Definition
“A line separating tracts of unglacierized terrain of strikingly different appearance, the appearance of one of the tracts being interpretable as due to recent deglaciation” (Cogley et al. 2011).
Formation
Trimlines record the most recent high-ice stands along the walls of glacial valleys, generally represented by a contrast in albedo above and below the trimline or as a contact between vegetated land above the trimline and bare surface below. Trimlines have also been used to identify mountains within glaciated terrain that escaped glacial erosion. These can represent unglaciated nunataks, standing proud of the ice surface, in which case the regional trimline represents the maximum surface elevation of the ice. Alternatively the trimline may represent an englacial boundary between warm-based (eroding) and cold-based (non-eroding) ice. The trimlines in the Scottish highlands are now regarded as marking an englacial thermal boundary because cosmogenic isotope exposure ages of...
References
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McCarroll, D. (2014). Trimline. In: Encyclopedia of Planetary Landforms. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-9213-9_383-1
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DOI: https://doi.org/10.1007/978-1-4614-9213-9_383-1
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