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In the arid region of northern Chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation. Previous studies of denudation rates from cosmogenic 10Be and 26Al concentrations are limited to single drainages. In this study, we examine catchment‐ to orogen‐scale spatial variation in denudation rates between 18 and 23°S in the Coastal and Western Cordilleras of northern Chile. 10Be and 26Al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment‐averaged denudation rates. At broader scales, we examine whether denudation rates and orogen topography reflect the 3‐D plate geometry of the region. Cosmogenic nuclide‐derived denudation rates range from 0.4 ± 0.5 to 20.6 ± 1.5 m/Myr in the Coastal Cordillera and from 1.4 ± 0.7 to 168.0 ± 19.8 m/Myr in the Western Cordillera. The controls on the denudation rates are evaluated using a statistical factor analysis of 10 selected catchment parameters. Denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates, drainage area, stream order, mean elevation, mean local relief, mean basin slope, and grain size of the sampled sediments. Moreover, denudation rates are better correlated with tectonic controls at catchment scale than orogen‐scale plate tectonics in the Western and Coastal Cordillera. Analyzing tectonic and climatic influences on 10Be‐and 26Al‐derived denudation rates in a syntaxial orogenSignificant correlation and covariation of denudation rates and channel steepness indicesCatchment‐scale tectonic processes rather than orogen‐scale topographic trends control denudation rates in this arid setting

Alpine glacial erosion exerts a first‐order control on mountain topography and sediment production, but its mechanisms are poorly understood. Observational data capable of testing glacial erosion and transport laws in glacial models are mostly lacking. New insights, however, can be gained from detrital tracer thermochronology. Detrital tracer thermochronology works on the premise that thermochronometer bedrock ages vary systematically with elevation, and that detrital downstream samples can be used to infer the source elevation sectors of sediments. We analyze six new detrital samples of different grain sizes (sand and pebbles) from glacial deposits and the modern river channel integrated with data from 18 previously analyzed bedrock samples from an elevation transect in the Leones Valley, Northern Patagonian Icefield, Chile (46.7°S). We present 622 new detrital zircon (U‐Th)/He (ZHe) single‐grain analyses and 22 new bedrock ZHe analyses for two of the bedrock samples to determine age reproducibility. Results suggest that glacial erosion was focused at and below the Last Glacial Maximum and neoglacial equilibrium line altitudes, supporting previous modeling studies. Furthermore, grain age distributions from different grain sizes (sand, pebbles) might indicate differences in erosion mechanisms, including mass movements at steep glacial valley walls. Finally, our results highlight complications and opportunities in assessing glacigenic environments, such as dynamics of sediment production, transport, transient storage, and final deposition, that arise from settings with large glacio‐fluvial catchments. Mountain glaciers flow down valleys and erode the underlying rocks. Furthermore, rivers that are fed by glaciers, rock falls, and hillslope processes contribute to the erosion of glaciated landscapes. Understanding these processes and where erosion occurs in a catchment is important because these factors affect how landscapes evolve over time and under changing climate conditions. It is difficult to directly study processes that occur under glaciers because these regions are inaccessible. As a result, computer models of glacier erosion are often used to predict where and how erosion occurs. One technique to test these models is to trace where sediments, that were deposited in a glacial moraine or that are being transported by a river from a glacier, originated from within the catchment. We applied this technique to moraine and river samples from the Northern Patagonian Icefield, Chile, to determine at what elevation most erosion occurred during neoglacial times, 2.5 thousand years ago, and to better understand the influence of sediment size and sampling location along a river on study results. Our main finding confirms previous computer models and observational studies that erosion during glacial times is focused in a narrow elevation sector, where glacier sliding velocity is highest. Integration of bedrock, detrital moraine, and fluvial thermochronometer samples documents spatial variations in catchment erosionApproximately 2.5 ka (or earlier) glacial erosion is focused at the Last Glacial Maximum equilibrium line altitude and limited at higher elevationsA well‐constrained bedrock map of cooling ages is essential for quantifying erosion and sediment routing within catchments Integration of bedrock, detrital moraine, and fluvial thermochronometer samples documents spatial variations in catchment erosion Approximately 2.5 ka (or earlier) glacial erosion is focused at the Last Glacial Maximum equilibrium line altitude and limited at higher elevations A well‐constrained bedrock map of cooling ages is essential for quantifying erosion and sediment routing within catchments

Ice shelves around Antarctica can provide back stress for outlet glaciers and control ice sheet mass loss. They often contain narrow bands of thin ice termed ice shelf channels. Ice shelf channel morphology can be interpreted through surface depressions and exhibits junctions and deflections from flowlines. Using ice flow modeling and radar, we investigate ice shelf channels in the Roi Baudouin Ice Shelf. These are aligned obliquely to the prevailing easterly winds. In the shallow radar stratigraphy, syncline and anticline stacks occur beneath the upwind and downwind side, respectively. The structures are horizontally and vertically coherent, except near an ice shelf channel junction where patterns change structurally with depth. Deeper layers truncate near basal incisions. Using ice flow modeling, we show that the stratigraphy is ∼9 times more sensitive to atmospheric variability than to oceanic variability. This is due to the continual adjustment toward flotation. We propose that syncline‐anticline pairs in the shallow stratigraphy are caused by preferential snow deposition on the windward side and wind erosion at the downwind side. This drives downwind deflection of ice shelf channels of several meters per year. The depth variable structures indicate formation of an ice shelf channel junction by basal melting. We conclude that many ice shelf channels are seeded at the grounding line. Their morphology farther seaward is shaped on different length scales by ice dynamics, the ocean, and the atmosphere. These processes act on finer (subkilometer) scales than are captured by most ice, atmosphere, and ocean models, yet the dynamics of ice shelf channels may have broader implications for ice shelf stability. Ice flows from Antarctica's interior toward the coast. At the contact point between ice and ocean, the ice becomes afloat and forms fast‐flowing ice shelves. Snowfall continuously accumulates at the ice shelf surface, and at the ice shelf bottom the relatively warm ocean water can melt ice from below. Ice shelves sometimes exhibit a network of surface depressions resembling a river network. At the base, the depressions are accompanied by large incisions termed ice shelf channels. Using radar as a tool for echolocation, we investigate how the shape of this network is formed. We find that snow preferentially collects in the upwind side of the surface depressions. This makes ice shelf channels move to the downwind side. We also find that ice shelf channels can form junctions through localized ocean melting. This is important because it helps us to better understand how the Antarctic ice sheet interacts with the surrounding ocean. The radar stratigraphy in ice shelves is 9 times more sensitive to variability in snow deposition than to variability in basal meltingSome ice shelf channels at Roi Baudouin Ice Shelf deflect from flowlines; the radar stratigraphy reflects related processesVariable snow deposition causes slow deflection, and basal melting can form ice shelf channel junctions far from the grounding line