Beryllium-10 derived erosion rates from the Hangay Mountains, Mongolia: landscape evolution in a periglacially-dominated continental interior

Abstract

Terrestrial cosmogenic nuclides such as beryllium-10 have recently been used as a way to determine basin-average erosion rates around the world. These erosion rates are useful to geomorphologists investigating landscape evolution. The Hangay Mountains in Mongolia are a prime location to use beryllium-10 because of the granitic rocks that provide the quartz needed for cosmogenic analysis as well as the lack of observed evidence of recent or old mass wasting events that mobilize sediment and bedrock with much lower cosmogenic concentrations that cause underestimations of erosion rates. Basin-average erosion rates observed in seven basins across the eastern Hangay Mountains range from 12 m/My to about 20 m/My. These are of similar magnitude to those found in tectonically inactive regions such as the southern Appalachians. Comparing basin-average erosion rates to basin parameters, whole basin relief had the highest calculated R2 value and elevation had the lowest P-value. No strong relationships were seen between erosion rate and mean slope angle, hypsometric integral, area, or mean local relief. The basin-average erosion rates observed in the Hangay were compared to previous studies by Ahnert (1970), Portenga and Biernman (2011), and Matmon et al. (2009). We found erosion rates from the Hangay to be much lower than expected in our analyses. The differences in erosion rates from the Hangay Mountains compared to other places around the world are likely due to the fact that the streams in the Hangay are eroding into alluvium as opposed to bedrock, and are located in a landscape dominanted by diffusive hillslope sediment transport mechanisms. The erosion rate is limited to the amount of sediment that can be transported by the streams.