Long-lived records of climate and erosion from hillslope cores: central Appalachia
Plain English: The chemistry of deeply buried sediments tell me that the chemical and physical breakdown of rock changed when central Appalachia began to experience cold temperatures almost a million years ago.
In August 2018 we drilled an 18 m core through periglacial debris and into an ancient saprolite on a hillslope in a headwater catchment in central Pennsylvania. Using paired cosmogenic nuclides 10Be and 26Al, I find that (a) periglacial debris was first deposited about 800,000 years ago, demonstrating extremely slow erosion rates and long residence time of regolith and (b) erosion rates in the pre-periglacial saprolite are 2-5x slower than erosion rates derived from modern and ancient periglacial debris. See a recent poster showing this work, and the GSA Bulletin paper from my master’s thesis that reported similar results.
Paired paleoecology-paleoerosion records from the Pleistocene-Holocene transition: central Appalachia
Plain English: By studying sediments accumulating in a bog whose history spans a cold-to-warm climate transition, I can learn about how erosion and ecosystems responded to changes in climate. I can also figure out how long it took for the landscape to reach its current form once climate change began.
I have collected a number of cores from Bear Meadows Bog, which began forming at the end of the Pleistocene. I am learning that sedimentation in the basin continued into the Holocene, and the shift to peat accumulation likely corresponds to an ecological shift from cold-tolerant species like pine and spruce to warmer-weather species like oak. Though preliminary, my results imply that high erosion rates may continue long after permafrost has disappeared from a once-frozen landscape, and that the pace of warming, and vegetation assemblage, may also control erosion rates.
(Micro)climate controls on permafrost hillslope processes: western Alaska
Plain English: We use drones and sediment samples to track how Arctic soils evolved both thousands of years ago and today. We also use complex numerical models to simulate the physics of water, ice and soil as permafrost thaws to predict where and when soils might be vulnerable to erosion.
Through a graduate research funding program at the Department of Energy, I am working with scientists at Los Alamos National Lab on the NGEE-Arctic project to study this critical ecosystem. In this project I am interpreting Holocene sediment accumulation rates in the context of erosion rates and mechanisms modulated by climate, interpreted from paleoecological records from the Seward Peninsula. I am also using drone-acquired photos and topographic data to identify spatial variability in disturbances in permafrost soils. I am also teaming up with numerical modelers to employ advanced permafrost hydrology models in modeling force balances in a thawing permafrost soil column to better predict the hydroclimate and topographic controls on slope instability.
Channel geometries shaped by bedrock fracture density and orientation: western New York
Plain English: The dramatic gorges of the Finger Lakes are formed in layered sedimentary rocks with pervasive 90-degree fractures. Rivers display a spectrum of forms – from round, sculpted chutes to broad, blocky falls. Why are some waterfalls tall and skinny, short and wide, and everything in between? I’m trying to connect the fracturing of the bedrock to the variety of river shapes we see in western New York and elsewhere.
In a study that grew from a class project, I am investigating how both horizontal and vertical variability in rock strength control bedrock incision styles. Despite the fact that most gorges in the Finger Lakes are formed in the same 100 meters or so of sedimentary rock, channel width and steepness are quite varied. I am learning that, in addition to rock strength variability imparted by the layered deep marine rocks of the Ithaca Formation, vertical fracture density and orientation impart important cross-site variability in channel form. This is particularly relevant if we try to reconstruct base-level changes from knickpoint size and elevation. Tectonic and climate signals are generally assumed to produce oversteepend reaches that migrate through a landscape, but that story might be complicated by spatially-variable rock strength.
Soils and chemical weathering in steep bedrock landscapes: San Gabriel Mountains, California
Does landslide debris act as an important source of solute in steep bedrock landscapes? For my senior thesis at Pomona College, I worked with visiting professor Karl Lang and Keck Sciences professor Colin Robins to investigate deeply weathered sedimentary deposits in the eastern San Gabriel Mountains. We quantified chemical weathering, classified soils forming on the debris and used luminescence dating to determine the age and chemical alteration of the deposit, which we determined was a landslide about 40,000 years old. Comparing our field data to chemical weathering models, we determined that eroding landslide deposits can act as steady sources of solute, but that their contribution does not outpace chemical weathering of erosion and thin soils that characterize most of the steep landscape. We published this work in Earth Surface Processes and Landforms, and the British Society of Geomorphology awarded this paper the Wiley Award for 2019.
Aspect-modulated diffusion on cinder cones: San Francisco Volcanic Field, Arizona
This was my first official research project! As part of a joint Northern Arizona University/Arizona State University Research Experience for Undergraduates (REU), I compared the north- versus south-facing slopes of dated cinder cone volcanoes in northern Arizona to determine how sediment transport efficiency might be affected by aspect. I used statistical tests to determine whether aspect, as well as vegetation, produced significantly different slopes. I then compared this field data to numerical model simulations of cinder cone diffusion at various transport efficiencies. (In true newbie fashion, I saved precisely zero files associated with this project, so the only record I have is the poster I saved from GSA 2014 that may have been KonMari’d in one of my grad school moves. Save your files, kids!)