Abstract

General

The late Pleistocene deglacial history of the Laurentide ice sheet in Vermont, specifically 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 and levels in Vermont as deglaciation proceeded, not inferred ice margin positions as taken from evidence provided by proglacial water bodies, as has been suggested by Chapman and other subsequent researchers. This reflects the absence of end moraines in Vermont, which 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, the last remaining ice mass of the Laurentide ice sheet in Vermont, leading to its rapid recession, perhaps 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 Laurentide 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 late recessional history of the Champlain lobe in Vermont represents destabilization, again perhaps a “collapse(?),” bears on present-day issues of global warming with relevance to the stability of modern ice sheets, making the closing of this gap more important for “modern” day concerns.

This study was originally 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 elevations, as a general guide. In this study it was assumed, using the “Bath Tub Model,” that certain stagnant ice margin deposits and other ice margin features (formed in positions oriented perpendicular to ice sheet flow lines as opposed to such deposits formed at lateral margins), which occur at similar elevations formed at approximately the same time. 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 this report. 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.

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 more 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 Vermont’s varying Styles and Glacial Dynamics, including calving, streaming, 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 time).

As noted in the above Preface, this report is in two parts. The first part was completed in January 2026, when this report was believed to be complete. However, discussions with David Franzi and Etienne Brouard led to further study of a certain issue which helped to identify new ice margin features, leading to a revision of my understanding of deglacial history, as reported by an Addendum to my original report.

Ice Margin Features

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. In VCGI mapping the State Surficial Geology Map was frequently consulted and used for the identification of stagnant ice deposits. However, LiDAR imagery greatly helped to identify and map numerous additional such deposits, with better definition of the topographic expression and boundaries of such deposits. 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. As just noted, 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, based on elevations.
“Bedrock Grooves:” Bedrock Grooves are formed by fluvial meltwater erosion along Cold active ice margins capable of restraining or impounding meltwater, typically as large, 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 incidental stagnant ice deposits, and tend to form in conjunction with other deposits such fluvial deposits graded to kame deltas which together represent “Drainage Lines.” Bedrock Grooves and Drainage Lines are especially common in the foothills 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, which were major proglacial lake water bodies in the upland interior of the Green Mountains, as previously identified and mapped by others.
Kame Deltas: Whereas kame deltas, also called “ice contact deltas,” have long been recognized, in my 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 or altering the stability of the ice margin, which was particularly important for the Champlain lobe, as part of a significant Glacial Dynamic. As discussed, 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.

In addition, LiDAR imagery for large kame deltas and associated stagnant ice deposits on the floors of major basins, specifically the Missisquoi, Lamoille, and Otter Creek Basins, shows markings which represent progressive ice margin recession, likely associated with crevasse fracture and drainage patterns on ice lobe tips at different times.

“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 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 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, formed along the margins of ice masses which became “Disconnected” (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 which became “Disconnected (but not necessarily implying en masse stagnation to the south in this Basin beyond Vermont). 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 elevations and therefore times. In general, Ice Marginal Channels in Vermont have been carefully examined and are interpreted as having formed: 1) sub-glacially, 2) along active “Cold Ice” margins, 3) beneath immediately overlying “Warm Ice,” 4) by sub-glacial meltwater drainage, 5) under elevated hydrostatic head, confined by inverse polythermal Cold over Warm ice, 6) in a manner analogous to spillways across terrain protuberances for drainage of proglacial lake impoundments, but in this case for impounded subglacial water.

Further, in many places these Channels are very numerous, occurring as nested series of multiple Channels, 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 in a similar way to the preceding explanation, but with the base of the ice sheet warmed by the T3/T4 ice readvance over terrain that had been warmed during the preceding recession. 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 and following 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 formed 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 therefore the absence of active ice.

b) In the northern Champlain Basin where and when the waning Champlain lobe in T7 and 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 of margin to a frontal type of margin. Further study of these features is needed.
Shattuck Mountain Pothole Tract: This tract, which has been reported previously by others, is believed to have formed from drainage of either supraglacial meltwater drainage via moulins or by ice marginal drainage, 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. These features have been interpreted differently by several researchers and deserve further study.
Calving Ice Margin Features: Calving is identified at receding lobe tips for five discrete, narrow ice streams in physiographic re-entrants in the “Middlebury Bench,” a slightly raised eastern portion of the Champlain Basin floor, and in the “Trough” and “Deep Lake” portions of the Champlain Basin to the west, the latter mostly in New York State.¹ 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 basin floors. Whereas these features are interpreted as indicating calving, for which substantial supporting evidence exists, these features likely do not specifically mark grounding lines, which generally are unmarked, except for one location in the Champlain Basin as described below.
“Ice Margin Lines:” These are long linear shallow groove-like elements, the origin of which is mostly uncertain but in some places for certain Lines by further study came to be identified as “Mega-Scale Lineations” associated with streaming.
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.
Streaks: These are ice margin features identified in the Addendum study, and are detectible as linears on LiDAR. They are believed to represent both compressional and shear Glacial Dynamics along the Champlain lobe margin when it was destabilized by the lowering of Lake Vermont from the Coveville to the Fort Ann level, when calving of re-entrant ice masses in the Middlebury Bench occurred.
Scarps: Likewise identified in the Addendum study, these again are LiDAR linears, also marked by field topographic evidence, a distinctive type of till, and bedrock outcroppings associated with substantial erosion. Scarps are believed to represent lateral shear margins of ice streaming of the Champlain lobe. Also associated with these features are Transverse Morainic Ridges and Mega-Scale Lineations.
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 are of interest, 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, but 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, in his opinion 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 in Vermont remains to be studied and understood.

Nature of Ice Margin Recession and its Complexity

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 generally 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 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,” only 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 (the latter as recently suggested by Franzi), with the evidence indicating recession during individual T times. Thus, in this report reference is made, for example, to early and late T6 and early and late T7 times, and similarly early and late Coveville and Fort Ann 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 positions, with drainage features marking meltwater drainage from ice remaining in the higher, older stagnant ice margin, extending downgradient to the new, lower active, cold ice margin, where such drainage was blocked and diverted. Thus, ice margin recession, which conventionally is thought of as a simple progressive recession, instead 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.” Further, the distinction between Cold versus Warm ice is important in that the former was capable of restricting and diverting meltwater.
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, and by Drainage Lines. This reflects the fact that water in liquid form is a very effective thermodynamic heat transfer agent for melting ice. These are identified in this report as “Disaggregated” ice margin water “corridors.” As reported in the literature, such “Disaggregated” ice margin corridors were 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.

Several examples of corridors include:

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.

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 northward 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.

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 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, with moulin drainage leading to a basal tunnel with confined drainage. In addition, meltwater drainage along the cold ice 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, again referred to in this report as “Styles.”

Whereas the focus of this study is on deglacial history, as just stated the evidence for this history reflects Glacial Dynamics and Styles, elements which add complexity that is explored 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.

Vermont Deglacial History

The deglacial history reported herein includes an early Nunatak Phase and a later Lobate Phase, with these developing and progressing earlier in southern Vermont. 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, and at the Nunatak to Lobate Phase transition are associated with a readvance, indicating a T3-T4 margin which correlates with the Dixville moraine in Quebec and the WMMS 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 in three en masse stagnation events related to “Disconnections.”

In T1 and T2 times ice sheet recession and surface lowering resulted in thinning of ice at divides between the Champlain Basin and first 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 recessional lowering and thinning of the ice sheet in T4 time, 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, 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, in the Memphremagog and Champlain Basins, including its distinctive “Signature,” generally 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, mostly in New York, were mapped independently by DeSimone and LaFleur, but are found to closely correspond with ice margin positions mapped here 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, with the trace of the T3/T4 ice margin from the Winooski Basin extending into the Memphremagog Basin and thence into the Upper Connecticut Basins. This margin 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 water bodies coalesced.

Stagnant ice deposits and associated kame delta features show that in early T6 time this coalescence of proglacial water bodies led to regional Lake Vermont, beginning with the Coveville level which extended as a narrow open water corridor, likely along a “Disaggregated Ice Margin, extending progressively northward from its outlet in New York, into Vermont along the western flank of the Taconic Mountains, around the nose of the Taconics, and expanding progressively northward, eventually reaching 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 ice margin in the Missisquoi Basin extended 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.

The subsequent deglacial history in late T6 through T8 times, including Coveville and Fort Ann Lake Vermont and the Champlain Sea were addressed in my original January 2026 report. However, the January-August Addendum study substantially revised this history, providing significant new information about calving, ice streaming, and perhaps the “collapse(?)” of the Champlain lobe.

Report Organization and its Amendment

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). The pre-Addendum report found that:

in late T6 and T7 time, the lowering of Lake Vermont from the Coveville to the Fort Ann level , triggered calving of long narrow ice masses in the re-entrant basins of the Middlebury Bench.
in late T7 time the ice margin stood at the western margin of the Bench, along the Trough, with a readvance in T8 time when Fort Ann lowered to the Champlain Sea, based on the correlation of readvance evidence reported by Wright in the LaPlatte Basin, by Connally near Bridport, and by evidence reported by Cannon and Wagner in the Missisquoi Basin. Thus, the pre-Addendum report found that the Champlain lobe was long and convex at a late glacial and Champlain Sea time.

As discussed herein, conversations with David Franzi led to re-examination of this issue in the January-August 2026 Addendum study, including detailed study of LiDAR imagery in the Champlain Basin which identified new, never before recognized, remarkable features attributed to calving and streaming of the Champlain lobe, triggered by multiple, different Glacial Dynamics with different associated Styles. This LiDAR study was then followed by a focused field examination, which confirmed the LiDAR findings.

Addendum Findings

As just stated, this report originally was “completed in January 2026, providing a complete deglacial history for the State of Vermont in eight time steps from T1 through T8, including, as just described, the finding of a long, convex Champlain lobe with a readvance at a late (T8) time. This long , late convex lobe was re-examined by the Addendum study as separately reported herein, which disproved the presence of this late lobe and instead provided substantial, new information about the late deglacial history of the Champlain lobe, including:

The sudden and substantial lowering of Lake Vermont from the Coveville to the Fort Ann level, served as an “externality, ” resulting in destabilization of the Champlain lobe, as marked by many new, never before recognized linear features identified in the Addendum on LiDAR imagery which are termed “Streaks.” Such Streaks serve as “Signature” ice margin markers in a sense comparable to moraines. Streaks mark the late T6 and early T7 margin at the time of destabilization.
Ribbed Lacustrine Deposits, Headless Deltas, and Thickened Bouldery Lacustrine Deposits in narrow re-entrant basins of the Middlebury Bench document the resultant recessional calving in T7 and Fort Ann time associated with this destabilization.
In later T7 and Fort Ann time, the Champlain lobe cleared the Middlebury Bench, with its margin then standing along the eastern margin of the Trough, a physiographic low portion of the Basin floor. This recession removed an important buttress support for the Champlain lobe, triggering streaming, as marked by “Scarps “which likewise are new, never before recognized, distinctive linear features identifiable on LiDAR imagery. These are interpreted as marking the lateral shear margin of the now streaming Champlain lobe. Streaming is also marked by Mega-Scale Lineations. Transverse Morainic Ridges are identified, marking the grounding line for the calving of the frontal tip of the streaming Champlain lobe at this time.
Scarps are mostly absent in the northern portion of the Champlain Basin, north of a sector identified as the Onset Zone for the streaming Champlain lobe. It is believed that the clearing of this Onset Zone resulted in the more rapid recession of the Champlain lobe, perhaps representing the “Collapse(?)” of the lobe, leading to the opening of the Champlain Basin for the Champlain Sea.
Finally, the evidence in the Missisquoi Basin indicates that in T8 and Champlain Sea time the Champlain lobe readvanced, but that this was restricted to the Missisquoi Basin, disproving the pre-Addendum finding of a long convex lobe at a late T8 and Champlain Sea time.

The Addendum study findings underscore the importance of environmental conditions along and beneath the ice margin, referred to a “Styles,” and as well the interaction between the ice sheet and these environmental conditions , or “Glacial Dynamics.” The nature of the recession of the entire ice sheet in the context of deglacial history, Styles, and Glacial Dynamics is reviewed in separate Addendum sections added to this report. These Dynamics include:

Disconnections of large portions of the ice mass in the Connecticut Basin from the parent ice sheet, resulting in en masse stagnation of the Connectivut Basin lobe at multiple T 1 and T2 times .
Early warming of the fringe of the ice sheet at an early time in the Nunatak Phase, and more substantially in conjunction with a readvance of the ice sheet in late T3 and T4 time associated with the readvance of the ice sheet over heated terrain, as marked by Ice Marginal Channels . Study of these Channels indicates that they formed as spillways for impounded meltwater beneath the outer fringe of the ice sheet.
Warming of the ice, which continued and increased with the time, with the Champlain lobe becoming fully warmed by late T6 and early T7 time. This warming was a significant factor in the destabilization of the Champlain lobe.
Also, volumes of meltwater substantially increased, both along the margins, and as well subglacially beneath the Champlain lobe in late T6 and early T7 time, again a significant part of the Dynamic.
The lowering of Lake Vermont from the Coveville to the Fort Ann levels in late T6 and early T7 time served to destabilize the entire, now warmed and lubricated Champlain lobe, as marked by Streaks, and as well triggered calving and perhaps streaming of multiple narrow ice masses in the reentrant basins of the Middlebury Bench.
Still further recession of the ice sheet in later T7 and Fort Ann time led to loss of buttress support from and by the Middlebury Bench, triggering ice streaming of the Champlain lobe, now confined to the Trough of the Basin as marked by Scarps, with an onset zone at a physiographic necking of the Trough.
Further recession led to the clearing of the Onset Zone, which until then had provided buttressing support for Champlain lobe to the north. This led to accelerated recession at the end of T7 and Fort Ann time, and may represent the “collapse(?)” of the Champlain lobe, associated with the opening of the Champlain Basin for the incursion of the Champlain Sea into Vermont, which may have contributed to the “collapse(?).”
Finally, a readvance of the Champlain lobe took place in T8 time, restricted to the Missisquoi Basin.

Whereas the immediately preceding discussion is intended to underscore the nature and importance of Glacial Dynamics, as discussed in the Addendum such Dynamics were an important part of a now revised deglacial history for the later portion of the Champlain lobe deglacial history:

The Addendum studies found that the Champlain lobe was destabilized by the lowering of Lake Vermont from the Coveville to the Fort Ann level in late T6 and early T7 time as marked by distinctive LiDAR features termed “Streaks,” with the eastern margin transforming from a lateral toward a frontal margin with the development of a “Disaggregated,” more or less open water corridor, which rapidly progressed northward along the eastern margin to and beyond the Quebec border in T7 and Fort Ann time, increasing the convexity of the Champlain lobe. This destabilization also triggered calving along re-entrant basins within the “Middlebury Bench,” a slightly raised portion of the Champlain Basin floor, again as marked by distinctive features termed Ribbed Lacustrine Deposits, Headless Deltas, and Thickened Bouldery Lacustrine deposits which filled basin floors with distinctive flat bottoms. Steaks are very numerous and have been mapped in many places throughout the Champlain Basin,again specifically and only at the lateT6-T7 levels, providing information about the Glacial Dynamics and as well serving as distinctive “Signature” markers for late T6 and early T7 times.
As recession of the Champlain lobe progressed, still in T7 and Fort Ann time, as just described above the loss of buttressing support provided by the Middlebury Bench triggered streaming of the lobe, as marked by “Scarps, identified on LiDAR” and confirmed by field examination. These features are interpreted as representing lateral shear margins associated with streaming. Also identified on LiDAR and field confirmed are Mega-Scale Lineations, and Transverse Morainic Ridges representing ice streaming and the grounding line for calving, respectively. Likewise an Onset Zone for the streaming Champlain lobe is identified, representing buttressing support for the early streaming of the Champlain lobe.
After clearing the Onset Zone further lowering and recession of the Champlain lobe, perhaps in conjunction with the opening of the Basin for the incursion of the Champlain Sea, led to accelerated streaming and calving, perhaps representing its “collapse.” This interpretation is supported by the absence of Scarps in the northern Champlain Basin, north of the Onset Zone, and by the identification of unique LiDAR markings and as well possible iceberg deposits on the Onset Zone terrain near Shelburne. As discussed in the literature, such collapse in a reverse gradient setting, as in the Champlain Basin, typically is not marked by ice margin features (which again is reflected by the absence of Scarps north of the Onset Zone). This represents a philosophical conundrum of how to prove the negative, in the face of the absence of specific evidence. Further study of this issue is needed, perhaps by examination of soil boring and water well drilling logs, which may provide evidence regarding such a collapse.

It is suggested that the configuration of the Champlain lobe at this late glacial collapse (?) time, associated with the clearing of the Onset Zone and the draining of Fort Ann Lake Vermont and incursion of the Champlain Sea, likely was tri-lobed, with remnant sublobes projecting southward into the Champlain Basin, southwestward into the Ontario Basin, and northeastward into the St. Lawrence Basin. Whether or not the ice sheet completely receded from Vermont in T7 and Fort Ann time when the Basin opened for the incursion of the Champlain Sea is unknown. This was followed in T8 time and Champlain Sea time by an ice margin readvance restricted to the Missisquoi Basin, which likely was minor in scale.

Footnotes:

1
Whereas the “final” version of this report in January 2026 identified early 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 2026 led to a different interpretation as explained in an added Addendum.