The late Pleistocene deglacial history of the Laurentide ice sheet in Vermont, specifically meaning the lowering elevations of the ice sheet surface levels and the receding positions of its margins through time, has never been established in its entirety. By this is meant the specific, explicit delineation of successive ice margins in Vermont as deglaciation proceeded, not inferred ice margin positions as taken from evidence provided by proglacial water bodies as suggested by Chapman and other subsequent researchers. This reflects the absence of end moraines in Vermont. The absence of such features has long been recognized, and itself is significant. As discussed in this report, this absence is related to the nature of the ice sheet “Glacial Dynamics” and the environmental conditions along its margins, referred to as “Styles.” Whereas Vermont lacks such end moraines as a consequence of its unique conditions, these same conditions instead favored the destabilization of the Champlain lobe and its “collapse,” which itself is an important story unique to Vermont, again thanks to its Glacial Dynamics and Styles.
By contrast, considerable information about ice margins, levels, and deglacial history of the ice sheet recession in neighboring Quebec, New York, and New Hampshire has been published, reflecting the presence of end moraines in these areas. Thus, Vermont represents a gap in the historical record. This gap is crucial for the understanding of regional deglacial history of the Laurentide ice sheet in as much as the Champlain Basin in New York and Vermont, the Memphremagog Basin in eastern Vermont, and the Connecticut Basin in Vermont and New Hampshire likely served as pathways for a significant portion of the ice sheet. This gap in the historical record is important as a matter of the academic understanding of deglacial history and needs to be filled by correlations with neighboring regions. However, the evidence presented here, especially in the Addendum to this report, suggesting that the history of the Champlain lobe in Vermont represents a “collapse” of the lobe, with relevance to modern ice sheets in our era of global warming, makes this a more important “modern” story.
This report was inspired by research reports in southern Quebec, near Vermont, which have identified moraines that can be correlated on the basis of their elevation, orientation, and alignment. This suggests a physiographic “Bath Tub Model” might be used to correlate different types of ice margin features which are quite numerous in Vermont, such as stagnant ice deposits, on the basis of their elevation differences, as a general guide. In this study it was assumed, using the “Bath Tub Model,” that frontal margin deposits (as opposed to deposits formed at lateral margins) which formed at the same time along thinning ice margins, oriented perpendicular to ice sheet flow lines, tend to occur at similar elevations. The usage of such a model is made more reasonable by the fact that much of the ice sheet recession in Vermont took place at a late time when the ice sheet was relatively thin, and in a “reverse gradient” setting, much like a northward sloping “Bath Tub,” with the ice margin in most places influenced or controlled by both physiography and standing water, all of which is discussed in detail in the text. Multiple arguments in defense and support of the usage of elevation, again as a guide, in such a Model for reliably developing Vermont deglacial history are presented. Both the collective weight of the evidence and as well independent evidence support the validity of the “Bath Tub Model,” and thus the deglacial history so determined.
Quebec reports also suggest that environmental conditions along the ice sheet margins varied, that these conditions represent different “Styles,” and that these conditions were associated with “Glacial Dynamics,” whereby the physical nature and condition of the ice sheet was influenced by ice sheet boundary conditions. This report thus explores Vermont’s deglacial history by the usage of a “Bath Tub Model,” “Styles,” and “Glacial Dynamics.”
Previously unpublished information from my field mapping in the 1960s and 1970s, current online information provided by the Vermont Center for Geographic Information (VCGI), including LiDAR imagery, limited recent field work, and pertinent previously published reports in the literature were used to explore Vermont deglacial history as presented in this report. This study identifies conventional types of ice margin features, such as stagnant ice deposits, and as well types which reflect varying Styles and Glacial Dynamics, including calving and other types of ice margin features. A Section of this report identifies and describes the ice margin features identified and used in this study. This is followed by a Section dealing with deglacial history. The mapping reported here identifies and delineates eight ice margin positions, levels, and times from the oldest and highest at T1, through the youngest and lowest at T8 (with the hint of a possible T9).
Ice margins are conventionally thought of as like simple lines on a map. However, this study recognizes that ice sheet recession in Vermont was more complex:
- Ice margin recession was a continuous, progressive, rapid, step-down recession of ice margins marked by distinctive ice margin features at progressively lower levels, times, and positions. Features associated with such time steps are recognized and mapped as “T” times, levels, and positions, identified as T1 -T8, as marked and mapped on VCGI maps. These T times, levels, and positions represent “stillstands” in the sense that time was required for the formation of ice margin features.
- T times and levels were diachronous, similar to strandlines for major proglacial water bodies such as Coveville and Fort Ann Lake Vermont, with the evidence indicating recession during individual T times. Thus, in this report reference is made, for example, to early versus late T6 and T7 times.
- Recession involved active cold and warm ice margins and stagnant warm ice margin components, as “hybrid” margins. Owing to the insulating properties of sediment cover, stagnant ice deposits at individual T time positions persisted while their associated active ice margins receded to a new, lower level position, with drainage features marking drainage from the higher stagnant ice margin extending downgradient to the new, lower active ice margin, where such drainage was blocked and diverted. Thus, ice margin recession, which conventionally is thought of as a simple progressive recession, can be likened to a “dance” of multiple active and stagnant ice margins through time, again as hybrid margins. This overlapping temporal and spatial relationship is referred to as a Style described as “Everything, Everywhere, All at Once and Continuing.”
Whereas deglacial history can be parsed by the usage of elevation in a Bath Tub Model, obviously the ice sheet was not flat. The configuration of the ice sheet surface was influenced by the regional Glacial Dynamics associated with ice flow which in Vermont at an early time was northwest to southeast, generally athwart the regional physiographic and bedrock structural grain. As time progressed the thinning ice sheet increasingly adjusted through time to favor physiography. But individual drainage basins themselves are not uniform, instead having topographic irregularities. As a consequence, Glacial Dynamics and Styles were not uniform and ice margin features in Vermont were not formed and distributed in a uniform or bilaterally symmetrical manner. Instead, ice margin features formed at many favored locations and likewise were locally absent along the ice margins at any given times.
In addition to the Glacial Dynamics of the ice sheet itself, drainage of meltwater on the ice sheet surface was directed by the configuration of the ice sheet surface. At an early time, regional drainage on the ice sheet in Vermont was northwest to southeast, with meltwater configuration influenced by and in places trapped by the terrain. For example, the Shattuck Mountain Potholes near Bakersfield, which are remarkable features, are believed to represent the entrapment of meltwater from a large portion of the Champlain lobe ice sheet watershed by large scale terrain irregularities. In addition, meltwater drainage along the margins of the ice sheet, such as Bedrock Grooves along the Green Mountain foothills in northern Vermont, likewise resulted in the formation of ice margin features which were not uniformly distributed, but instead were affected by terrain irregularities, referred to in this report as “Styles.”
Whereas the focus of this study is on deglacial history, the evidence for this history reflects Glacial Dynamics and Styles, elements which themselves are only touched on in this report but deserve much more attention and study. It may be possible for future research to identify and delineate conceptual models, for example, with equipotentials and flow lines for both the ice sheet surface itself, and as well for both confined and unconfined meltwater hydraulic heads within and beneath the ice. To some extent, this present work begins to lay the groundwork for such studies.
This report, which again, primarily deals with Vermont deglacial history, is in two parts. The great bulk of this report, as the first part, was completed in January 2026, and as such was “published” on a dedicated website. This January 2026 report presented evidence leading to the identification of a long, convex Champlain ice lobe in late deglacial times (identified as T7 and T8 times). As discussed further below, conversations with David Franzi led to re-examination of this issue, including more recent detailed study of LiDAR imagery in the Champlain Basin which identified new, never before recognized, remarkable features attributed to calving of the Champlain lobe ice stream triggered by lowering of Lake Vermont from the Coveville to the Fort Ann level. These were then examined by focused field examination, which confirmed that the Champlain lobe stood as a long convex lobe in T7 time and Lake Fort Ann time, which “collapsed” in T7 time, leading to the complete withdrawal of the ice sheet in late T7 time and the subsequent entry of the Champlain Sea, followed by an ice margin readvance back into the northern portion of the Champlain basin, restricted to the Missisquoi Basin portion in T8 time. Thus, these findings were added as a second part Addendum dated April 2026, both of which are presented in vermontdeglacialhistory.org. Obviously, it would be preferable to rewrite the entire report. However, for personal reasons, I have instead elected to simply add the Addendum, recognizing that some of the January 2026 findings conflict with subsequent April 2026 findings. More generally, I regard this entire report as far too long, and would much prefer that the entire January and April 2026 findings be resolved and presented in a greatly condensed summary overview report.
The following is a summary of ice margin features which were identified and mapped on VCGI “Project Sheets:”
- Stagnant Ice Margin Deposits: These deposits, as conventionally understood, include a wide array of features formed in conjunction with stagnant ice, such as kame and kettle deposits and eskers. As discussed below, kame deltas likewise are stagnant ice margin features even though they tend to be regarded as standing water features.In VCGI mapping the State Surficial Geology Map was frequently consulted and used for the identification of stagnant ice deposits. However, LiDAR imagery helped to identify and map numerous additional such deposits, with better definition of the topographic expression and boundaries of such deposits.Whereas eskers were recognized in the 1960s and 1970s, generally speaking these were then few in number. LiDAR imagery has led to the identification of many eskers, in some places being commonly found in a multitude of small neighboring physiographic basins occupied by local ice sheet sub-lobes. Such eskers identified on LiDAR imagery are extremely numerous, perhaps in the hundreds, in many places identified as very minute, subtle traces. A prominent and important “esker,” previously identified and reported in the Missisquoi Basin, has been shown to possibly instead represent an end moraine, illustrating the need for great care in such studies.Again, an important distinction is made between stagnant ice deposits formed along lateral versus frontal ice margins, with ice sheet flow lines oriented more or less parallel to the former and perpendicular to the latter. This distinction is important for the usage of the Bath Tub Model, because frontal but not lateral margins are believed to provide markers for identifying ice margins of approximately the same age, and likewise conversely for differentiation of features of different ages.
- ‘Bedrock Grooves:” Bedrock Grooves are formed by fluvial meltwater erosion along active ice margins, typically as deep, incised, channel-like grooves, which in many places reflect bedrock structural elements which were enhanced by ice marginal drainage erosion. Such Grooves commonly are associated with fluvial sedimentary deposits, and stagnant ice deposits, and tend to form in conjunction with other deposits such as kame deltas which together represent “Drainage Lines.” Bedrock Grooves are especially common along the western margin of the Green Mountains, along the receding eastern margin of the Champlain lobe, especially north of the Lamoille Basin, but as well at scattered locations to the south, including drainage from the upland interior associated with proglacial Lakes Winooski and Mansfield as identified and mapped by others.
- Kame Deltas: Whereas kame deltas, also called ice contact deltas, have long been recognized, in past mapping in the 1960s and 1970s these were not generally recognized or used in Vermont as ice margin features. However, LiDAR imagery helps to identify and map many ice contact deltas, both shoaling and Gilbert-type deltas, which are very common and important as they indicate the close proximity of the ice margin to proglacial water body strandlines at specific elevations. Whereas kame deltas generally are regarded as marking the levels of standing, proglacial water bodies, these features are so intimately and closely related to ice margins as to be regarded as ice margin features.
In general, ice margin recession tended to be associated with the progressive development of local proglacial lakes, in a recurrent step-down pattern for the development of lower proglacial water body levels as lower outlets were uncovered by ice margin recession, as commonly marked by kame deltas. This step-down pattern shows the progressive coalescence of proglacial water bodies into increasingly lower and larger water bodies. This step-down coalescence is a very significant element pertaining to Vermont deglacial history because larger regional water bodies had the capability of substantially controlling and altering the stability of the ice margin, which was particularly important for the Champlain lobe, as part of a significant Glacial Dynamic. As discussed herein such coalescence is likewise believed to be significant for modern day global warming concerns. Kame deltas are a major part of this step-down recessional history. Drainage features associated with both active and stagnant ice margins commonly show meltwater drainage in a downgradient direction toward and into standing proglacial water bodies as marked by kame deltas.
In addition, LiDAR imagery for large kame deltas on the floors of major basins, specifically the Missisquoi, Lamoille, and Otter Creek Basins, shows markings which represent progressive ice margin recession, possibly associated with crevasse fracture and drainage patterns on ice lobe tips at different times.
Step-down recessional ice margins of the receding ice sheet tended to be penetrated by standing water, forming more or less open water corridors marked by a close association with stagnant ice deposits, commonly including kame deltas. This reflects the fact that water in liquid form is a thermodynamically effective agent for melting ice. These are identified in this report as “Disaggregated Ice Margin Water Corridors.” As reported in the literature, such corridors are associated with “Disaggregated” ice margins, which are highly fragmented ice margins penetrated by standing water. Whereas in this report such margins are not specifically and formally identified as ice margin features per se, they are so common and important as to merit identification as such features. Such Corridors are marked in many places, most commonly by stagnant ice deposits and kame deltas, in close association with fine-grained silt-clay fresh water or marine ponded water bottom sediments. For example:
1) A corridor is identified in the Memphremagog Basin in association with proglacial Lake Memphremagog in conjunction with the T6 ice margin. The literature regarding Disaggregated ice margins underscores the highly fragmented nature of such margins, with meltwater, usually but not necessarily associated with standing water, penetrating a “chicklet-like” maze of ice blocks. In the Memphremagog Basin such blocks tended to include very large blocks of ice, now identifiable as kettle holes with unusually deep present-day ponds. Also in the Memphremagog Basin, many of the larger present day lakes, such as Lake Willoughby, likely formed in overdeepened basins similar to the Finger Lakes in New York (which in itself deserves further study). These overdeepened basins as well were occupied by long lasting ice blocks as part of the Disaggregated ice margins.
2) A corridor is also mapped along a T4 margin in conjunction with proglacial Lake Winooski, a major proglacial water body in the interior uplands as identified and mapped in previous literature. Along the eastern margin of Lake Winooski this corridor shows the development of this water body by rapid penetration of standing water along its strandline around the eastern perimeter of an ice mass within the footprint of the Lake Winooski Basin, with associated stagnant ice margin deposits such as eskers graded downward to kame deltas at the Lake Winooski strandline, basically a step-down hybrid ice margin record. Along Lake Winooski’s western margin this corridor was associated with “Disconnections” of active ice masses in deep valleys on the eastern flank of the Green Mountain front range, as marked by Scabby Terrain deposits in those basins. The “Disconnection” term and concept is taken from the literature.
3) Similarly, a corridor is identified and mapped along the south- and east-facing margins of the Champlain Lobe. This corridor was associated with the rapid recession of this lobe, by penetration of first Coveville, and then Fort Ann Lake Vermont waters along the eastern ice lobe margin. The ice margin associated with this corridor in time became a calving type margin. As a consequence of the rapid northward growth of this corridor along the Champlain lobe eastern ice margin, with residual ice remaining on and buttressed by a raised portion of the Basin floor identified here as the “Middlebury Bench,” the Champlain lobe became long and convex in plan-view shape. As a consequence, this convexity resulted in and was associated with ice margin recession which had both westward and northward recessional components, along highly irregular ice margins. Thus, the ice margin and its recession was not a simple pattern of northward recession of an ice margin as conventionally regarded. The understanding of the recessional history of this ice margin was initially developed in the January 2026 report, but significantly modified by the April 2026 Addendum findings.
- “Drainage Lines:” Fluvial meltwater along receding ice margins tends to be marked by erosional and depositional evidence which is readily detectible on topographic maps and LiDAR imagery, but as well such Lines are associated with soil textural differences on published surficial geology maps, Vermont Highway Department maps, and on USDA Soil Conservation Service soil maps, all provided by VCGI. These Lines mark the margins of the receding ice sheet at different places and times. Drainage Lines extend a) downgradient from or along ice margins within individual basins, b) across interfluves between neighboring basins, and c) across drainage divides via spillways between neighboring basins. Such Drainage Lines in some places can be traced and correlated for long distances, serving as important links thereby helping to correlate regional ice margins across the State in support of the Bath Tub Model. For example, an approximate 30 mile long (48 km) Drainage Line from a specific (T4) ice margin near the Quebec border in the Memphremagog Basin can be traced southward in a downgradient direction, linking to the strandline for the Lake Winooski in the Lamoille and Winooski Basins, which in turn can then be traced southward for another 30 miles (48 km) in close association with a T4 ice margin; and further, this strandline can then can be linked via another Drainage Line into the Champlain Basin to a Lake Vermont strandline, which likewise can be traced further southward to T4 ice margin positions in southern Vermont. Thus, such Drainage Lines can provide support for the viability and usage of the Bath Tub Model as links for correlating margins across the State and are important elements of Vermont deglacial history.
- “Scabby Terrain:” This is a deposit with a peculiar LiDAR signal identified and mapped in many places on VCGI. These deposits formed along the margins of ice masses which became “Disconnected” (again, a term and concept identified in the literature for modern ice sheets and glaciers) from the parent ice sheet and as a consequence stagnated en masse. Both individual “patches” and long tracts of Scabby Terrain are mapped, the latter being especially important and interpreted as indicating the margins of large portions of the Connecticut Basin lobe in Vermont (not necessarily to the south in this Basin beyond Vermont), which became “Disconnected.” Such Disconnections are identified at three times and places related to the lowering of the ice sheet across divides, cutting off the active ice supply from the parent ice sheet via the Champlain and Memphremagog basins into the Lower, Middle, and Upper Connecticut Basins. These “Disconnections” reflect the higher terrain along the perimeter of the Connecticut Basin where and when at different times and places, ice supply from the parent ice sheet became critically limited.
- “Ice Marginal Channels:” These are erosional features which have been widely reported in recent literature, with different terminology and theories for their formation. Such features are numerous and quite common in Vermont, especially in certain areas, along certain ice margins, and at certain specific times. In general, Ice Marginal Channels are here interpreted as having formed subglacially along “Cold Ice” but beneath “Warm Ice,” specifically along active ice margins, and tend to mark ice margins in an early “Nunatak Phase” of recession. In many places these Channels are very numerous, clearly marking the progressive lowering of the ice sheet in the Nunatak Phase, leading to the development of ice lobes in the subsequent Lobate Phase.
Certain Ice Marginal Channels at a particular T level and time (T3/T4) occur at the base of the Nunatak Phase where together with stagnant ice deposits they define a “Hybrid” margin at the beginning of the Lobate Phase. These particular T3/T4 Hybrid margin features, which are mapped across Vermont, represent a “Signature” that facilitates mapping, semi-independently from the usage of ice margin elevations in the Bath Tub Model.
Further, the T3/T4 Ice marginal Channels in the Upper Connecticut Basin in Vermont, representing active ice, are correlated with a portion of the White Mountain Moraine System (WMMS) in New Hampshire, which has been reported as representing a significant readvance of the ice sheet. These particular Ice Marginal Channels are believed to have formed along active ice margins, beneath Cold Ice, the base of which was warmed by the T3/T4 ice readvance over terrain that had been warmed during the preceding recession. These Channels are thus interpreted as associated with inverse polythermal ice. Further, these Channels are believed to have formed by erosion by sub-glacial meltwater under confined elevated hydrostatic head, across terrain protuberances, in a manner analogous to spillways for drainage of subglacial lake-like impoundments. This T3/T4 readvance is part of the aforementioned “Signature,” which can be identified and correlated across Vermont, including correlation with readvance evidence reported by others in the Winooski Basin and the Vermont Valley in the Rutland and Bennington vicinities. Thus, these T3/T4 Ice marginal Channels are regarded as an important marker of a readvance of the ice sheet that occurred at an early time across Vermont.
The Ice Marginal Channels in the Upper Connecticut Basin are associated with Scabby Terrain and stagnant ice deposits indicating the en masse stagnation of the ice mass in this basin following the WMMS readvance. Together, these particular Ice Marginal Channels and associated deposits mark the margin of a lobe in this Basin at T3/T4 time which stagnated en mass in conjunction with the recession associated with the WMMS readvance. This lobe-shaped Upper Connecticut ice mass is mapped as extending southward to a stagnant ice margin position near Bradford, Vermont with an associated outwash plain which is graded to deltaic deposits in Lake Hitchcock.
The deglacial history in the Upper Connecticut Basin as just described is related to a long standing debate in the literature as to the manner of ice recession, whether by massive stagnation of large portions of the ice sheet in that basin as opposed to progressive recession of discrete active ice margins. The evidence presented here indicates that the recession initially involved active ice margin recession associated with and following the WMMS readvance, but that the ensuing recession then led to en masse stagnation of the Connecticut lobe in the Upper Connecticut Basin, again with a terminous near Bradford, Vermont, with drainage evidence, essentially an outwash plain, graded to the Lake Hitchcock strandline.
Significantly, Ice Marginal Channels generally are absent:
a) In the Lower and Middle Connecticut Basins, where, as noted, the ice sheet in these basins became Disconnected and stagnated en masse at two early times (T1 and T2). The absence of Ice Marginal Channels is taken as evidence consistent with the en masse stagnation of ice in these basins and the absence of active ice.
b) In the northern Champlain Basin where and when the waning Champlain lobe in T7 and especially T8 times is believed to have been a fully Warm Ice type, such ice being unfavorable for Ice Marginal Channel formation.
- “Ice Tongue Grooves:” These features are erosional grooves believed to have formed at the mouths of the major basins, including the Missisquoi, Lamoille, Winooski, and Otter Creek Basins in conjunction with the sudden and substantial lowering of proglacial water bodies in these basins, resulting in disequilibrium marked by increased surface ice gradients associated with the transformation of the eastern margin of the Champlain lobe from a lateral type margin to a frontal type margin. Further study of these features is needed.
- Shattuck Mountain Pothole Tract: This tract, which has been reported previously, is believed to have formed from drainage of either supraglacial meltwater drainage via moulins or by ice marginal drainage, or both, as suggested by others, in either case associated with extraordinary meltwater drainage volumes/velocities associated with a physiographic barrier that served to collect and direct meltwater from a large catchment area of the Champlain lobe. Again, such features represent drainage history closely associated with deglacial ice margin history, which likewise deserves much more study.
- Calving Ice Margin Features: Calving was identified in the initial January 2026 Phase of this study for discrete ice streams in five physiographic re-entrants in the vicinity of the “Middlebury Bench,” a slightly raised eastern portion of the Champlain Basin floor, and in the “Trough” and “Deep Lake” portions to the west, mostly in New York State. 1 Whereas the “final” version of this report in January 2026 identified calving in the western Deep Lake portion of the Trough at a late T6 time, mostly in New York State, then believed to be part of the development of a long, convex Champlain lobe in T7 and T8 time, subsequent reexamination of this interpretation in early 2026 led to a different interpretation as explained in my added Addendum. Calving ice margin features include 1) “Headless Deltas,” 2) Ribbed Lacustrine Deposits,” and 3) “Thickened Bouldery Ponded Water Deposits” associated with unusual, conspicuous, and mappable flat valley floor terrain. Whereas these features are interpreted as indicating calving, for which substantial supporting evidence exists, these features likely do not specifically mark grounding lines.
In the April 2026 addendum, additional calving ice margin features were identified, including “Scarps” which represent lateral shear margins, associated Ribbed Lacustrine deposits, Transverse Morainic Ridges, and Mega-Scale Lineations. Whereas the Champlain lobe was reported in January 2026 as a long convex lobe in T7 and Fort Ann and T8 and Champlain Sea times, these newfound features resulted in a revised interpretation, essentially pointing instead to the collapse of a long convex T7 lobe leading to its complete withdrawal from Vermont, followed by a readvance in T8 time restricted to the Missisquoi Basin.
- “Ice Margin Lines:” These are long linear shallow groove-like elements, the origin of which is uncertain but in some places were suspected to include “Mega-Scale Linears” associated with calving, or other ice marginal drainage marks. The later Addendum study confirmed some of these as “Mega-Scale Linears.”
- Ice Margin Steps: These are features resembling stepped terrain, usually in glacial till ground moraine, interpreted as having formed along ice margins by a mechanism which may represent imprinting by ice blocks on till substrate or by some other mechanism which is as yet uncertain. Such Steps are less common but closely related to Ice Marginal Channels, and believed to be part of the larger, regional ice margin record at the transition from the Nunatak Phase to the Lobate Phase.
- Miscellaneous and Uncertain: In this category are a wide variety of markings, commonly identified on LiDAR imagery, which are believed to be related to ice margins, and likely are very important but their origin and meaning are as yet unknown. This is particularly the case for the Memphremagog Basin, and to some extent for the Champlain Basin, especially in late glacial times. For example, on the floor of the Memphremagog Basin are many features which are recognized on LiDAR and which appear to be related to both ice margins and associated drainage. Whereas these features represent details which do not need to be understood for the regional perspective on deglacial history given here, nevertheless it is likely that much can be gained from more detailed study. Some of these features near Newport appear to correspond, for example with features identified by Wright in his detailed mapping of the Memphremagog Basin, but these need to be better understood as to what they mean and how they fit in the larger perspective of deglacial history. As suggested in a conversation with Jeff Munroe, until recently at Middlebury College, the power of LiDAR is incredible and no doubt much more information leading to a better understanding of the Laurentide ice sheet and its history, and of ice sheets including modern analogs, remains to be studied and understood.
As noted above, the deglacial history reported herein includes a Nunatak Phase and a Lobate Phase. Evidence for ice margins in the early “Nunatak Phase” were identified but generally not correlated and mapped across Vermont except in the Memphremagog Basin where they are remarkably numerous, indicating a T3-T4 margin which correlates with the Dixville moraine in Quebec and the WMMSA in New Hampshire. The evidence indicates that the ice sheet in the subsequent “Lobate Phase” developed distinct lobes in the Champlain Basin, the Memphremagog Basin, and to some extent the Connecticut Basin, with a multitude of sub-, sub-sub-, etc., lobes as recession progressed. The Champlain lobe was more substantial and longer lasting owing to its lower elevation floor and more direct, less obstructed opening to the parent ice sheet to the north. The Memphremagog Basin became deglaciated earlier than the Champlain Basin owing to the elevation of its floor being significantly higher than the Champlain Basin floor. The Connecticut lobe was nourished by ice primarily from the Champlain Basin and the Memphremagog Basin, accounting for Scabby Terrain and its en masse stagnation.
In T1 and T2 times ice sheet recession and surface lowering resulted in thinning of ice at divides between first the Champlain Basin and the Lower Connecticut Basin in T1 time, and then with the Middle Connecticut Basin in T2 time, resulting in en masse stagnation as marked by Scabby Terrain and the absence of Ice Marginal Channels or other evidence of active ice. The surficial geology of the Lower and Middle Connecticut Basins in Vermont consists mostly of widespread, thin till ground moraine and scattered small stagnant ice deposits, consistent with the lack of active ice and associated Lobate Phase margins in these Basins.
T3-T4 times, levels, and margins correlate with the White Mountain Moraine System (WMMS) in New Hampshire, in what is referred to here as the Upper Connecticut Basin. The WMMS has been reported as marking a significant readvance, associated with the Older Dryas cooling event and dated at approximately 13,800- 14,000 years BP. The ice sheet in T3 time associated with the readvance extended across divides from the Memphremagog Basin, with insignificant flow from the north in the Connecticut Basin itself owing to the constricted physiography and high elevation of the terrain in the headwaters of the Connecticut Basin. The active ice margin associated with this readvance as mapped by Thompson et al in conjunction with the WMMS is believed to have been associated with an ice lobe extending southward in the Upper Connecticut Basin , again approximately to the Bradford, Vermont vicinity where, as noted above, the evidence indicates a margin with drainage into Lake Hitchcock.
With recession in T4 time with lowering and thinning of the ice sheet, the supply of active ice from the Memphremagog Basin to the Upper Connecticut Basin ended , as marked by the later and lower moraines at the WMMS and by Scabby Terrain related to en masse stagnation of the ice mass in the Upper Connecticut Basin, and as marked by widespread and substantial stagnant ice deposits extending across divides between the Memphremagog and Upper Connecticut Basins.
The T3-T4 margin is mapped across Vermont, including its distinctive “Signature,” in the Memphremagog and Champlain Basins, representing the beginning of the Lobate Phase. In the Memphremagog Basin the T3/T4 margin is well and substantially marked by Ice Marginal Channels and stagnant ice deposits, as a hybrid margin at T4 time with the Ice Marginal Channels indicative of active ice correlated with the Dixville moraine in Quebec. Continued recession in the Memphremagog Basin is marked by a step-down sequence of hybrid margins marking T5 and T6 times, with the T6 margin representing the last ice presence in this basin.
In the Champlain Basin, the T3/T4 margins are likewise well marked with the T3 margin marked by numerous Ice Marginal Channels showing the recession of a well-developed lobe in the Vermont Valley, with a substantial T3 stagnant ice deposit in the Bennington vicinity. The T3 margin is mapped on VCGI as extending northward on the eastern flank of the Champlain Basin to the Lincoln vicinity, north of which the ice sheet was in the Nunatak Phase. VCGI evidence shows progressive recession of stagnant ice margins from the T3 margin near Bennington to the T4 margin near Rutland, with an almost continuous recession of stagnant ice deposits on the floor of the Vermont Valley. The T3 and T4 stagnant ice deposits at Bennington and Rutland are correlated with T3/T4 features at the WMMS. Evidence reported in the literature supports a possible readvance of the ice sheet at these locations, although further research on this issue is needed. The T3 and T4 margins in southwestern Vermont, near New York State, were mapped independently, but later found to closely correspond with ice margin positions mapped by DeSimone and LaFleur, mostly in New York, but extending into Vermont. However, those authors specifically state that they found no evidence of an ice readvance.
T3 and T4 margins mapped on VCGI in the Champlain Basin are marked by stagnant ice margin deposits and Ice Marginal Channels as part of the aforementioned “Signature” pattern. The trace of these margins extend across divides between the Champlain Basin and the Memphremagog Basin, with evidence suggesting ice as well extending across low col divides between the Winooski and Upper Connecticut Basins. The T3 and T4 margins in the headwaters of the Winooski Basin show recession leading to the development of Lake Winooski in T4 time, again as mapped by others. Evidence reported by Wright, Larsen and others for a readvance, mostly within the footprint of Lake Winooski, is here taken as T4 time, but as well at slightly higher and earlier T3 levels, is correlated with the WMMS readvance but the trace of the T3/T4 ice margin from the Winooski Basin into the Memphremagog Basin and thence into the Upper Connecticut Basins was quite convoluted and irregular owing to physiographic influence on the ice margins.
The Champlain lobe was the largest and longest lasting of the ice sheet lobes, in Vermont. VCGI mapping shows the traces of the ice margins marking the progressive recession of the Champlain lobe from the T3/T4 levels as just described, through T7-T8 times. This recession is marked by diverse types of ice margin features showing the progressive step-down ice margin recession, likened to “multiple rings on a slowly draining bath tub,” with the close association of the ice margin and many local proglacial water bodies , as standing water “Corridors” which became progressively larger as these coalesced.
Stagnant ice deposits and associated kame delta features at the early T6 time show that Coveville Lake Vermont extended as a narrow open water corridor, likely along a “Disaggregated Ice Margin, extending northward from its outlet in New York, into Vermont along the western flank of the Taconic Mountains, around the nose of the Taconics, and continuing northward to the vicinity of the mouth of the Winooski Basin. Stagnant ice deposits and multiple kame deltas are mapped demarcating this margin, as for example at Benson Landing, Castleton, Proctor (near Rutland at the mouth of the Vermont Valley), Pittsford, Brandon, East Middlebury, Bristol, and South Hinesburg. As reported previously by others, including Wagner(1972),the Bristol delta at the Coveville level was formed by outwash from an ice margin here identified as T6, and the South Hinesburg delta at the Coveville level was formed by drainage from Lake Winooski, which required an ice dam across the mouth of the Winooski Basin. Notwithstanding the identification of many features as just noted as representing Coveville Lake Vermont, it is noted that the evidence for a regional Coveville stage deserves further study. It is possible that so-called Coveville features instead are local proglacial water bodies which have been mistakenly correlated as a regional water body by Chapman and subsequent researchers, including myself.
The T6 margin in the Missisquoi Basin extends into Quebec so as to correlate with the Sutton moraine. However, the information here suggests that the ice sheet in T6 time in the Missisquoi Basin was quite thin, with an intricate pattern of sub-lobes closely associated with the local physiography.
As noted above, this report is in two parts or phases, dated January 2026 and April 2026. In the January 2026 Phase 1 report, prior to the Addendum study, an initial, first phase of calving was inferred at early T6 and Coveville time, based on the physiography of the basin floor, with low elevations of the terrain, mostly on the New York side of the Basin which were thought to likely have resulted in substantial water depths capable of supporting calving. It was believed that the configuration of the Champlain lobe at this time was substantially convex, demarcated by the early T6 open water Coveville corridor along the south facing, east facing, and perhaps west-facing margins, with significant asymmetry imparted by the more substantial spanse of a large, open Coveville water corridor on the western, New York side.
Also in the January 2026 report, a second phase of calving was identified in late T6 and early T7 time, when Coveville Lake Vermont lowered to the Fort Ann level. The Coveville to Fort Ann water level change was substantial and sudden, which again as reported in the Phase 1 January 2026 study report, was thought to trigger a second phase of calving. As described by Franzi (personal communication, 2024) this transitional time may have been associated with the breakout of Lake Iroquois in the Ontario Basin into the Champlain Basin. This time was also closely associated with the opening of the Winooski Basin, by subglacial leakage, not catastrophic ice dam failure, leading to the draining of Lake Mansfield (the successor to Lake Winooski) in the Winooski Basin, briefly opening the Winooski Basin to Coveville waters, shortly followed by Fort Ann entry into this Basin.
This second phase of calving was marked by in the re-entrant basins within the “Middlebury Bench,” such as the LaPlatte River, Lewis Creek, New Haven River, Little Otter Creek, and Otter Creek, by calving ice features as referred to above. The evidence also indicates that this water level lowering destabilized the eastern margin of the Champlain lobe whereby it transformed from a lateral to a frontal margin, as suggested by Ice Tongue Grooves.
The January 2026 report likewise found evidence suggesting that the lowering of the Fort Ann level to the Champlain Sea level in T8 time triggered a third round of calving, with readvance evidence in the Missisquoi Basin in Champlain Sea and T8 time correlated with readvance evidence reported by Wright in the Charlotte area and likewise with readvance evidence reported by Connally in the Bridport area. Thus, this interpretation suggested a long convex lobe in T8 time, with rapid northward recession of a calving margin, again in T8 and Champlain Sea time.
Franzi (2025, personal communication) has not found evidence supporting such a long convex Champlain lobe in New York, and believes that the lobe ice margins in Coveville, Fort Ann, and Champlain Sea times were substantially flattened, again in plan view, approximately as drawn for example by Chapman. Further, Franzi has examined model information of ice sheet profiles which he believes suggest it is unlikely that the Champlain lobe was physically able to sustain such a long convex lobe of active ice for such a readvance.
My rejoinder, again as presented in my January 2026 report, was that his evidence for the ice margin in Coveville, Fort Ann, and Champlain Sea times being far to the north is consistent with the opening of the large open water spanse on the western, New York side of the basin, and that the theoretical inability of the ice sheet to sustain such a long convex lobe needs to be viewed in the context of the Champlain lobe at T8 time in the basin being the remnant of the much larger ice mass left remaining from an earlier time.
Franzi’s observations were helpful as they question the nature of the recession of the Champlain lobe. As suggested in the January 2026 report, the evidence indicates that the recession was rapid, associated with calving, with suggested instability, essentially the collapse of the Champlain lobe. Substantial recent literature exists suggesting that collapsing ice lobes, especially in reverse gradient settings, exhibit erratic, “spasms” of short lived surge-like oscillations. Thus, whereas the evidence in the Missisquoi Basin for a readvance is substantial, it is possible that the readvance evidence in the Charlotte and Bridport areas associated with the long convex lobe in T8 time was part of a “spasm” associated with the Champlain lobe collapse. By this explanation, the long convex lobe in T8 time, south of the Missisquoi Basin may have been stagnant ice, not active ice, marked by “spasms” when the ice was reactivated in local, narrow ice streams in the Middlebury Bench. Clearly, this is an intriguing matter deserving further study.
The more recent April 2026 Addendum re-examined the issue of the long convex lobe extending far to the south in a late glacial time, first by a very close, detailed study of LiDAR imagery in the Champlain Basin. Substantial new evidence was found indicating the position of the ice margin and associated calving in T7 time, which was corroborated by followup field examination. This new evidence includes “Scarps,” which are thought to be lateral shear margins, Transverse Lateral Moraines, and Mega-Scale Lineations, all associated with calving ice streams. The Addendum evidence thus showed that the lower terrain of the Champlain Basin favored the development of a long Champlain lobe in T6 and T7 times, with no early phase of calving, that the lowering of Lake Vermont from the Coveville to the Fort Ann level in T7 time resulted in calving, much as previously reported, but that calving progressed rapidly in T7 time, leading to the complete recession of the Champlain lobe, again in T7 time, followed first by the incursion of the Champlain Sea, and then followed by a readvance in T8 time which was restricted to the Missisquoi Basin. The evidence indicates that the Wright and Connally readvance features which were major parts of the evidence for a long convex lobe in T8 time were instead associated with and caused by shearing associated with the lateral shear margin of the calving Champlain lobe ice stream in late T7 time.
Beyond deglacial history, this report also considered three sidebar topics:
- Archaeological evidence pertaining to the migration of Paleoindians into and around Vermont: Whereas this is a topic largely beyond the scope of this study, as noted, this is a long standing interest. As is well known, Paleoindian migration tended to shadow the receding Laurentide ice margin. This matter is briefly examined, primarily as a suggestion of the potential benefit of cross-discipline research.
- Global warming: As is made clear, I am not an expert on global warming, but I share the concern for the potential effects of modern day global warming on modern ice sheets. It is believed that the information gained from this study of the recession of the Laurentide ice sheet in Vermont may provide insights about potential impacts of global warming on present day ice sheets, especially Greenland. This is touched on briefly.
- Pre-T1 Vermont glacial history: The finding here that the entire deglacial record here represents a history of the ice sheet presence and recession during a very late portion of the last glaciation is, for me, as stated, quite surprising and remarkable. This obviously leads to the larger question of evidence for the preceding times when Vermont, for a much longer time, was covered by ice. A chance encounter with Paul Bierman whose research includes studies of the long-term Pleistocene record of glaciation has prompted me to add some thoughts in a separate section of this report having to do with the issue of what happened in Vermont in pre-T1 time. At issue, and still needing to be considered, are questions as to when and how erosional features such as striations, roche moutonnée, overdeepening, etc., and other erosional features occurred, and as well depositional features, such as glacial till itself formed, including the possibility that larger elements of the regional physiography may have been shaped by long term multiple glaciations, which is the thrust of Bierman’s continuing studies. Accordingly, thoughts are offered in regard to possible avenues for his further studies in Vermont which may be fruitful.