For more than a century, geologists have sought to measure the distribution of erosion rates on Earth's dynamic surface. Since the mid-1980s, measurements of in situ 10 Be, a cosmogenic radionuclide, have been used to estimate outcrop and basin-scale erosion rates at 87 sites around the world. Here, we compile, normalize, and compare published 10 Be erosion rate data (n = 1599) in order to understand how, on a global scale, geologic erosion rates integrated over 10 3 to 10 6 years vary between climate zones, tectonic settings, and different rock types.Drainage basins erode more quickly (mean = 218 m Myr −1 ; median = 54 m Myr −1 ) than outcrops (mean = 12 m Myr −1 ; median = 5.4 m Myr −1 ), likely reflecting the acceleration of rock weathering rates under soil. Drainage basin and outcrop erosion rates both vary by climate zone, rock type, and tectonic setting. On the global scale, environmental parameters (latitude, elevation, relief, mean annual precipitation and temperature, seismicity, basin slope and area, and percent basin cover by vegetation) explain erosion rate

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We use 10 Be and 26 Al to determine long-term sediment generation rates, identify significant sediment sources, and test for landscape steady state in Nahal Yael, an extensively studied, hyperarid drainage basin in southern Israel. Comparing a 33 yr sediment budget with 33 paired 10 Be and 26 Al analyses indicates that short-term sediment yield (113-138 t• km-2 •yr-1) exceeds long-term sediment production (74 ± 16 t• km-2 •yr-1) by 53%-86%. The difference suggests that the basin is not in steady state, but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield. Nuclide data indicate that (1) sediment leaving the basin is derived primarily from hillslope colluvium, (2) bedrock weathers more rapidly beneath a cover of colluvium than when exposed, and (3) long-term erosion rates of granite, schist, and amphibolite are similar.

Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10 Be in river sediment samples and found that south-central South Africa is eroding ~5 m m.y. −1 , a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10 Be and 26 Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of <0.2 m m.y. −1 (median, 0.34 m m.y. −1), consistent with no Quaternary movement on faults that displace the underlying quartzite but not the silcrete cover. We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10 Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known.

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Analysis of in situ-produced cosmogenic nuclides, including 10 Be, 26 Al, and 36 Cl, has changed how geologists understand desert surface processes. Here, we provide a series of examples from arid mountain-piedmont systems that illustrate both the power and limitations of this geochronometer. Analyses of samples collected from bare bedrock surfaces at the Alabama Hills, California, demonstrate slow but variable (1.4-20 m m.y. −1) rates of erosion, whereas cosmogenic dating of the Blackhawk landslide debris (~6.5-31 k.y.) and the Castle Dome piedmont allows linkages between landscape-scale processes and climate change. However, data show that nuclides inherited from prior periods of exposure, as well as the effect of post-depositional surface change, limit the accuracy and precision of exposure dating in some settings. On the broad Castle Dome piedmont, detailed isotopic stratigraphies, coupled with analysis of desert soils, indicate depositional histories over the past ~70 k.y. in the absence of radiocarbon-datable organic material. Transect-based amalgamated sampling techniques allow for estimation of sediment velocity down mountain-fringing piedmonts. In drainage basins, the concentration of 10 Be in fluvial sediment demonstrates the efficacy of fluvial mixing even in areas where surface flow is intermittent. Considered together, these applications of the cosmogenic technique allow the delineation of sediment budgets in areas where no other technique has been useful. Such data are important for the arid Southwest, where population is increasing rapidly, as is the interaction of society and surface processes.

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