Introduction Think of a glacier as a slow‑moving river made of ice. Once the ice is thick enough—about 30 meters or more—its own weight makes the bottom layers creep forward. That steady flow lets glaciers carve and carry rock in ways snowfields never could (National Snow & Ice Data Center [NSIDC], 2024).
How Glaciers Grow and Shrink A glacier gains ice from snowfall (accumulation) and loses ice to melting or calving (ablation). When gains beat losses, the ice front creeps downhill; when losses win, it pulls back. Because temperature and snowfall control that balance, glaciers react quickly to climate change (Intergovernmental Panel on Climate Change [IPCC], 2023).
Ice at Work: Erosion Flowing ice acts like a sheet of sandpaper:
- It scratches bedrock, leaving long grooves called striations.
- It digs out bowl‑shaped hollows called cirques.
- It widens stream‑cut V‑shaped valleys into broad U‑shapes. Yosemite Valley in California is a postcard example—the steep granite walls and flat floor were gouged out by Pleistocene ice (National Park Service [NPS], 2024).
Ice at Rest: Deposition When the ice melts, it drops everything it was carrying:
- Till piles up at the glacier’s nose to form a ridge called a terminal moraine.
- Meltwater sorts sand and gravel into flat outwash plains. Long Island, New York sits on two stacked terminal moraines left by the Laurentide Ice Sheet about 21 000 years ago (New York State Geological Survey [NYSGS], 2023).
Why It Matters The landforms we see today tell a climate story from the past, and today’s shrinking glaciers warn us that the story is changing fast.
References
Intergovernmental Panel on Climate Change. (2023). AR6 synthesis report: Climate change 2023. https://www.ipcc.ch/report/ar6/syr/
National Park Service. (2024, February 12). Geology of Yosemite Valley. U.S. Department of the Interior. https://www.nps.gov/yose/learn/nature/geology.htm
National Snow and Ice Data Center. (2024). Glaciers. University of Colorado Boulder. https://nsidc.org/learn/parts-cryosphere/glaciers
New York State Geological Survey. (2023). Long Island geomorphology map. New York State Museum. https://www.nysm.nysed.gov/research-collections/geology