This Addendum is aimed at evaluating the findings presented in my January 30, 2026 report on the Deglacial History of Vermont, specifically that the Champlain lobe of the Laurentide ice sheet extended southward as a long convex lobe at a late deglacial time, including a readvance associated with the Champlain Sea. More specifically, the previous report found, as already noted above, that:
- As part of the general step-down recession of the Laurentide ice sheet from its earlier T3-T6 ice margin positions, in T6 time the Champlain lobe extended southward in the Champlain Basin as a long, convex, bifurcated lobe with an eastern sublobe extending into the mouth of the Vermont Valley and a western sublobe southward to and beyond Benson Landing in the main, western “Trough” portion of the basin, with the ice margin wrapping around the nose of the Taconic uplands in the intervening area. Associated with this step-down sequence, the ice margin was fronted by local proglacial water bodies, which progressively coalesced through time into larger, more regional water bodies, becoming Coveville Lake Vermont in late T6 time. A first phase of calving was surmised to have begun in the “Deep Lake” portion of the western Trough area at this time.
- In T7 time this long lobe underwent a second phase of calving, triggered by the sudden and substantial lowering of Lake Vermont to the Fort Ann level, with calving in re-entrant basins in the “Middlebury Bench” and the southern lobe tip in the main “Trough” Basin.
- In T8 time this same long lobe underwent a third phase of calving associated with the sudden and substantial lowering from the Fort Ann to the Champlain Sea levels, with a readvance of the ice margin, as marked by evidence reported previously by others in the Missisquoi Basin, the Charlotte area, and the West Bridport areas.
Thanks to discussions with David Franzi, the validity of such a long lobe was questioned. Accordingly, this Addendum evaluated this issue, by detailed study of LiDAR imagery and follow-up field investigations in the southern portion of the Champlain Basin, basically south of the Winooski Basin. This found evidence indicating that:
- The early and late T7 ice margins are marked in many places in the Champlain Trough Basin, southward to the Orwell area at a late time. As such, the development of a first phase of calving in T6 time as previously suggested is not possible, because of the presence of the Champlain lobe extending so far to the south (south of the “Deep Lake “area) in T7 time.
- The early and late T7 ice margins are marked in many places in the Champlain Trough Basin, southward to the Orwell area at a late time. As such, the development of a first phase of calving in T6 time as previously suggested is not possible, because of the presence of the Champlain lobe extending so far to the south (south of the “Deep Lake “area) in T7 time.
- The Champlain lobe developed multiple calving ice streams beginning in early T7 time, including in individual re-entrant basins within the “Middlebury Bench” and in the “Trough” portion of the main Basin. The evidence for this in the Bench portion includes Ribbed Lacustrine deposits,” “Thickened Bouldery Lacustrine deposits, and in the Trough portion: includes Scarps associated with Ribbed Lacustrine Deposits, Mega-Scale Lineations, and Transverse Morainic Ridges
- The margin of this T7 lobe receded northward to and beyond the Quebec border by calving in T7 time.
- A readvance of the Champlain lobe in T8 and Champlain Sea time is marked by features restricted to the Missisquoi Basin.
Thus, the finding of a long convex lobe in T7 and T8 time, as previously reported, which was the primary focus of this Addendum study, was incorrect and is now amended.
This Addendum reports new features not previously recognized, associated with calving and ice streaming, specifically as identified above in the Trough portion of the Basin in T7 time, as follows:
- “Scarps” and associated “Ribbed Lacustrine” deposits were identified by LiDAR imagery and confirmed by field investigation. These represent lateral shear zones for the calving Trough ice stream, as described in relatively recent literature, at locations between the faster moving ice stream and slower moving, commonly stagnant ice in Ribbed Lacustrine deposits along lateral margins. These features are mapped at many places in the Trough ice stream, indicating the recession of the Champlain lobe ice stream in T7 and Fort Ann time, and its complete, rapid withdrawal from Vermont, preceding and likely leading to the incursion of the Champlain Sea.
- Scarps are identified and mapped on LiDAR imagery, and as well have been verified by focused recent field mapping. As such, Scarps represent major, important ice margin features, again associated with lateral shear zones of the Champlain lobe ice stream, at elevations slightly above the grounding line of the associated ice stream.
- Mega-Scale Lineations and Transverse Morainic Ridges are likewise identified on LiDAR imagery and confirmed by field mapping. These features are less common than Scarps but are consistent with and add to the evidence of ice streaming and calving of the Champlain lobe.
- The northward recession of the Champlain lobe tip likely was progressive and at times halting, as suggested by Transverse Morainic Ridges for the Trough ice stream and as well by features associated with multiple tributary ice streams in the re-entrant basins within the Middlebury Bench.
- The recession of the T7 lobe from its frontal position near Orwell to and beyond the Quebec border was astoundingly rapid and took place in a very short period of time. As indicted in the previous report, the T3 and T4 margins (which preceded T7 time) are correlated with the White Mountain Morainic System which has been dated as approximately 14,000- 13,800 years BP. And the incursion of the Champlain Sea has been dated as about 13,000 years BP. Therefore, the recession of the long convex T7 lobe in the Champlain Basin likely occurred in substantially less than 800-1,000 years. This likely reflects the destabilization of the Champlain lobe, again triggered by the sudden and substantial lowering of proglacial water levels from the Coveville to the Fort Ann level, and augmented by the breakout of Lake Iroquois, and the draining of Lake Mansfield. This destabilization likely also reflects a) the decrease in the buttressing support of both the lowered proglacial lake water levels associated with the lowering of Lake Vermont to the Fort Ann level, b) the diminished buttressing support associated with the irregular topography of the Basin floor in the Middlebury Bench, and as well c) the prevalence of a “reverse gradient” setting which has long been recognized as causing ice sheet destabilization. This destabilization and rapid recession is regarded as a “collapse” of the Champlain lobe.
- The term “collapse” and its associated concept is significant, presently a controversial and debated topic pertaining to present day concerns for global warming. This term and concept is not used here lightly. Establishing and proving a “collapse,” as to what exactly constitutes a “collapse,” how a “collapse” is defined, and what constitutes evidence for and proof of a “collapse,” are challenging and difficult, whether for the geological record for past glaciations, or for modern day ice sheets and glaciers. However, the recession of the T7 margin of the Champlain lobe as found and reported here is regarded as being as close to proof of a collapse as can be established by geological studies. In my opinion, these findings in fact document a collapse. This finding has significant implications for modern ice sheets. The message here is that global warming, in this case natural warming at the end of Pleistocene time, in a reverse gradient settings, resulted in collapse related to the progressive coalescence of regional proglacial water bodies, such that sudden changes in the levels of these water bodies can and likely did result in the massive destabilization of the Champlain lobe, leading to its “collapse.” Again, of prime importance is the development of associated proglacial water bodies, which is related to basin physiography, especially when regional in scale, with sudden and rapid changes in these levels having the capacity to alter the ice sheet by a Glacial Dynamic linkage. The findings reported here in my January 2025 original report and as well this Addendum provide information about conditions deserving further study in regard to the concern for the stability of modern day Antarctica, Greenland, and other glaciers.
The proof of this deglacial history, as with any story in geology and in the natural sciences generally, comes not from a single fact or finding, but instead from multiple lines of evidence which together represent a consistent preponderance of evidence. The discovery of Scarps, initially from the study of LiDAR imagery, which were then confirmed by field examination as bonafide geological features, served as the Rosetta Stone-like key for a better understanding of the deglacial history of Vermont. Scarps are regarded as bonafide, mappable features, consistent with our present understanding of calving ice streams. Parker Calkin in his studies of the Middlebury area long ago argued for exercising care in regard to the identification of ice margin features possibly suggestive of ice margin readvance, instead recognizing evidence indicative of calving. In fact, the evidence found here indicates that readvances proposed by Connally in the West Bridport area and Wright in the Charlotte area represent lateral shear zones of the calving Champlain lobe Trough ice stream. This finding is supported by substantial evidence, all of which fits with such a finding in a remarkable, consistent way.
As has long been observed and lamented, Vermont lacks end moraines as found in neighboring Quebec, New Hampshire, and New York, making the deciphering of Vermont deglacial history more challenging, It turns out that this reflects the unique physiography and other conditions of the Champlain Basin in Vermont which are unfavorable for the formation of moraines but instead favor the development of calving ice streams as marked by Scarps and other associated features. These features provide remarkable evidence of deglacial history every bit as important and meaningful as moraines.
Thus, the enigma of the long lobe at a late time in the deglacial history for Vermont is now resolved, albeit in a surprising way, with findings representing both an intriguing deglacial history which is of considerable academic interest and as well with implications for modern global warming, deserving further study. As stated, the findings presented here represent only part of the story for the Champlain lobe. This 2026 Addendum mapping focused on the southern Champlain Basin, basically in the Middlebury Bench, south of the Winooski Basin and the Burlington area. Whereas Scarps have been identified to the north in the Lamoille and Missisquoi Basin, based on a limited reconnaissance level examination of LiDAR imagery, the physiography further north in the Basin is more irregular and does not appear to be as favorable for the formation and/or preservation of Scarps, or other ice streaming features. However, by contrast the terrain in the northern portion of the Basin in New York is more favorable for lateral shear zones and Scarp development, albeit on the western side of the Champlain lobe which the evidence in Vermont suggests as being less favorable. In any case, this deserves further study.