Cosmogenic nuclide analysis of river sediment provides insight into catchment‐wide erosion rates and dynamics. Here, we investigate spatial patterns and controls on10Be‐inferred erosion rates in Madagascar, a moderately seismically active microcontinent surrounded by passive margins with locally steep topography and a climate that varies from humid tropical to semiarid. We use a compiled dataset of 99 detrital10Be measurements, 63 of which are new, covering more than 30% of the country and a wide range of topographic, bioclimatic and geologic characteristics. Overall,10Be erosion rates are low (2.4–51.1 mm kyr−1), with clear differences between regions. The lowest rates are measured on the central highlands ( 8 mm kyr−1), in the Alaotra–Ankay graben ( 11 mm kyr−1) and in the large north‐central catchments ( 11 mm kyr−1). Higher rates are found on the steep eastern escarpment ( 20 mm kyr−1), in the northwest ( 31 mm kyr−1) and in the southwest ( 29 mm kyr−1). A stepwise linear regression model identified elevation as the main factor associated with variations in10Be erosion rates (lower rates for higher catchments). Random within‐between statistical models (REWB), on the other hand, indicated that the differences between different regions can be explained by differences in river concavity, seismic events and gully (lavaka) densities, whereas additional variation within regions is only linked to seismicity. We find no correlation between catchment or river steepness and10Be‐inferred erosion rates. Our results indicate that in Madagascar, long‐term erosion rates are overall low and that simple topography‐based models do not explain variations in rates of landscape change inferred from10Be concentrations in river sediment. We demonstrate that identifying different regions aids in interpreting spatial patterns of erosion rates and that REWB models can be a powerful tool in deciphering environmental controls on10Be erosion rates.
Paired in situ cosmogenic nuclides14C and10Be present an opportunity to explore erosion rate disequilibria over Holocene to latest Pleistocene timescales and are a new avenue in surface processes research.14C and10Be concentrations in quartz from river sand collected at the outlets of five mountainous catchments in the Argentine Andes are compared in this study. River gauge and10Be‐derived erosion rates are in good agreement; however,14C concentrations are approximately 2.7–4 times lower than expected relative to10Be under steady‐state erosion. Low14C to10Be ratios imply that sediment eroded from the high mountains was shielded for at least 7–15 ky. Neoglacial advances and storage in terraces may account for some of the reduced14C concentrations but are insufficient alone. Transient storage in dynamic talus slopes in the steep topography of the High Andes provides the best explanation for the observed14C concentrations.
more » « less- NSF-PAR ID:
- 10393782
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 24
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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