Presently we have permanent ice caps on Antarctica, the northern Arctic Ocean, Greenland, and isolated alpine ice fields in major mountain ranges. Our glacial age started a little less than 2,000,000 years ago when the Antarctic continent, and the ring of northern continents obstructed warm ocean currents from reaching the poles.

There appears to have been 19 to 20 intensely cold periods within this time as predicted by the Milankovitch cycle (see later paragraph). This does not mean that there have been 19-20 major glaciations. In the beginning each cold period probably resulted in relatively minor glaciations that didn't recede as far back during the warm period or interglacial period. In general each glaciation was a bit larger and more extensive than the last.

The area of greatest accumulation appears to have been in central British Columbia, with ice up to 1 kilometre deep during a glaciation. Another area of accumulation occurred west of Hudson's Bay, but it is unlikely that these two ice sheets ever converged until fairly "recently". During these early advances, mountain glaciers probably never advanced beyond the front ranges.

• Cavell Advance (Little Ice Age) Ended 50 BP (1900-1850?) Began 750 BP (1200 A.D.)
• Crowfoot Ended before 6600 BP Began after 11,000 BP
• Late Wisconsinan Ended 11,000 BP Began 20,000 BP
• Early Wisconsinan Ended 64,000 BP Began 75,000 BP
• Illinoian or Great Glaciation (Riss) Ended 128,000 BP Began 240,000 BP

The Cavell advance was a very minor advance that occurred within the present interglacial period. The well defined terminal moraines at the parking lot at Mt. Edith Cavell and behind the old information centre at the Athabasca glacier represent the maximum extend of the advance before receding.

The Late Wisconsinan glaciation was a major advance that buried most of Canada. Cordillera (mountain) ice sheets and continental ice sheets (from west of Hudson's Bay) did converge in central and northern Alberta. When the two ice sheets began receding they left an ice free corridor, that combined with the lower ocean levels exposed Beringea (the land bridge formed between Alaska and Siberia) and allowed the migration of animals between the two continents. The oldest known camps have been found along the ice free corridor, 11,000 BP. It is most likely that travel occurred during the winter as melt water and runoff from the ice sheets would have been extensive. This was our most recent major glaciation, and there is good evidence of its presence in the Athabasca valley.

The Illinoian or Great glaciation is the stuff of science fiction. This was the big one, covering all but the highest summits of the Rockies, and burying Canada and the northern United States for millennia. All those blocks of gog quartzite on the summits of peaks made of entirely different rock are erratics left by this glaciation. The pink garage sized quartzite erratic near the summit of the Whistlers is a good example.

Why do Glacial Ages Occur?

It appears that several factors can contribute to the onset of a glacial age:

Tectonic Movement of Large Land Masses to Higher Latitudes

Presently it is believed that the position of Earth's land masses is the single most important factor contributing to glacial ages. The surface of the planet is composed of a series of solid plates floating on a very hot molten core. Convection currents within this molten mass are continuously moving the surface plates. Though the movement is imperceptibly slow, the continents are in a continuous drift. When large land masses approach the poles they begin to interfere with the flow of warm temperate ocean currents from the equator. Without the moderating effect of warm water, the northern latitudes develop cold spots. As snow fall accumulates and remains it reflects more of the solar radiation from the sun back into space, causing a further cooling process.

Presently Antarctica blocks flow of temperate ocean currents to the south pole. Similarly the ring of land masses around the Arctic ocean (North America, Greenland, Europe, and Asia) prevents most ocean currents from reaching the north pole.

The theory of continental drift means that on occasion a continental plate collides with another. When this happens at least one edge of the colliding plates is thrust upward, or uplifted. The Himalayas and the Tibetan plateau are an examples of what happens when both edges uplift. The Andes are the result of only the edge of one plate uplifting. With the rise in elevation, these high mountains and basins are not only cooler, they also have a significant impact on air currents, and the long term climate. Submerged mountain ranges also have an effect on ocean currents, and therefore on world climate. During the last three glacial advances, there is supporting evidence that greater than average uplifting had occurred.

Carbon dioxide is considered to be a greenhouse gas. Essentially it lets in heat, but will not let it out. Minor changes in the level of this gas in the atmosphere may have long term consequences in the average temperature of Earth. We are presently testing this theory on a global basis, the results should be available by the year 2100.

Galileo determined that the Earth orbited the sun. Kepler discovered that the Earth orbited the sun in an ellipse, not a circle. Today we know that the ellipse changes in shape, the Earth wobbles, and the days do not line up with the years. This all has a very powerful influence on glaciations, but not so much for glacial ages (it affects short term ice advances more than the long term cooling trend). This phenomenon is called the Milankovitch cycle. It is a 100,000 year cycle based on three interrelated cycles:

• Elongation of the Earth's Orbit-This is a 105,000 year cycle in which the Earth's orbit becomes more elongated, and then returns to its original orbit path.
• Obliquity of the Ecliptic-The tilt of the planets axis relative to an axis perpendicular to our orbital plane varies between 21.8 degrees and 24.4 degrees and returns to its original angle every 41,000 years. In other words the planet wobbles like a slow top. The amount of wobble changes, and returns to its original angle every 41,000 years.
• Procession of the Equinoxes-Equinox occurs when the north and south pole are perpendicular to the orbital plane of Earth. It is the first day of spring and the first day of fall, when everyone has 12 hours of daylight and 12 hours of darkness. This however does not occur on the same point on our orbit around the sun every year. If the last equinox occurred at the point of orbit closest to the sun, it will be 21,000 years before it happens again.

The Milankovitch cycle does not change the amount or solar radiation that the earth receives, only when we receive it. When the cycle produces mild summers, and cool winters then snow accumulates at higher latitudes and altitudes allowing the development and advance of ice fields and glaciers. Hot summers and cold winters will result in the retreat or recession of glacial ice. Glaciations within a glacial age seem to be closely linked to the Milankovitch cycle.

Glaciology References

Gadd Ben, Handbook of the Canadian Rockies, Corax Press, Jasper Ab., pg 189-193, 1986, ISBN 0-9692631-0-4

Pielou E.C., After the Ice Age, University of Chicago Press 1991, pg 5-12, ISBN 0-226-66811-8