Showing posts with label Wrangellia Terrane. Show all posts
Showing posts with label Wrangellia Terrane. Show all posts

Saturday, August 16, 2014

Northern Convergence: Victoria, Finding Geology and a Rare Ecosystem in a Beautiful City


We start our blog journey through Canada with a view of alpine peaks, forests and birds. If the picture seems a little fuzzy, it's because it is a highly cropped view down one of the main avenues in the city of Victoria on Vancouver Island (below). And truth be told, the peaks are actually in the United States. They are the Olympic Mountains, across the Strait of Juan de Fuca. We had not gone far into Canada yet!

Victoria is a pretty little city (population around 80,000, with a suburban population of about 340,000) that feels a little like it was carved from a wilderness, being surrounded by deep forests and rocky shorelines. All cities are imposed on geology, and Victoria is a vivid example. Just 12,000 or 13,000 years ago, the entire region lay beneath thousands of feet of glacial ice.
Glacial landscapes are exceedingly uneven, and the city's most venerable building is a victim of that fact. The Empress Hotel, constructed in 1908 (and no, we didn't get a chance to have High Tea there), has settled unevenly because portions are built on bedrock and the remainder on looser soils. As a consequence, one part of the foundation is a full meter lower than the other.

I suppose it is useless to point out the "Victorian architecture" when we are discussing a visit to Victoria, but the city was one of the oldest British settlements on the west coast of North America (1843), and the city has kept the flavor of old Britain (although most of our restaurant servers had Aussie accents or mentioned that they spent time living in Modesto!). Carriage rides are a staple of the tourist trade, and the city parks have tried to replicate the kind of flower gardens found in London, but the geology in some ways refuses to cooperate: glaciers didn't cover London, but they covered Victoria. Irregular knobs of bedrock pop out everywhere, and in those spots the park engineers surrendered to nature. Beacon Hill Park was our first geologic stop on the second morning of our trip.

The rocks themselves are quite unlike the rocks found across the Strait in Olympic National Park. Instead of deposits formed deep inside a subduction zone complex, the rocks exposed in Beacon Hill Park are metamorphic rocks derived from gabbro and granodiorite, a mixture called a migmatite. These rocks are derived from deep in the crust. They may date to 200 or 400 million years ago. 

The rocks were abraded by the glaciers, forming small roche moutonnées or crag and tail features. Such rocks are smoothed off on one side and plucked on the other, forming an asymmetrical linear ridge.

It occurred to me that the natural areas of the park were dry and out of character compared to other parts of the northwest coast of America, a place I associate more with rainforests. And there were oak trees, something I've never associated with western Canada. I thought that the northwest was all about conifers. It turned out that we had stumbled on one of the rarest biologic entities in Canada, the Garry Oak Ecosystem. Yes, it's really called that. The Garry Oak (Quercus garryana) is the only native oak species found in Washington and British Columbia.

Victoria is the driest locality on the west coast of Canada, averaging only about 24 inches of precipitation a year, with little and sometimes no snow. The local climate benefits from the moderating effect of the Pacific Ocean and Strait of Juan de Fuca, and lies in the rain shadow of the Olympics and other coastal mountains. Douglas Fir could still thrive in a climate like this, but wildfires keep them at bay. The Garry Oak Ecosystem covers far less than 1% of the land area of British Columbia, and is considered highly endangered (mainly due to development). It's also a harbinger of the future. With global warming, the oak woodland may become more widespread due to warmer and drier conditions.

Beacon Hill itself offers stunning views of the Strait of Juan de Fuca with the Olympic Mountains on the horizon. The coastal strip leading down to Finlayson Point is covered by glacial deposits.

Where wave erosion has removed the loose sediments, fresh exposures of glaciated bedrock can be seen. The rocks have been scored by striations and groves.


The southwest corner of the park holds one human-made distinction. It is Mile '0' (really, kilometer '0') of the Trans-Canada Highway that transects the entirety of the nation of Canada. It a sense it was mile zero of our journey through Canada as well.

Our next post will explore some of the fascinating geology of Vancouver Island beyond the city boundaries of Victoria.

Friday, July 18, 2014

Ah, the Life of the Mariner! Well, Maybe...

Ah, the open sea! The adventures of the water world of planet Earth! The mysteries of the deep! Yes, it's the mariner's life for me. Well maybe, maybe not. It's hard to develop a real opinion on the basis of a single ferry ride across the Strait of Juan de Fuca. It sure was pretty, in any case.
The Port Angeles-Victoria ferry crosses the Juan de Fuca Strait that separates the Olympic Peninsula from Vancouver Island on the the Pacific Coast between the United States and Canada. Although the peninsula and the island are both situated in the same geographic location (the western coast of North America) and are only a few miles apart, they have few similarities. The Olympic Peninsula is composed of seafloor sediment and ocean crust that has been shoved to very high elevations by the Cascadia subduction zone. Vancouver Island has a sliver of some of these rocks, but is mostly composed of metamorphic rocks of the Wrangellia Terrane, a collection of Paleozoic and Mesozoic rocks that formed someplace else, maybe thousands of miles away, and which was slammed (geologically speaking) into the west coast by subduction zone and transform fault movements.

We are out doing a bit of reconnaissance for our field studies class that meets next week. We got out to the Sooke region along the south island for a look at the Crescent terrane, and some nice erosional potholes along the Sooke River. Details to follow in later posts!
Oh, and there were lagomorphs too! Cute ones. We passed dozens of them grazing in a freeway median of all places (no, I didn't stop on the freeway for the picture; this one was at East Sooke Regional Park).
The nice thing about traveling this far north is that the sun sets late (this statement does not apply in winter, though!). We had this wonderful view of the Olympic Mountains across the Strait of Juan de Fuca around 8:30, and still had an hour of light.

I guess I'm still a landlubber though...I love the solid ground and the rocks too much.