Suspended Sediments in Chilean Rivers Reveal Low Postseismic Erosion After the Maule Earthquake (Mw 8.8) During a Severe Drought

Abstract

We address the question of whether all large‐magnitude earthquakes produce an erosion peak in the subaerial components of fluvial catchments. We evaluate the sediment flux response to the Maule earthquake in the Chilean Andes (Mw 8.8) using daily suspended sediment records from 31 river gauges. The catchments cover drainage areas of 350 to around 10,000 km2, including a wide range of topographic slopes and vegetation cover of the Andean western flank. We compare the 3‐ to 8‐year postseismic record of sediment flux to each of the following preseismic periods: (1) all preseismic data, (2) a 3‐year period prior to the seismic event, and (3) the driest preseismic periods, as drought conditions prevailed in the postseismic period. Following the earthquake, no increases in suspended sediment flux were observed for moderate to high percentiles of the streamflow distribution (mean, median, and ≥75th percentile). However, more than half of the examined stations showed increased sediment flux during baseflow. By using a Random Forest approach, we evaluate the contributions of seismic intensities, peak ground accelerations, co‐seismic landslides, hydroclimatic conditions, topography, lithology, and land cover to explain the observed changes in suspended sediment concentration and fluxes. We find that the best predictors are hillslope gradient, low‐vegetation cover, and changes in streamflow discharge. This finding suggests a combined first‐order control of topography, land cover, and hydrology on the catchment‐wide erosion response. We infer a reduced sediment connectivity due to the postseismic drought, which increased the residence time of sediment detached and remobilized following the Maule earthquake.

Pulsed carbon export from mountains by earthquake-triggered landslides explored in a reduced-complexity model

“…The export of OC during the post-seismic period depends strongly on the fine sediment export rate (Hovius et al, 2011;Tolorza et al, 2019;Wang et al, 2015;Wang et al, 2016). A few examples have shown that, in wet climates, suspended load fluxes after a large earthquake are characterized by a rapid increase directly after the seismic event, which is sustained for less than a decade, before returning to background levels (Hovius et al, 2011).…”

“…The export of OC from mountain river catchments is linked to that of fine clastic sediment (Galy et al, 2015;Hilton et al, 2012). Following widespread earthquake-triggered landsliding, fine sediment can be evacuated as fluvial suspended load within a decade in wet, subtropical settings such as Taiwan (Dadson et al, 2004;Hovius et al, 2011), or over several decades in more arid locations (Tolorza et al, 2019;Wang et al, 2015). The total landslide-derived sediment volume, including coarse material which can be mobilized by debris flows and transported as bed load, may take decades to centuries to export (Croissant et al, 2017;Fan et al, 2018;Yanites et al, 2010).…”

Natural and anthropogenic controls on sediment rating curves in northern California coastal watersheds

“…Application of RFM to catchments in Minnesota showed that the offset was primarily controlled by land use, whereas the shape and slope were controlled by factors related to the geomorphic characteristics and geologic history of the basin (i.e., near-channel relief, channel gradient, and the number of lakes within the channelfloodplain corridor) (Vaughan et al, 2017). Tolorza et al (2019) used a similar technique to identify physical factors that regulate changes in suspended sediment concentrations following a large tectonic event.…”

“…Prolonged shifts in SRCs can also occur in response to major land-use changes and (Warrick et al, 2013) and extreme hydrologic events (Gray, 2018;Gray et al, 2015). Chile (Tolorza et al, 2019). This suggests that SRCs may respond to punctuated sediment loading, whether from tectonic activity or intensive timber harvest activities, in similar ways.…”

“…sediment into and through river networks (Czuba & Foufoula-Georgiou, 2014;Czuba et al, 2017;Langbein & Schumm, 1958;Merritts et al, 1994;Mueller & Pitlick, 2013;Murphy et al, 2019;Riebe et al, 2001;Syvitski & Milliman, 2007;Vaughan et al, 2017). Over thousands to millions of years, there is a well-demonstrated coupling between tectonics and sediment production (Ahnert, 1970;Kirby & Whipple, 2012;Pazzaglia & Brandon, 2001;Tolorza et al, 2019).…”