Events leading up to the sharp climate-cooling period known as the Younger Dryas, or more familiarly as the "Big Freeze," unfolded after glacial Lake Agassiz, at the southern edge of the Laurentide ice sheet
covering Hudson Bay and much of the Canadian Arctic, catastrophically broke through an ice dam and rapidly dumped thousands of cubic kilometers of fresh water into the ocean.
Broecker, W.S., Kennett, J.P., Flower, B.P., Teller, J.T., Trumbore, S., Bonani, G., and Wolfli, W., 1989, Routing of meltwater from the Laurentide Ice Sheet
during the Younger Dryas cold episode: Nature, v.
We interpret this vertebra as probably deriving from an animal living in a tundra or taiga setting at a distance of 100 to 200 km from the southern edge of the Laurentide ice sheet
By the end of this time window, the margin of the Laurentide ice sheet
, although highly lobate and irregular, lay across the Upper Peninsula.
In response, West and his colleagues suggest that the impact struck the 3-km-thick Laurentide ice sheet
that was sitting atop eastern and central Canada at the time.
The Laurentide ice sheet
covered nearly half of North America, and Arctic sea ice extended well south of where it is today.
Spanning all the way to New York, the eastern shoulder of the Laurentide Ice Sheet
also gouged out the Ohio River Valley.
That's the time when the Laurentide Ice Sheet
began to melt and retreat from northern portions of the Great Plains, the team suggests.
At the time, most of North America down to what is now the northern tier of the United States lay beneath a massive but melting blanket of ice, known as the Laurentide ice sheet
. Assuming the theory is correct, the comet would have slammed into the ice at unimaginable speed.
Turns out, most are related to a population of hardy chipmunks that once lived next to a towering block of ice called the Laurentide ice sheet
Early on reconstructions of the Laurentide Ice Sheet
retreat pattern in Labrador-Ungava were to a large extent based on the spatial pattern of glacial meltwater traces (e.g., Ives 1960; Barnett 1963; Barnett and Peterson 1964; Peterson 1965).
At the end of the Late Wisconsinan glacial epoch, fluctuations in the Lake Michigan Lobe of the Laurentide Ice Sheet
resulted in the formation of three moraine systems around the south end of the Lake Michigan basin: in decreasing age, the Valparaiso, Tinley and Lake Border ridges.