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Evento
AEG Oregon Chapter - February 2024 Meeting
Abstract:
In thin-soiled settings, we presume that trees play a significant role in converting rock into mobile sediment via physical weathering, with most models centered on tree throw. However, little is known regarding how - or how often - trees damage rock. Combining novel force sensors at the tree-rock boundary with precipitation, solar radiation, wind, tree sway, and acoustic emission data, I have begun to quantify tree-driven rock damage mechanisms. Charismatic tree throw may matter less than belowground damage. Results suggest that while wind forces matter, conifers bang repeatedly on rock while bendy deciduous trees can dampen wind loads significantly. Field data and physical modeling shows that even daily root water uptake can generate significant cracking. Finally, I will posit (speculate wildly) that current soil production functions should be recast to consider a 'Middle Earth' production function, one that combines disturbance agents like trees and water from above with non-steady fracture mechanics from below. This recasting might unify conflicting soil production functions (humped vs. exponential) and provide a framework for a more general theory of how bedrock vs. soil-mantled landscapes emerge and persist under steady state conditions as well as provide insight as to the why and when rock cracks and fails under subcritical cracking conditions.
Speaker Bio:
Dr. Jill Marshall, Assistant Professor of Geology, Portland State University
Dr. Marshall is a geomorphologist and Critical Zone scientist. The Critical Zone is the life-sustaining, constantly evolving, surface and near-surface earth region extending from the top of the vegetative canopy where it intersects with the atmosphere to the subsurface limit of groundwater. Her research delves deeply into the role of biota, climate and lithology (or more specifically rock properties) in determining the rates and styles of surface processes through time. Broadly, her current work centers on two overlapping themes: 1) how variations in rock properties and climate- mediated changes in processes (such as bedrock weathering via trees vs. frost) control the rates and style of landscape evolution starting with progressive rock failure, and 2) dis-entangling the legacy of Pleistocene glacial intervals in regions that remained unglaciated during cold intervals. She has a particular interest in how past processes shape modern sub-surface architecture (e.g. fracturing and porosity) of the Critical Zone as the physical architecture supports diverse functions such as hydrologic routing, net primary productivity, carbon and water storage, and mineral supplies for the geochemical reactor. She has recently started working in the Arctic where the trees are short but the opportunity to study frosty vs. more temperate processes in a warming world is dishearteningly outstanding.
Before returning to school for her PhD, Dr. Marshall worked for several decades on applied problems in water quality, with a focus on watershed and stream studies, and restoration design. As a stream specialist for the State of California, she pioneered the development of stream protection policies, developed stream monitoring and restoration trainings for both urban and rural communities, led studies on mercury transport in rivers, designed effective mercury containment projects at an abandoned mercury mine and developed water quality standards to protect fish-eating birds and humans from ill health effects due to eating mercury- contaminated fish. She is looking forward to (re) learning more about the wonderful Oregon landscapes and continuing her recent work meshing findings from experimental rock physics on crack propagation with improving predictions on near-surface properties and bedrock to sediment production via the trajectory of fracturing, porosity, and permeability attributes through time.
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UbicaciónOld Market Pub (Ver)
6959 SW Multnomah Blvd.
Portland, OR 97223
United States
Zona horaria: America/Los_Angeles Informacion de acceso en linea After you have registered for the event, the online access information for the Zoom meeting will be provided on the order confirmation page and email. Please make sure you copy this link prior to the meeting start time.
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