EARS 272: Topics in Historical Geobiology: Subglacial erosion rates and processes

Graduate Seminar, Dartmouth College, Department of Earth Sciences, 2023

Co-taught: Fall 2023, with Marisa Palucis

Course overview:

Glaciation can be a powerful geomorphic agent, both through erosive action but also by affecting the elevation-area relationships of mountainous regions, sea level rise and fall, and global-scale weathering rates. During this course, we will use primary literature, reviews, and data compilations to ask the seemingly simple question: how much and where do glaciers erode? This question has been tackled by geomorphologists and glaciologists since the early nineteenth century (Playfair, 1802; Penck, 1905), and while much work has been done on understanding the mechanisms by which ice can erode rock and how that leads to glacial landforms we see on the Earth’s surface (e.g., hanging valleys, U-shaped valleys, cirques), there are still major knowledge gaps. For example, glacial erosion rates are not spatially uniform and depend on both ice thickness and the thermal regime of the glacier - whether warm-based or cold-based - but erosion models that incorporate realistic ice rheology as a function of climate are rare. The loading and subsequent unloading of ice immediately post-glacial (paraglacial) can also lead to elevated erosion rates as recently deglaciated landscapes tend to be unstable due to oversteepened slopes, lack of vegetation, and unconsolidated sediment deposition. This also becomes important when thinking about past global glacial cycles (e.g., snowball earth) and how these are recorded in the rock record, as well as how modern-day landscapes are still potentially responding to past glaciations.

In this course, we will first investigate what the state of knowledge is regarding the connection between the thermal character of glaciers and bedrock erosion rates. We will do this through both readings as well as collecting and analyzing data we find in the literature. We will then discuss how glacial erosion (and deposition) is recorded in the rock record and how our perception of rates and processes might be affected by the timescales over which we are looking. This is often referred to as the “Sadler effect”. Thus, class time will be spent performing literature searches, compiling and analyzing previously collected data, and producing a written synopsis and figures that could potentially inform a review paper.