Forged Signatures: Tectonic versus climatic control on Cordilleran mountain heights and Andean topographic asymmetry - Livestream

A long-standing debate in the Earth Sciences bears on the question of whether top-down erosion processes govern mountain building processes, but how do we measure the topographic signature of the climate drivers independent of tectonics? We use two natural experiments to detangle a potential signature of climate and drivers of erosion using the large latitudinal range of Earth’s orogens and their rain shadows in order to vary temperature and precipitation while holding tectonic accretion (relatively) constant. In the past decades, glacial erosion has emerged as a driving surface process controlling the heights of mountains and as the cause of accelerated erosion of mountains in mid-latitudes on Earth. Here, we present topographic and erosion rate data from the Cordilleran-style mountain ranges from South America through Alaska to demonstrate that the distribution of mountain heights and overall mass correlate linearly with the rate of plate convergence. Given the large latitudinal range of our dataset, this should not be expected if climate governed these parameters. Thus, tectonic processes set the limits on mountain heights. In addition, coupled deformation-surface process models predict that orogenic asymmetries may be modified by dominant wind direction and erosion, i.e. the formation of orographic rainfall gradients across strike. We present data comparing the radius of curvature of the subducting Nazca slab with orogenic wedge widths of the Andes and present correlations between slab-dip and arc position to suggest that as the arc position changes with slab dip, the asymmetry of an orogenic wedge may consequently change. Given that erosion rates do not mirror rain shadows, the slab geometry must be accounted for when assessing the climatic influence on orogenic asymmetry. Possibly, climate signals may be imprinted on hillslope processes, but not erosion rate magnitude.

Speaker: Jane Willenbring, Stanford University

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