Thursday, September 19, 2019

Travels in Cascadia: The Southernmost Fjord in Western North America: Howe's that Sound?

Our journey through the Pacific Northwest and British Columbia continued. We had spent several days on Vancouver Island, exploring Goldstream Provincial Park, Mt. Douglas and the Mutton Rocks of Victoria, Sitting Woman Falls, and the gabbro oceanic crust of East Sooke Park. It was now time to head back to the mainland and our goal was to explore the geologic environments of Howe Sound, the southernmost glacial fjord in western North America.

We would spend several days looking at this fascinating geological environment. To get there we would need to take a ferry from Nanaimo on Vancouver Island back to the mainland at Horseshoe Bay inside Howe Sound. We just missed an earlier ferry, so we cooled our heels for a couple of hours in the tourist traps at the ferry terminal. Our attention was distracted by a pair of otters hiding out in the shade beneath the ferry building.

After a few hours we were underway, leaving behind the fairly muted glacial topography of Vancouver Island, and heading towards the decidedly more mountainous country of the mainland. The main contrast was that glacial ice sheets covered Vancouver Island, but the mountains rose above the glaciers on the mainland. We could see the city of Vancouver off to the south.

As we scanned the horizon from the upper deck of the ferry, we could see that we were still definitely in the land of volcanoes. Off to the east we could just make out the lower flanks of Mt. Garibaldi, one of the northernmost of the Cascades Volcanoes. Garibaldi is one of the most unusual of the Cascades because a large portion of the edifice was erupted onto a glacier. When the glacier melted away at the end of the ice age, the flank of the volcano collapsed into the adjacent valley in a series of huge debris flows.
Mt. Garibaldi, with Howe Sound in the foreground

The clouds were playing hide and seek, and mostly 'hide' with the summit of Mt. Baker off to the south in Washington. The glacier-covered peak of Mt. Baker is geologically young, and the mountain seemed on the verge of erupting back in 1975, but it fizzled out to the disappointment of geologists and to the relief of everyone else.
Mt. Baker, partly hidden by clouds, from Howe Sound

My favorite sight from the ferry ride was of the Black Tusk or t'ak't'ak mu'yin tl'a in7in'a'xe7en in the language of the Squamish people, who considered the strangely shaped peak to be the landing place of the Thunderbird, a principle figure in First Nations mythology. In geological terms, the mountain is a deeply eroded stratovolcano, once like Mt. Baker or Mt. Hood, but now a spikey remnant of the original cone
The Black Tusk from Howe Sound

As noted before, Howe Sound is a glacial fjord, a deep bay with steep flanks that was carved by glaciers. It is a bit difficult to pick out the entrance from the Strait of Georgia because it includes several islands. The sound is 26 miles long, ending at the town of Squamish at the upper end. The urban center of Vancouver is just south of Howe Sound where there is more level ground.

The sound is full of geological delights. We would spend the next four days in the immediate vicinity. That's where we'll pick up the story next time.

Monday, September 9, 2019

The Way It Was: Yosemite on a September Saturday

Not what I was expecting...

I generally avoid Yosemite Valley in the summertime, and I try to avoid Saturdays especially, but I was a glutton for punishment; we hadn't been to the valley since last spring and were kind of curious about how it would be. We expected crowds and dryness and dust.
That's not what we found. In September, the meadows are often brown and the waterfalls dry. Instead, Bridalveil Meadow was green and filled with wildflowers, and Bridalveil Fall, while not roaring by any means, was flowing nicely. The wind occasionally picked up and blew the water in odd directions.
Even Yosemite Falls had a trickle. I don't know if it was left over from the spring, or if it was from the recent thunderstorms, but it was nice to see.
Half Dome is spectacular, no matter the time of year. The afternoon cumulus cloud buildup provided a nice backdrop.
Sentinel Rock is another towering cliff that is an incredible sight no matter the season. It's one of those rocks on the "wrong" side of the valley that is not noticed as often because it is opposite of Yosemite Falls. If it were anywhere else on the planet besides Yosemite, it would be a national landmark all on its own.
A late afternoon treat is the Valley View at the west end of Bridalveil Meadow. There's a small pullout, but it is often ignored by people rushing home from their day in the valley. We found a spot despite the traffic, and simply sat for awhile.
The wonderful thing about late summer is that the low water on the Merced River is often calm and provides a wonderful reflective surface. It was gorgeous and serene.

And that's the way it was...

Monday, September 2, 2019

Travels in Cascadia: You Can Have Your Niagara Falls, and I'll Have Mine...Goldstream Provincial Park, B.C.

Our journey through British Columbia last July continued. We were on Vancouver Island and were leaving the city of Victoria to catch the ferry back to the mainland at Nanaimo. But there were still some sights along the way. The town of Victoria was built on the lowlands at the south end of the island, but as we began traveling north the landscape grew more rugged and mountainous. The vast ice sheets of the last ice age covered the entire island, but the ice could not remove the tougher bedrock of the island's interior. Looking south from Malahat Summit (l,155 feet/352 meters) we could see the hills we had just explored, including the delightful Goldstream Provincial Park.
The park hosts a surprising variety of plant and animal life, due to a wide variety of habitats. Part of the value of the park is that it has not been logged, and thus preserves old-growth forests, including 700 year old Cedar trees. It includes an estuary/wetland at the end of the Finlayson Arm of the Strait of Georgia, part of the Salish Sea. The long inlet exists because the glaciers were able to exploit a fault zone that left the rocks weakened and broken. The Leech River Fault, a major terrane boundary, cuts through the park, dividing the Pacific Rim Terrane (the Leech River Complex) from Wrangellia. Wrangellia is made up of igneous intrusive rocks and metamorphic rocks from the Mesozoic Era, the age of the dinosaurs.
Looking south from the Nature Center one can see Mount Finlayson (below), another feature that indicates the presence of glaciers in the past. The rounded form of the mountain identifies it as a roche moutonnée, a larger-scale version of the rounded forms seen at Mt. Douglas and Mt. Tolmie in Victoria.
The title of today's post refers to one of the small delights of the park. The erosive action of the glaciers was oriented mostly north to south, and the ridgelines drop steeply into the valley containing the Finlayson Arm. Small creeks and rivers occasionally form modest waterfalls, including the easily accessed Niagara Falls. Visiting the waterfall, one realizes it was not named for the similarity of its volume to the better-known falls back east, but to the height. At 155 feet, it's just a bit shorter than Niagara's 167 feet (note the people at the bottom of the canyon for scale).
One might wonder why Goldstream Park has the name it has. The rocks of the Leech River Complex were altered by superheated mineralized water, and quartz veins with minor amounts of gold were emplaced in the area. The gold was discovered in 1858, and a minor rush involving perhaps 300 miners ensued a few years later. There was not a great deal of gold to be had, and the boom soon petered out, but the name remained. A few old tunnels and mines can still be seen in the park.
I know this is a geology blog, and most of the time I don't have much patience for trying to get pictures of deer, but as I was walking up the trail to the falls, I broke with tradition. Up ahead of me I could see some kind of four-footed animal, and it turned out to be the cutest little fawn ever. It was happy to share the trail with me for a few moments, until the rest of the crew caught up with me. It then took off into the underbrush.

Goldstream Provincial Park is west and north of Victoria on the Trans-Canada Highway 1. We were there on a holiday weekend and the parking lots filled quickly (we made some people very happy when our four vehicles left all at once). If you have the time and energy, a trail climbs to the summit of Mt. Finlayson.

Thursday, August 29, 2019

The Seismometer Has Gone Crazy! What's Going On?? (Don't worry, no disasters)

Nothing like putting up a seismometer going crazy to be accused of click-baiting. I mean, what's going on? Is it harmonic tremor, the movement of magma near the surface, ready to cause a catastrophic eruption? Is it a new earthquake swarm? Nah, it's not any of those things. It's education in action.

Our seismometer is a simple version, and the detector is right there in the geology storeroom on the third floor of our science building. It picks up the foot traffic in the corridor outside, so when classes began this week, the unit faithfully recorded the arrival of hundreds of students for the new semester. The large "earthquake" at the very bottom is the exodus of my students at the end of the evening from their class in physical geology.

Welcome all to the new semester!

Monday, August 26, 2019

Travels in Cascadia: Sitting Woman Falls. She's Sitting on Geological Pillows.

There are so many charming little corners to be found on Vancouver Island. We were well underway on our two-week field course on the geology and anthropology of British Columbia, and on this day we had already explored the Sooke Potholes and the base of the ocean crust at East Sooke Park (along with a couple of interesting petroglyphs). It was getting late in the afternoon and the crew was getting pretty tired, but I had heard that there was another site of interest at the end of a short trail, so we made one more stop. It was a place called Witty's Lagoon, which sounds like a theme park or something, but it actually is a geologically interesting section of coastline along the Salish Sea.

This area (and indeed all of Vancouver Island) was covered by glacial ice as recently as 13,000 years ago. When the ice melted, sea level rose to cover some of the previously exposed lands forming a series of bays and coves. Witty's Lagoon is a nice example of one of these, and it is largely unaffected by urban development. Metchosin Creek flows over a ledge of basalt to form Sitting Woman Falls at the upper end of the cove (above).
The basalt, part of what is called the Crescent Terrane, has an interesting story to tell. The basalt erupted on the floor of the Pacific Ocean around 50 million years ago at a divergent plate boundary. It originally melted because of the release of pressure at the mid-ocean ridge, and accumulated in plutons several miles beneath the ocean floor. As the crust spread apart, fractures formed and the basalt followed the breaks all the way up to the sea floor where it erupted out. When basalt erupts in water, it forms odd looking lumps about the size of old-fashioned down pillows, around two or three feet across. These pillows accumulated in layers hundreds of feet deep.

The sequence of gabbro plutons, sheet dikes (the filled fractures), and pillow basalts constitute an ophiolite sequence that in this area is called the Metchosin Igneous Complex. In our previous post we had a chance to see the gabbro as it was exposed on the shoreline of East Sooke and Becher Bay. We didn't get to see any good examples of the dikes, but the cliff at Sitting Woman Falls was composed of pillow basalts. I've zeroed in on the section of the cliff to the right of the falls in the picture above. The pillows are not really well exposed, so I've cheated by adding some pictures below of pillow basalts that we've seen elsewhere in Washington and California.
The picture above shows pillows exposed in the cliffs at Cape Disappointment at the mouth of the Columbia River in Washington. Below we can see some pillow basalts exposed near Nicasio on the Marin Headlands in California.

It's incredible to think of the forces involved in taking the oceanic crust from the bottom of the sea, and mashing it into the edge of the North American continent where it ended up being exposed at Witty's Lagoon, and indeed throughout the region, including the high peaks of the Olympic Peninsula across the Strait of Juan de Fuca.

Thursday, August 22, 2019

Travels in Cascadia: Walking Under the Ocean Floor at East Sooke Bay, British Columbia

We continued our explorations of British Columbia with a hike at the south end of Vancouver Island at East Sooke. It's an unusual place, out of place with the rocks that make up most of the island. The majority of Vancouver Island is made up of metamorphic rocks of the Wrangellia Terrane. These rocks originated as island arcs and continental fragments in the Pacific Ocean which added to the west coast of North America as the ocean crust sank beneath the continent at the Cascadia Subduction Zone.
Source: Chris Yorath
But the south tip of the island is made up of rocks related to the Olympic Peninsula which lies 20 miles away across the Strait of Juan de Fuca. These rocks are parts of the ocean crust, and are called the Metchosin Igneous Complex, or the Metchosin Ophiolite. They formed in Eocene time, around 50 million years ago as vast amounts of basaltic lavas spilled out on the Pacific Ocean floor
The Olympic Mountains seen from East Sooke across the Strait of Juan de Fuca
Ophiolites are generally considered to be slices of oceanic crust that form at divergent plate boundaries. The oceanic crust is pulled apart by extensional forces, relieving pressure on the underlying asthenosphere where the rocks are close to the melting point. The loss of pressure causes some melting to take place, and the resulting basaltic magma rises through fractures caused when the sea floor is pulled apart. An ophiolite has three distinct parts, with pillow basalts making up the ocean floor (more on pillows in a coming post), sheet dikes (the fractures), and gabbro plutons at the base. Gabbro is a coarse-grained igneous rock with the same composition as basalt (it cools slowly, allowing for crystal growth). A pluton is any kind of rock that has been intruded into the crust.
East Sooke Regional Park lies a few miles west of Victoria along the shoreline of the Salish Sea. For a coastal park it has an unusual 'feel'. Because the Salish Sea consists of a series of straits and inlets, wave energy is considerably diminished, at least at the times that I've been able to visit. The waves barely register and the shoreline seems more like a large lake, much like Lake Tahoe in my own home region. But the water is definitely salty!
My goal for our class this day was to get a close look at the rocks of the gabbro pluton portion of the ophiolite. In other words, we were going to go walking beneath the ocean floor. The class, a combined dyad of geology and anthropology students had other ideas. The anthropologists slightly outnumbered the geologists, so they were intent on finding some reported petroglyphs in the region. We went hiking on the Alyard Farm Trail, which was a loop of about two miles, first along the rocky shore, and ending in a thick conifer forest.
Luckily, the petroglyphs had been carved out of boulders of the gabbro, so we got the best of both worlds, with some glacial grooves as icing on the cake. Can you see the first one in the picture below? Without looking ahead, can you tell what it was meant to be (remember the landscape setting)?
I'm told that this is the representation of a sea lion. One source on the internet (the arbiter of all truth) mentions the following myth about the petroglyph: "Long years ago a great supernatural animal like a sea lion killed many of the Becher Bay Indians while they were canoeing. The tribe nearly became extinct; the remaining members were afraid to go on the water until one day a mythical man caught the sea lion and turned him into the stone representation on Alldridge Point" (Anonymous, Report of BCPM, 1928).

Note the grainy nature of the rock in the picture below. Gabbro is a dark-colored plutonic rock that has the same composition as basalt, but the individual grains are visible because of the slow rate that the magma cooled. The gray minerals are plagioclase feldspar, while the black minerals are mostly a variety of pyroxene, perhaps augite. Small grains of olivine are scattered throughout the rock.
There is a second petroglyph nearby of a salmon (below), but it has seriously faded. Both petroglyphs are attributed to the T'Sou-ke First Nation people, but the age of the rock carvings is not known. They quite likely are thousands of years old, based on the amount of weathering.
I'll probably say something similar to this many more times as we continue our exploration of British Columbia, but here we go: if you ever have the opportunity to visit Victoria and Vancouver Island, set aside some time to explore the East Sooke area. In addition to the beautiful coastal trail, there is also the East Sooke Potholes, a series of deep pools eroded out of the rocks after the last ice age. We didn't have the time to explore further up the coast, but the guides mention a number of fascinating places to investigate.

I had three main resources for the geology in and around the city of Victoria and East Sooke:
The Geology of Southern Vancouver Island by Chris Yorath
Roadside Geology of Southern British Columbia by Bill Mathews and Jim Monger
Geology of British Columbia, A Journey Through Time by Sydney Cannings, JoAnne Nelson, and Richard Cannings.

Tuesday, August 20, 2019

Travels in Cascadia: Victoria B.C., the City of Mutton Rocks

The next stop in our recent travels through Cascadia was the city of Victoria on Vancouver Island in British Columbia. We got there by way of a ferry from Port Angeles, Washington, as described in the last post. Victoria is an attractive city, one of the most temperate in Canada, given its location on the Pacific shoreline (the adjacent ocean moderates the seasonal temperature extremes). It is also unique in another respect. The city is partially constructed on bedrock (the solid rock that underlies surface soils and sediments), and the land was under a vast 1,000 meter thick ice sheet only 14,000 years ago.

This geologically unique combination means that Victoria is sort of a city of mutton rocks.

I imagine that sentence needs explanation...

The term roche moutonnée describes an asymmetrical glacially scoured rock outcrop that has a smooth slope on the side facing the flowing ice, and a steep cliff on the side where the glacier pulled away from the outcrop ("stoss and lee structure" is a related term). The scale can range from a few meters to many hundreds. They are common features in regions of bedrock that have been scoured by massive continental ice sheets, such as happened in Victoria. One of the tallest hills within the city, Mt. Tolmie (below), is an excellent example. In the picture one can see the gently sloping forested flank on the left side of the hill, and the steeper plucked side to the right.
Mt. Tolmie, a roche moutonnée in Victoria

The problem with roche moutonnée as a geological term is that we geologists can only barely agree on its meaning. It's derived from French, and the "roche" part isn't a problem. It means "rock". But "moutonnée" is the tricky aspect. It can be translated loosely as "sheep" (think "mutton""), but not exactly (French: "mouton"). Moutonnée (with the extra e's) translates to "frizzy", and is taken as a reference to sheep's wool. The term originated in the 1700s with a naturalist named Horace-Bénédict de Saussure (it would be decades before the term "geologist" was coined) who noted that the rocks looked like a type of wig apparently well-known at the time whose locks were held in place with mutton grease. Except that there seem to be few or no references to wigs that were actually called that (the closest version was a tête de mouton).

So we teachers are left with trying to define the term as meaning "rock sheep" based on the nebulous idea that the rocks look like sheep grazing in meadows. Which they really don't. But it's still easier than trying to describe obscure French wigs from the 1700s and mutton grease.

There are consequences to building on such rocky landscapes. There are plenty of large patches of glacial till that are easy to plane off with a bulldozer for building construction, but when the rock crops out, allowances have to be made. Perhaps it might involve blasting to construct a flat foundation. The rock is pretty tough stuff, gabbro, diorite, and greenstone of the Wrangellia terrane, dating back to the era of dinosaurs.

There are problems in this kind of situation. When the Empress Hotel (see the picture above) was constructed in 1904-1905 it was placed partly on solid rock and partly on mud-rich sediments. Complications quickly ensued. The south part of the building subsided several centimeters within the first year and ultimately sank about a meter. It's a real headache for those who must maintain the building.

Still, Victoria is a truly beautiful city, and the city has a unique personality. The city has miles of coastline, and there are dozens of scenic shoreline parks. We pulled up at Cattle Point to look at smaller roches moutonnée along with glacial scour marks and striations. Strangely enough, there was a piano sitting on the bluff. It was brightly painted, there was a bench, and the piano was in tune! I wondered what was going to happen to it if it rained, but then noticed a waterproof cover. We later found that there are five such pianos in the parks, and we were actually treated to a tune by a passing jogger, followed by a song by one of our students!

If you ever have a chance to visit Victoria, enjoy the city, but be sure to follow the shoreline drive to see the glacial heritage of the landscape (as well as seeing some dramatic coastal scenery). But the other thing you should do is to hike or drive to the summit of the mutton rocks of the city. Mt. Tolmie is a good choice within the city limits, or you can go just north of the city to the much higher summit of Mt. Douglas. It's a short hike from the parking lot to a summit with a 360 degree view of the region. The Olympic Mountains are visible across the Strait of Juan de Fuca to the south beyond the city, and the many islands of the Strait of Georgia and Saanich Inlet are visible to the north and east. Glacial polish, striations and grooves are present underfoot.

On the day we were there, I saw some unusual looking clouds far to the southeast. I took a few highly zoomed shots and forget about them until weeks later. I started working with the contrast and exposure of the picture and realized I had captured an image of Mt. Rainier across the Puget Sound. The volcano is more than 130 miles away (below)!

I had three main resources for the geology in and around the city:
The Geology of Southern Vancouver Island by Chris Yorath
Roadside Geology of Southern British Columbia by Bill Mathews and Jim Monger
Geology of British Columbia, A Journey Through Time by Sydney Cannings, JoAnne Nelson, and Richard Cannings.