In the old days, Richard Foster Flint’s textbook on Pleistocene geology was the “Bible” for glacial geology, providing a catalogue of standard, classic ice margin features, which were generally recognized and widely agreed upon. For example, moraines of different types and styles, and stagnant ice deposits including kames, kame fields, kame terraces, kame deltas, and eskers, have long been recognized, and in fact stagnant ice deposits, but not end moraines as typically found in the Midwest and the West of North America, are very common in Vermont.
LiDAR has dramatically enlarged and complicated this catalog, as for example illustrated by a more modern text by Bennett and Glasser(2009).1 Bennett, M.R. and Glasser, N.F., 2009, 2nd Edition, Glacial Geology – Ice Sheets and Landforms; Wiley-Blackwell; 385 p. The mapping here began with an a priori sense of ice margin features based on the classics. However, as mapping progressed LiDAR revealed numerous features not found in Flint, requiring study, thought, and review of published literature as to their origin and significance, with ongoing learning repeatedly making it necessary to go back and revisit areas previously mapped. Mapping ice margin features in Vermont, and as well reporting the findings, thus became a protracted, progressive, and iterative learning process, slowly building an understanding about the nature, mode of formation and significance of such features. The names of these newer features are used here informally, simply as a convenient means of reference.
In reports such as this it is customary to first present the evidence, in this case the ice margin features, and then subsequently in a separate section, present the historical interpretation. However, for some of these features, in order to convey their nature and origin, advance discussion of the historical context is necessary. Thus, both aspects are woven together here.
As just noted, in the examination of the new-age features in the Vermont landscape using LiDAR to map ice margin features an effort was made to understand how such features have been interpreted by others, as reported in current literature. It became evident that many researchers have recognized the same types of features, but that different theories or ideas have been advanced for their formation, and as well different names or terms for these features have been used. Take for example features which are referred to here as “Ice Marginal Channels.” Some researchers have suggested that these were formed by surface water fluvial action along the side margins of the ice sheet. Others have interpreted these as subglacial erosional channels, in some cases making a distinction between cold-based versus warm-based conditions. Whereas I feel quite strongly that the “Ice Marginal Channels” features I identified in Vermont could not possibly have been formed by “normal” subaerial fluvial action, rather than go through a prolonged discussion, I have chosen to simply present my own personal interpretations about the origins of such features, with supporting reasons. In the final analysis, there is general consensus that such features mark ice margins, regardless of the differences in interpretations relating to details, but some of these details are quite important.
The following provides an overview of ice margin features. This begins with a subsection discussion of the different “Types” of ice margin features identified and used in the VCGI mapping to delineate ice margins across the State at different levels and positions, according to the Bath Tub Model, and thereby deduce deglacial history. This is followed by a subsection discussion of the “Nature,” of the ice margins identified here, representing different Styles of ice margins, which were used in the “Bath Tub Model.” Next, the mechanics of ice margin feature usage and interpretation is examined, as to how such features are used as deglacial history markers. Finally, it is suggested that our conventional way of thinking about ice sheets, ice margins, and recession is biased by our old, conventional way of thinking, or “Paradigm Traps and Blinders.” This subject is briefly discussed to make clear, as learned here in the VCGI mapping, that such thinking needs to be revised. As just noted, substantial historical information is woven into the discussion where ever needed.
Footnotes: