Multiple types of ice margin features are identified, most of which were found and used substantially in VCGI mapping, as discussed below. These include:
- Stagnant ice deposits
- Ice Margin Channels
- Ice Margin Steps
- Drainage Lines
- Kame deltas
- Scabby Terrain
- Bedrock Grooves
- Ice Tongue Grooves
- Shattuck Mountain Potholes
- Calving ice margin features, including a) “bouldery lacustrine and marine silts and clays,” b) “Headless Deltas,” and “Ribbed Lacustrine deposits.”
- Ice Margin Lines, including different types of linear markings on VCGI maps, which in general are incompletely understood.
- Other- a category for interesting but baffling and mysterious features not as yet understood.
Some features are tentatively identified but may not be bonafide ice margin markers This includes:
- “Ice Margin Lines,” which are marked on VCGI along the margin of the Champlain lobe on the Basin floor at various place, in particular along the western flank of the Taconics, on the basin floor west of Snake Mountain, on the east flank of Snake Mountain, and north of the St Albans vicinity.
- “Wave Washed Till” as mapped by Stewart and MacClintock on the north flank of Yantz Hill which is here suggested but not proven to have formed as part of the subglacial leakage beneath an ice margin dam for Lake Mansfield.
- Ice Tongue Grooves, which, as discussed below, are features identified and mapped on VCGI at four locations, all at the mouths of the major sub-basins of the Champlain Basin, specifically the Missisquoi, Lamoille, Winooski, and Otter Creek Basins. The Missisquoi features are more fully documented, leading to the interpretation that these formed at the southern corner of the Missisquoi Basin mouth where an ice lobe is believed to have extended as an ice tongue appendage eastward from the Champlain lobe, upward into this sub-basin. It is believed that these features were formed by drainage along a steeply sloping ice tongue margin and indicate destabilization of the ice margin. The Lamoille and Winooski features have a similar setting and appearance but are less well documented. The Winooski Ice Tongue Grooves are located on the northeast flank of Yantz Hill where mapping by Springston and DeSimone (2007) 1 Springston, G. and DeSimone, D., 2007, Surficial geologic map of the Town of Williston, Vermont; VT. Geol. Survey Open File Report VG07-5. provides information which is suggestive of drainage along steeply sloping recessional ice margin positions. And finally, possible Ice Tongue Grooves are identified at the mouth of the Otter Creek Basin. However, at this time the available information about Ice Tongue Grooves is not sufficient to be certain about their nature and origin, and thus these features are included in the interpretation of deglacial history with the caveat that their identification and interpretation is tentative and uncertain. However, based on a careful examination of the available evidence it is my belief that these are bonafide ice margin features, and are of considerable importance in that they represent destabilization of the Champlain lobe eastern margin whereby it transformed from a lateral to or toward a frontal margin.
- “Streaks” – these are linear tonal patterns most evident on LiDAR imagery, often in close association with Ice Marginal Channels, Steps and Drainage Lines. However, such Streaks lack any clear and definite topographic expression by topographic contours or LiDAR shading, and as well lack of evidence of distinctive soil differences. Whereas such Streaks likely are ice margin markers, in some places where ice margins and major proglacial water body strandlines are closely associated the distinction between the two is challenging, owing to the lack of more detailed confirming evidence. Whereas Streaks are identified and mapped on VCGI in some places, in general these features generally are not used as markers for identifying deglacial ice margins, and require further study.
The following is a summary overview of each of the ice margin feature types identified and used in this VCGI mapping.