Northern Convergence: The Olympics, Where a Trench Became Sky-Piercing Peaks

Our journey through Western Canada and the Pacific Northwest began as we met with our students in the Seattle area one evening in late July. After a complicated couple of hours of meetings and negotiating van rentals (reservations three months earlier are only the preliminaries), we settled in for the night, and prepared to hit the road at 6:30 AM. We had a long day ahead that wouldn't end until we rode the last ferry across the Strait of Juan de Fuca, arriving in Victoria at 11 PM. It wasn't the kind of itinerary I like, but in the end it worked out (as noted in one of the few posts I was able to complete during the trip itself).

We wove through the morning traffic of Tacoma and Olympia (luckily most everyone was headed the opposite direction). We reached the village of Blyn near Port Angeles by 9 AM or so where we stopped at a roadside rest to have our first introductory presentations on the geology and anthropology of the Puget Sound and Olympic Peninsula. The skies were somewhat overcast, which was worrisome because a storm was rolling in soon, and we had hopes of having a clear view of the Olympic Mountains from Hurricane Ridge.

Mrs. Geotripper and I had paid a visit to the ridge a few days earlier and were treated to spectacular views, and I would have been heartbroken if we had showed up with the students to a fogged-in viewpoint. It's happened before; you can ask my students of their memories of seeing Mt. St. Helens in 2011 and get blank stares. We spent most of a day at St. Helens looking at fog, rain, and a few downed trees next to the highway. I didn't want such a thing to happen again, so I was tense as we started the climb out of Port Angeles towards Hurricane Ridge. In fog.

To my great relief, we broke through the clouds and drove into bright sunlight. We climbed the winding highway through the thick forest with increasingly far-ranging views. But nothing quite prepares anyone for the view from the end of the paved road at Hurricane Ridge. It is simply astounding.

The Olympic Mountains are geologically distinctive, to say the least. The mountains rise from sea level to nearly 8,000 feet and are extremely rugged. They capture prodigious amounts of rain and snow on the western flanks, so much so that temperate rainforests coat the western slopes. It would have been a nightmare for geologists who were trying to unravel the geologic history.

Subduction is the story of the Pacific Northwest. For most of 200 million years a convergent boundary has been active in the region, as the crust of the Pacific Ocean basin has been sinking against the edge of the North American Continent. In some places, for instance California, the subduction zone has been replaced by a transform boundary (the San Andreas fault). But in Northern California, Oregon, Washington, and part of British Columbia, the subduction zone is still active, still producing earthquakes, and still raising mountains. It's called the Cascadia Subduction Zone

Source: Geological Society of America

In a "normal" subduction zone, there are four parts: the trench, an accretionary wedge, a forearc basin, and a magmatic arc. The trench is the deepest part of the ocean floor where the oceanic crust sinks back into the mantle. The accretionary wedge is a collection of seafloor sediments and crust that has been scraped off the subducting plate and added to the edge of the continent. The forearc basin is a shallow sea that may develop inland of the accretionary wedge (California's Great Valley originated in this fashion). The magmatic arc is a system of volcanoes and intrusive plutons resulting from the melting of rocks in the lower crust and upper mantle above the descending slab (water released from the slab lowers the melting point of the rock, leading to the formation of the molten rock). Other features may develop, depending on the angle of subduction or the geometry of the plate boundary. There will be more on those later in the series.

Looking at the thickly forested slopes below Hurricane Ridge, I cannot envy the geologists who originally mapped the Olympic Mountains. Simply finding an exposure of rock must have been challenging at times. What these geologists did was to take the rare rock exposures and extrapolate them into a semi-coherent map that reveals the structure of the Olympic Mountains. They did the equivalent of taking a few pieces of a jigsaw puzzle, putting them in the right location relative to the others, and then drawing in the remainder of the puzzle from scratch. I've been way too spoiled by the naked rock exposures of places like Death Valley and the Mojave Desert!

The geologic map reveals the basic structure of the Olympics. A "horseshoe" of basalt and sedimentary rocks (the Peripheral Rocks, or Crescent Formation) partially surrounds the "Core Rocks", an assemblage of lightly metamorphosed sandstone and shale layers. The Core Rocks are characteristic of the types of deposits that form from underwater landslides ("turbidity currents") within the trench and accretionary wedge of a subduction zone. The fact that these rocks are now thousands of feet above sea level is the interesting conundrum. Accretionary wedges are generally below sea level, or exist as small islands. They can be pushed higher. For instance, the rocks of the Cascadia accretionary wedge are exposed in the Coast Ranges of  Washington, Oregon and California, but nowhere are the exposures as spectacular as the Olympic Mountains.

Convergent boundaries can be exceedingly complex places. Bits and pieces of continents and island arcs may randomly arrive at the subduction zone, mucking up the subduction process the way too many sheets of paper at once can muck up a paper-shredder. In the case of the Olympics, there was a mass of land north (Vancouver Island) and an accreted terrane to the south (the North Cascades), and a bend in the subduction zone itself. In essence, too much material was being stuffed into the subduction zone, so the excess material went the only way it could, which was up (see my earlier post on this subject, "Sorry, this trench is full..."). The mountains have been rising for around 15 million years. They would be higher, but the incredible amount of precipitation tears the mountains down at a roughly equivalent rate.

The basalt is exposed along the Hurricane Ridge Road and along trails near the viewpoint. The slopes below Hurricane Ridge also include exposures the intensely folded shale layers.

When we first visited Hurricane Ridge the prior week, the highest peaks were obscured by clouds. When the class arrived, the mountains were clear and we could easily observe the glaciers that scour the upper reaches of the mountains. Glaciers technically shouldn't exist here. Although we were at a high enough latitude, the nearby Pacific Ocean moderates the climate, keeping things warmer than they would otherwise be (the Olympics are at the same latitude as Great Falls, Montana, or St. Paul, Minnesota). But temperature isn't the only factor in glacier development. The sheer amount of snowfall in combination with temperatures that are just cold enough allows glaciers to exist at these unusually low elevations.

We had a good introduction to the basic features of alpine glaciation as we gazed across the valley to Mt. Olympus. We could clearly see bergshrunds (the cracks that develop at the top of glaciers where they pull away from cliffs), and crevasse fields in the lower parts where the glaciers flowed over obstructions. There were horns, aretes, and cirques as well. Glaciers were going to be a big part of the story of British Columbia, and Hurricane Ridge provided a spectacular setting for the first discussion of how they worked.

We gave the students some time to wander the network of trails around the visitor center, and I set off to Sunrise Point to get a panoramic view. I was so relieved that the storm had not yet arrived, but of course it was still out there, and there would be a few consequences for our trip. But not on this most beautiful of days.

We headed down to Port Angeles for lunch and to find to road to the other major locale the day: Neah Bay and lands of the Makah people.

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.

Northern Convergence: A Geological Journey Through Canada and the Pacific Northwest

Some of the world's most dramatic landscapes exist within the strip of the North American continent between the High Plains of Canada and Montana and the Pacific Coast. The geologists call it the Western Cordillera, part of the mountain system that extends from the tip of South America to Alaska.

This mountainous terrain exists in large part because of a subduction zone that is or was once active offshore in the Pacific Ocean. This convergent boundary provided the mostly compressional forces that lifted these mountains.

We've just completed a journey across this incredible landscape, with the first ever extended tour of Canada by our department. Our travels took us from the Olympic Peninsula of Washington State to Vancouver Island, on a ferry across the Strait of Georgia to the Coastal Belt mountains and then into the western interior. We passed through Yoho, Banff, and Jasper National Parks in the Rocky Mountains, and spent some time on the High Plains before heading back into the States at Glacier National Park.

The journey was a collaboration between the geology and anthropology programs at Modesto Junior College. We learned the geological history of the land as well as the human history. It is a tough landscape, but people have lived and thrived here for at least 12,000 years.

The land also preserves the story of the ice times. Canada and the northern tier of states were once covered by thousands of feet of glacial ice. The glaciers had a profound effect on the landscape, and many of them still persist in the high country.

The High Plains reveal many secrets of past life forms on Earth. We paid a visit to one of the finest paleontology museums anywhere, the Royal Tyrrell in Drumheller, Alberta.

On our way back through Montana and Washington, we observed the effects of one of the greatest flood events in world history, the Spokane Floods of 16,000-12,000 years ago.

Our journey ended at one of the most visible effects of convergence: active volcanism. We explored part of Mt. Rainier, one of the most spectacular volcanoes on the planet.

Our route took us through some fascinating geology, and this new blog series will share some of the incredible things we saw. Stay tuned!

Whither Go the Redwoods? Smoke in the Temperate Rainforest

Our long journey through western Canada and the Pacific Northwest ended a few days ago, but we lingered in Oregon and Northern California for a few days to visit family, and frankly, to avoid the heat wave that seemed to engulf the southwest and interior valleys. Our route took us down the Oregon coast and into California at Crescent City and Fortuna, and then into the incredible Redwood forest.

Something was off...

The sunlight just wasn't "right". It was as if someone had put a dimmer switch on. Everything looked the way it was supposed to, but there was sort of an orange-brown glow. The shadows were bluish. We had heard vague reports about fires burning across the west, but we couldn't see any obvious smoke plumes. But the smoke was there.

The forest was stunningly beautiful, though. We had a long road ahead of us that day, but we couldn't help but linger through the early afternoon. The Coast Redwood (Sequoia sempervirens) is an ancient species with a heritage that extends back into the era of the dinosaurs. They were once widespread across the northern hemisphere, but the ice ages restricted their range and now they exist only in a narrow coastal strip from the Big Sur coast to the Oregon border region.

The trees require moist temperate conditions, with plentiful winter rains, and summer coastal fogs. As we wandered through the coastal temperate rainforest, we noticed something disquieting: it wasn't moist. It was very dry.

The understory was green, and the shade was cool, but there was none of the dampness that I associate with these forests. My perceptions were confirmed when we stopped in at the visitor center for Humboldt Redwoods State Park. The rainfall for the 2013-2014 water year was an astounding 27.96 inches. In the Central Valley where I live, that much precipitation would be astounding, but here in the rainforest, it's scary. A display offered the rain totals for the last 70 years, and in all that time, only once before has the yearly total been less than 40 inches.

Once.

The average yearly rainfall is around 60 inches, and four times the totals have exceeded 100. But this year is the second driest ever at Humboldt, and in most of the state it is the driest year ever recorded. We are in the grip of a horrific drought, and there are no signs that it is going to break soon.

We are witnessing and living through huge changes in the climate regime we tend to regard as stable and constant. Glaciers worldwide are receding, snowfall totals in our Sierra are declining. We are unaware on a daily basis unless there is an unusual heatwave or extended drought like the one we are experiencing now. But the changes are happening. The summer fogs are not as common as they once were. Temperatures are warming. Sea level is rising.

And the fires are burning. In places the climate has changed so much that when the vegetation returns, it will be different than what was burned away. Wildlife species are moving uphill to escape warming conditions, and some are disappearing because they can no longer move upwards.

It may be that in a few decades or centuries, California's state tree will only be able to grow in Oregon or Washington. We've cut down 96% of the original old growth Redwood forests, and now climate change may very well take care of the rest. 

I'm praying for a break in the drought this year. But I'm also hoping that those who govern us will finally come to terms with the huge threats that global climate change presents. Money still does all the talking in politics, and the money says to protect the status quo. We need people of vision, not political hacks who look out for their financial benefactors. I'm hoping, but I'm not hopeful.

Common Buckeye (Junonia coenia) at Humboldt Redwoods

There are lots of beings who depend on us. There are the animals and plants, of course, but there are also our children and grandchildren. What world will we leave to them?

Reservoir Closed in Sierra Nevada Village Over Concerns of Possible Failure

National Weather Service

A flash flood warning in the Sierra Nevada town of Twain Harte has been cancelled this evening after earlier concerns over a possible dam failure. Twain Harte Reservoir is a small (143 acre foot) dam that drains into Sullivan Creek and Don Pedro Dam. People reported hearing loud "booming" noises and seeing new cracks in the bedrock around the damsite. Water was said to be leaking from the dam. Authorities closed the lake and are monitoring the situation, but are now saying that dam failure is unlikely.

My impression of pictures posted on facebook and in early news reports is that the fractures in the granite are exfoliation sheets, and I can't tell if they are new or old. Exfoliation or jointing occurs as the once deeply buried rock is exposed at the surface and the pressure of burial is released. The rock fractures, often into slabs that run parallel to the surface. Such slabs are often the source of rockfalls along cliffs like those of Yosemite Valley.

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!

Mystery Photo For a Saturday

So, with no sense of scale or other clues, anyone want to try and explain/describe this surface? For certain people I know, the answer may be in three...two...one...

Just a bit of fun for a Saturday morning...