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Quantification of transport rates in sediment routing systems related to el Niño climatic perturbation in Peru, and to the Pleistocene/Holocene climate change in Swiss Alps

English title Quantification of transport rates in sediment routing systems related to el Niño climatic perturbation in Peru, and to the Pleistocene/Holocene climate change in Swiss Alps
Applicant Schlunegger Fritz
Number 100220
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geology
Start/End 01.04.2003 - 31.10.2006
Approved amount 199'131.00
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Keywords (4)

erosion; surface processes; remote sensing; climate and erosion

Lay Summary (English)

Lead
Lay summary
This project quantifies the response of the landscape and the sediment routing system to climatic perturbations. Analyses were carried out for the situation of the Piura drainage basin in northern Peru. They show that in the headwaters where climatic conditions are controlled by the easterlies (that result in a rather continuous pattern of precipitation rates), weathering rates appear to exceed sediment transport rates, and sediment is mainly mobilized by shallow-seated landslides. In contrast, climatic conditions further downstream of the drainages as well as in the depositional mudflats are controlled by the westerlies and, hence, by highly episodic ENSOs. There, sediment flux appears to by supply-limited, and hillslopes become dissected by channelized processes. Also, the supply-limited nature of sediment flux results in fluvial erosion and lowering of the channel floor in these lower portions of the drainage system. Hence a climate with highly episodic precipitation results in efficient export of sediment in channels. It also tends to roughen the topography by incision of channels on hillslopes. In contrast, the continuous nature of precipitation enhances formation rates of sediment by weathering that can then be exported by channelized processes.
The determination of the location of the sediment source during the1997/1998 warm ENSO event supports this morphometry-based interpretation.This part of the research was accomplished using Synthetic Aperture Radar(SAR) intensity images. The analyses show that the sediment source is mainly located in the segments where both climate systems overlap (i.e.the easterly-driven continuous nature of precipitation, and the highly episodic ENSOs derived from the west). Importantly, locations of sediment sources are also coupled with the channel network. This implies that the seasonal easterlies are responsible for the production of sediment through weathering, and the highly episodic El Niños result in export of sediment through channelized sediment transport. Both systems overlap showing a coupled sediment production-delivery system.
In summary, the study shows that a situation of a dual climate as seen in the Piura region in particular, and in the Andes of Peru and northern Chile in general, provides the condition to maximize sediment flux. Even in the case of the Atacama desert, a severe ENSO-equivalent precipitation event would potentially see enough sediment to become exported. Hence, the sediment routing system will be efficient mainly in the stage of maximum energy, but only if the sediment is made available through weathering in a first stage. Consequently, an efficient sediment routing system not only requires high energy discharge events, but also a ‘low energy’ seasonal climate to produce the sediment.
Direct link to Lay Summary Last update: 21.02.2013

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