2019 Theses Doctoral

Glacial limitation of tropical mountain height

Cunningham, Maxwell

One of the profound realizations in Earth science during the last several decades has been that the solid earth and climate system interact through mountain belt evolution. Tectonic forces generate topography, and erosion, driven largely by the climate, destroys topography. Perturbations to the competition between these processes may, for example, have driven the transition from greenhouse to icehouse climate during the Cenozoic. Erosion is the ultimate connection between the climate and solid earth system, and because landscapes are shaped by erosion, they hold in their form information about climatic and tectonic forcings. Reading climatic and tectonic processes from the landscape requires an understanding of how these processes drive erosion. One way that climate influences erosion is by setting the elevation at which glaciation occurs. It has been thought for over a century that erosion by glaciers can limit the height of cold, heavily glaciated mountains. In this thesis, I argue that the prevalence of this phenomenon is underappreciated, and that glacial erosion has imposed an upper limit on the growth of warm, tropical mountains. The argument is premised on a combination of field observations from two (sub)tropical mountain ranges in Costa Rica and Taiwan (including 10Be and 3He surface exposure ages), a new method of topographic analysis that identifies previously unrecognized patterns of landscape rearrangement introduced by high elevation glaciation, and a study of ten tropical mountain ranges that reveals a widespread glacial control on their height. The results of this thesis demonstrate the efficacy of glacial erosion even in the warmest mountains, and challenge the hypothesis that quickly uplifting and eroding landscapes have approached a steady state balance between rock uplift and fluvial erosion during the Pleistocene.