The shifting history of North America’s ancient ice sheet
by Clarence Oxford
Los Angeles CA (SPX) Nov 05, 2024
Imagining a vast ice sheet sprawling over Canada and extending down into what is now the northern United States, reaching as far south as Pennsylvania, Ohio, Indiana, Michigan, and Wisconsin, helps us grasp the scope of ancient glacial coverage between 19,000 and 26,000 years ago.
Yet, while picturing this immense ice mass is fascinating, the present-day implications of its retreat – particularly concerning land shifts and sea-level changes – are of pressing interest. Ph.D. candidate Karen Williams, from the Department of Geosciences at Virginia Tech, has taken on this challenge. Using advanced computer models, Williams is investigating how Earth’s landscape transformed as the ice receded and how these changes may inform current issues like sea-level rise and sinking land.
Williams’ research, conducted with Associate Professor D. Sarah Stamps and collaborators Daniele Melini of Italy’s Istituto Nazionale di Geofisica e Vulcanologia and Giorgio Spada of the Universita di Bologna, has been published in the ‘Journal of Geophysical Research: Solid Earth’.
Modeling Land Response to Glacial Retreat
Williams employed computational simulations to evaluate how the melting Laurentide ice sheet impacted vertical land movements today. Her research modeled nearly 130,000 scenarios, testing assumptions related to the Earth’s structure and how it responds to the forces released as the ice melted – a process termed “glacial isostatic adjustment.”
The findings revealed a trend of downward land movements – translating to relative sea-level rise – in the eastern United States, while eastern Canada experienced uplift, which has the opposite effect on sea levels there.
Understanding Sinking Land
These models also shed light on why certain regions are sinking. According to Williams, by refining models of land elevation changes, researchers can better determine which areas are affected by natural shifts or by human activities, like extensive groundwater extraction. For instance, as Stamps noted, “Some of the greatest differences between modeled influence of glacial isostatic adjustment and observations occur where there is known groundwater extraction, like Houston, Texas.”
Helping Communities with Coastal Planning
The study’s insights will contribute to mapping tools for scientists involved in aquifer management, Williams noted. The research findings will also be included in a U.S. Geological Survey report aimed at helping Chesapeake Bay area stakeholders assess the financial, ecological, and social impacts of rising seas.
“With the improved estimates of vertical displacement driven by glacial isostatic adjustment,” Williams explained, “we can better predict land subsidence and relative sea-level changes, which will help address the impacts of present-day coastal hazards.”
Research Report:Vertical Displacements and Sea-Level Changes in Eastern North America Driven by Glacial Isostatic Adjustment: An Ensemble Modeling Approach
Related Links
Department of Geoscience at Virginia Tech
Beyond the Ice Age
