Collaborative Research: GEMT: Bridging Multiple Time Scales of Erosion and Rock Uplift in Taiwan

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). Mountains appear static to the casual observer, yet in many locations they are actively growing upward in response to plate tectonics, while their shape, height and width is altered by climate-driven erosion. How fast mountains change elevation depends on the timescale and locations in which one observes them. During an earthquake, mountains can move many meters in a matter of seconds, yet when earthquake motions are averaged over millions of years, and combined with the slow motion of faults that may happen between earthquakes, the rate that mountains move is much slower. How these slow, but continuous motions combine with short high-magnitude events to build topography of mountainous regions over millions of years is an important question to answer to understand how short-term, hazardous events like earthquakes, landslides, and floods integrate over long periods to build the spectacular scenery of mountain systems. In this proposed work, Taiwan is a natural, ongoing experiment of how uplift and erosion is integrated over a range of timescales to build the mountain range. The investigators will examine uplift and erosion over decadal, millennial, and million-year timescales to document changes in measured rates and build a framework for understanding discrepancies among the different approaches. The project will bring together US and Taiwanese scientists across career levels and disciplines to address this fundamental research question in tectonics. In year 2, U.S. and Taiwanese graduate students will come together for a month-long cross-disciplinary modeling workshop. Additionally, the project will support recruitment to STEM through an innovative course involving 1st year undergraduates who will be exploring geodetic and geomorphic data of Taiwan. This project is a collaborative effort between U.S. and Taiwanese researchers under the aegis of the NSF/GEO/EAR - MOST-Taiwan (GEMT) Collaborative Research opportunity. This project will build a new framework for bridging measurements of deformation rates across geodetic to geologic timescales, by building a suite of models that link deformational and erosional processes. The active Taiwan mountain belt is an excellent location to test hypotheses of how short-term processes such as the elastic earthquake cycle, river incision, and exhumation aggregate to build orogens and evolve topography. Taiwan is widely invoked as a case study for mountain belts in erosional or topographic steady-state, however, a number of observations challenge this classical view. Highly variable estimates of denudation and incision rates inferred over disparate time intervals raises questions about the time periods over which the concepts of steady-state mountain building are relevant in Taiwan. In addition, present-day uplift rates from geodesy are also not easily reconciled with the millennial and longer time-scale erosion rates. These confounding observations suggest that the mechanisms of mountain building broadly, and in Taiwan specifically, are not fully understood and fundamental questions remain unanswered about the relationship of deformation, tectonic uplift, and erosion over a wide range of time scales. We will build a series of kinematic models that simulate potential fault geometry and evolution and evaluate if the history of fault activity and geometric evolution is consistent with >0.5 Ma exhumation history constrained by thermochronology, geomorphically inferred millennial rates constrained by erosion and incision data, and present-day rock uplift rates constrained by geodesy. Our integrated approach will ensure that the model fault geometry and slip rates that dictate deformation kinematics, and their influence on the uplift field that drives river incision and exhumation, be compatible across time scales. To accomplish this integration, we propose a five-part research plan: (1) Build hundred-thousand to million-year kinematic orogenic models constrained by geology and thermochronology; (2) Build a millennial time-scale erosion model using river incision rate data, basin-wide CRN, and channel morphology; (3) Construct an updated geodetic vertical velocity field; (4) Construct earthquake cycle models of present day deformation; (5) Bridge time scales through model integration. 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.