Hot and Cold: Volcanic and Climatic Impacts on Landslides, Erosion, and Sediment in Hawai'i

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Presenter

Justin Higa
Postdoctoral Researcher
University of Hawai'i at Mānoa

Description

Tectonic activity, variable climate, and diverse lithologies can influence the evolution of landscapes through erosive processes such as stream downcutting and deadly landslides. The Hawaiian Islands are often used as “natural laboratories” to study the impacts of climate on erosion due to its low tectonic activity, constant basalt lithology, and prevailing northeasterly trade winds that create rainy climates on the east and arid climates on the west flanks of most islands. However, variations in basalt strength due to volcanic alteration and flow type can complicate the lithology of these islands. Here, I present two experiments on West Maui Volcano, Hawaiʻi, to examine how variations in climate and lithology may control erosion over million-year to decadal timescales. First, we examine volumetric erosion rates across West Maui by estimating the missing volume of rock within valleys on this edifice, which were carved over ~1 million years. Results suggest that valley erosion rates increase as both rainfall and hydrothermal alteration of basaltic bedrock increase. Second, we measure sediment size along 50+ transects of West Maui streams to examine sedimentation patterns that vary over annual to decadal timescales. At similar drainage areas, windward valleys with high stream discharge have larger sediment than leeward valleys with low discharge. However, different basalt flow types (e.g., 'a'ā and pāhoehoe) may also erode differently sized particles into streams and likely affect downstream sediment size. Both experiments suggest that while climate plays an important role in erosion, bedrock lithology controlled by historical volcanism can influence erosion over geologic and human timescales. Therefore, understanding variations in bedrock lithology is vital for hazard mitigation of landslides, debris flows, and other erosional natural disasters.