As discussed above, the formation of Ice Marginal Channels is believed to have involved a Warm basal layer beneath an overlying Cold layer such that meltwater at the base of the ice sheet became hydrostatically confined by the overlying Cold ice as an aquitard. Ice Marginal Channels are numerous in the Nunatak Phase in T3 time, suggesting that at this early time in deglacial history the basal ice along the outer fringe of the ice sheet became warmed while overlying ice remained Cold. The question then becomes how this heating of basal ice occurred. It is suggested that warming of shallow ice generated meltwater at the outer fringe of the ice sheet which, owing to the reverse gradient setting, then penetrated a relatively short distance beneath the ice, warming the basal ice layer. This water thus became hydrostatically confined in the manner similar to ponded surface water, entrapped by terrain protuberances where Ice Marginal Channels formed by subglacial fluvial erosion as subglacial “spillways,” beneath a confining Cold ice layer.  The Ice Marginal Channels at late T3 time formed in a similar manner but it is suggested that the readvance of the ice sheet associated with the White Mountain Morainic System served to warm the outer fringe by the readvance of ice across terrain previously heated prior to the readvance.

This mechanism is a testament to the power of meltwater for melting ice. Thus, Ice Marginal Channels are interpreted as evidence of warming of the outer fringe of basal ice at an early time when the ice sheet was predominantly Cold.  Thus, their presence is taken as an indicator of the thermal status of the ice sheet. The absence of Ice Marginal Channels in T7 and T8 time is likewise taken as an indicator that the Champlain lobe at that late time had become substantially Warm ice.

Ice Marginal Channels are mapped on the VCGI Project Sheet in Vermont in association with  ice margins continuing through T6 time. However, evidence of substantial ponding along ice margins is increasingly common along step-down ice margins as marked by kame deltas and Drainage Lines leading to spillways for local surface water  proglacial lakes.  This indicates that the volumes of meltwater substantially increased through time, beyond the capacity of subglacial drainage.

As discussed elsewhere, these local proglacial lakes along the ice margin became progressively larger, coalescing through time to become regional lakes, notably Lake Vermont in the Champlain Basin. Also as discussed elsewhere the development of Disaggregated more or less open water “corridors” along the ice margin is a testament to the effectiveness of meltwater for melting ice. Lake Vermont developed along both the frontal margin of the Champlain lobe and as well along its eastern margin in this Disaggregated corridor, the head of which rapidly penetrated northward through time, resulting in the Champlain lobe becoming increasingly long and convex.

The northward penetration of this corridor was part of an important Glacial Dynamic by which, as suggested by the evidence, the eastern margin of the Champlain lobe transformed from a lateral toward a frontal type margin. This transformation is suggested by Ice Tongue Grooves which formed at the time of lowering of Lake Vermont from the Coveville level to the Fort Ann level. The northward penetration of the corridor was diachronic and likely progressed northward in T7 time, extending beyond the Quebec border, ultimately leading to the draining of Fort Ann to the Champlain Sea level associated with the incursion of the Sea into the Basin.

As discussed below, the Coveville to Fort Ann lowering in late T6 and early T7 time was a destabilizing event for the Champlain lobe, triggering calving along the frontal tip and along its eastern margin at the heads of re-entrant basins. Subsequently the lowering of Fort Ann to the Champlain Sea likewise was destabilizing, triggering a second phase of ice streaming and calving, and possible collapse(?), the earlier first phase having been triggered by the loss of buttressing support.

With regard to the  thermal status, of the Champlain lobe, as discussed in the Addendum study below, by  T7 and T8 times the Champlain lobe had become substantially Warm, as indicated by the absence of Ice Marginal Channels at these times.  However, it is believed that the evidence associated with Streaks, again as discussed in the Addendum, provides significant information about the thermal condition of the ice at this time.  As suggested, Streaks are interpreted as a “jolt” to the entire Champlain lobe in Vermont  at the time of the late T6 and early T7 lowering of Lake Vermont from the Coveville to the Fort Ann levels, when the head of the Lake Vermont corridor stood in the vicinity of Burlington, as an ice dam across the mouth of the Winooski, with Ribbed Lacustrine deposits near Richmond and Waterbury indicating the opening of the Basin at the Coveville to Fort Ann transition.

The question then becomes how or why the Champlain lobe in its entirety became affected by this water level lowering, even far to the north of the head of the corridor at that time. The explanation is believed to be related to the thermal condition of the Champlain lobe by which the jolt became transmitted throughout the lobe. It is suggested that by late T6 and early T7 time, the base of the ice sheet over much of the lobe had become warmed by a) the penetration of meltwater,  including  both a  water “film,” as for example represented by the “Wave Washed Till” on the north flank of Oak Hill of Stewart and MacClintock, which is here interpreted as formed by leakage of Lake Mansfield 2 by winnowing of till in this basal ice water “film,” and b) the penetration of basal tunnels, as for example illustrated by the drainage of Lake Mansfield 2  on the south side of Oak Hill.  The Shattuck Mountain Pothole tract likely is another example of very substantial meltwater reaching the base of the Champlain lobe at this time.

Thus, it is suggested that the “jolt” throughout the  Champlain lobe represents a hydrodynamic Glacial Dynamic  whereby the base of the Champlain lobe over much of its entirety in Vermont was hydrostatically  connected but confined by and beneath a Cold ice stratum. Thus, the “jolt” represented a system wide pressure response in a confined “aquifer.”  The nature of Scarps and associated evidence is discussed at length in the Addendum.  Numerous reports in the literature provide both field and theoretical information supportive of or consistent with this interpretation, as for example:

1. Alley, R. B. (1989). Water-pressure coupling of sliding and bed deformation: I. Water system. Journal of Glaciology, 35(119), 108–118. https://doi.org/10.3189/002214389793701527
2. Creyts, T. T., & Schoof, C. G. (2009). Drainage through subglacial water sheets. Journal of Geophysical Research: Earth Surface, 114, F04008. https://doi.org/10.1029/2008JF001215
3. Rempel, A. W. (2026). Thermomechanical and hydraulic controls on basal water pressures outside subglacial drainage conduits. Journal of Glaciology, 72, e94. https://doi.org/10.1017/jog.2026.10199
4. Irvine-Fynn, T. D. L., Hodson, A. J., Moorman, B. J., Vatne, G., & Hubbard, A. L. (2011). Polythermal glacier hydrology: A review. Reviews of Geophysics, 49, RG4002. https://doi.org/10.1029/2010RG000350
5. Lefeuvre, P.-M., Zwinger, T., Jackson, M., Gagliardini, O., Lappegard, G., & Hagen, J. O. (2018). Stress redistribution explains anti-correlated subglacial pressure variations. Frontiers in Earth Science, 5, Article 110. https://doi.org/10.3389/feart.2017.00110
6. Rempel, A. W. (2017). Transient effective stress variations forced by changes in conduit pressure beneath glaciers and ice sheets. Annals of Glaciology, 58. https://doi.org/10.1017/aog.2017.24
7. Perol, T., Rice, J. R., Platt, J. D., & Suckale, J. (2015). Subglacial hydrology and ice stream margin locations. Journal of Geophysical Research: Earth Surface, 120, 1352–1368. https://doi.org/10.1002/2015JF003542
8. Boulton, G. S., & Caban, P. (1995). Groundwater flow beneath ice sheets: Part II—Its impact on glacier tectonic structures and moraine formation. Quaternary Science Reviews, 14(6), 563–587. https://doi.org/10.1016/0277-3791(95)00058-W
9. Jóhannesson, T. (2002). Propagation of a subglacial flood wave during the initiation of a jökulhlaup. Hydrological Sciences Journal, 47(3), 417–434. https://doi.org/10.1080/02626660209492944
10. Fountain, A. G. (1992). Subglacial water flow inferred from stream measurements at South Cascade Glacier, Washington, U.S.A. Journal of Glaciology, 38(128), 51–64. https://doi.org/10.3189/S002214300000959X
11. Chu, W., Creyts, T. T., & Bell, R. E. (2016). Rerouting of subglacial water flow between neighboring glaciers in West Greenland. Journal of Geophysical Research: Earth Surface, 121, 925–938. https://doi.org/10.1002/2015JF003705
12. Hall, A., & van Boeckel, M. (2024). Hydraulic damage in subglacial conduits: Evidence from rock hydrofracture and hydraulic jacking for high fluid pressures during rapid melt of the Fennoscandian Ice Sheet. Quaternary Science Reviews, 343, Article 108917. https://doi.org/10.1016/j.quascirev.2024.108917
13. Hooke, R. L., & Jennings, C. E. (2006). On the formation of the tunnel valleys of the southern Laurentide ice sheet. Quaternary Science Reviews, 25(11–12), 1364–1372. https://doi.org/10.1016/j.quascirev.2006.01.018
14. Mooers, H. D. (1990). Ice-marginal thrusting of drift and bedrock: Thermal regime, subglacial aquifers, and glacial surges. Canadian Journal of Earth Sciences, 27(6), 849–862. https://doi.org/10.1139/e90-088

Obviously, a full discussion of these reports in detail is beyond the scope here. In sum, the thermal condition of the ice sheet and its  progressive development relates to and is part of Glacial Dynamics.

In addition, it is suggested that by later T7  time when Fort Ann lowered to the Champlain Sea, the Champlain lobe  had become fully Warm, which allowed the lobe to lose its integrity, leading to its collapse(?).