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Naturalists speaker talks of cooler time in B.C.

B.C's Ice Age leaves its footprint With only a handful of glaciers dotting the nearby landscape these days it's hard to imagine there was a sheet of mile-high ice covering Whistler 15,000 years ago.

B.C's Ice Age leaves its footprint

With only a handful of glaciers dotting the nearby landscape these days it's hard to imagine there was a sheet of mile-high ice covering Whistler 15,000 years ago.

Yet, for the past two million years there have been huge ice sheets waxing and waning over the Northern Hemisphere - a time period collectively known as the Ice Age.

"We are smack dab in the middle of that period," said Dr. John Clague, professor of earth sciences at Simon Fraser University.

Clague cooled things down for the crowd at Millennium Place last Thursday night with his presentation on "A Time When Glaciers Ruled - The Ice Ages in B.C." hosted by the Whistler Naturalists.

Among other things, Clague talked about the icy footprint the glaciers had on the surrounding area and the more obvious physical features they left behind.

"We have such a profound signature of glaciation in B.C.," he said.

Clague took the audience on a slideshow journey beginning 27,000 years ago.

That period of time marked the beginning of the last major onset of ice in B.C. and subsequently, geologists get the best information about the Ice Age from this period.

It was around this time the ice in the mountain ranges began to expand.

Roughly 5,000 years later glaciers from different mountain ranges started to meet and merge into each other.

By 15,000 years ago they had merged together to form a complex ice sheet with flow moving in different directions and extending across Vancouver Island and into the Pacific Ocean.

In fact, the whole country except northern Yukon, which does not have enough moisture in the air to sustain an ice field, was covered in ice at this time.

This was the peak of the last ice age.

Then the glaciers began to retreat and 5,000 years later they had disappeared altogether. In geological time, this is considered a fairly fast retreat.

"This requires a radical change in climate," said Clague.

He said the change in climate was probably related to changes in the earth’s orbital path or to some complex interplay between the oceans and the atmosphere.

But currently there is no way of knowing for sure what caused the rapid retreat.

As the ice began to decay all of present-day Vancouver was covered in water.

The weight of the ice sheet had pushed the land down, depressing the surface by about 500 metres, causing it to be submerged by the sea.

But after a couple of thousand years the land began to bob back to the surface again and now only relatively small glaciers can be found in B.C. The only existing ice sheets are in Greenland and Antarctica.

Clague used physical evidence in his slideshow to prove the ice was here.

He said geologists use three different techniques to reconstruct a snapshot of the past.

They study sediment, landforms and surface features and use geological dating tools like the carbon dating.

For examples of the first technique, Clague showed slides of Savory Island, which is made up of loose sands.

"These are deposits of former rivers that were running off the glacier," he said.

Other sediment examples are found throughout B.C. in the form of till - another direct deposit of glaciers.

But studying sediment is just one way to prove the glaciers were here.

More obvious proof comes from the surface landforms.

Clague sited the Squamish Chief and Shannon Falls as prominent landform features, which were affected and indeed, created by glacier movements.

The Chief is made up of a series of vertical slabs. (The vertical joints control many of the rock climbing routes on the Chief.)

Over the course of several glaciations, a large glacier flowing down from Howe Sound towards Vancouver, continually plucked away at the Chief, selectively scouring parts of the rock, resulting in today's eroded rock face.

At the same time there was another, much smaller glacier, flowing in a different direction higher up on the Shannon Creek.

The Howe Sound glacier was bigger and faster and eroded a lot more than the glacier above.

The smaller glacier created the gentle gradient of the Shannon Creek and the larger glacier carved into the rock below.

This created the dramatic plunge of the Shannon Falls.

In the geological world, the Shannon Falls in more commonly referred to as a hanging valley.

Looking back, these ice sheets can be effectively used as huge thermometres. By studying the glaciers' retreat, geologists can tell how much cooler the earth was even a short time ago.

"In Garibaldi Park the amount of ice that exists today is probably 30 to 40 per cent less than it was even 1,000 years ago," said Clague.

This can be attributed to the natural metronome of the earth - the variability in climate that occurs naturally.

Or it might be a result of human impact.

"1998 was probably the warmest year on earth in the last 1,000 years," he said.

And the last 20 years have been far warmer than usual.

"The anomalous warmth could be the first more obvious sign of human changes to the atmosphere.

"We're playing a huge experiment with the atmosphere. It's a bit of a crap shoot."

Clague is one of Canada's leading authorities on environmental earth sciences whose excellence in research has been recognized by several awards.

The next speaker in the Whistler Naturalists Speaker Series has yet to be announced.