Travels in Cascadia: Traversing the Salish Sea, and Leaving the USA

Morning in Port Angeles, looking across the Salish Sea

It was the third day of our journey through Cascadia, and after our exploration of the Olympic Peninsula, it was now time to leave the United States. We were in Port Angeles, Washington at the north end of the peninsula, and our route to Canada was by way of ferry across the Strait of Juan de Fuca. The landscape was undergoing a dramatic change. First of all we weren't in mountains anymore, we were crossing a sea. That seems an obvious point, but one has to wonder why the mountains abruptly end in a sea, and why similar mountains don't occur across the water. Second, we had reached the southern reach of the vast ice sheets that covered Canada and part of the United States during the Ice Ages that ended only around 12,000 years ago.

These two things, the end of the mountains and the end of the glaciers are related. The Strait we were crossing, along with the Strait of Georgia and the Puget Sound, are collectively known as the Salish Sea. The term was coined in the late 1980s as a way of recognizing the interconnectedness of these bodies of water as a single environmental entity. The name originated with the indigenous people who first colonized the landscape around the sea.

The Salish Sea (from http://blogs.agu.org/fromaglaciersperspective/2015/06/08/salmon-challenges-from-glaciers-to-the-salish-sea/)

The Salish Sea covers about 17,000 square kilometers (6,600 square miles), and has 7,470 kilometers (2,900 miles) of coastline, along with 419 islands. It is a unique ecosystem, a sea in the Pacific Northwest that is somewhat protected from the worst storm violence and wave action out of the Alaska region. Something like 8 million people call the shoreline home, in a megalopolis that extends from West Vancouver to Olympia. Along with people, there are 37 species of sea mammals, 172 species of birds, 247 species of fish, and over 3000 species of invertebrates.

The western margin of the Salish Sea is formed by the Olympic Peninsula and the mountains of Vancouver Island. The Strait of Juan de Fuca slices between the two landmasses. It was the strait that we were traversing on our way to the city of Victoria. 

The Olympic Peninsula is made up mostly of ocean floor sediments and basaltic rock pushed up as material was stuffed into the trench. Vancouver Island has a different origin. It is a piece of continental crust that traveled across the Pacific (at the feverish rate of a few inches per year) only to collide with the western edge of North America. Such far-traveled landmasses are called exotic terranes.

Source: http://www.deq.idaho.gov/regional-offices-issues/coeur-dalene/rathdrum-prairie-aquifer/geologic-history/

The Salish basin was shaped in large part by the ice sheets that covered essentially all of Canada and a good portion of the northern United States. As recently as 12,000 years ago, a mass of ice a mile (1.6 km) thick pushed south through the basin as far as Tacoma. A lobe of ice also extended west through what would become the Strait of Juan de Fuca.

The ferry ride took about 90 minutes to cover the 20 miles of open water between Washington and Vancouver Island. It's a beautiful ride, made all the more interesting as one realizes this entire body of water was once covered by ice. As one gets further out to sea, the higher snow-capped peaks of the Olympic Mountains come into view.

It may be that the water can get pretty choppy, especially during winter storms, but on my four trips across the strait, conditions were very calm. I almost felt like I was on a lake instead of a sea. We were still on dangerous "ground", though. The Strait of Juan de Fuca is not immune to the effects of huge earthquakes, whether in the immediate vicinity (along the Cascadia Subduction Zone), or from those at great distances (such as the 2011 Tohoku earthquake in Japan). The problem, of course, will be tsunamis.

Sometimes confined bodies of water can weaken the effect of tsunamis by dispersing the energy of the waves, but in some circumstances they can magnify the energy instead. There is some evidence of ancient tsunamis along the shorelines of some of the interior islands of the Salish Sea. The effects will probably muted compared to the damage along the Pacific Coast, but more developments are located there as well. On a positive note, the cities in the region are recognizing the threat and are talking action to minimize the damage (see an example here).

It was a beautiful cruise. Soon, we pulled into the harbor at Victoria and got ready to disembark. We were in Canada!

This post is part of a series on our field study of the geology and anthropology of British Columbia and the Pacific Northwest.

Saturday's Mystery Photo Revealed: They're Mima Mounds!

Scale is everything. This morning's mystery photo could have been on another planet, a satellite image of somewhere on Earth, a few inches across, or microscopic. Without scale, we can imagine just about anything because symmetry exists at all levels. I've seen dinosaur skin impressions that looked just like the image I posted. I've also seen Mars images that resemble these as well.

Aerial shot of the Rocky Prairie mima mounds from a Seattle flight several years ago.

The photo yesterday is an image of several dozen acres of prairie in the Puget Sound region of Washington State. They show an unusual surface feature called Mima Mounds (as correctly guessed by several commentors). They're showing up in today's post because I finally had the opportunity to visit the original examples. I've discussed mima mounds in the past, because we have superb examples of them in our own home region of the Central Valley of California.

Mima mounds are found over a fairly wide area in the southern Puget Sound region, but many of them have been plowed over or covered by forest growth. A few small areas have been preserved as Natural Area Preserves or parks, most notably at Mima Mounds Natural Area Preserve (the site we visited yesterday) and Rocky Prairie near Offut Lake.

The mounds are a few feet high, several yards across, and are spaced rather evenly across the prairie surface. Their origin is still a bit of a mystery: early European explorers thought they were Native American burial mounds, some geologists feel they may be an unusual manifestation of seismic waves, and many explanations involve glacial outwash erosional or depositional processes (the prairies lie just south of the where the great continental ice sheets of the last Ice Age ended). Permafrost thawing and freezing has been suggested. Marvelous arguments have been marshaled for most of these hypotheses, but the issue is far from settled.

As I've mentioned in previous posts, some researchers suggested that the origin might be a bit simpler (remembering Occam's Razor: among competing hypotheses, the hypothesis with the fewest assumptions should be selected). They suggested generations and centuries of activity by ground squirrels or gophers resulted in the formation of the mounds. In the prairie environment, the mounds would give the rodents a better view of approaching predators, and their burrows would stay drier, being above the impermeable clays.

There is some current research on the origin of these enigmatic mounds by Manny Gabet at San Jose State University that supports the gophoer hypothesis. Generation after generation of gophers, building their mounds in the same place over time, could produce features like these in 500 to 700 years. Gabet doesn't insist that this is the absolute explanation for all mounds, but the computer modeling provides strong support for the idea.

Because the mounds occur in some conditions that are similar (prairie-type environments), but with some important differences (periglacial environments versus warmer temperate dry prairies), I find the pocket gopher argument the most compelling, as they are native to each of the environments, and apparently the mounds are of a size similar to gopher territories. I have to also say that the question is still wide open, as some important confirming evidence is not present, such as the presence of active gopher colonies on the mounds today.

In the meantime, I enjoyed wandering through the original mima mounds. They are just west of the town of Little Rock south of Olympia, and are only a few miles off of Interstate 5. There are some nice paved trails around the mounds, and an excellent interpretive display with a second floor lookout. 

The Native Americans used fire to keep the forest from encroaching on the prairie environment, and present park policies are using a variety of management tools to maintain their historical appearance. One interesting species in the area is the Garry Oak, or Oregon White Oak (Quercus garryana), the only oak species found in the state. The oak is usually quickly overrun by fir trees, but can thrive in the prairies.

As one might expect, wildflowers are diverse and widespread during the right time of year.

The park provided a nice respite from the long slog down Interstate 5. We're on the home stretch of three weeks on the road, but now it's just Mrs. Geotripper and myself. Our students have scattered to the winds, and we are only responsible for ourselves for the next few days. The story of our adventures in Canada will begin soon!