Development of a glacial abrasion rule for landscape-evolution models

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Glacial landscapes are sculpted by the ice that slides above them. The constant flow of ice wears away at the underlying bedrock, eroding it through time. The rates and patterns of this wear stem in part from a process called abrasion, which results from sediment entrained in basal ice being pressed into the underlying rock and drug along by the glacier. A number of theories have been proposed to estimate abrasion rates, which depend on a multitude of parameters. In order to accurately model the evolution of glacial landscapes, a mathematical “abrasion law” is needed that accurately captures the physics relevant to abrasion. The form of the abrasion law is difficult to determine beneath real glaciers because their beds are often inaccessible and the controlling factors are difficult to measure in the field. Further compounding these difficulties is the fact that abrasion rates are miniscule and therefore require decades or centuries to pass before the eroded volume is measurable. The goal of this project is to develop a mathematical relationship that describes the physics of glacial abrasion using a novel set of laboratory instruments, so that it can be implemented in numerical landscape evolution models. In the laboratory, conditions can be controlled and measured with the precision needed to accurately determine the abrasion law. The project will support a graduate and an undergraduate student from UW-Madison and provide training for underrepresented students from the College of Menominee Nation. A large-diameter ring shear device and a direct shear device at UW-Madison will be used to slide debris-laden ice at the pressure melting point over rock beds that vary in shape and composition. The striations produced by abrasion will be analyzed using a white light interferometer capable of measuring the volume of eroded material down to 10-18 cubic meters. With the ability to measure these miniscule volumes, the sliding experiments can be conducted in relatively short timeframes (less than one month each) and still generate sufficient abraded volume to determine the abrasion law. Using these instruments, an abrasion law will be developed that relates the rate of erosion to independent variables, such as sliding speed, basal melting, bed shape, debris hardness, and debris concentration. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.