Controls on Holocene denudation rates in mountainous environments under Mediterranean climate

Abstract

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Linking Mesoscale Meteorology With Extreme Landscape Response: Effects of Narrow Cold Frontal Rainbands (NCFR)

“…If averaged over the basin area of 2,560 km 2 , mobilizing 350,000 t of hillslope material equates to a sediment yield of 137 t/km 2 or a bedrock denudation rate of 52 mm/kyr (assuming bedrock density of 2,650 kg/m 3 ). These are reasonable long‐term values expected for a mountainous region experiencing a Mediterranean climate (Molliex et al, 2017). However, those values indicate a remarkable erosion event given that they were generated not from the entire basin over a full year but rather from only 0.04% of the basin in one storm.…”

“…Sediment budget calculations for the flux of landslide material transported downslope (based on landslide area mapping and field measurements of a 0.4 m mean mobilized sediment depth; Text SC) indicate that~360,000 metric tons (t) of material were mobilized to the river as a result of the storm (350,000 t of hillslope material mobilized by landsliding, and another~10,000 t by bank erosion opposite a newly enlarged debris fan; see Text SC Journal of Geophysical Research: Earth Surface mobilizing 350,000 t of hillslope material equates to a sediment yield of 137 t/km 2 or a bedrock denudation rate of 52 mm/kyr (assuming bedrock density of 2,650 kg/m 3 ). These are reasonable long-term values expected for a mountainous region experiencing a Mediterranean climate (Molliex et al, 2017). However, those values indicate a remarkable erosion event given that they were generated not from the entire basin over a full year but rather from only 0.04% of the basin in one storm.…”

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

“…Sediment yield of 1440 t/km 2 corresponds to a bedrock denudation rate of 542 mm/ky, higher than 10 Bederived long-term denudation rates (141-473 mm/ky for the Santa Cruz Mountains, 288 mm/ky for the San Lorenzo basin; Gudmundsdottir et al, 2013). Such high denudation rates are an order of magnitude higher than in steep, tectonically active terrain in Corsica similarly exposed to a Mediterranean climate (15-95 mm/ky; Molliex et al, 2017). Regarding the longstanding question of the relative roles of various-sized events in landscape evolution (Wolman and Miller, 1960), the series of nine closely spaced 2-10-year floods in the San Lorenzo watershed did more than half the geomorphic work of a 100-year flood, comparing the 850 000 tons of sediment exported in 2 days by the January 1982 flood (Griggs, 1987) with our estimated values for water-year 2017 (Table I).…”

“…the 2.86 t/km 2 hindcast for WY14; Table I) and >100 times the total sediment export during several consecutive severe drought years, as in the recent drought that ended in 2015. Such high denudation rates are an order of magnitude higher than in steep, tectonically active terrain in Corsica similarly exposed to a Mediterranean climate (15-95 mm/ky; Molliex et al, 2017). Such high denudation rates are an order of magnitude higher than in steep, tectonically active terrain in Corsica similarly exposed to a Mediterranean climate (15-95 mm/ky; Molliex et al, 2017).…”

Orbital forcing and abrupt events in a continental weathering proxy from central Europe (Most Basin, Czech Republic, 17.7–15.9 Ma) recorded beginning of the Miocene Climatic Optimum

“…The element composition of geochemically mature sediments reflects mainly sediment grain size (Al/Si, Bouchez et al, 2011;Matys Grygar and Popelka, 2016;von Eynatten et al, 2016;Liu et al, 2017), chemical weathering intensity (K content, Zabel et al, 2001, Clift et al, 2014Wan et al, 2017, Matys Grygar et al, 2017b, Molliex et al, 2017, and the past (micro)environments in the sediment-water interface (chemogenic components, here Fe and Sr minerals). The Al/Si ratio in mature sediments is proportional to the content of clay minerals, in particular in the Most Basin kaolinite (Al/Si=1) relative to quartz (Al/Si=0; Bouchez et al, 2011;Matys Grygar and Popelka, 2016;Xu et al, 2018).…”