Martha Cary Eppes
Biography - Martha Cary Eppes
University of North Carolina at Charlotte (UNCC), USA, USA – France Fulbright Research Scholar & USIAS Fellow, Strasbourg Institute for Earth and Environment (ITES), University of Strasbourg and CNRS, France
Dr. Martha Cary Eppes is a full professor of Earth sciences at the University of North Carolina at Charlotte, where she has worked since 2003. She holds BS and MS degrees in geology, with theses focused on soils and geomorphology, and a PhD in Earth and Planetary sciences from the University of New Mexico - where she researched the influence of soil development and weathering on landscape response to tectonic perturbations and faulting. Her current research interests include mechanical weathering processes, soil geomorphology and Quaternary geology of post-glacial landscapes, and soil geomorphology of the piedmont of the eastern United States.
Her most recent body of published work has focused on mechanical weathering processes and the insight that fracture mechanics concepts can provide to understanding natural rock fracture. Eppes and Keanini (2017) recognized and quantified, for the first time, a previously unrecognized role of climate in subcritical rock fracture in the context of Earth surface processes; Eppes et al., 2020 verified that study’s theoretical models with field data. This contribution to the fields of Quaternary geology and geomorphology was recognized by the Geological Society of America (GSA) through its Kirk Bryan award in 2020.
Martha Cary Eppes has served as Chair of the Quaternary Geology & Geomorphology Division of GSA and served as co-leader of the 2022 GSA Penrose Conference – PRF2022 Progressive Failure of Brittle Rocks. Dr. Eppes is a Fellow of the Geological Society of America and is a US Fulbright Research Scholar.
During her time in Strasbourg, Martha Cary Eppes will be hosted by Dr. Mike Heap at the Strasbourg Institute for Earth and Environment (ITES).
Project - Rock fracture over geologic time: seeking insight at the crossroads of rock physics and Earth surface processes
01/09/2022 – 30/06/2023
The mechanical weathering – cracking – of rock is a foundational geologic process that contributes to a myriad of Earth surface systems spanning from carbon sequestration, to soil formation, to the evolution of life. Yet, natural rock cracking rates and processes are poorly quantified and documented in the context of these Earth surface processes. In contrast, due to a global interest in fracking and geothermal energy, there is a growing wealth of experimental data collected by rock physicists and engineers centered on time-dependent rock fracture and the factors that influence it. It is therefore the goal of this USIAS/Fulbright project to accelerate a merger between Rock Physics and Earth Surface Processes disciplines to gain new insight into the evolution – over geologic time - of the processes and character of natural rock fracture at and near Earth’s surface.
Mechanical weathering-related research assumes that the primary factors controlling rock fracture rates are rock type and tectonic-, topographic-, or climate-related stresses. However, for chemical weathering, time is also a crucial factor. Even though demonstrating a similar time-effect on mechanical weathering would have immense implications for understanding geologic processes – including landslide hazards and bedrock erosion – there had been no documentation of how – or if – mechanical weathering evolves over geologic time. In recent years, Dr. Eppes has been a leading proponent of novel ideas regarding how time-dependent rock cracking theory from rock physics disciplines can be applied to understanding mechanical weathering at Earth’s surface (see Eppes et al., 2015 ; 2016 ; 2018 ; 2020 and Eppes and Keanini, 2017).
In ongoing field-based work with students and colleagues in California (USA) and in Antarctica, Martha Cary Eppes has measured crack characteristics on thousands of rocks. These rocks were located on alluvial fan, glacier, and river terrace surfaces ranging from 0-106 years in age. Cosmogenic radionuclide dating of the exposure age of the surfaces was combined with crack measurements to calculate cracking rates through time. Without exception for climate or rock type, cracking rates are initially very high (e.g. as high as 30 mm/ka (kiloannum)) and then level off through time. These are some of the first data to directly show that mechanical weathering rates decrease non-linearly through geologic time. Now, the next step – and the goal for the USIAS/Fulbright research – is to begin to document the cause of this decrease. Specifically, rock samples of known absolute and relative exposure ages were collected from sites of Dr. Eppes’ past field work. Rock physical parameters will be measured on these samples in the Rock Deformation Laboratory of the ITES Experimental Geophysics team at the University of Strasbourg. As such, the evolution of these parameters – known to control fracture rates and processes in laboratory settings – will be compared to the evolution of natural fractures measured in field data. Ultimately, the rock physical parameters measured at the University of Strasbourg will be employed to better understand the processes and evolution of rock breakdown at and near Earth’s surface.
Links
- Martha Eppes’ web page at UNCC
- Strasbourg Institute for Earth and Environment (ITES)
- Article - Peering into the cracks, Eppes, M. C., Keanini, R. (2017), Eos, 98
- Marguerite T. Williams Award 2022 - American Geophysical Union
