Northern Convergence: Moving Pictures of the Canadian Wilderness, from Whistler to Lillooet

I PROMISE to reveal the origin of yesterday's mystery picture SOON! In the very next post, in fact, barring any major earthquakes in Northern California, or other major geologic distractions. It's just that I value continuity and order...I wrote about our journey up the Sea to the Sky Highway yesterday as well, and I complained mildly about the rainstorm and overcast conditions that prevented us from seeing the mountains of the Coast Belt. I was looking at my photographs, and from Whistler to our next stop at Lillooet I didn't take any pictures. I was driving after all, and we weren't able to stop, due to a tight schedule. There was a good 120 kilometers of what I recall was a pretty spectacular drive through the Coast Mountains and the Cadwellder Range.

What I forgot is that Mrs. Geotripper was next to me snapping picture after picture as we sped around curves and over passes. I went over to her photo files and found a wonderful record of "moving pictures". Moving pictures can mean "movie", or "emotionally striking", or "taken from a moving car". In this case the term today refers to the third meaning, with a smattering of the second. The drive was just stunning.

The Coastal Belt mountains, as described in the previous posts, are composed largely of Mesozoic granitic plutons that intruded into older metamorphic rocks of exotic terranes, tracts of crust that were shuffled about the Pacific Ocean and ultimately slammed into the west coast of North America ("Slammed" in the geologic sense, of course. The terranes were moving a few inches a year).

As we passed beyond Whistler and Pemberton, we emerged into the "rain shadow" side of the mountains, and the storm that had caused us so much frustration in the morning had begun to break up. Like a feather boa dancer, the clouds revealed little bits of the high mountain ridges, and then just a little bit more. We started to see patches of blue sky, and then the long-forgotten sun appeared.

Evidence of glaciation was everywhere, from the horns, aretes, and cirques of the high peaks to the deep U-shaped valleys. As we moved east, the canyons became deeper and more rugged. I'm hard put to recall a more dramatic highway (except for later on the same trip!).

For sixty miles or more we followed the highway, seeing almost no other travelers, and not a single settlement or other evidence of human activity. It was the kind of road that looked blank on the maps during the trip planning process, but which just begged for a stop here and there to look at the rocks. But we had an appointment down the road. We drove on.

The high ridges of Mt. Brew became visible, and we switchbacked down into a dramatic valley containing Cayoosh Creek and Seton Lake. In the distance we could see the valley was blocked by the massive Fountain Ridge. It's sort of unusual for a glacial valley to make a ninety degree turn unless something really forced it to do so. In this case it was a major fault line, the Yalakom fault, which forced the original rivers to change direction, and the glaciers followed suit. The fault was active in late Cretaceous and early Paleogene time, around 65 million years ago. It must have startled more than a few dinosaurs...

There were a few more sharp turns beneath hulking masses of rock, and we rolled into the deep valley of the Fraser and the small village of Lillooet. The town has room to exist only because of terraces that lie high above the river. These terraces are the result of sediments backing up behind gigantic landslides into the Fraser River a few thousand years ago.

We arrived at our appointment, which just happened to be the place where our mystery photo was taken! More on that in the next post.

And thank you, Mrs. Geotripper, for the wonderful pictures! Pretty good for a photographer who was trapped in a speeding car...

Northern Convergence: A Confusion of Orogens, Belts, and Terranes

The first thing to remember about Canada as we start our geological journey is that it is big. Really, really big. It's larger than the United States (including Alaska). And there are fewer people living there than live in California. I'm used to driving long distances across the wilds of the California desert and the American Southwest, but there were regions on our recent journey that made the southwest feel crowded. And even at that, we were in a crowded part of the country. There were actual paved roads and villages every so often. In some parts of Canada, the empty lands extend for thousands of miles.

The Olympic Mountains from Vancouver Island across the Strait of Juan de Fuca

The second thing to know is that the western part of Canada is mountainous and geologically active. As noted in the previous post, this mountain belt is called the Cordilleran Orogen or North American Cordillera. An orogen is a word constructed from the Greek oros for "mountain" plus genesis for "creation" or "origin". The mountain system extends from the southern tip of South America to Alaska.

The Belts of British Columbia and Alberta, Canada. Source: Wikipedia and Black Tusk

It doesn't take long to realize that as one crosses the Cordillera the appearance and topography of the mountains changes. There are definable belts across the mountain system in which a series of mountain ranges that share a similar tectonic origin can be distinguished from adjacent ranges of different topography. Five such belts have been defined in western Canada: the Insular, Coast, Intermontane, Omineca, and Foreland. The Interior Plains are the stable part of the continent that haven't undergone mountain-building activity in any kind of recent geologic time.

And finally, there are the terranes. The age of a mountain range bears little relationship to the age of the rocks exposed in the mountain range. There are youthful mountain ranges around the world that have existed for no more than 3-4 million years, but contain rocks that formed billions of years ago. The Black Mountains of Death Valley National Park in California are an excellent example. The tectonic belts of British Columbia contain rocks that not only are not the same age as the physical mountains, but which formed in an entirely different part of the world! A terrane (or tectonostratigraphic terrane) can be defined as a section of the Earth's crust that has been transported by tectonic processes from its place of origin. Terranes are usually bounded by faults. Some of the terranes in western Canada have traveled thousands of miles, while others originated fairly close to the Pacific Coast.

The Insular Belt is the tectonically active edge of the continent, characterized by far-traveled exotic terranes exposed on Vancouver and other coastal islands. We explored parts of Vancouver Island on the second day of our journey.

The granitic dome Stawamus Chief from Shannon Falls Provincial Park

The Coastal Belt also includes far-traveled metamorphic terranes, but the province mainly includes vast amounts of intrusive granitic rock as well as the northernmost volcanoes of the Cascades Range (Mt. Garibaldi being the most prominent volcano). Examples of the terrain (landscape) can be seen in the picture above of Stawamus Chief, a granite dome on the edge of Howe Sound, and below in a picture of a part of the Chilcotin Range near Lillooet.

Part of the Chilcotin Mountains near Lillooet, British Columbia

The Intermontane Belt consists of somewhat more muted topography with eroded plateaus and lower elevation mountain ranges containing several prominent metamorphic terranes. Some parts of the region experienced volcanic activity as well, mostly of horizontal flows of basalt. We spent a night at Kamloops in the midst of the province.

Eroded plateaus in the vicinity of Kamloops, B.C. Photo by Mrs. Geotripper

The Omineca Belt is a region of highly metamorphosed rocks that connected exotic terranes of the Pacific Ocean basin with the rocks of the original North American Continent. The Monashee and Selkirk Mountains were spectacular. Have you ever been at a concert where the warm-up band played as well as the featured headliners? That's how I felt about the mountains of the Omineca; they are as stunning as the adjacent Rocky Mountains. We spent time at Mount Revelstoke National Park during the journey, and spent a night in Golden at the foot of the Selkirks.

The Monashee Mountains from Mount Revelstoke.

The Foreland Belt is the region normally recognized as the Rocky Mountains of British Columbia and Alberta. The mountains are composed mostly of sediments deposited along the margins of the North American Continent which were subsequently pushed up and over the continental margin, forming a series of thrust faults. Thrusts have the effect of pushing older rocks up and over younger rocks, and in Banff, Yoho, and Jasper National Parks one sees a series of thrust sheets that repeat the sequence of rocks over and over. It's a complicated mess!

Emerald Lake in Yoho National Park

Because of the high elevations and plentiful precipitation, the Omineca and Foreland Belts are among the best places in southern Canada to see active glaciers. Literally all of Canada was covered by glacial ice sheets as recently as 12,000 years ago, but the ice retreated to the highest peaks. Active glaciers can still be easily accessed along the Icefields Parkway in Banff and Jasper National Parks.

Peyto Lake in Banff National Park

Our journey begins in the next post as we gathered in Seattle to start the class.