Doctoral Dissertation Research: The Origin and Development of Cryoplanation Terraces

点击翻译按钮获取中文摘要

This doctoral dissertation research project will determine the age and development rates of cryoplanation terraces, terraces formed through the erosive action of snow and frost. Cryoplanation terraces are large upland landform features that give the impression of gigantic staircases, found in periglacial, or cold but nonglacial environments. Although these elevated bedrock terraces have been identified and discussed in scientific literature for more than a century, debate continues about the nature of the processes responsible for their formation. Development rates, calculated from dates of rock exposure across terrace treads, will be used to test one of the more prominent hypotheses advanced in the literature. This hypothesis states that these terraces are formed through intensified erosion associated with snowbanks that last well into the summer months. Recent methodological developments in geochemistry, specifically the method known as cosmogenic nuclide dating, will provide the infusion of contemporary technology necessary to make progress on this long-standing scientific issue, and has the potential to make transformative advances in the understanding of landscape development in periglacial regions. Results from this research will be shared with the U.S. National Park Service and used to enhance park management as well as the experiences of park visitors through development of interpretive displays and trail guides in several national parks and monuments. Further, the project will enable a graduate student to establish an independent research career.The great antiquity of cryoplanation terraces makes terrestrial cosmogenic nuclides the most appropriate dating method for determining their age and rates of development. Rock samples for cosmogenic nuclide dating were collected from two locations in the interior of Alaska using a transect-based sampling strategy across individual terrace treads. Dating the exposure of the clastic rocks (clasts) will facilitate calculation of erosion rates for individual terraces, and can be compared to known erosion rates at existing late-lying snowbanks. The PIs hypothesize that: (a) calculated development rates will be comparable with those of measured snowbank erosion; (b) exposure dates for individual rock clasts will coincide with Quaternary cold intervals; and (c) terrace treads are time-transgressive surfaces with the exposure age of clasts increasing toward the outer edge of terraces. The landforms in this region where the rocks for this analysis were collected are representative of those in the much larger domain of unglaciated landscapes of the Northern Hemisphere. Therefore, the methodologic and analytic approach adopted for this project are potentially applicable throughout this vast region.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.