As stated in the Introduction, the goal of this study had a modest beginning, but thanks to the services of the Vermont Center for Geographic Information, which makes LiDAR imagery available across the State, along with diverse other information about soils, topography, and so on, this study expanded throughout the State of Vermont to encompass three elements, specifically:
- the late Pleistocene deglacial history of the ice sheet recession, as marked by progressively lower levels of the ice sheet surfaces and the associated recession of its margins,
- the nature of the ice margin environments, or “Styles,” and
- the dynamic interplay between the ice sheet and its surroundings, or “Glacial Dynamics.”
This report is presented here, not to declare victory – the history of the ice sheet in Vermont is not conclusively established and understood as a finality – but instead to provoke further study.
At the heart of this study was the identification of ice margin features, including both long established, well known types, and as well newer features. These include:
~ End moraines and stagnant ice deposits.
~ Ice Marginal Channels – features believed to have formed at the base of and close to the margin of the active ice sheet. As noted, these features are believed to have significance along with associated ice margin features as “signature markers which are helpful and important for the study of deglacial history.
~ Ice Margin Steps – terrace-like features similar to Ice Marginal Channels formed along the ice sheet margin, generally in glacial till.
~ Drainage Lines – meltwater features formed along the margins of the ice sheet.
~ Kame Deltas – deltaic deposits formed in close proximity to the ice sheet margin.
~ Scabby Terrain – a peculiar and distinctive LiDAR observed texture associated with deposits formed by “Disconnected” ice sheet masses, leading to en masse stagnation.
~ Bedrock Grooves – shallow to deep ravines cut into bedrock by meltwater along frontal or lateral ice margins.
~ Ice Tongue Grooves – similar deep ravines eroded into bedrock along the lobe tips of ice tongues, related to ice sheet destabilization by proglacial water bodies.
~ Calving ice margin features including, Thickened Bouldery Lacustrine deposits, Ribbed Lacustrine Deposits, which are hummocky stagnant ice deposits composed either entirely of fine grained, ponded water sediment or with veneers of fine grained sediment overlying coarser clastic materials, and Headless shoaling deltas, which are similar to “normal” deltas but originating from drainage associated with remnant stagnant ice margins.
~ Ice Margin Lines, which are linear to curvilinear features on VCGI maps, with uncertain origin and meaning for deglacial history but in southwestern Vermont possibly representing grounding line markings for calving ice margins.
These, and in addition other features of less certain or unknown origin and historical meaning, are identified, again all deserving further study.
This study reached several intriguing and unexpected findings. One is that ice margins were not simple, like lines on a map as conventionally regarded, mapped, and conventionally drawn. Instead, ice margins are identified as wide complex zones, not narrow knife edged margins as suggested by ice margin lines, including features formed at both active and stagnant ice margins, having overlapping temporal and spatial relationships, and confronted by increasing volumes of meltwater in close association with standing proglacial waters. Ice margins are characterized as active, stagnant, hybrid (which include both stagnant and active ice), step-down, destabilized, calving, Disaggregated, Diachronic, Calving, Oscillatory versus Readvance types, and Warm vs Cold.
As discussed, the interpretation of deglacial history for Vermont as presented here required the exploration of new ways of thinking, or paradigms. The nature of ice margins and their recession in Vermont is explored in terms of deglacial history, using elevation as a guide, referred to as a “Bath Tub Model.” The evidence indicates that the deglacial history of Vermont was late in the regional recession of the Laurentide ice sheet when it had substantially thinned relative to the physiography, such that elevation can reliably serve as a helpful guide for delineating ice margin recessional history, as suggested and supported by previously published reports in Vermont and neighboring regions of Quebec, New York, and New Hampshire.
In addition, the environment of the ice margin, or “Styles,” and the dynamic interaction between the ice sheet and these environmental conditions, or “Glacial Dynamics,” are examined. Styles and Dynamics represent an unexpected finding. Whereas the Bath Tub model used for deducing deglacial history initially represented an assumption, basically a hypothesis, its application and testing led to not just the determination of deglacial history, but as well the role of meltwater, especially standing or ponded water, as a Dynamic which interacted with the ice sheet, as a major factor – a controlling agent affecting the ice margin positions, nature, and configuration. This Dynamic is reflected by what has come to be seen as a standard step-down sequence, involving stagnant ice features in close association with kame deltas and Drainage Lines, giving way to increasingly larger and more regional water bodies, remarkably similar to lowering levels in a “bath tub,” albeit with a highly irregular margin configuration. The links between ice margin features and meltwater features both within and between basins not only provide supporting evidence to the validity of the “Bath Tub Model,” but as well show the role of meltwater in largely influencing and in some places and times actually controlling ice margins.
Standing and flowing water along ice margins had pronounced effects on the ice sheet and its margins, as a major Glacial Dynamic, in multiple different ways: 1) ice margins became increasingly associated with and likely at least partially controlled by standing or ponded water; 2) proglacial waters penetrated and were intimately associated with ice margins, in certain locations and circumstances resulting in Disconnections; 3) lateral margins of ice lobes became fringed by long narrow standing water corridors; 4) these corridors in some cases served to destabilize the ice sheet, as marked by a unique type of ice margin feature; (“Ice Tongue Grooves”) 5) as part of the destabilization, calving ice margins developed, again as marked by multiple types of unique features; 6) once initiated, such destabilization appears to have reached a “tipping point” whereby the demise of the ice sheet in Vermont was accelerated and its end fated and sealed.
In general, the lowering of the ice sheet began with a “Nunatak Phase,” followed by a “Lobate Phase,” in which the ice lobes in the Champlain, Memphremagog, and Connecticut Basins developed, their levels lowered, and their margins receded.
Ice margin recession in Vermont generally was progressive, with a step-down pattern of the receding ice margins, likened to “multiple rings in a slowly draining bathtub.” However, some “rings” were more substantial, helping to define eight levels and times, marking ice margin recession, levels, and ice margin positions in a proposed chronology. However, as just suggested, these “rings” and the associated recession were temporally and spatially complex, with overlapping spatial and temporal relationships described as “Everything, Everywhere, All at Once, and Continuing.” The eight successive levels and times are correlated across the State, representing “stillstands” which may or may not have been climatically related, but other possible causes are identified and briefly explored.
At multiple times in the early history, emerging high elevation physiographic divides served to “Disconnect” different masses of ice in the Connecticut Basin from the parent ice sheet, resulting in en masse stagnation. This finding adds to a long standing debate about wholesale stagnation of ice in this basin.
The evidence indicates that the receding Champlain lobe developed a calving ice margin, with several phases of calving, including 1) a possible initial phase associated with a low portion of the Basin floor, a second phase triggered by the lowering of Lake Vermont from the Coveville to Fort Ann level, and a third phase associated with the lowering from the Fort Ann level to the Champlain Sea. Evidence is found indicating that the receding, calving ice sheet was more convex in shape than conventionally depicted, with both northward and westward recession of the Champlain lobe margin, with ice margin presence close to proglacial strandlines, including both Lake Vermont and Champlain Sea, possibly even continuing into the latter’s, lowering stages.
Correlations of Vermont deglacial ice margins with neighboring regions of Quebec, New York, and New Hampshire, are tentatively suggested, again requiring further study. Evidence of ice margin “oscillations,” is identified and two “readvances”, as suggested by previous research. Whether or not these had climatic significance can not be determined based on the VCGI information in this study. Nor can the scale of such “readvances” be established meaning a) the distances of recession and readvance of the ice margin, and b) the regional versus local geographic extent. The T3/T4 time, level, and ice margin is correlated with the White Mountain Morainic System in New Hampshire, which reportedly is dated as about 13,800 -14,000 years BP. This readvance is correlated with reports of a readvance in the Winooski Basin by Larsen, Wright, and others. Also, evidence is found here which suggests the possibility of such a readvance in the Vermont Valley in the Rutland and Bennington areas. However, reports from the western Taconics in New York indicate that no evidence for a readvance for the equivalent T3 and T4 time has been found.
The later readvance was associated with T8 ice margin feature in the Missisquoi Basin. This readvance occurred in Champlain Sea time shortly after the incursion of the Sea into Vermont which reportedly is dated as about 13,000 years BP. This readvance is correlated with reports in the literature by others further south in the LaPlatte Basin and Bridport area. But neither the climatic significance, if any, nor the scale of this as a bonafide “readvance,” versus a more minor and less significant oscillation and its local or regional geographic event, is established. The possibility is raised that this readvance may be related to the “collapse” of the Champlain lobe during which the majority of the lobe may have been mostly stagnant but with “spasms” of activation. The nature of this collapse deserves further study, both as a matter of historical interest, and as well in regard to present day global warming.
The dates above for the T3/T4 and T8 ice margins indicates that the entire deglacial history of Vermont as found in this study is surprisingly young and brief. As discussed, physiography around and beneath the Laurentide ice sheet during its recession, specifically in a reverse gradient setting, in conjunction with the development of coalescing water bodies led to destabilization of the ice sheet in Vermont and its accelerated recession, as just stated, probably beyond a tipping point And it is suggested that early humans may have been witness to the ice sheet dramatics.
The preceding represents my Summary and Conclusions prior to my re-examination of the issue of the long convex lobe in the Champlain Basin. As should be clear, this re-examination has modified these findings. As has been repeatedly stated in the above report, research of the deglacial history of Vermont has entailed epiphanies which represent the maturation of my thinking. With the penning of these April 2026 Summary and Conclusions I have gained further perspective related to an overview having to do with the validity of my findings.
- As part of my post-January 2026 reexamination I have once again reviewed LiDAR imagery, including both as given by VCGI for Vermont and as well regional LiDAR imagery provided by other agencies across New England, New York, and Quebec. This includes tinted and shaded LiDAR maps which clearly show the regional physiography in a stunning way. If I were to rewrite this report, I would include such imagery, which illustrates the role of the Champlain Basin and to a lesser extent the Memphremagog Basin as pathways for regional ice flow into and beyond Vermont to the south, the terrain in the upper Connecticut Basin which limited this pathway, and the spatial relationship between Vermont and New England to the regional physiography of the St Lawrence basin, which Quebec reports show had a major Glacail Dynamic effect on the recession of the ice sheet. This imagery also shows the Vermont “Bath Tub,” with its reverse gradient setting which was quite important in the ice sheet recession. Vermont served as an important pathway as part of this Glacial Dynamic during the early part of the recessional history, but as well was part of the larger St Lawrence Dynamic in later deglacial time. This larger story is generally understood but deserves to be further explored and then told in more detail. In that sense, the information provided by this report serves as an important building block for this larger story.
- As previously indicated the deglacial history of Vermont can be divided into Nunatak and Lobate Phases. Ice margin features, chiefly Ice Marginal Channels, are identified but not correlated as mappable ice margins, showing the progressive recession and emergence of Nunataks in the Nunatak Phase. My deglacial history for Vermont begins with in T1 and T2 time in late Nunatak Phase time when and where ice flow “Disconnections” from the parent ice sheet occurred, as marked by Scabby Terrain in the lower and middle Connecticut Basins. In my opinion, whereas the exact position of the T2 ice margin in the Middle Connecticut Basin needs further study, in general the identification of T1 and T2 times and the ice margin positions at these times is relatively well established, again by Scabby Terrain. The recognition, identification, and mapping of Scabby Terrain and the associated T1 and T2 margins, and the concept of Disconnections representing en masse stagnation of the Connecticut Basin lobe, are important, significant, and relatively well documented findings from this study.
- The T3 and T4 margins, which represent the beginning of the Lobate Phase in Vermont in the Memphremagog and Champlain Basins, are relatively well marked on LiDAR imagery, including by Ice Marginal Channels as part of a “Signature” which tends to identify these ice margins in a very remarkable and again stunning way, which tends to be quite evident on LiDAR imagery. Whereas LiDAR imagery in neighboring regions, beyond Vermont, likewise shows such Ice Marginal Channels, these have not been studied here. The correlation of Vermont T3 and T4 ice margins with the White Mountain Morainic System and its associated readvance is significant. The suggestion that this readvance resulted in the warming of the basal ice along the T3/T4 ice margins, leading to an inverted polythermal Cold and Warm ice margin which enabled the formation of the Ice Marginal Channels is quite intriguing, and may help to explain the prominence of such T3/T4 features across much of the State, again as part of a regional late glacial readvance.
- The T4,T5, and T6 margins are part of the step-down sequence associated with increasing amounts of meltwater and the progressive coalescence of local water bodies leading to Lake Vermont. As noted above, in my opinion the concept of Coveville Lake Vermont deserves to be re-examined and may instead represent multiple local water bodies. Owing to highly irregular physiography in the foothills, the T4-T6 ice margins were very complex. It is believed that these margins as presented on maps in this report are generally valid but very approximate, and deserve further study. However, such study requires a level of detail which is far more substantial than possible in regional studies such as given in this report. My 1972 report included an effort to delineate such local water bodies, but this study was incomplete and lacked the benefit of the regional perspective given by this present report. The subsequent work by Wright and his colleagues represents the level of detail which is required for correctly understanding the step-down deglacial history. My sense is that these researchers have compiled an enormous amount of good and useful information which could, should, and needs or deserves to be part of the story. As noted above, whereas I intended to include such details in my regional study of the deglacial history of Vermont, this regrettably did not happen. The T4-T6 step-down sequence is especially important in my opinion not just as a matter of deglacial history but as well as it relates to the destabilization of the Champlain lobe, which is a story of considerable importance for modern day global warming.
- This April Addendum re-examines the T7 and T8 margins. The early T7 margin as originally mapped and presented as part of my January 2026 report, including the initiation of calving which was triggered by the lowering of Lake Vermont to the Fort Ann level, remains valid. However, the re-examination of T7 time ice margin has led to a better understanding of the associated deglacial history, with the identification of a “late T7 margin,” which was not specifically delineated in my pre April 2026 report. The T7 margin, like all Lobate Phase ice margins, was both diachronic and hybrid in nature, which makes this a complicated story to tell.
- The “late T7 margin” is marked by “Scarps,” “Transverse Morainic Ridges,” and “Mega-Scale Lineations” indicative of calving. These are added to the catalog of ice margin features, but strictly speaking, these do not actually mark the ice margin per se. Scarps mark the position of a lateral shear margin, which is close to but at an elevation above the Grounding Line. Transverse Morainic Ridges lie close to or at the Grounding Line, which is not the ice margin per se. And Mega-Scale Lineations occur near but upgradient from the Grounding Line.
- The suggested of an early first phase of calving in late T6 time in the Deep Lake portion of the basin is now disproven and should be discarded from the above report. Instead it is now beloved that the Champlain lobe in “early T7 time” extended far to the south in the Basin, when the lowering of Lake Vermont resulted in destabilization and the initiation of calving.
- The “late T7 margin” is especially significant in that it shows that by this time the Champlain lobe was reduced to the Trough portion of the Basin, as marked by Scarps, Transverse Morainic Ridges, and Mega-Scale Lineations. These are very significant features and represent an important and, thanks to the Addendum study, relatively well documented part of Vermont deglacial history. As noted above, I have briefly examined LiDAR imagery in Quebec and New York in an attempt to assess whether or not such features are identifiable in these neighboring regions, but without success. The Addendum discusses conditions which may explain the lack of such features. In any case, as already noted, the Champlain lobe receded northward in latest T7 time, into Quebec beyond Vermont. In essence, a latest T7 margin and time, in latest Fort Ann time, is suggested but as such stood north of the Quebec border.
- Whereas it is suggested that the T3 and T4 ice margins may correlate with the Frontier and Dixville moraines, and the T6 margin with the Sutton moraine in Quebec, the positions of the ice margin in late T7 time in Quebec is undetermined.
- The readvance of the ice margin in T8 time back into Vermont is marked by deposits as described above and as documented by Cannon (1964) and Wagner (1972) in the Missisquoi Basin. The exact position of this T8 margin in Vermont is not marked, and it is unknown if the raised water levels associated with this readvance re-established Fort Ann Lake Vermont. In any case, the “readvances” reported by Connally in the Bridport area and by Wright in the Charlotte area are here regarded as associated with the lateral shear margins of the calving Champlain lobe in “late T7” time. In essence, the concept of a long convex T8 lobe as proposed prior to the April 2026 findings is now discarded. As noted above, the readvance of the Champlain lobe back into Vermont in the Missisquoi Basin is relatively well documented, albeit with the T8 ice margin position itself not marked or recognized. This readvance is believed to represent a significant event in deglacial history deserving further attention (which was the intent of my Open Letter to the Vermont State Geologist, which as it turned out served as the impetus for this present study). Whereas the geological evidence for this readvance is substantial it as yet remains to be determined whether or not this readvance had any climatic significance.