G l a c i a t i o n

Glaciations not only shape the landscape, but they also form land and water habitats. Over time species of plants and animals will adapt and evolve in these new habitats. Sea-levels and climate can be quite dramatic during the transition between interstadial and glaciation which further affects the life cycle and survival rate of species.

The Processes of Glaciation Glaciation is caused by climate change. A prerequisite to glaciation is an increase in high altitude land mass. This can occur due to plate tectonics, or continental uplift from glacial retreats. This causes changes in eustatic oceanic and atmospheric circulation which affects the climate. The Milankovitch theory attempts to explain the Pleistocene glacial-interglacial cycles in terms of variations in the Earth's orbit around the sun. This in turn influences the distribution in insolation (solar radiation) across the Earth which changes the climate. Global cooling has been associated with changes in CO2 levels, and changes in albedo.

The Wisconsinan Glaciation The Wisconsinan glaciation began approximately 2 mya and ended around 10,000 ya. It has been divided into 3 subintervals: the Happy interval (2 mya-80,000 or 60,000 ya), the Boutellier Interstadial (80,000 or 60,000 ya-30,000 ya), and the Duvanny Yar interval (30,000-13,000 ya). Late Wisconsinan glaciation range is 22,000-10,000 yr. The most recent glacial warming began around 14,000 ya. The Younger Dryas briefly interrupted this warming between 11,000 and 10,200 radiocarbon ya and is characterised by a rapid and intense drop in temperature (Mathewes et al, 1993). The Boutellier interval and the Holocene are both times of interstadial warming which caused the glaciers to retreat. We are currently experiencing the Holocene interglacial warming which began 10,000 ya. Partial thaws occur every 100,000 years during an ice age which cause the ice to retreat. Another advance is expected around 10,000 years from now!

The Continental Ice Sheets During the Pleistocene, glaciation peaked 18,000 ya and 1/3 of the land was covered by glaciers compared to 1/9 of the land currently covered by glaciations. During peak glaciation, the Laurentide Ice Sheet in North America and the Scandinavian Ice Sheet in Europe locked up most of the planet's water. The Laurentide Ice Sheet was the largest of the two. The Laurentide Ice Sheet was more than 3 km (2 miles) thick and covered most of Canada. The Cordilleran in the west was much smaller than the eastern Laurentide ice sheet. Remnants of the Laurentide ice sheet covers 80% of Greenland and is 3 km think at its center. Polar sea ice covered Greenland and Iceland but the southernmost part of Iceland and England was not glaciated.

How Ice Sheets Form Ice sheets form when snow accumulates, compresses, and then recrystallizes to form ice. Once an ice sheet is 50 m think it flows from its center anywhere from 0.3-50 m per day. A glacier floats once it reaches water, and can form cliffs that are greater than 60 m high. Moraines of till can provide more than 10 m deep fertile soils. Ice sheets also provide gravel and sand, water, and basins. All these are suitable for human settling. (Source: National Geographic Society, 1993)