Streamlined subglacial bedform sensitivity to bed characteristics across the deglaciated Northern Hemisphere

co-authored by L. Miller, S.M. Principato, and S. Munevar Garcia

In this work, the development of a semi-automated slope identification tool was utilized to identify 11,628 sedimentary and bedrock streamlined subglacial bedforms across 9 sites in the deglaciated Northern Hemisphere. Morphometrics from the streamlined bedforms were correlated to underlying site topography and lithology to identify controls of bed characteristics on bedform development, extrapolated to signify different conditions of warm-based ice flow. Published by Earth Surface Processes and Landforms in 2022. Publication can be found at: All data and semi-automated identification tool is publicly available at:

Differential impact of isolated topographic bumps on glacial ice flow and subglacial processes

co-authored by L. Miller, J. S. Slawson, E.J. Mackie, and S. wang

Topographic highs (“bumps”) across glaciated landscapes have the potential to temporarily slow glacial ice flow or, conversely, increase ice flow through strain heating and subglacial meltwater production. Isolated bumps of variable size across the deglaciated landscape of the Cordilleran Ice Sheet (CIS) of Washington state present an opportunity to assess the influence of topographic highs on ice-bed interactions and ice flow organization. This work utilizes semi-automatic mapping techniques of subglacial bedforms to characterize the morphology of streamlined subglacial bedforms including elongation, surface relief, and orientation – all of which provide insight into subglacial processes during post-Last Glacial Maximum deglaciation of the landscape. We identify a bump-size threshold of ~ 4.5 km3 in which bumps larger than this size will consistently and significantly disrupt both ice-flow organization and subglacial sedimentary processes – fundamental to the genesis of streamlined subglacial bedforms. Additionally, sedimentary processes are most mature downstream of bumps as reflected by enhanced bedform elongation and reduced surface relief, likely due to increased availability and production of subglacial sediment and meltwater. While isolated topography is found to play a role in disrupting ice flow, not all bumps have the same degree of impact. The variable influence of isolated topographic bumps on ice flow in this system has significance for outlet glaciers of the Greenland Ice Sheet (GrIS) due to general topographic similarities.

Published by The Cryosphere in 2023. Publication can be found at: All data and semi-automated identification tool is publicly available at:

Outcrop perspectives on spatial and temporal effects of topography on the marine-terminating Puget Lobe of the Cordilleran Ice Sheet

co-authored by L.M. Miller, A.P. lepp, and r. dewitt

Preserved stratigraphy along the coastal bluffs in the Puget Lowland, Washington state provides the rare opportunity to assess temporal and spatial variability in marine ice-sheet behavior and coupled marine to subaerial landscape evolution. The outcrops record glacial and interglacial sediments that mark ice advance and retreat across the formerly marine landscape, as well as processes and conditions that were in place at the time of deglaciation; therefore, detailed assessments of the stratigraphy and sedimentological analyses elucidate ice-bed interactions at local outcrop scales across the region. Other than deglaciation of the Puget Lowland, GIA has played a major role in landscape evolution, the preservation of these outcrops, and potentially in periodically stabilizing the Puget Lobe during its final retreat from south to north into British Columbia as effective water depth was reduced due to rapid solid Earth rebound.

This project utilizes over 300 discrete sediment samples in addition to radiocarbon and optically stimulated luminescence samples. Here, we develop a local marine reservoir correction for the Puget Lowland, identify ice residence in the Puget Lowland for 3,000 years longer than previously thought, constrains dates and rates of land emergence and submergence, and empirically observe step-wise retreat of the ice margin and variable styles of deglaciation.

Physical and digital data are available from the Washington Department of Natural Resources (WADNR). This manuscript is currently in prep for submission to Climate of the Past and available upon request.

The Puget Lowland work is conducted on land historically cultivated and inhabited by the Skokomish, Suquamish, Squaxin, Stl’pulmsh, Steilacoom, Puyallup, Muckleshoot, and Duwamish peoples. The majority of the writing and data analysis for these works was conducted on land cultivated and inhabited by the Monacan Nation. The peoples of these Nations were custodians of the land for time immemorial before forced removal and genocide during colonization. I acknowledge their ongoing stewardship of the lands.

My other ongoing projects and interests cover topics in sedimentology, coastal carbon sequestration, short-term coastal processes, and various types of bedform mapping. I’m always happy to chat and/or collaborate — do not hesitate to reach out to me via email ( if our interests align!