A. Overview
The deglacial history of northeastern North America has been a subject of interest and study for a long time. Louis Agassiz first introduced the concept of the Ice Ages in 1837 based on his observations of erratics, striations, moraines, and other features in Europe.[1] After moving to the United States in 1846 he continued his observations, leading him to conclude that large portions of much of North America had been covered by ice. Interestingly, in 1847 he visited the White Mountains in the Littleton-Bethlehem area of New Hampshire where he recognized moraines, which, as discussed below, are believed to correlate with features in Vermont, Quebec and New York.
[1] Agassiz, L., 1840, Etudes sur les glaciers; Neuchatel; Gent et Gassermann.
More recently, moraines also have been found and studied in the relatively gently sloping terrain along the flanks of the Adirondack Mountains in New York, in the Piedmont of southern Quebec close to the Vermont border, and in New Hampshire at and beyond the Littleton-Bethlehem area, these last having been shown to extend eastward across much of that State. But such moraines generally are absent in Vermont. Many researchers have suggested that this absence is due to Vermont’s highly irregular topography. This likely is correct, as suggested below, especially owing to the accumulation of meltwater in such terrain. Regardless of the explanation, the deglacial history of Vermont as a whole, meaning the changing positions of ice sheet margins on a statewide basis, has remained unknown.
As noted above, many years ago I was on the faculty at the University of Vermont (UVM), initially involved with teaching and research in glacial geology. I have long been curious about the Ice Ages, specifically where, when, how, and to some extent why, the ice sheet retreated in Vermont. For example, as traditionally thought and expected, did the ice sheet in fact lower so as to progressively uncover the Green Mountain peaks as nunataks, followed by the development of ice lobes in the major Champlain, Memphremagog, and Connecticut Basins, with northward receding ice margins in a simple pattern, as would be marked by a series of semi-parallel large, more or less convex lines on a map? If so, how did this recession take place? Where were the nunataks and lobe margins? What were the environmental conditions along these ice margins, and how did the ice sheet interact with these environmental settings and conditions? And so on.
My geology research at UVM culminated in several publications, including a 1972 report on ice margins and water levels in the Champlain Valley and adjacent uplands. 1 Wagner, W.P, 1972, Ice Margins and Water Levels in Northwestern Vermont, 1972 64th Annual Meeting, New England Intercollegiate Conference Guidebook, pp. 317- 347. This was my “magnum opus” in Pleistocene research, after which my focus changed to environmental geology and hydrogeology. Its major contribution was in providing more data points for a profile of proglacial standing water body strandlines in the Champlain Basin, but fundamentally was in agreement with the previous findings of Chapman. 2 Chapman published two reports on strandlines in the Champlain Valley. The first was entitled Late-Glacial and Postglacial History of the Champlain Valley, published in 1937 in Amer. Jour. Sci., Vol. 34, pp 89 – 124. The second was published in the Report of the Vermont State Geologist, 1941-42, pp. 49 – 83. These reports are similar but not identical. As for ice margins and deglacial history, whereas I had mapped many ice margin features over a broad area from the Canadian border to Middlebury, chiefly stagnant ice deposits which are numerous and widespread, I lacked a reliable methodology for differentiating and correlating these in a relative chronology. Thus, I was unable to establish a deglacial history of the changing positions of the ice margins through time in any comprehensive and meaningful way. In 1980 I left UVM to pursue a career in hydrogeology. But glacial geology and the deglacial history of Vermont has remained an interest.
In September 2023 on a bike ride in the lower Missisquoi Valley in northern Vermont, close to the border with Quebec, I was reminded of geology I had seen back in the 1970s. This prompted me to review my old maps and notes, including some recent literature, and collect my thoughts, leading me to write an “open-letter” about certain geological features in that area, which I gave to Ben DeJong, Vermont State Geologist. 3 This open-letter is reproduced here in its entirety in Appendix E, as it contains helpful information bearing on late deglacial history. The goal of my open-letter was to call attention to ice margin features which might correlate with reported moraines in Quebec, and to share insights and encourage research into the Missisquoi area which I saw as a possible link between the geology of Quebec and Vermont, and perhaps by extension into New York.
In my “open-letter” I stated: “I have not revisited, nor do I intend to revisit, this story in any serious way.” But afterward I decided to explore the nearby Memphremagog Basin using the online services of the Vermont Center for Geographic Information(VCGI), “just for the fun of it.” At the outset I thought of this as “dabbling,” not serious or substantial research. This introduced me to LiDAR imagery. Thanks to LiDAR, numerous ice margin features that I had never seen before became apparent. From my point of view as an old timer, when mapping was done the old-fashioned way with a shovel and USGS topo maps, 4 Procedurally, in my days in the 1970s the primary way of studying glacial geology was by field mapping, as just stated using topographic maps, a shovel, and handwritten notes. Topographic maps were USGS hardcopy quadrangle sheets, mostly at a scale of 1:24,000, but for large portions of Vermont were 1:62,500, which is extremely limiting. Today, advances in digital technologies have dramatically changed the process of mapping. VCGI allows detailed examination, both at large scale for overview but also in “zoomable” detail at a scale up to about 1:3600, nearly 20 times better than the 1:62,500 maps. VCGI and LiDAR made me feel like the proverbial kid in a candy store. LiDAR imagery for me is mind-blowing, enabling the examination of the land with new eyes. It is difficult for me to express and impossible to exaggerate the benefit of using VCGI with LiDAR and its other tabs versus the old way of surficial geology mapping. VCGI and LiDAR provide an entirely different, more wholistic and comprehensive way of looking at the glacial landscape, perhaps, as suggested below, comparable to the revolution brought to the field of geology by plate tectonics. I thus was inspired at an early point in my dabbling to dive into the late glacial history of Vermont, as summarized in this report.
Thanks to many previously published reports, especially by researchers in Quebec, specifically Michel Parent et Serge Occhietti, and their colleagues (see references below), I was inspired to explore the usage of elevation as a guide for correlating these features around the Memphremagog Basin. I refer to this as a “Bath Tub Model,” meaning the assumption that features formed along the frontal margins 5The term “frontal margins” is meant to indicate locations along the ice sheet margins where its flow lines are approximately perpendicular to the ice margins. of ice lobes at the same time are likely to be at about the same elevations, and vice versa. This resulted in the identification and delineation of multiple ice margins marking the deglacial history of Vermont.
My exploration started in the Memphremagog Basin. It turns out that at an early deglacial history time ice margins in this Basin extended across divides with neighboring Lamoille and Connecticut Basins, with valley head type stagnant ice deposits (remarkably similar in many ways to the Finger Lakes region of New York, including over-deepened basins) extending across these divides in adjoining basins, and thus my “limited exploration” proved to be a slippery slope – pun intended – carrying me into neighboring basins, and eventually across the State of Vermont – hence this report. In the process my “dabbling” became more serious.
In my exploration I came across exciting information about new and different types of ice margin features, and evidence about the nature of the environment at ice margins and the interaction between the ice sheet and its environment, what Quebec researchers refer to as “Styles” and “Glacial Dynamics.” This led to new insights about Vermont and regional deglacial history, a fundamentally new and different model, or “paradigm” about deglacial history, and as well information that relates to the concern for global warming. As indicated by the title of this report, this is intended to be thought-provoking, identifying new, plausible interpretations of Vermont deglacial history, suggesting possible directions for future research.
A brief sidebar about paradigms:
Paradigms are powerful stuff! The Bath Tub Model represents a paradigm, just as Stewart and MacClintock, who presented the only prior comprehensive analysis of Vermont glacial history, operated under their own paradigm, which is hugely different from the “Bath Tub Model.” Both are methodologies or models for deciphering geological history, based on an intellectual premise or way of thinking about the subject, or, as lawyers say, a “theory of the case.” In philosophical terms, development of geological history, in this case Vermont deglacial history, requires a carefully, well thought out, and sound way of thinking, or i.e., a valid or correct paradigm.
Paradigms are important elements in the development of scientific thought, and indeed all human thinking generally:
“Paradigm:” ‘a philosophical and theoretical framework of a scientific school or discipline within which theories, laws, and generalizations and the experiments performed in support of them are formulated.’(Merriam-Webster dictionary).
Philosopher Thomas Kuhn elaborates, stating that paradigms reflect: “a set of “universally recognized principles (underscore added), methodological processes and cultural concepts that refers to the work of the scientific community of a certain era. The scientific community is made up of scientists who, possessing the same paradigm, share the same ethical vision, assessment criteria, interpretative models, methods and solutions for solving problems and who believe their successors ought to be educated on the basis of these same contents and values.”
The word “principle” is underscored in the above quote to signify that paradigms can be so basic as to lead to important Principles or Theories. Geology has many examples of the importance of paradigms, principles, and theories for examining geologic history. For example, when Louis Agassiz in 1837 introduced the then new concept of the Ice Ages, this replaced the biblical flood theory of “catastrophism,” representing a major “paradigm shift.” Another example is a more recent breakthrough beginning in the 1970s in the field of bedrock geology, which led to the emergence of plate tectonics as opposed to geosynclinal theory. In a retrospective review of Vermont’s bedrock geology, Doolan 6Doolan, B., 1996, The Geology of Vermont; Rocks and Minerals, pp 218 – 225. refers to the emergence of plate tectonics as a major, entirely new and different “paradigm” for looking at geologic history.
The choice of the word “paradigm” by Doolan is quite appropriate, for, as just stated, paradigms are powerful mental models by which we think about, evaluate, synthesize, and eventually come to understand information about any subject, in this case the bedrock geologic history of the earth. In retrospect, my own inability to process and understand deglacial history in Vermont in the early 1970s reflected the lack of a useful or valid paradigm-based model for correlating and differentiating ice marginal features of the same versus different ages. Similarly, Stewart and MacClintock’s 7 David Perry Stewart and Paul MacClintock contracted with the State of Vermont through the State Geologist to map the State’s surficial geology, leading to the first statewide evaluation of Vermont’s glacial history. However, as explained herein, the S & M research employed a different geological history paradigm that did not lead to the identification of receding ice margins. thinking about Vermont glacial history was shaped, and in a sense both strengthened and limited, by their preconceived paradigm, their mental model theory on how glacial history can be deduced
For surficial geology, a new paradigm began to emerge about 20 years ago. Part of this came in the form of LiDAR and digital technologies. Like the benefit of satellite imagery of the earth for plate tectonics in bedrock geology, LiDAR was revolutionary, as noted above, giving glacial geologists the ability to see the landscape with new eyes. Coupled with LiDAR has been the digital availability of information in a form suitable for integrated application. In Vermont this capability is provided by the Vermont Center for Geographic Information(VCGI). In addition to LiDAR, VCGI provides a wide variety of other visuals as tabs on its online site.
More specifically, VCGI’s tabs for aggregate and soil suitability for onsite sewage disposal both provide information related to the occurrence of different types of surficial materials. The aggregate tab is largely based on the work of the Vermont Highway Department in the 1960s and 1970s, specifically geologists Frank Lanza and Franklyn Paris’ extensive soil boring program, which systematically identified sand and gravel deposits across Vermont for the purpose of supporting road construction.8 If the logs for this soil boring program have been preserved and still exist, these logs would represent an important resource that could be greatly helpful for future research. The on-site sewage tab is taken from the Soil Conservation Service’s extensive and detailed soil mapping program in Vermont, which likewise was completed in the 1960s and 1970s, under the direction of Bruce Watson who had a strong background in glacial geology and was a good friend and colleague. Favorable soils for onsite sewage disposal tend, though not always, to indicate sand or gravel deposits. VCGI’s online site makes LiDAR and a variety of tabs available across the State, enabling the viewer to see and map the surficial geology landscape devoid of vegetation, in remarkable detail.
Whereas LiDAR and VCGI paved the way for a new paradigm in this report by providing a better way of seeing the landscape for identifying ice margin features, like the development of plate tectonics, a new, better theoretical model, or way of thinking, is required as a basis for interpreting the data. In a philosophical sense, this is what this report is about.
As just noted, to date, prior to this report, no comprehensive Statewide delineation of late glacial ice sheet margin levels and positions during the deglacial history of the State has been published. I believe the Bath Tub Model is the only available methodology for determining a Statewide Vermont deglacial history vis a vis receding positions of the ice margins across the State. This entails a new, different paradigm. This is a brash assertion, certain to raise the hackles of folks who have labored long and hard to decipher deglacial history, just as I did in the 1960s and 1970s. But, in my opinion, absent the Bath Tub Model, the delineation of State-wide deglacial history for Vermont would not be possible, or at least would take a long time to develop by other means, such as traditional surficial geology mapping, almost on a geological time scale.
Doing geological research by remote mapping, as was the primary methodology here, has both advantages and disadvantages. On the plus side, this allows the study of large areas in a short time, which is helpful for gaining an overview perspective. However, this type of mapping obviously lacks the advantages and benefits of field work, as identified and discussed elsewhere herein. Again, I see the results presented here as preliminary findings which are intended to help identify areas and features for further study, including by direct field examination.
VCGI, where I did my online mapping, is open-source, and as such is available for anyone to review my online map in great detail by a link which can be provided upon email request. In essence, this is an invitation to review my findings on a VCGI “Project Sheet.” Unfortunately, as is the way with modern digital technology, VCGI plans to introduce a newer digital format for their online system which will be incompatible with the present one, and thus the Project Sheet will only be available online at VCGI in its entirety for a limited time. This Project Sheet is laborious and difficult to copy or print in its entirety owing to limitations of the geographic information system, but, time and energy permitting, I hope to develop a hard copy which, if completed, can be made available upon request. This report presents the findings in detail for selected Locales across the State, as part of the Appendix.
I want to stress and restate, as should by this point be clear, that having examined the glacial record on VCGI and gained a sense of the answers to my questions about how it all happened – meaning the where, when, how, and some of the why of Vermont deglacial history, I recognize that my findings are not the final, last word on the subject, but rather more of a beginning, giving insights for others to pursue, for the many generations of curious folks who follow. Proof, meaning real “proof,” is a difficult, elusive goal in geology and natural sciences generally.
Fundamentally, this report is for any and all who have an interest in, and an open mind to, exploring Vermont deglacial history and learning about ice sheets relative to global warming. In fact, it has become obvious to me, as stated in the Abstract and briefly touched on in the following text, that much of the findings presented here are not just academic history, but are pertinent to present day global warming issues and concerns. I am especially interested in encouraging students to pursue this further and see prospects for many projects and theses, all the more so in that it is the future generations that have a stake in the fate of modern ice sheets.
But the bottom line, for me, is that this “dabbling” has been a fun journey back to my academic roots, an opportunity to explore and understand Vermont’s geological history about how, when, and where the Ice Ages ended in Vermont. I am happy to leave it there and get back to other fun things.