Pfeiffer, Allison M.Morey, SusannahKarlsson, Hannah M.Fordham, Edward M....
19页
查看更多>>摘要：Bed material abrasion is a major control on the partitioning of basin-scale sediment fluxes between coarse and fine material. While abrasion is traditionally treated as an exponential function of transport distance and a lithology-specific abrasion coefficient, experimental studies have demonstrated greater complexity in the abrasion process: the rate of abrasion varies with clast angularity, transport rate, and grain size. Yet, few studies have attempted to assess the importance of these complexities in a field setting. Here, we develop a new method for rapidly quantifying baseline abrasion rate in the field via Schmidt Hammer Rock Strength. We use this method, along with measurements of gravel bar lithology, to quantify abrasion in the Suiattle River, a basin in the North Cascades of Washington State in which sediment supply to the channel is dominated by recurrent debris flows from a tributary draining Glacier Peak stratovolcano. Rapid downstream strengthening of river bar sediment and a preferential loss of weak, low-density vesicular volcanic clasts relative to non-vesicular ones suggest that abrasion is extremely effective in this system. The standard exponential model for downstream abrasion, using single-lithology abrasion rates fails to reproduce observed downstream patterns in lithology and clast strength. Incorporating heterogeneity in source material strength as well as transport rate-dependent abrasion largely resolves this failure. Further work is needed to develop a comprehensive quantitative framework for the dependence of bed material abrasion on grain size and transport rate.
Webb, N. D. S.Regmi, N. R.Soreghan, G. S.Madden, A. S. Elwood...
14页
查看更多>>摘要：Mass wasting plays an important role in carbon cycling and sequestration by exposing fresh bedrock and delivering hillslope sediments to lowlands and fluvial systems. Chemical weathering signatures of landslide-derived fluvial sediments can be used to understand linkages between hillslope and fluvial processes and thus to characterize spatiotemporal dynamics of sediments. However, chemical signatures of fluvial sediments derived by landslides are yet to be fully understood. Here, we compare the bulk chemistry, mineralogy, and grain size of fluvial sediments collected pre- and post-Hurricane Maria in the Rio Guayanes and Rio Guayabo watersheds in southeastern Puerto Rico to help fill this knowledge gap. Comparison of the mud fraction (<63 mu m) of fluvial sediments collected before Hurricane Maria with similar mud fractions collected after the storm reveals that the post-hurricane muds exhibit a wider range and higher average weathering index values, but coarser grain size modes. We infer that small landslides triggered by Hurricane Maria transported slope materials from shallow depths, including weathered topsoil and saprolite, as opposed to previous deep-seated landslides, which likely sampled regolith and bedrock. Variances in weathering indices observed that pre- and post-hurricanes do not necessarily reflect average climate signatures, but rather reflect subtle differences in a transport mechanism, which produce significant differences in weathering indices recorded by fluvial sediments. We propose that weathering indices provide a means to understand sediment dynamics in mountainous regions, particularly for sediment transported immediately after landslides triggered by extreme events, such as precipitation and earthquakes, and also provide important data sets required for mapping potential carbon sequestration across landscapes.
查看更多>>摘要：Climate change may affect sediment fluvial export from high mountain regions, leading to downstream environmental disruptions and direct impacts on human activities. In this paper, three decades (1990-2020) of turbidity measurements, along with climate and hydro-glaciological variables, were used to investigate the interannual and interdecadal variability in the number of extreme turbidity events (ETE) in the glacierized Maipo River basin, located in the western subtropical Andes. ETE are defined as a sequence of days (most often 1 or 2) during which the daily maximum turbidity was in the 99% quantile of the entire study period. Some of these events compromised the drinking water provision for the city of Santiago, with more than 6 million inhabitants. ETE are more frequent during summer and are mostly associated with melt-favourable conditions. The number of ETE tends to increase in summers with large glacier ice melt and low snowmelt (outside or over glaciers). Most notable, the mean annual number of ETE exhibits a 6-fold increase in the last decade compared with the 1990-2010 period. After 2010, ETE also shifted their seasonal maximum from late spring to mid-summer and their occurrence became strongly coupled with large ice melt rates. We hypothesize that such regime change was caused by an enhanced hydrological connectivity of subglacial sediment pools that increased the sensitivity of the sediment system to glacier melt. The latter is in line with recent research and is consistent with the ongoing glacier retreat due to strong regional warming and drying.
NSTL
Amer Geophysical Union