Relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the Central Alps of Switzerland

Abstract

[1] A north-south traverse through the Swiss Central Alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution. This result emerges from a study of in situ-produced cosmogenic 10 Be in riverborne quartz in Central Alpine catchments. As a prerequisite, we took care to investigate the potential influence of shielding from cosmic rays due to snow, glaciers, and topographic obstructions; to calculate a possible memory from Last Glacial Maximum (LGM) glaciation; and to identify a watershed size that is appropriate for systematic sampling. Mean denudation rates are 0.27 ± 0.14 mm/a for the Alpine foreland and 0.9 ± 0.3 mm/a for the crystalline Central Alps. The measured cosmogenic nuclide-derived denudation rates are in good agreement with post-LGM lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 Ma. In general, denudation rates are high in areas of high topography and high crustal thickness. The similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways: (1) Postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time; (2) the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data; (3) both are driven by ongoing convergence where their similarity might hint at some form of long-term quasi steady state; or (4) enhanced continuous Quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present-day rock uplift.

Erosion-driven uplift of the modern Central Alps

“…It is important to note here that the use of suspension load measurements over a short time period can often result in substantial underestimates of sediment transfer (e.g., Kirchner et al, 2001;Schaller et al, 2001). Wittmann et al (2007) observed such underestimates for the Central Alps by comparing river loads with cosmogenic nuclide-derived denudation rates (figs 2B and 2C). Underestimates possibly arose because of the lack of inclusion of solute and bedload transport, sediment trapping by retention dams, or because the time span during which suspended load concentrations have been measured is too short to sample the high-magnitude floods that are considered to be the most effective mechanisms for sediment discharge (Kirchner et al, 2001;Molnar, 2001;Dadson et al, 2003).…”

“…In a recent publication, Wittmann et al (2007) applied in situ-produced cosmogenic nuclides to estimate erosion rates for various catchments in the Central Swiss Alps. This method, using the concentration of Be in river sediment 10…”

“…Active shortening between the Adriatic Promontory and the Eurasian Plate (Persaud and Pfiffner, 2004), often associated with mantle processes (Lyon-Caen and Molnar, 1989;Kuhlemann, 2007), melting of ice (Gudmundsson, 1994;Stocchi et al, 2005;Barletta et al 2006), or erosion (Guillaume and Guillaume, 1981;Schlunegger & Hinderer, 2001;Cederbom et al, 2004) are invoked to explain the observed rock uplift. The finding that erosion rates are so similar to rock uplift rates let Wittmann et al (2007) to discuss possible causal relationships between uplift and erosion across temporal scales. Amongst these were: (i) coincidental agreement between erosion rates and rebound rates after ice melting; (ii) accretionary flux by active plate convergence being balanced by erosion; (iii) enhanced continuous Quaternary erosion and isostatic compensation of the mass removed .…”

“…The Holocene denudation rates from Wittmann et al (2007), as well as the consideration of the importance of the mass balance associated with erosion (Champagnac et al, 2007) provide new constraints to quantitatively explore the hypothesis that rock uplift can be understood as flexural accommodation of the Alpine lithosphere to surface forcing. This paper explores whether modern rock uplift is a response to surface denudation, and thus to environmental effects.…”

“…(ii) Geodetic levelling data calculated from centennial re-measurements of a first-order levelling line relative to a reference station north of the Alps yield information about vertical rock motion (Kahle et al, 1997;. (iii) Sediment yields that are based on suspended loads of river sediment (Schlunegger & Hinderer, 2001;Schwab, 2007), integrate denudation over decadal time scales, and concentrations of cosmogenic nuclides in riverborn sand (Wittmann et al, 2007, Norton et al, 2008 integrate denudation over late Holocene time scales. (iv) Volumetric calculations of lake and valley fills yield information about the post Last Glacial Maximum (LGM) redistribution of mass from the Alps to neighboring sedimentary sinks (Hinderer, 2001).…”