As noted in the Preface, for me this entire study has been a “voyage of discovery” involving multiple epiphanies leading to a new paradigm understanding about Vermont deglacial history. As this Addendum study was drawing to a close, I had yet another Epiphany, which is that this study is as much about Glacial Dynamics as it is about Deglacial History. The Addendum study resulted in a revision of the Champlain lobe deglacial history, showing that the previous finding of a long convex Champlain lobe at a late T8 time is incorrect, and that instead a long, convex T7 lobe became destabilized by Glacial Dynamics, resulting in its rapid recession, perhaps a collapse, followed by a readvance in T8 time which was restricted to the Missisquoi Basin. This destabilization came from and shows the importance of Glacial Dynamics.
My sense is that in the past glacial historians, including me, in the “old days” have tended to focus on climate as the control of deglacial history. Whereas recession of the ice sheet took place under a warming climate, the Addendum study shows that the interplay between the ice sheet and its ambient environmental conditions played a significant role affecting the recession of the ice sheet and its margins in Vermont. Much of this recognition is thanks to LiDAR.
The following is a side bar reflection about the way we approached deglacial history in the “old days:”
I cut my teeth in glacial geology in what might be called the “Richard Foster Flint era” of classic thinking. Flint’s introductory text to glacial geology once was the “bible” for such studies. Classical thinking about glacial history was based on a “layer cake model.” Much of the early research about the Ice Ages came from studies in the late 1800s through the mid-1900s in the mid-western United States, where the ice sheet extended as a broad ice mass across relatively flat terrain with low relief. Early studies led to the identification of multiple layers, which were thought to represent the Pleistocene history of the “Ice Ages.” Thus, four major glacial stages were identified, namely “Nebraskan,” “Kansan,” “Illinoisian,” and “Wisconsin.” Obviously, these names themselves reflect the early influence of studies in the mid-west.
Conceptually added to this layer cake model was the identification of the southern margins of each layer, represented by a moraine or morainic complex, so-called “terminal moraines,” with “recessional moraines” marking the progress of deglaciation. Thus, the Wisconsin, for example, became subdivided into “Iowan,” “Tazewell,” “Carey,” and “Mankato” substages. In time, subsequent research came to modify these details, but in general the same kind of “layer cake” and moraine model thinking, persisted, representing the classical, prevailing paradigm about the Ice Ages. Early thinking elsewhere, as for example in Europe, likewise followed a similar “layer cake” model.
In the western United States differences were recognized, attributable to the more mountainous terrain, but in general early western researchers followed the same mid-western way of thinking. And likewise, in the eastern United States, where the terrain is more hilly as compared to the mid-west, the same way of thinking about the Ice Ages was applied, though with difficulty.
For me, my way of thinking about glacial history was modified somewhat by experiences in Montana, Alberta, the Yukon, and Alaska, but nevertheless when I began my career at the University of Vermont, I was fundamentally steeped in the same classical model, which served as the underpinning of my teaching and research. As noted previously, I spent fourteen years at UVM, the first part of which was focused on the glacial history of Vermont. I learned a lot about Vermont glacial geology in those early days, culminating in glacial geology maps from the Quebec border southward to the Middlebury area in the Champlain Valley, and as well a substantial part of the upland interior of the Green Mountains. However, whereas this led to a better understanding of proglacial water level history, in general I was unable to decipher deglacial history, and thus these maps were never published. As noted above, I then transitioned into environmental studies, specifically hydrogeology.
As I reflect back on those early days, three aspects standout:
- One has to do with the tendency in those days to focus on so-called glacial “readvances,” which were taken as markers of short term climatic cooling events. For career advancement and gaining professional peer recognition, the goal of many academicians came to be the identification and naming of new readvances. I recall having conversations with Parker Calkin, a friend and colleague who at that time had just finished studies in the Middlebury area under Stewart and MacClintock in their seminal statewide Vermont study. Whereas Parker found substantial evidence of multiple layers of different types of glacial deposits, to his credit, Parker (who went on to significant studies in Antarctica leading to a glacier being named in his honor) struggled with this evidence, in the end concluding that these multilayered deposits likely represented oscillations associated with calving, and not glacial readvances.
- A second has to do with Joe Hartshorn and Skip Pessel. Both were good friends – Joe having given a series of guest lectures at the University of Michigan while on a sabbatical leave from the USGS. Skip was a colleague of mine as a grad student at UM. Whereas all of us in those days were steeped in the mode of classic glacial thinking, Joe’s work in New England for the USGS led him to recognize a new and different way of thinking about and deciphering deglacial history. Joe and Skip both subsequently worked together at the USGS and eventually, along with Carl Koteff, published reports on deglacial history of Massachusetts which recognized the progressive step-down recession of the ice margin and the close interplay between the ice margin and proglacial water bodies in a reverse gradient setting. My sense is that their work basically represented early exploration of a new and different model, or paradigmic way of thinking about deglacial history. This thinking later came to be termed “glacial dynamics” by researchers in Quebec, who as well recognized the importance of such dynamics and greatly advanced our understanding of the nature of the ice sheets and ice margins. As noted above, their reports about Quebec deglacial history were part of the inspiration prompting me to revisit Vermont deglacial history in this present study, especially with the benefit of LiDAR.
- The final reflection has to do with a report I published about glacial features in a mountainous area of Vermont, while I was still at UVM, at the tail end of my glacial days, about local, independent mountain glaciation. This thinking reflected my experience with mountain glaciation in the western North America. Morainic looking features in multiple areas on the east flank of the Green Mountains (such as Miller Brook Valley) to me so greatly resembled end moraines I had seen in Montana and Alberta that I was prompted to suggest local valley glaciation. Subsequent work by Wright and others led them to conclude that these features instead formed in association with the recession of the Laurentide ice sheet, and were not in fact formed by local, independent glaciers as I had suggested. However, the findings as discussed here in this present report have led me to believe that these features were associated with “Disconnections” of possibly still active ice masses (left behind by the receding Laurentide ice sheet and severed by the rapid penetration of a Disaggregated water corridor along the western margin of proglacial Lake Winooski). Again, this interpretation points to a newer way of thinking about deglacial history as opposed to the classic model.
As previously stated, numerous reports by Parent et Ouchietti and others in Quebec, who recognized the importance of Glacial Dynamics, served as part of the inspiration for this study. As just stated, LiDAR imagery used throughout the entire study but especially in the Addendum required an understanding of Styles and Glacial Dynamics associated with deglacial history. Discussions with Etienne Brouard, then of the Canadian Geological Survey, and David Franzi, State University of New York, likewise have been very helpful, prompting me to take a closer look at Glacial Dynamics.
Recent publications in Quebec, New York, and Ontario have likewise been helpful. For example, both Brouard in Quebec and Franzi in New York have provided me with reports which utilize a systems approach to deglacial history in which Glacial Dynamics is an important element. Similarly, a recent report by Syed Bukhari and colleagues in Ontario suggest a “depositional systems approach,” which they contrast with older, layer-based thinking. Thanks to all of this, a better understanding of Glacial Dynamics, especially in this Addendum, has led to a new and different understanding of Vermont deglacial history.
And interestingly whereas I did much of this study on my own, meaning in ignorance of some of these more recent studies, as I perused the literature in regard to my findings, I came to understand that many of the elements of my Vermont deglacial history findings fit surprisingly well with recent findings elsewhere, in a remarkably similar way. For me this understanding came about by multiple epiphanies and has been both surprising and gratifying, leading me to a new paradigmic understanding about the nature of deglacial history in Vermont and nearby areas which is quite different from the classical layer cake model.
This entire study, but especially the Addendum findings as just discussed, showed that LiDAR imagery reveals new and different features, such as Ice Marginal Channels, Scabby Terrain, Streaks, Scarps, Mega-Scale Lineations, and others. These need to be carefully studied to understand how they formed in terms of Glacial Dynamics. Such understanding has led me to a fuller and better understanding of their nature, which in turn led to a better understanding of deglacial history. With this perspective in mind, the following reviews the findings in this study related to and about Glacial Dynamics. The terms “Epiphany” and “Paradigm” are repeatedly used throughout this report, reflecting the progressive learning process, but as just stated much of this came about by a better understanding of Glacial Dynamics.