of BK is similar to that of other studies in the region, though with slightly less variability, and possibly reinforces the hypothesis from other researchers that in tropical climates with significant mean rainfall, soil depth effectively armors hillslopes and prevents bedrock erosion from occurring.

Rupture associated with the 25 April 2015 M w 7.8 Gorkha (Nepal) earthquake highlighted our incomplete understanding of the structural architecture and seismic cycle processes that lead to Himalayan mountain building in Central Nepal. In this paper we investigate the style and kinematics of active mountain building in the Himalayan hinterland of Northwest India, approximately 400 km to the west of the hypocenter of the Nepal earthquake, via a combination of landscape metrics and long- (Ma) and short-term (ka) erosion rate estimates (from low temperature thermochronometry and basin-wide denudation rate estimates from 10 Be concentrations). We focus our analysis on the area straddling the PT 2 , the physiographic transition between the Lesser and High Himalaya that has yielded important insights into the nature of hinterland deformation across much of the Himalaya. Our results from Northwest India reveal a distinctive PT 2 that separates a Lesser Himalaya region with moderate relief (∼1000 m) and relatively slow erosion ( 2 has persisted in the same relative position since at least the past 1.5 Ma. We interpret these observations to suggest that strain accumulation in this hinterland region throughout at least the past 1.5 Ma has been accomplished both by crustal thickening via duplexing and overthrusting along transient emergent faults. Despite the >400 km distance between them, similar spatiotemporal patterns of erosion and deformation observed in Northwest India and Central Nepal suggest both regions experience similar styles of active strain accumulation and both are susceptible to large seismic events.

Rivers draining the semiarid Transhimalayan Ranges at the western Tibetan Plateau margin underwent alternating phases of massive valley infill and incision in Pleistocene times. The effects of these cut-and-fill cycles on millennial sediment fluxes have remained largely elusive. We investigate the timing and geomorphic consequences of headward incision of the Zanskar River, a tributary to the Indus, which taps the >250-m thick More Plains valley fill that currently plugs the endorheic high-altitude basins of Tso Kar and Tso Moriri. In situ 10Be exposure dating and topographic analyses show that a phase of valley infill gave way to net dissection and the NW Himalaya's first directly dated stream capture in late Marine Isotope Stage (MIS) 6, ∼135 ka ago. Headwaters of the Indus are currently capturing headwaters of the Sutlej, and rivers have eroded >14.7 km3 of sediment from the Zanskar headwaters since, mobilising an equivalent of ∼8% of the Indus' contemporary sediment storage volume from only 0.3% of its catchment area. The resulting specific sediment yields are among the rarely available rates averaged over the 105-yr timescale, and surpass 10Be-derived denudation rates from neighbouring catchments three- to tenfold. We conclude that recycling of Pleistocene valley fills has fed Transhimalayan headwaters with more sediment than liberated by catchment denudation, at least since the last glacial cycle began. This protracted release of sediment from thick Pleistocene valley fills might bias estimates of current sediment loads and long-term catchment denudation.

Conventional methods for the determination of past soil erosion provide only average rates of erosion of the sediment's source areas and are unable to determine the rate of at-a-site soil loss. In this study, we report in-situ produced cosmogenic 10Be, and 14C measurements from erratic boulders and two depth-profiles from Younger Dryas moraines in Scotland, and assess the extent to which these data allow the quantification of the amount and timing of site-specific Holocene soil erosion at these sites. The study focuses on two sites located on end moraines of the Loch Lomond Readvance (LLR): Wester Cameron and Inchie Farm, both near Glasgow. The site near Wester Cameron does not show any visible signs of soil disturbance and was selected in order to test (i) whether a cosmogenic nuclide depth profile in a sediment body of Holocene age can be reconstructed, and (ii) whether in situ 10Be and 14C yield concordant results. Field evidence suggests that the site at Inchie Farm has undergone soil erosion and this site was selected to explore whether the technique can be applied to determine the broad timing of soil loss. The results of the cosmogenic 10Be and 14C analyses at Wester Cameron confirm that the cosmogenic nuclide depth-profile to be expected from a sediment body of Holocene age can be reconstructed. Moreover, the agreement between the total cosmogenic 10Be inventories in the erratics and the Wester Cameron soil/till samples indicate that there has been no erosion at the sample site since the deposition of the till/moraine. Further, the Wester Cameron depth profiles show minimal signs of homogenisation, as a result of bioturbation, and minimal cosmogenic nuclide inheritance from previous exposure periods. The results of the cosmogenic 10Be and 14C analyses at Inchie Farm show a clear departure from the zero-erosion cosmogenic nuclide depth profiles, suggesting that the soil/till at this site has undergone erosion since its stabilisation. The LLR moraine at the Inchie Farm site is characterised by the presence of a sharp break in slope, suggesting that the missing soil material was removed instantaneously by an erosion event rather than slowly by continuous erosion. The results of numerical simulations carried out to constrain the magnitude and timing of this erosion event suggest that the event was relatively recent and relatively shallow, resulting in the removal of circa 20–50 cm of soil at a maximum of ∼2000 years BP. Our analyses also show that the predicted magnitude and timing of the Inchie Farm erosion event are highly sensitive to the assumptions that are made about the background rate of continuous soil erosion at the site, the stabilisation age of the till, and the density of the sedimentary deposit. All three parameters can be independently determined a priori and so do not impede future applications to other localities. The results of the sensitivity analyses further show that the predicted erosion event magnitude and timing is very sensitive to the 14C production rate used and to assumptions about the contribution of muons to the total production rate of this nuclide. Thus, advances in this regard need to be made for the method presented in this study to be applicable with confidence to scenarios similar to the one presented here.

Cosmogenic nuclide exposure dating of glacial clasts is becoming a common and robust method for reconstructing the history of glaciers and ice sheets. In Antarctica, however, many samples exhibit cosmogenic nuclide ‘inheritance’ as a result of sediment recycling and exposure to cosmic radiation during previous ice free periods. In-situ cosmogenic 14C, in combination with longer lived nuclides such as 10Be, can be used to detect inheritance because the relatively short half-life of 14C means that in-situ 14C acquired in exposure during previous interglacials decays away while the sample locality is covered by ice during the subsequent glacial. Measurements of in-situ 14C in clasts from the last deglaciation of the Framnes Mountains in East Antarctica provide deglaciation ages that are concordant with existing 26Al and 10Be ages, suggesting that in this area, the younger population of erratics contain limited inheritance.