The slide occurred around 4200 cal BP, when the surface
connection with Lake Laflamme (Bouchard and Saarnisto, 1989)
was possibly still active (Fig. 7A). As the LIS decayed, its geometry evolved and the ice margin would have receded toward the site of the subglacial lake. As the distance to the ice margin decreased, the ice-surface slope above the lake would have increased causing the lake volume to shrink. At the same time, the reduced ice thickness would reduce water pressure in the lake, whereas the pressure of pore fluids in low permeability sediments would remain high and could promote slope instability. The MWD could thus be related to slope instabilities associated with the rapid exorheic drainage through channels observed on the outer crater rim following the deglaciation (see section 2.4).
Another trigger mechanism of the MWD could have been an
earthquake, as the area is seismically active ..
Adams et al., 1991
" If other study sites in such low
productivity environments suffer from old carbon effects, this new
sedimentary record from northernmost Ungava has produced
a reliable new means of dating the disappearance of the last
remnants of the Laurentide Ice Sheet at 6850 cal BP, which coin-
cides with a major climatic and environmental transition
throughout the eastern Canadian Arctic."
Nice data. Seems to refute your conjecture.
“Lies require commitment.”
― Veronica Roth, Divergent