Climatic and geodynamic influences on ocean island geomorphology

Abstract

With homogeneous bedrock, dramatic rainfall gradients, and remnant surfaces that constrain their age, initial topography, and vertical motions relative to sea level, volcanic ocean islands provide an exceptional natural experiment in landscape evolution. Analyses traversing gradients in island climate and bedrock age have the potential to advance our understanding of landscape evolution in a diverse range of continental settings. Yet, islands are initially conic, net subsiding, boundary-dominated, and initially permeable landmasses, in many ways dissimilar to most continental landscapes. This thesis examines unique aspects of island landscape evolution, and it exploits steep climate gradients and variations in bedrock age on volcanic ocean islands to understand controls on rates and patterns of erosion and the contribution of lithosphere and mantle processes to surface deformation at hotspots. Through physically-based modeling, analysis of remote sensing and geochronologic data, and field measurements, this thesis examines (1) the dominant mechanisms of vertical motion in the Hawaiian Islands, (2) the influence of wave power on cliff retreat rates in the Hawaiian Island over geologic timescales, (3) the control of rainfall rates on the efficiency of bedrock river incision on the Hawaiian Island of Kaua'i, (4) the evolution of erosion rates over the course of landscape development on Kaua'i and other volcanic ocean islands, and (5) the mechanisms that cause volcanic ocean islands to ultimately subside below sea level to form atolls and guyots. These analyses provide empirical evidence for climatic control on erosion processes and they constrain the dynamics of plume-plate interactions at oceanic hotspots.