EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Late Quaternary Climate Variability Constrains River Incision and Aggradation in the Spiti Valley, Western Himalaya

Bodo Bookhagen1, Manfred Strecker1, Samuel Niedermann2, and Rasmus Thiede1,3
Bodo Bookhagen et al.
  • 1Universität Potsdam, Institut für Geowissenschaften, Potsdam-Golm, Germany
  • 2Helmholtz Zentrum Potsdam Deutsches GeoForschungsZentrum, GFZ, Potsdam, Germany
  • 3Universität Kiel, Institut für Geowissenschaften, Kiel, Germany

The intensity of the Asian summer-monsoon circulation varies over decadal to millennial timescales and impacts surface processes, terrestrial environments, and marine sediment records. The duration and magnitude of this climatic forcing on erosion processes varies, depending on duration and intensity of the climatic events, as well as on the tectonic and geomorphologic preconditioning of the landscape. In this study, we focus on a region in the transition zone between continuous and episodic monsoon impacts: the Spiti River, the largest tributary (12x103 km2 ) to the Sutlej River in the western Himalaya. The river valley is located in the northern lee of the Himalayan orographic barrier in a presently arid environment. The Spiti Valley has received significant precipitation during intensified monsoon periods during the late Pleistocene and Holocene and thus constitutes an ideal location to evaluate effects of episodic moisture transport into an arid, high-relief mountainous region.

Here we present 21 new surface-exposure ages of fluvial-fill terraces combined with previously published data to quantify temporal patterns in river incision and erosion rates. Our data include catchment-wide erosion rates and in-situ cosmogenic nuclide ages derived from 10Be, 26Al, and 21Ne and document that terrace formation (i.e., terrace abandonment) occurred during intensified monsoon phases at ∼100 ka, ∼65 ka, ∼43 ka, and ∼12 ka, although dating uncertainties prevent the calculation of exact correlation between monsoonal strength and terrace formation. We show that incision into Late Pleistocene valley fills that integrate over several cut-and-fill cycles at 105 y are comparable to exhumation rates determined from thermochronology studies averaging over 10^6 y in that area. We argue that the limiting factor for sediment removal and river incision on shorter, millennial timescales is due to large bedrock landslides that impounded the river network and formed transient sedimentary basins lasting for 103 -104 years. We suggest a feedback process between sediment removal and landsliding, where large landsliding predominantly occurs when the transiently-stored valley fills have been carved out, leading to exposed valley bottoms, bedrock erosion, lateral scouring of rivers, and ultimately to the over-steepening of hillslopes. We suggest that Late Quaternary climatic variability is the main forcing factor in filling and evacuating transiently stored sediments in high mountain ranges and thus plays a direct role in controlling bedrock incision.

How to cite: Bookhagen, B., Strecker, M., Niedermann, S., and Thiede, R.: Late Quaternary Climate Variability Constrains River Incision and Aggradation in the Spiti Valley, Western Himalaya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15369,, 2021.

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