Rockwall erosion rate inferred from in situ 10 Be concentration of supraglacial clasts: a review

Decoupling of long-term exhumation and short-term erosion rates in the Sikkim Himalaya

Long-term erosion rates of Panamanian drainage basins determined using in situ 10Be

Abstract. In several low mountain ranges throughout Europe, high-grade metamorphic and granitic rocks of the Variscan orogen are exposed – even though the topography of this Paleozoic mountain range was largely leveled during the Permian and later covered by sediments. The Bohemian Massif is one of these low mountain ranges and consists of high-grade metamorphic and magmatic rocks that dip southward below the weakly consolidated Neogene sediments of the Alpine Molasse Basin. Morphologically, the Bohemian Massif is characterized by rolling hills and extensive low-relief surfaces above 500 m, which contrast with deeply incised canyons characterized by steep and morphologically active valley flanks. These morphological features and the occurrence of marine sediments several hundred meters above sea level are a clear indication of relief rejuvenation due to significant surface uplift during the last few million years. To constrain landscape change and its rate, we used the concentration of cosmogenic 10Be in river sands to determine 20 catchment-wide erosion rates and correlated these with topographic metrics characterizing both the hillslopes and the drainage systems. Erosion rates range from 22 to 51 m Myr−1, which is generally low compared to tectonically active mountain ranges such as the Alps. Low erosion rates in the Bohemian Massif seem to contradict the steep topography observed close to the receiving streams (i.e., the Danube River and the Vltava River), which have morphological characteristics of alpine landscapes. We found that erosion rate is correlated with catchment-wide topographic metrics, representing both hillslope and channel morphology. Highest erosion rates occur in catchments featuring high channel steepness and a large area fraction with significant geophysical relief. Catchments with abundant deeply incised canyons erode about twice as fast as those characterized primarily by elevated low-relief surfaces. We interpret the measured erosion rates and related topographic patterns as the landscape response to slow and large-scale uplift in concert with strong variations in bedrock erodibility between rocks of the Bohemian Massif and the Neogene Molasse Basin. We propose that lithology is ultimately responsible for the topographic difference between the mountainous Bohemian Massif and the low-relief Molasse zone despite a common uplift history during the last few million years. As erosion progresses, the basement rocks with their high resistance to erosion are exposed. The repeated emergence of such bedrock barriers reduces the erosion rate during topographic adjustment and governs the evolution of elevated low-relief surfaces at different elevation levels. The resulting stepped landscape requires neither spatial nor temporal changes in uplift rate but can form by erodibility contrasts under uniform uplift conditions.

The Himalayan-Tibetan Plateau presents an exemplary setting to explore the intricate interactions among tectonics, erosion, and climate. Since achieving its elevated stature in the Miocene, the plateau's landscape has undergone significant transformation, largely influenced by several major rivers. The Yarlung Tsangpo River, the largest river on the plateau, has been instrumental in this geomorphic evolution. Throughout the Neogene and Quaternary periods, this river has facilitated the extensive removal and transportation of massive rock volumes from the plateau into the southern Himalayas. Consequently, it has profoundly affected the patterns and intensities of erosion and uplift within the orogenic system, contributed to the reorganization of river networks, and influenced sedimentary processes in the adjacent foreland basin. Nevertheless, the specifics of river erosion evolution process in southeast Tibet and its driving factors remain a subject of considerable debate. In this study, we present an in-depth analysis of both long- and short-term denudation processes in southeast Tibet, particularly along the Yarlung Tsangpo River. The long-term denudation history is elucidated through exhumation rate simulations derived from published low-temperature thermochronological data. Near the hanging wall of the Woka normal fault (upstream), the data indicates an average exhumation rate of 0.23 km/Ma, predominantly from samples older than 10 Ma. In contrast, the footwall experienced an initial rapid exhumation phase around 10.25 ± 0.81 Ma, with rates approximating 0.53 km/ myr. This rate was comparatively steady at 0.31 ± 0.01 km/ myr further from the fault. Subsequently, at 7.12 ± 0.36 myr, the exhumation rate increased to 0.42 ± 0.02 km/myr. Post 5 Ma, rapid exhumation, reaching rates of 0.57 ± 0.05 km/ myr, was confined to the Jiacha Gorge, continuing up to ~1 Ma as indicated by AHe dating. Short-term erosion processes were assessed through millennium-scale catchment erosion rates, determined by cosmogenic nuclide analyses of river sediments. A sample from the hanging wall of the Woka normal fault indicated a catchment-wide erosion rate of 19.9 m/myr. Conversely, samples from outside the Jiacha Gorge, including two from main river tributaries and two from secondary tributaries, demonstrated significantly higher erosion rates, ranging from 47.5 to 67.3 m/myr. Subsequently, we employed 3D thermo-kinematic modeling to reconstruct the region's topography as it appeared approximately 15 million years ago, integrating both long-term exhumation and short-term erosion rates. The model suggests the formation of a peneplain in southern Tibet around 15 Ma, after notable uplift in the early Miocene and substantial exhumation between 20 and 15 Ma. The drainage patterns during this period in southern Tibet likely differed markedly from the present, as the eastward-flowing Yarlung Tsangpo River had not yet formed. It is hypothesized that the river flowed directly towards the Himalayan foreland until around 6 Ma. At this time, the river channel was altered through capture by the Jiacha Gorge, redirecting its flow eastward.

Differential surface uplift and knickpoint evolution along the transient Teesta river in the eastern Himalayas

Abstract. Long-term erosion rates in Tasmania, at the southern end of Australia's Great Dividing Range, are poorly known; yet, this knowledge is critical for making informed land-use decisions and improving the ecological health of coastal ecosystems. Here, we present quantitative, geologically relevant estimates of erosion rates for the George River basin, in northeast Tasmania, based on in situ-produced 10Be (10Bei) measured from stream sand at two trunk channel sites and seven tributaries (mean: 24.1±1.4 Mgkm-2yr-1; 1σ). These new 10Bei-based erosion rates are strongly related to elevation, which appears to control mean annual precipitation and temperature, suggesting that elevation-dependent surface processes influence rates of erosion in northeast Tasmania. Erosion rates are not correlated with slope in contrast to erosion rates along the mainland portions of Australia's Great Dividing Range. We also extracted and measured meteoric 10Be (10Bem) from grain coatings of sand-sized stream sediment at each site, which we normalize to measured concentrations of reactive 9Be and use to estimate 10Bem-based denudation rates for the George River. 10Bem/9Bereac denudation rates replicate 10Bei erosion rates within a factor of 3 but are highly sensitive to the value of 9Be that is found in bedrock (9Beparent), which was unmeasured in this study. 10Bem/9Bereac denudation rates seem sensitive to recent mining, forestry, and agricultural land use, all of which resulted in widespread topsoil disturbance. Our findings suggest that 10Bem/9Bereac denudation metrics will be most useful in drainage basins that are geologically homogeneous, where recent disturbances to topsoil profiles are minimal, and where 9Beparent is well constrained.

Geomorphic process rates in the central Atacama Desert, Chile: Insights from cosmogenic nuclides and implications for the onset of hyperaridity

Rockwall erosion due to rockfalls is one of the most efficient erosion processes at high elevations. It is, therefore, important to quantify this erosion to understand the long-term evolution of mountain topography. This is especially crucial since rockfall frequency is increasing in high-Alpine areas, such as in the Mont-Blanc massif (MBM), due to regional scale permafrost degradation (which occurs through thickening of the active layer, the subsurface layer freezing and thawing throughout the year), a consequence of climate warming and the multiplication of heat waves.To better understand rockfalls as a permafrost-related process, we quantify the erosion rates at different time scales by i) a short-term (  ̴ ten-year scale) quantification of the dynamics of the rock walls based on the diachronic comparison of topographic measurements carried out by terrestrial laser scanning (LiDAR) and ii) a long-term quantification (102-104 year scale) based on the 10Be concentration of sediment sampled downglacier on medial moraines. Our analysis considered that once the rockfalls have occurred, clasts are transported within the ice stream and amalgamated by ice melt in the ablation zone, forming medial moraines. The 10Be concentration is linked to the rockwall erosion rate and the time needed to transport from the glacier equilibrium line to the sampling location.Scanned rockwalls and rockwall sources vary in elevation, aspect, slope, and area, allowing us to assess whether these factors influence the measured 10Be concentration and erosion rates. We studied rockwalls located on the French side between 2800 m and 4200 m a.s.l. and between 2500 m and 4600 m a.s.l. on the Italian side. We collected 8 (Géant basin and Vallée Blanche, France) and 10 supraglacial samples (Brouillard and Frêney glaciers, Italy), respectively.  Our results reveal substantial variations in 10Be concentrations. On the French side of the MBM, 10Be concentrations vary from 1.2 ± 0.2 to 6.7 ± 0.4 x 104 atoms g-1, while they range from 3.0 ± 0.2 to 92.0 ± 3.2 x 104 atoms g-1 on the Italian side. These results suggest that the long-term erosion rates vary between 0.8-1.7 and 0.1-0.3 mm.yr-1, respectively. The short-term erosion rates for the French side are 4.3 mm.yr-1 for 2005-2014 and 39.3 for the period of 2015-2022. On the Italian side, they are 0.8 mm.yr-1 for 2005-2011 and 6.1 for 2011-2017.Our results show spatial differences in erosion rates on both sides of the MBM. Short-term erosion rate is lower on the Italian side, and 10Be concentrations are higher, meaning that the rock walls are more stable in this area. However, on both sides of the MBM, erosion rates have increased significantly recently, with a further acceleration during the last decade. This suggests that high-altitude rockwalls, previously unaffected by global warming, are progressively entering a state of permafrost degradation.

Landscape form and millennial erosion rates in the San Gabriel Mountains, CA

Contemporary glacial erosion rates based on sediment yields in southeast Alaska merit considerable attention because they are unsurpassed worldwide, and they significantly exceed long‐term exhumation rates in the region. Two issues are likely to contribute to these high rates: contemporary sediment yields in fjords (1) have generally been overestimated by failing to account for the considerable input of subaerially derived material and (2) are exceptionally high because tidewater glaciers in southeast Alaska have been anomalously dynamic and erosive during the past century of rapid retreat. To investigate these influences and to quantify the rate at which Tyndall Glacier erodes its basin we present seismic data defining the volume of sediments in Taan Fjord, Icy Bay. We subtract the contribution of subaerially derived sediments from the fjord sediment package to determine the sediment yield directly from Tyndall Glacier during the most recent period of retreat: 1962–1999. Using a numerical model of proglacial glacimarine sedimentation, we then calculate the annual sediment yield from, and the corresponding erosion rate of, Tyndall Glacier during this period, which averages 28 ± 5 mma−1. A strong correlation emerges between glacial retreat rates and glacial sediment yields, implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to contemporary erosion rates that are a factor of 3.5 ± 1.5 higher than in the long term. Hence we estimate the long‐term erosion rate for Tyndall Glacier to be 9 ± 2 mma−1.

Erosion and exhumation in the Himalaya from cosmogenic isotope inventories of river sediments

In contrast to the mountainous topography and high relief of the eastern Tauern window, the adjacent Nock Mountains (Gurktal Alps, Austria) are characterized by hilly topography, lower relief and rounded summits with elevations of ca. 2000 m. Although the unusual landforms in the Nock Mountains have long been recognized (Hejl, 1997; Frisch et al., 2000, and references therein), little is known about rates of landscape evolution in this area, which was deglaciated ~15 ka ago (Wölfler et al., 2022). Here we present a new set of 16 catchment-wide erosion rates from the Nock Mountains derived from cosmogenic 10Be concentrations in stream-sediment samples. Samples from 10 major streams that drain the Nock Mountains toward the Mur-Mürz valley, the Katschberg-Lieser valley and the Drau valley range between ~130 and ~300 mm/ka. Smaller subcatchments with low relief located in the upper part of the larger catchments erode at lower rates between ~80 and ~160 mm/ka. A comparison between 10Be-derived erosion rates and exhumation rates obtained from low-temperature thermochronology and thermokinematic modelling reveals that short-term and long-term erosion rates are remarkably similar. In the central Nock Mountains, 10Be-derived erosion rates of 110-160 mm/ka are similar to the long-term exhumation rate of ~160 m/Ma since ~34 Ma (Wölfler et al., 2023). The southern Nock Mountains (Millstatt Complex) show higher short-term erosion rates of 170-300 mm/ka and also a higher long-term exhumation rate of ~270 m/Ma since 18 Ma (Wölfler et al., 2023). The similarity between short-term and long-term erosion rates suggests that the pace of erosion in the Nock Mountains did not change significantly during the late Cenozoic. A comparison of our data with 10Be erosion rates from the eastern Tauern Window (>500 m/Ma) and the Lavanttal Alps (

We use cosmogenic 10Be analysis of fluvial sediments and bedrock to estimate erosion rates (104-105 year timescale) and to infer the distribution of post-orogenic geomorphic processes in the Blue Ridge Province in and around Shenandoah National Park, Virginia. Our sampling plan was designed to investigate relationships between erosion rate and lithology, mean basin slope, basin area, and sediment grain size. Fifty-nine samples were collected from a variety of basin sizes ( Inferred erosion rates for the medium sand fraction of all fluvial samples from all lithologies range from 3.0 to 21 m/My. The area-weighted mean erosion rate for single-lithology basins in the Park is 12.2 m/My. Single-lithology erosion rate ranges for fluvial samples are: granite, 7.0 to 20 m/My; metabasalt, 3.8 to 21 m/My; quartzite, 3.8 to 15 m/My; and siliciclastic rocks, 5.2 to 15 m/My. Multilithology basins erode at rates between 3.0-16 m/My. The Shenandoah River basin (3305 km2) is eroding at 6.6 m/My. Bedrock erosion rates range from 1.8 to 11 m/My across all lithologies, with a mean of 6.5 ± 4.3 m/My. Grain-size specific 10Be analysis of four samples showed no consistent trend of concentration with grain size. Cosmogenic analysis of bedrock and sediment from the Shenandoah National Park area allows us to speculate about why some parts of the Appalachian Mountains erode more slowly and some more rapidly. Overall, it appears that steep drainage basins erode more rapidly than gently sloped basins. Climate and lithology may also influence basin-scale rates of erosion as suggested by the difference in average erosion rates east and west of the divide and the difference between the erosion rates of quartzite- and granite-dominated basins. Data are conflicting in regards to the evolution of relief over time. Analyses made of exposed bedrock along ridgelines suggest that such rock is eroding either more slowly than adjacent drainage basins (Susquehanna River, Shenandoah National Park region) or at similar rates (Great Smoky Mountains) providing a mechanism for growing relief at the scale of individual ridgelines. However, considering relief on a landscape or physiographic province scale, by comparing erosion rates of the highlands versus the lowlands, suggests that relief of the range as a whole is either steady or very slowly decreasing over multi-millennial timescales. The presence of significant erosion rate/slope relationships negates a broad Hackian view of the landscape because there is not uniform erosion across this landscape. The aspect-erosion rate and slope-erosion rate relationships present in the Shenandoah area suggest that the landscape is not fully adjusted to rock strength.

In contrast to the mountainous topography and high relief of the Hohe Tauern, the adjacent Nock Mountains (Gurktal Alps) are characterized by hilly topography, lower relief and rounded summits. Although the peculiar landforms in the Nock Mountains have long been recognized, little is known about the rates of landscape evolution in this area. Here we present the first set of 16 10Be-based catchment-wide erosion rates from the Nock Mountains. Our results show that the 10 main catchments erode at rates between ~ 120 and ~ 280 mm/ka. Sub-catchments comprising a high percentage of low-relief surfaces erode at lower rates than the steeper lower parts of the main catchments, which indicates active river incision and relief growth. A comparison between 10Be erosion rates and exhumation rates derived from thermochronology and thermokinematic modelling reveals that short-term and long-term erosion rates are remarkably similar. In the central Nock Mountains, the average 10Be erosion rate (166 ± 35 mm/ka) is almost identical to the average exhumation rate (160 ± 20 m/Ma since ~ 34 Ma). The southern Nock Mountains show a higher 10Be rate (202 ± 58 mm/ka) and a higher long-term exhumation rate (270 ± 30 m/Ma since ~ 18 Ma). The agreement between short-term and long-term erosion rates suggests that average erosion rates in the Nock Mountains did not change significantly during the late Cenozoic. Comparing our data to surrounding regions shows that erosion rates from the Nock Mountains fit to the general W–E decrease in catchment-wide erosion rates observed in the Eastern Alps.Graphical abstract

Erosion rates of the Bhutanese Himalaya determined using in situ-produced 10Be