The Big Ice Meeting
On and off for the last 2 Mega-annum (2Million years) many cold periods caused most of Canada to be covered by glacial ice. The Late Wisconsinan, also called the Wisconsin Glacial Episode, was the most recent glacial period of the North American ice sheet complex. During the Late Wisconsin the first clear traces of human presence in North America became evident, though there are some indications that humans may have arrived even earlier.
This most recent covering of ice (peaking about 20K Years ago) the Cordilleran Glacial System flowing eastward from the Rocky Mountains met with the Laurentide Ice Sheet from northern and eastern Canada.
The Laurentide Ice Sheet, principal glacial cover of North America. At its maximum extent it spread as far south as latitude 37° N and covered an area of more than 13,000,000 square km (5,000,000 square miles). In some areas its thickness reached 2,400–3,000 m (8,000–10,000 feet) or more.
Cordilleran Ice Sheet covered up to 2,500,000 square km (970,000 sq mi). The eastern edge abutted the Laurentide ice sheet. The sheet was anchored in the Coast Mountains of British Columbia and Alberta, south into the Cascade Range of Washington. This Glacier held one and a half times the water held in the Antarctic.
The City of Calgary is one place where the two Giant Ice Cubes met. The dividing line in Calgary was along what is now, Nose Creek and was one meeting place of these two vast sheets of ice. Erratics are large rocks carried long distances by glaciers and are plentiful along this corridor. A string of them, the Foothills Erratics Train, marks the junction of the Laurentide and Cordilleran glaciers. The Ice may have been a 1000 meters thick here.
During the last glacial period, much of northern Europe, Asia, North America, Greenland and Antarctica were covered by ice sheets, which reached up to three kilometres thick during the glacial maximum about 20,000 years ago. The enormous weight of this ice caused the surface of the Earth's crust to deform and warp downward, forcing the viscoelastic mantle material to flow away from the loaded region. At the end of each glacial period when the glaciers retreated, the removal of this weight led to slow (and still ongoing) uplift or rebound (Isostatic Rebound Effect) of the land and the return flow of mantle material back under the deglaciated area. Due to the extreme viscosity of the mantle, it will take many thousands of years for the land to reach an equilibrium level.
Please send the CO a message with your answers to the following. Logs without answers will be deleted.
1) Which one of the two Glacial Systems delivered most of the erratics to Southern Alberta?
2) Why do you think most of the erratics came from this system and not the other?
3) What do you think is still happening to this area due to the melting of the ice sheets?
4) Determine your altitude at Ground Zero with your GPS'r or Google Earth. What is that altitude?
5) Using your present day altitude at GZ from your Gps'r , and the diagram/formula below, calculate what your altitude would have been if you were standing on top of the ice sheet when it was at its maximum thickness in the area. Assume we are back in isostatic equilibrium today and the net erosion/sedimentation is zero.
6)SE of the Bridge about 10M is a Telephone Pole. There is a Tag on the pole about 8" long. What are the last 2 digits on this tag?
