EES Seminar Series - Dr. Jill Marshall

“(Subcritcally) Cracking the Critical Zone- When Earth, Wind, Water, and Trees Intersect”

Feb 16, 2024 at - | Hayden Hall 358

Geoscience Colloquium

The Department of Earth & Environmental Science

University of Pennsylvania

Invites you to attend a EES Seminar Series

Friday, February 16, 2024 - 3:00 PM


“(Subcritcally) Cracking the Critical Zone- When Earth, Wind, Water, and Trees Intersect”


In thin-soiled settings, we presume that trees play a significant role in converting rock into mobile sediment via physical weathering, with 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 soil-production 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, if time allows, I will posit (speculate wildly) that current soil production functions should be recast to consider a climatically-calibrated Middle Earth soil production function -one that combines eco-geomorphology and often frosty processes from above with non-steady fracture mechanics from below.


Dr. Jill Marshall

Assistant Professor

Department of Geology

Portland State University 


Dr. Jill Marshall is trained as a geomorphologist and Critical Zone scientist (the zone where rock meets water and life) and is drawn to science that crosses disciplinary boundaries. Her research delves deeply into the role of biota, climate and lithology (or more specifically rock properties) in determining the rates and styles of earth 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 and 2) dis-entangling the legacy of Pleistocene glacial intervals in regions that remained unglaciated during cold intervals. 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.


Dr. Marshall is also a college dropout, who first returned to school thanks to the affordability and flexibility of a community college education. Before returning to school for her PhD, Dr. Marshall worked for several decades on applied problems in water quality, with a focus on watershed studies, and restoration design.