Hurricanes alter 10Be concentrations in tropical river sediment but do not change regional erosion rate estimates. Issue 5 (1st March 2022) - Quock, Melinda
Abstract: Tropical islands, including many in island arcs, are subjected to recurring disturbances from extreme storms such as tropical cyclones. To test whether such storms influence cosmogenic nuclide concentrations such that they do not reflect long‐term rates of erosion, we measured meteoric and in situ 10 Be in river sediment samples from Dominica, an andesitic island in the Caribbean, before and after category five Hurricane Maria (in 2017). Populations of before‐ and after‐storm concentrations are statistically indistinguishable ( n = 7 pairs for in‐situ 10 Be, n = 11 pairs for meteoric 10 Be). 10 Be concentrations vary from −138% to +73% within before–after sample pairs relative to the mean of the pair. These new data suggest that the effects of extreme storms on the depth and amount of near‐surface erosion on Dominica vary spatially. Our data support the calculations of Niemi et al. (2005) and Yanites et al. (2009) suggesting that basin‐by‐basin comparisons of erosion rates based on cosmogenic nuclides should be approached with caution in small (<~100 km 2 ) watersheds affected by mass movements and extreme storms. Erosion rates determined from in‐situ 10 Be on Dominica (geometric mean = 0.102 mm y −1, n = 12) are low compared to similarly steep and wet areas globally and correlate positively with the spatial density of mass movements. Abstract : Direct landfall of Hurricane Maria on the Caribbean island of Dominica in fall 2017 caused widespread landsliding, streambank erosion, and flooding. Isotopic analysis of river sediment collected before and after the storm is consistent with mass movement frequency controlling long‐term erosion rates. Long‐term erosion rates for this wet, steep, tropical island are low compared to other similar locations around the world. Although results from same‐site before‐ and after‐storm pairs differ from each other, median erosion rates are similar for both sample sets.