The evidence suggests that ice margins as defined here at eight levels and times were “diachronic,” to borrow a term introduced by Franzi for Lake Vermont strandlines, which greatly differs from the classically held paradigm-ic view of ice margins as represented on maps by well-defined lines suggestive of a staccato like, simple ice margin recession. In general, it is suspected that all ice margin levels and times were diachronous.
Reference to ice margins as being diachronous simply means that individual T time ice margins as defined here varied in age from place to place. The best example is the T7 time, level, and ice margin. As explained elsewhere, multiple events took place in T7 time, associated with shifting positions of the ice margin through time. For example:
- In time T7-1 the T7 margin stood at the head of the re-entrant basins when calving was initiated, triggered by the sudden and substantial lowering of Lake Vermont from the Coveville to the Fort Ann level.
- In time T7-2 and Fort Ann time the calving tips of these ice masses in the re-entrant basins receded westward, with the Champlain lobe eastern margin clearing the Middlebury Bench, standing along the margin of the Trough. This loss of buttressing support resulted in the initiation of a first phase of ice streaming, as marked by Scarps, with an Onset Zone near Shelburne.
- In time T7-3, the lowering of Lake Vermont from the Fort Ann level to the Champlain Sea, along with the clearing of the Onset Zone, in a manner likened to a surface water dam break, triggererd a second phase of ice streaming.
- In still later T7-4 time the ice margin rapidly receded by streaming and calving northward to and beyond the Quebec border, perhaps as a collapse(?)
This chronology was developed and recognized in the Addendum study, with a different history recognized in the pre-Addendum study. However, this understanding came about and evolved while I was still in the process of the Addendum study. As a consequence at that time I lacked the understanding and perspective which only became clear as the Addendum study was concluding, near the end of the report writing. With full apology to the reader, my description of events becomes confusing. Were I to start afresh, I would turn to report writing devices to make this history easier to understand, such as the presentation of T7-1 to T7-4 times as given here.