NSF-BSF: Quantifying climate-dependent subcritical cracking and mechanical weathering over geologic time

University Of North Carolina At Charlotte, Charlotte NC

Investigators

Abstract

Mechanical weathering - the physical breakdown of Earth's surface rocks by cracking - is a vital cog in the wheel of Earth's biologic, hydrologic, atmospheric and geologic systems, influencing everything from carbon cycling, to the soils in which life thrives, to aquifer formation. Yet the environmental and rock mechanical features that control mechanical weathering remain poorly characterized, and the long-term evolution of cracking itself has not been observed. This work brings together a multidisciplinary team from the United States, Israel, Japan and the United Kingdom to collect some of the first ever geologic time scale (10^3-10^5 years) data sets for both mechanical weathering as well as for a suite of special rock mechanical properties - those related to climate-dependent subcritical cracking. The project will develop a Science-Art collaboration with the UNC Charlotte College of Arts + Architecture to communicate the project results to diverse public audiences. The investigators will conduct a workshop at the Geological Society of America on the basic subcritical cracking concepts explored in this work and will mentor students with a focus on broadening participation of women and underrepresented minorities. The investigators will test hypotheses including: a) mechanical weathering rates over geologic time are primarily controlled by rock subcritical cracking rates; b) similar to chemical weathering, mechanical weathering rates decrease through geologic time; and c) under different environmental conditions, mechanical weathering rates are higher in climates where conditions favor faster subcritical cracking - separate, and in addition to, the previously recognized influence of climate on stress loading mechanisms. The following will be measured: 1) Mechanical weathering (cracking) rates and characteristics for boulders (granite and limestone) found on different aged late Quaternary deposits, in the Sierra Nevada, CA, and the Negev Desert of Israel. 2) Subcritical cracking parameters - measured under different environmental conditions - for samples from the same locations. Laboratory data will then be incorporated into numerical models that will calculate long-term subcritical cracking-driven cracking rates under different environmental conditions. Model results will be validated and refined using field data. The project will shed new light on mechanical weathering, and the factors controlling it, over geologic time. 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.