Collaborative Research: Transient landscapes, temporally variable erosion rates, and the impact of glaciation and climate change on landscape morphodynamics.
James Spotila, Virginia Tech Lewis Owen, University of Cincinnati
Over the past two decades, geologists have determined that erosion and climate, processes that work at the Earth?s surface, directly influence plate tectonics and mountain building, processes linked to the dynamics of Earth?s interior (crust and upper mantle). One climatic variation that has enormous influence of the effectiveness of erosion is temperature, as represented by the vast difference between erosion by rivers (i.e. fluvial erosion) and glaciers. A profound global acceleration in erosion several million years ago has been ascribed in countless studies to the onset of global cooling and the expansion of glaciers. This has lead to the idea that glaciers are absolutely efficient agents of erosion, acting like buzz saws that can erode rock as fast as plate tectonics pushes up mountains. Yet when this is examined in detail, there are numerous observations that suggest the behavior is more complex. We have identified heavily glaciated mountain ranges in tectonically active areas that may be eroding very slowly. There are also glaciated mountain ranges that may have experienced rapid erosion, despite being dominated by frozen beds (normally linked to slow erosion) and a lack of tectonic uplift. These observations suggest that there may be complex conditions that operate as thresholds for the onset of the extremely rapid, efficient glacial erosion. To test this, we will quantify what factors act as thresholds that control the response of mountain erosion to glaciation, including the factors of rock uplift rate, precipitation, and tectonic relief. This will be accomplished by expanding the case knowledge of glacial erosion controls, by quantifying chronologies of erosion rate over a range of timescales and erosive depths in four very different mountainous regions that span a range of conditions, including the Chugach and Kenai Ranges in Alaska, northwest Scotland, and the Presidential Range of New England. In each location we will test whether erosion accelerated with the onset of a specific stage of glacial development, by measuring erosion rates using several methods of radiogenic helium thermochronology (million year timescale) and cosmogenic dating, optically stimulated luminescence, and sedimentary records (spanning ten thousand to a hundred years).
By contributing to our understanding of erosion, climate, and tectonics, we will in effect help satisfy an innate human curiosity for how the landscape around us formed. We will also enable a better, more predictive understanding for how glacial and alpine landscapes respond to climate change, which is of timely, practical importance. In parallel with our research, our educational and museum outreach program will serve to connect to both students and the general public, kindling curiosity for Earth processes while conveying an experience of how geoscience problems are framed and tested through experimentation.