Postdoctoral Fellowship: EAR-PF: Does topographic stress connect subsurface to surface through influencing bedrock strength, clast size, and landslides?

Higa, Justin T, Los Angeles CA

Investigators

Abstract

Dr. Justin Higa has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out research and professional development activities under the mentorship of Dr. Scott Rowland at the University of Hawaiʻi at Mānoa. Dr. Higa will examine the effects of topographic stress weathering in the valleys of Mt. Kahālāwai, Maui, Hawaiʻi, USA. Landslides from rocky, fractured mountains are deadly natural disasters that kill thousands of people every year. Research suggests that the shape of the land surface, the topography, can alter stresses within mountains to create some of these fractures and may help cause landslides. This process, called topographic stress weathering, is a budding frontier for understanding how fractures form in mountains. These fractures may weaken rock and generate fragments of rock that fall from steep slopes and collect in streams. Thus, there is a need to study whether topographic stress weathering is a major or minor contribution to the number and size of dangerous landslides on a mountain. Comparing calculations of topographic stress to rock strength, the size of rock fragments in streams, and mapped landslides may show how topographic stress weathering might affect landslide hazards. This project is important because it presents a new way to study natural disasters by linking topographic stress with field observations. Scientists can use such information to help protect people from landslides. Higa aims to engage with landowners and stakeholders of Mt. Kahālāwai to understand how this research can benefit local communities. Higa will also use this project to partner with Earth science students and help train a geologic workforce for the next generation of natural hazard scientists in Hawaiʻi. Recent studies on topographic stress weathering target how subsurface stress fields affect the extent and width of bedrock fractures. However, it remains unclear if topographic stresses are a major control of surface processes and natural hazards, such as landslides. This project will attempt to understand the relative contributions of topographic stress weathering versus climate in the generation of fractured rock and landslides. Previous work suggests that steep, narrow valleys concentrate fracture-inducing topographic stress perturbations at valley bottoms, whereas wider valleys may have such perturbations over larger areas. The study here will build off such work and focus on the valleys of an extinct volcano, Mt. Kahālāwai (also known as the West Maui Mountains), characterized by narrow and wide valleys with steep walls, a strong orographic rainfall gradient, and a lack of regional tectonic activity. First, a boundary element computer model will be used to predict the spatial distribution of topographic stresses within valleys of various morphologies (i.e., narrow or wide) and climates (i.e., windward or leeward). Next, researchers will collect (1) rebound hammer strength measurements of exposed bedrock, (2) size distributions of stream clasts, and (3) satellite mapping of landslides over decadal timescales from these valleys. If topographic stress controls surface processes, wide valleys may have weaker rocks, smaller clasts, and more landslides than steep, narrow valleys in similar climates. Then, comparing models and observations from valleys of similar morphologies but different climates will classify the effect of precipitation on weathering. Together, these tests will examine how topographic stress and climate work to erode steep valleys. Determining connections between topographic stress and geomorphic transport processes will help quantify the impact of stress-induced fracturing on various landscape evolution problems, which researchers can implement worldwide. Thus, this project may showcase a globally applicable method for examining weathering, erosion, and landslide hazards by establishing a framework linking topographic stress weathering and field observations. This project is jointly funded by the Division of Earth Science Postdoctoral Fellowship Program and the Established Program to Stimulate Competitive Research (EPSCoR). 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.