Monday, September 1, 2014

Northern Convergence: The Mystery Photo Explained

Thanks for all of your conjectures about yesterday's mystery photo! The Earth is such a fascinating place, and there are so many different kinds of strange patterns that have different origins. Let's review some of the guesses (and they were very good, by the way):
a. Sinkholes and karst topography
b. Bison wallows
c. Ground squirrel or prairie dog workings
d. Periglacial patterned ground
e. Dried marshes, evaporative processes
f. Pithouses

Take a look at the depressions from ground level. The rocks are gravel and sand, so karst is not likely (sinkholes most often result from the collapse of caverns in areas underlain by limestone). Something like a buffalo wallow makes some sense, but these are very concentrated, and the region is not really good buffalo habitat (too much mountain slope and not enough prairie). Rodents like prairie dogs or gophers tend to produce mounds (so called 'mima mounds') rather than hollows. The location of the site on a high river terrace tends to rule out the idea of swamps or evaporative processes.

Of the natural processes that could make this phenomena, periglacial processes make the most sense. Freezing and thawing of soils often result in rings and polygons that might resemble what we saw in the picture. The region underwent glaciation in the Pleistocene epoch and continues to have extremely cold temperatures in winter. It makes some sense, but then why are the pits filled with so many artifacts?

So yes, these pits are made by humans. We were paying a visit to the lands of the Xwisten people, a First Nations group whose traditional lands were along the Fraser and Bridge Rivers near Lillooet, British Columbia. This river terrace surface contains the remains of dozens of pithouses.

The former village along the Bridge River is the site of ongoing archaeological excavations by researchers and students of the University of Montana as well as local members of the Xwisten tribe.

We were being led on a tour of the archaeological site by several members of the Xwisten Bridge River Band who had been involved in some of the excavations. The setting was dramatic, with high mountain peaks on all sides.

As is the case with most archaeological digs these days, only a small portion of the site is being studied in detail. There is an expectation that future technology will be able to better analyze the site, so much of the village remains undisturbed for the time being. Only one of the pithouses was exposed when we visited.

The village site was abandoned over a century ago, although many Xwisten live in a modern village just a few hundred yards away. Evidence from the site investigations show nearly continuous occupation of the site beginning about 1,800 years ago. Many of the sites were used over and over, with some of the pits containing 12 levels of occupation.

A few years ago the Xwisten decided to build a pithouse on the site using the knowledge of their elders. One of our guides noted that what took their ancestors several weeks to construct took them more like three years even though they had modern tools. Entry was usually through a square hole in the room, although some may have had side entrances. The ladders, as you can see below were notched logs. With well insulated ceilings the pithouse seemed like it would be roomy and warm in winter conditions.

The Xwisten subsisted in part on salmon, and part of the demonstration was the preparation of salmon for eating and preservation. Our tour concluded with a salmon dinner. The sun was getting low, and we had another two hours of highway ahead of us. We drove into the night arriving at our hotel in Kamloops sometime after ten o'clock. It was a long, but fascinating day. We had left the Coastal Belt and were now making our way through the Intermontane Belt. We'll pick up the story in the next post!

To AF, the commenter in the last post who lives in Lillooet, let me know if I got anything wrong! Our visit was very quick, and I'm just a geologist, not an anthropologist!

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...

Sunday, August 31, 2014

A Sunday Mystery Photo...

Here's a little mystery to start off your Sunday morning web browsing. What's going on here? Clues: Trees and sage provide scale, and it's in British Columbia. No shame in wrong guesses!

Saturday, August 30, 2014

Northern Convergence: The Sea to the Sky Highway in British Columbia (the Sky wins)

Porteau Cove Provincial Park
We are continuing our "Northern Convergence" journey through Canada and the Pacific Northwest. Our last post saw us observing the geology in and around Vancouver Island and Goldstream Provincial Park, and having a look at the story poles (totem poles) of the First Nations people. That evening we caught the ferry to North Vancouver. The new day would see us heading into the mainland interior along the Sea to the Sky Highway to Whistler, British Columbia. Of all the our planned tours, this was the day I anticipated the most.

It's funny sometimes how perfect the weather is in promotional materials. No matter the climate, pictures of tourist destinations are always bathed in sunlight. It's clear that the most important item on the luggage list is sunscreen. Oh, that it were like that in real life!

The problem with a field studies class in a foreign country is that the schedule is very rigid. Reservations have to be made months in advance, and though we might try to schedule for times when the weather might be the best, there is just no way to know. Much of the region is technically a rainforest. It rains (and snows). Your best bet is always flexibility. Stay in one place for a week, Vancouver, say, and wait for the sunny days. They have great museums in the area for those gloomy ones. We didn't have that luxury, unfortunately.
Porteau Cove Provincial Park
The day's route, the Sea to the Sky Highway, follows Canada's Highway 99 from Vancouver through Howe Sound to the mountain towns of Whistler and Pemberton. We were traversing the Coastal Belt, a geologic province that shows the effects of convergence, both in the past, and ongoing today.

The Cascadia Subduction Zone has been plunging beneath the western edge of North America for tens of millions of years. The sinking slab is heated, and parts of it (under the influence of water in the rock and sediments) melts, forming plutons of magma. The molten rock is buoyant and rises through the crust, sometimes reaching the surface as volcanic eruptions, but much of it remains at depth, cooling slowly to form granitic rock. Uplift and erosion has exposed the deep-forming rocks at the surface.
Porteau Cove Provincial Park
The highway hugs the base of the cliffs on the south side of Howe Sound, a deep glacial fjord, one of the southernmost on the Pacific coast of North America. The weather, true to the predictions, was overcast and rainy. There was some hope that it might clear later in the day. Since we couldn't look upwards, we concentrated on the rocks in front of us. We made our first stop at Porteau Cove Provincial Park, one of the few accessible shorelines along the steep walls of Howe Sound.
The park is popular with divers, but there is plenty to see in the rocks and on the shoreline as well. Across the highway we could see exfoliating sheets of granitic rock, which in most other places are covered with thick vegetation. We didn't have to beat on any rocks to see the minerals because the railroad hugs the cliff here as well, and they used granitic rock for the track bed. The phenomenon of exfoliation is a problem in this area. Because the breaks slope towards the shoreline, rockfalls are a constant hazard, and the highway is sometimes disrupted. Porteau Cove actually has an emergency ferry terminal for when the highway is blocked. 

The cove and beach exists in part because there is a large recessional moraine hidden within the waters of Howe Sound, and Porteau Cove is part of its southern margin. As the ice age was ending, debris formed a ridge around the end of the glacier when it briefly stabilized.
It was a quiet morning, and few people were hanging about. We took our time, hoping for a bit of the storm to clear. No dice. We headed up the highway towards our next stop, Shannon Falls Provincial Park. Along the way we passed the Britannia copper mine, long shut down, but now hosting a mineral and mining museum. The mine produced around $1.3 billion of copper and was the largest such mine in the British Empire. Shortly afterwards we arrived at Shannon Falls. Was there something up there in the mist? The clouds were playing a tantalizing game with us.
Shannon Falls are the third highest in British Columbia at 335 meters (1,105 feet). They are a fine example of a hanging valley, caused when the main Squamish glacier cut the very deep Howe Sound while the smaller glacier on Shannon Creek could not keep up. When the ice receded, the valley floor entered Howe Sound at a high elevation, so a waterfall resulted. Along the short trail to the falls overlook we could see a boulder with glacial striations.
Then the clouds parted and we got to have a view of the waterfalls! They were spectacular. They didn't fall over a single cliff, and instead rolled over a series of high ledges.
From the lower viewpoint, the whitewater seemed to be everywhere...
The clouds continued to lift and we finally had a view of the flank of Stawamus Chief, a 700 meter high dome of granitic rock. Although partly shaped by glacial ice, the dome shape results as much from exfoliation of the corners and edges of the granite monolith.
The clearing conditions ignited a spark of hope that we might see the big volcanoes among the high ridges above, Mt. Garibaldi and Black Tusk. As we reached the end of Howe Sound and started ascending the valley, those hopes were dashed. The cloud deck was impenetrable. Our remaining stops on the Sea to the Sky would need to be of the up-close variety.
Our next stop was Brandywine Falls Provincial Park. The rocks took a decidedly different appearance. Hidden in the clouds were two volcanoes, Garibaldi and Black Tusk, and volcanic flows covered exposures of the granitic rocks. A series of lava flows covered the path of Brandywine Creek. The slopes along the creek were covered with hexagonal chunks of basaltic lava broken from the low cliffs above us. The lava flow had cooled and contracted into a large number of columnar joints.
The lava flows followed a sinuous path along a former river drainage, forming what we would call an inverted stream, but which the park info described as a volcanic esker (eskers are stream deposits from rivers that flowed on or through glaciers). The flows are only a few tens of thousands of years old.
And then we broke out of the forest and found ourselves looking at marvelous Brandywine Falls. At 70 meters (230 feet), they make a single drop off the edge of the lava. Brandywine Falls formed in a different manner than Shannon. The top layer of basalt is more resistant than the others, so the underlying rocks are constantly being eroded and carried away. The lip of the waterfall is moving slowly upstream in an example of headward erosion.
After observing the falls and lava flows we headed into Whistler for lunch. It was unexpectedly crowded, and we soon realized we had stumbled upon preparations for an ironman triathlon. We scattered through the village, and were quickly reminded that Whistler was once a venue for the 2010 Winter Olympics. We had miles to go, and soon hit the road. As we made our way east through Pemberton and beyond, the clouds cleared and we were bathed in sunshine. We had reached the rain shadow of the Coastal Ranges.

We missed some things, but I had to count ourselves lucky for seeing two thirds of our scheduled sights. Yet I couldn't help being a bit disappointed at missing the big volcanoes. It doesn't take long to find what the sights are like on the internet, so I've including a few of them below.

I have to give credit where credit is due. This video shows more of the scenery than we saw on our way to Whistler, but it also shows rain and cloudy skies!

These scenes are mostly courtesy of Destination British Columbia (and no, I don't blame them for putting their best foot forward! The scenery is truly spectacular.).
 Below is Howe Sound and Highway 99 on a cloudless day.
The Black Tusk is the deeply eroded remnant of a volcanic cone. It is a former stratovolcano between and 1.3 and 1.1 million years old. A late eruption about 170,000 years ago formed the dark cone at the summit.
The peak of Mount Garibaldi is one of the more interesting of the Cascades volcanoes (and one of the northernmost). It began erupting dacite (silica-rich) lavas about 250,000 years ago. The most recent activity was around 8,000 years ago, so it has to be considered potentially active. The volcano erupted in part on an active glacier, and when the ice ages ended, a large portion of the volcano fell away into the Cheekye Valley.

I've got to get to this region in clear weather one day!

There is an excellent guide to the Sea to the Sky Highway available online:

Turner, B; Kelman, M; Ulmi, M; Turner, T., Sea to Sky GeoTour, geology and landscapes along Highway 99 from Vancouver to Whistler, British Columbia, Geological Survey of Canada, Miscellaneous G 377E

Thursday, August 28, 2014

Just a Neat Moment in My Day...

I'm back at work this week teaching geology, and after an unexpectedly busy summer organizing trips, I needed the rest! Being back on campus also allowed me to reacquaint myself with the campus "mini-wilderness", a drainage basin that has two or three acres of oak woodland and mature Eucalyptus trees. The area is occasionally used to graze sheep, but because it is fenced off, it protects an unusually diverse little ecosystem. Since I started observing bird species there last November, I have documented at least thirty-five species either living there, or passing through. There are no doubt more to be discovered.

For the last year I've been hearing rumors that a fox, or a fox family lived in the mini-wilderness, but for all my searching, I've never seen it. I was last told about it this very afternoon at our geology club meeting ("Have you seen the fox yet??"). So I was on a break and walking around the pond when I saw a furry creature walking through the underbrush. I'd seen one of the feral cats there just two days prior, so I figured it was the cat again...but it seemed bigger somehow. I continued walking, and in the finest tradition of all suspense movies, I felt like something was looking at me. I turned around and there it was!
It stared at me for a few moments, long enough for me to snap a few pictures, and then it loped off into the underbrush. My day had been fine enough, but it had just become a lot nicer.

One of Geology's Little Mysteries Solved: The Sliding Stones of Racetrack Playa in Death Valley

Bonnie Claire Playa in Nevada
There are side shows that happen in the sciences. There are the big mysteries of the cosmos and earth history that take many years and the work of dozens or hundreds of the greatest minds to solve: atomic theory, quantum physics, plate tectonics, DNA sequencing and so on. In geology, there are the big picture mysteries of how the continents have moved through time, the patterns of evolution of life on the planet, the origins of rock sequences. It's the great human adventure of exploration that carries us into a fascinating future.

And then there are those nagging little mysteries. Why does bread fall with the buttered side down? Why do cats land right side up? It's the kinds of things that have kept the Mythbusters at work for years. Well, it seems that one of those nagging little mysteries in geology has been solved. For years, stones have left mysterious trackways on the surface of Racetrack Playa in Death Valley National Park. They have been noted more than half a century, and have been the subject of a number of studies, but in all those years no one has seen it happen, or provided a convincing explanation of how it could happen. There have been numerous hypotheses, and of course outlandish ideas like magnetic force lines and alien interventions.
Bonnie Claire Playa, Nevada
But now, we are learning that Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, and Brian Jackson have shed light on the mystery, and produced digital images of the rocks in action. In their just released article, Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion, they document the conditions that resulted in the movement of numerous stones on the playa, especially during the winter of 2013-2014. The article can be read in its entirety here: (and thank you for the open access!).

In essence, the researchers marked the location of stones, and outfitted many with GPS trackers. When storms filled part of the playa surface, a thin sheet of ice formed on the water. As the ice began to melt during the day, large sheets of ice were seen moving and pushing the stones.  The winds recorded were not nearly as powerful as expected, as stones were moved when the winds were no more than 4-5 meters per second (9-11 mph). You can see the process happening in the video here:

I was sure all along that UFOs were swooping down and playing a form of ice hockey with complicated rules, but actually the phenomenon the researchers described made good sense. Racetrack Playa is not the only place where rocks have left trails. I've not been to Racetrack Playa yet, but I've seen tracks on Bonnie Claire Playa northeast of Death Valley National Park, and along Highway 50 in the Carson Sink of western Nevada. There were certain factors in common with each site: relatively high altitude, a source of rocks (the roadbed of Highway 50 was one source), and winters that occasionally have freezing conditions and high winds. Ice was suggested as a factor because many of the trails were parallel to each other as if the rocks were locked together.

I've been joking all day that my life feels empty now that the stones have been explained. But does solving the mystery of the sliding stones take away from our sense of wonder at the world? No, it doesn't. It is a marvelous example of how science works. I love to see mysteries solved by good old-fashioned hard work and persistence. 

This also allows me to say to the vandals and felons who have stolen the sliding stones from the surface of the Racetrack, thinking they have some taken possession of a magical key to the supernatural worlds encompassed within: "Guess what, moron! You've stolen a rock. You are an idiot".

Citation: Norris RD, Norris JM, Lorenz RD, Ray J, Jackson B (2014) Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. PLoS ONE 9(8): e105948. doi:10.1371/journal.pone.0105948

Tuesday, August 26, 2014

Northern Convergence: Stories on Trees, the Totems of the Northwestern First Nations

During the flurry of planning for our Northern Convergence journey through Canada and the Pacific Northwest, I was barely keeping up with the geology, and any background information on the anthropology/archaeology of the region fell to my colleague from our anthropology department. There were certainly some intriguing sights related to the First Nations people of  Canada, and the one of these impressed itself on me early in the trip.

We were rushing from one part of Vancouver Island to another, and I was running down the beach cliffs below Beacon Hill Park in Victoria while Mrs. Geotripper went wandering off somewhere.  I was vaguely aware that there was a really tall telephone pole or satellite receiver tower at the edge of the forest, and eventually I noticed that Mrs. Geotripper was motioning me over.
It slowly dawned on me that I was looking at one of the largest totem poles in the world. It was impossibly tall, and I had to go up and touch it to make sure it was made of wood. It was. The plaque at the base notes that the pole honors the First Nation people who fought in the world wars.
The pole was carved from a gigantic Western Cedar tree in 1956 by a team led by Mungo Martin, a Kwakiutl tribal chief. According to the city history, the pole was expected to last no longer than 50 years at which time it would return to the Earth. Major restorations a decade ago added some years, but it may not be there beyond 2020 or so. It stands 40.5 meters (133 feet) high, making it the fifth tallest in the world (or the tallest "free-standing"). The tallest in the world is in the village of Alert Bay on Cormorant Island at the north end of Vancouver Island. It is 53 meters (173 feet) high. We may not see many more poles of this height. There are few monster sized Cedar trees left to carve them from.
Totem poles haven't left much of an archaeological record for fairly obvious reasons. Wood disappears fast in this humid environment. They are known from the 1800s, and are known to have been present with some First Nation tribes prior to European contact. They are a beautiful art form, and communicate family histories, legendary stories, and clan status. They were apparently never objects of worship.
On our rainy day with the students on Vancouver Island, we made a stop at the town of Duncan in the Cowichan Valley, a region with a large First Nation presence. The town has embraced the display of totems, with around 80 in the town center. Each was carved by a local First Nation artisan..
It was an interesting area to take a break and learn a bit of local history. The town is also home to the Quw'utsun Cultural and Conference Centre run by the Cowichan tribe, the largest in British Columbia.
The rain continued (the blue skies in these pictures were from our reconnaissance trip a week earlier), and we needed to be in Nanaimo in a few hours to catch the ferry back to mainland. We drove north to Departure Bay. Our story will continue with our journey up the Sea to the Sky Highway.