A. Introduction
As stated above, this is a report on Vermont’s Deglacial History, Styles, and Glacial Dynamics, with the history based on the assumption that the Bath Tub Model is a valid and reliable basis for correlating ice margin features having similar elevations. Application of this methodology leads to the identification of specific ice margin elevation levels, positions, and associated times, all in a relative chronology ranging from T1 to T8, as summarized and presented in tabular and map formats as discussed below. More detailed information in support of the findings is given in specific “Locales” in Appendix 2, which also includes a map showing all Locale locations.
The history presented here is based on information developed by usage of the online services of the Vermont Center for Geographic Information(VCGI). This service provides users with access to a wide array of information, such as LiDAR imagery, and published information regarding Vermont geology, soils, and other relevant information. VCGI is accessed and viewable online at the following link:https://maps.vermont.gov/vcgi/html5viewer/?viewer=VCGI_IMV_v7.VCGI_IMV_Viewer_HTML&project=273d22a9a28f4d9191bb1a7a10e8107c&link=6065f1a7ee2648c3a16e8158b082efa1_40RtRPlto_iBBl-u
VCGI allows users to compile information on a “Project Sheet”, which in essence represents an online “field map.” My Project Sheet includes markings of ice margin features as described above along with miscellaneous notes and observations. The Project Sheet can be viewed at a range of scales, with the ability to zoom in for extremely detailed, close-up views. Elevations of features on the Project Sheet for ice margin features and levels are taken from VCGI provided USGS topographic maps. Elevations recorded on VCGI maps are “Local” levels. Many of these are adjusted to make corrections for isostatic rebound using the Quebec border as the reference point to provide corrected elevations showing the topography as it existed prior to rebound, which was then used for correlating and differentiating features formed at the same times and levels. 1 Adjusted levels are marked on VCGI by giving the local, present day elevation, plus an additional elevation to correct for isostatic differences, again using the distance to the Quebec border as the reference for a correction factor at a slope of 5 feet per mile along a north-south transect. As discussed above, future revisions of the isostatic correction factor may be warranted, but this is not believed likely to change the findings in a major way.
The VCGI Project Sheet developed from research reported here can be can be viewed with a link, which can be made available. As is the nature of all technology, VCGI is based on a geographic information system that is becoming outdated, with new versions in development. Unfortunately the next new version, scheduled for Spring 2026, will be incompatible with the present version, such that when VCGI converts to this new version the old version, including the Project Sheet used for the study reported here, will no longer be available. Also, unfortunately, the present VCGI project sheet can only be preserved by usage of an extremely tedious method of stitching together many screen shots, which generates a pdf file, which can be shared but is no longer accessible online and can not be modified and updated on VCGI. Thus, the usage of the link at some point will no longer be available. Time permitting I will endeavor to make a copy of my Project Sheet.
The mapping of ice margin features and associated water bodies on VCGI generated considerable detail on the VCGI Project Sheet. As noted above, the VCGI Project Sheet, which presently for the time being is viewable and shareable online, served as the “field” base map for identifying and marking ice margin features. However, whereas the VCGI service is helpful, and indeed remarkable, for examining, identifying and mapping at close up, detailed scales, unfortunately, my VCGI field map is not scalable and cannot serve as a statewide map for presenting a Statewide overview. To generate statewide maps of the different ice margins marking the deglacial history of Vermont, the VCGI map with its ice margins was used as a visual guide to manually trace ice margins onto a suitable base map showing the physiography of the State of Vermont as an entity. This is a tedious, cumbersome process, and only gives approximate ice margin locations on the Statewide map as compared to the VCGI map. Of course, again, the VCGI maps can be referred to for details, so long as they are available, examples of which are given throughout this report and in Appendix 2. For emphasis and to be made clear, it is again stated that the ice margins and proglacial lake footprints presented below on regional maps are only imprecise approximations and schematic, intended to illustrate the general concepts. The maps below are similar to maps presented previously in regard to calving ice margins, which likewise are intended to be conceptual representations.
The base map used for the development of the statewide ice margin maps presented below was taken from the following online source: https://en-ca.topographic-map.com/map-z4c3q/Quebec/?center=44.99106%2C-72.41132&zoom=15&overlay=0&base=2&popup=44.99257%2C-72.4072
The following were added to the Statewide map:
- The Vermont State boundary marked by a heavy dashed black line.
- For physiological perspective, 1) the present day 2000 foot(610 m) elevation contours across the State, marked by dark brown lines, and 2) major drainage basins, as shown on the following map, marked by yellow lines, including:
- Champlain Basin
- Memphremagog Basin
- Connecticut Basin, which is divided into the Upper Connecticut portion(includes the Passumpsic basin), the Middle Connecticut portion( includes the Stevens, Wells, Waits, Ompompanoosuc, White, Ottauquechee, Black, West, Williams, and Saxton basins) portion, and the lower Connecticut(Deerfield) portionHudson/Hoosic Basin
- Hudson/Hoosic Basin
- Metawee Basin
Obviously, present day physiography differed slightly from deglacial times owing to isostatic rebound, but the above base map and markings give a sense of the terrain in late glacial times. The ability to understand and visualize drainage basins is very important in as much as these were occupied by increasingly discrete ice lobes during deglaciation.
3. Moraines or ice margin positions in Quebec, New York, and New Hampshire, based on information taken from published literature as identified below. More detailed information related to these features is given in Appendix 1.
4. The footprint of regional proglacial Coveville and Fort Ann Lake Vermont, and large, but local proglacial Lakes Winooski and Mansfield in the Winooski/Lamoille Basins in pale blue shading. Again, the sources for this information is provided when and where appropriate, but generally came from Chapman, Wagner (1972), and Springston