Bedrock landsliding and fluvial landscape evolution: the Quebrada Arcas alluvial fan system, Atacama Desert, Northern Chile
Abstract
The large alluvial fan systems of the Central Depression in the hyper-arid core of the Atacama Desert of Northern Chile provide unique opportunity (through exceptional preservation) to examine the role that bedrock landsliding plays within catchment and fan evolution over geological (106year) time-scales in an actively growing orogen. Today the catchment area (1.7-4.3 km above sea level) receives rainfall of ~50 mm pa whilst modern rainfall in the lower elevation (1-1.7km above sea level) alluvial fan area is <1mm pa. Evidence from packrat middens suggests that even the wettest periods of the Quaternary were no more than 2 times wetter, thus maintaining a likely arid - hyperarid climate for the deposits and landforms examined in this study.
Quebrada Arcas catchment has an area of 760km2 that incorporates 2.6km of vertical relief. Within the catchment are a series of deep-seated (100-200m) large bedrock landslides ranging in size from <1km2 to >22km2 in area. The landslides mostly populate an active NNE-SSW compressional fault structure (W of catchment), steeply tilted (38°) ignimbrite/sedimentary unit discontinuity surfaces (E of catchment) or the sides of over-steepened slopes associated with the main incised (500m deep) ephemeral river gorges. Palaeolake deposits may occur where drainage is subsequently impeded both on top of landslide accumulation zones and within major valleys above landslide constrictions. These valley deposits contain large (m-scale) soft-sediment deformation units indicative of discrete and repeated seismic activity. The landslides are the main drivers of catchment area expansion, drainage re-routing and capture and dictate the style of deposition on the associated 688km2 alluvial fan. Cosmogenic dating using 21He of boulders in alluvial fan surface flows suggests an age of ~1Ma for the landslide (flood) related debris-hyperconcentrated alluvial fan flow deposits.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMEP43D2393M
- Keywords:
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- 1810 Debris flow and landslides;
- HYDROLOGY;
- 1815 Erosion;
- HYDROLOGY;
- 1825 Geomorphology: fluvial;
- HYDROLOGY;
- 1826 Geomorphology: hillslope;
- HYDROLOGY