A Convergence of Wonders, Day 9: Into the Depths of the Crust, and of Time

We've been traveling through the Pacific Northwest and northern Rocky Mountains on a class in geology and archaeology for the last nine posts. Yesterday we made our way south from Glacier National Park over a corner of the Great Plains. Today (that is, June 23rd) we would be headed someplace different: down to the deepest part of the Earth's crust, and into the depths of geologic time. We were going to have a look at some of the oldest rocks on the planet.

How does one get to the base of the Earth's crust, or even into the mantle? Given that the base of the crust is 15 or 20 miles beneath us, and the deepest tunnel ever dug is 2 1/2 miles, one cannot walk or ride there. What we have to do instead is find a place where the crust has been brought up to us. Such a place is the Beartooth Mountains on the Montana/Wyoming border near Yellowstone.

In late Cretaceous and early Cenozoic time, around 70-50 million years ago, the crust in the Rocky Mountains was being twisted and deformed by an errant and misguided slice of Pacific Ocean crust that had somehow become trapped sliding along the base of the continental crust until it reached Montana and Wyoming, where it was finally able to sink. The mountain-building event, which formed much of the Rocky Mountains (including the mountains around Glacier National Park), is called the Laramide Orogeny. The rocks of the Beartooth Mountains were pushed up and over Cretaceous sedimentary rocks. Way, way up. The rocks originated in the deepest part of the continental crust, and these rocks are old. Very, very old.

Our first stop was within the Stillwater complex, a unique sequence of rocks that may have originated in the deepest parts of the crust, and which may have had an ultimate source in the Earth's mantle very close to the outer core. The Stillwater complex is a layered intrusion, a pluton composed of various kinds of peridotite and gabbro (the rocks are composed largely of the mineral olivine, which is also known as the gemstone peridot). It formed 2.7 billion years ago, making these rocks almost the oldest we would see  on the trip (more in a moment). Such complexes are quite rare at the Earth's surface, and contain an interesting mix of rare elements and minerals. We were parked near the Stillwater Mine, which is actively extracting platinum, chromium, and other rare metals. The mine dumps include some nice samples of magnetite, olivine, pyrrhotite and other interesting minerals.

By early afternoon, we were done with the Stillwater, and headed to Red Lodge for a class in the park. The students were listening with rapt attention, they said. Their closed eyes made it easier for them to concentrate on the meanings of the words they were hearing. That's what they said, and since students in my classroom are always saying the same thing, it must be true...

Red Lodge marks the beginning of one of the most remarkable roads in the United States, the Beartooth Highway. From an elevation of about 5,600 feet, the road climbs to the summit region of the Beartooth Plateau at just short of 11,000 feet. It is a marvelous place to see the work of glaciers, but even more stunning is the age of the rocks that the road is built on.

The rocks are composed of metamorphic rocks like gneiss, schist, and quartzite, with an occasional intrusion of granitic rock. The rocks formed between 2.7 and 3.3 billion years ago, which makes them very old (more than a billion years older than anything in California), but remarkably, fragments in the quartzite are even older! Zircon is a very tough mineral that resists being destroyed by erosion or metamorphic activity. Grains of zircon survive the Earth's recycling process that tends to destroy almost any other mineral. Quartz is another durable mineral, but it cannot usually be dated easily, but zircon can be dated. Grains of zircon in these mountains have been dated at 4 billion years. For comparison, the Earth itself is 4.6 billion years old. These grains in these rocks are the most ancient objects I've ever held that didn't fall to Earth from space (meteorites are generally leftovers of the origin of the Solar System and are the same age as the Earth).

The Beartooth Highway provided the most spectacular glacial features seen on our trip outside of Glacier National Park. The picture above shows a wonderful example of a U-shaped valley. Glaciers tear away at the walls of a valley, unlike a river, which only erodes the valley bottom. Glaciers cannot turn corners well, so the U-shaped valleys tended to be very straight. Hanging valleys, smaller glacial troughs that couldn't cut to the same level as the trunk glacier, are seen high on the main valley walls.

The Beartooth Mountains take their name from the "fang" seen in the picture below, beyond the head of the circular valley called a cirque. These bowl-shaped valleys in the highest reaches of the mountains were the origin point for the glaciers (snow would blow off the highest summits and ridges, so glaciers couldn't form on them, but in the shaded cirques instead). Sharp knife-edged ridges between glacial valleys are called aretes (not pictured).

It was strange to drive from summer to winter in the space of an hour. The road had opened to traffic only a week or so before we arrived.

The summit plateau provided a wonderful panorama of the Beartooth and Absarokapre-European period.

As we drove out of the Beartooths towards tiny (and somewhat unfriendly) Cooke City, we had a nice view of Pilot Peak, an outstanding example of a glacial horn, a spike of rock that has been plucked by glaciers from three sides or more.

Driving through the Lamar Valley in the late afternoon, we were reminded of just how big the snowpack was this year, and how big the flooding danger was. The road was being undercut by the surging river.

We had arrived in Yellowstone National Park! We didn't have much chance to explore, as the sun was nearly down, and our camp was on the other side of the park, at Madison. And Yellowstone is a big park. Our explorations would start in the morning...

A Convergence of Wonders, Day 8: Of Time, Pressure and the Plain Truth

Day 8 of our journey through the Pacific Northwest found us in a time of transition...we weren't exactly in the northwest anymore, for we had left the Rocky Mountains and were traveling southward across the Great Plains. With an important exception, the landscape had become more subtle and its geologic secrets were well-hidden. In a historical note, we were just a few miles south of the northernmost point reached by the Lewis and Clark expedition in 1805.

The archaeologists were interested in the fact that we had arrived in the ancestral lands of the Plains Indians, and indeed since we had left Glacier National Park, we had been on the Blackfeet Indian Reservation. The billboard that greeted us at the edge of town was an acknowledgement that we were in the home of a different culture.

Our first stop was Museum of the Plains Indians in Browning. The museum (which did not allow photography) was filled with exhibits of Native American arts, and is well worth a visit.

At Browning, the landscape was irregular, with numerous small hills and isolated ponds. The hummocky topography is the result of the passage of continental glaciers moving south out of Canada. As we drove south, the shape of the land became more "normal" (for us Californians, anyway), with gullies and valleys carved by stream erosion. The Rocky Mountains remained in sight, off to the west.

At the small village of Choteau, we paid a visit to their modest museum, and had a look at some dinosaur specimens, including the display below on dino eggs. The region around Choteau is remarkable for two reasons. Excavations started in the 1970s revealed numerous dinosaur nesting sites, which were used repeatedly for tens, maybe hundreds of thousands of years. Not only were the eggs themselves important, but also the behaviour of the dinosaurs that laid them. Work by Jack Horner and others demonstrated that the Maiasaurs took care of their young, and that they moved in herds.We didn't have the time to arrange a trip to nearby Egg Mountain, so we settled for the displays.

Outside of the town of Augusta, we headed west towards Sun Canyon for a look at some remarkable Rocky Mountain geology. That glaciers had once emerged from the canyon onto the plains was immediately apparent, as the road traversed the rocky slopes of the terminal moraines.

Soft Cretaceous sediments were apparent in the streamcuts. In the picture below one can see a sweet little anticline, an upward pointing fold. The mountains loomed higher and higher as we continued west. And something was odd about them...

As can be seen in the picture below, there are two sets of prominent cliffs at different levels. They are made of the same rocks! The geology was repeating itself. It wasn't just once. As we drove up the canyon, the same carbonate rocks were repeated at least five times.

What we were seeing was another manifestation of the extreme compressional forces that resulted from the convergence of the North American continent with the oceanic crust of the Pacific Ocean basin. In latest Cretaceous and early Cenozoic time (70-50 million years ago), the crust was disconnecting from the underlying basement rocks in a series of blocks that were sliding up and over each other in a series of overthrusts. At least twenty such thrusts occurred in this part of the Rocky Mountains, and we drove past five of them.

 The outcrops and the scenery were incredible...

An additional point of interest for us...the carbonate rocks formed in a shallow sea in Devonian and Mississipian time, and were full of fossils of marine life, like crinoids, brachiopods, corals, and bryozoans. The students spent some time searching for the evidence of past life.

As we drove back down the canyon, we were reminded why creeks and rivers were flooding all over Montana and the Great Plains. There was still a tremendous, even unprecedented amount of snow left in the high country, and small reservoirs, like Diversion Lake, seen below, were filled to overflowing. 

 Going down canyon, we were given a different perspective on the repeating structural blocks.

We made one more stop in the lower canyon, looking for some ammonites. We instead found these strange burrowing structures in the Cretaceous rocks. They were identified by my Twitter colleagues as Thalassinoides burrows, something akin to burrowing crayfish or shrimp. They were huge! That's a quarter at the top of the sample.

 Back on the plains, we were treated to a view of a curious pronghorn.

The day was getting late, and we were delayed by a radiator leak, but we eventually made it to camp in Bozeman, where I had a chance to meet up with a fellow geoblogger, Callan Bentley of Mountain Beltway. He's normally at Northern Virgina Community College near Washington, D.C., but was on the road getting ready for a field class he was teaching in Montana. It was a nice to finally meet!

For whatever monotony there was on the long road across the plains, it would be made up for in our next day's journey...we were headed for Yellowstone via the Beartooth Highway.

A Convergence of Wonders, Day 7: Of Time and Pressure in Glacier National Park

There is a movie quote that I've always appreciated, from a movie with a several surprising references to geology, The Shawshank Redemption:

All they found of him was a muddy set of prison clothes, a bar of soap, and an old rock hammer, damn near worn down to the nub. I remember thinking it would take a man six hundred years to tunnel through the wall with it. Old Andy did it in less than twenty. Oh, Andy loved geology. I imagine it appealed to his meticulous nature. An ice age here, million years of mountain building there. Geology is the study of pressure and time. That's all it takes really, pressure, and time.

Time and pressure is the story of Glacier National Park. There are the glaciers, of course, for a while more, maybe twenty years, but there are also the rocks, and there are the mountains too. Glacier National Park in northern Montana has some of the most incredible scenery of any national park but it has a fascinating geological story as well.
I mentioned at the beginning of this mini-blog series that an overall theme was convergence, due to the influence of the subduction zone that has existed off the west coast of the U.S. for several hundred million years. It is not unusual to see the effects of subduction for eighty miles or so inland where stratovolcanoes like those of the Cascades develop. But we had been traveling east now for more than five hundred miles. How could a subduction zone influence the crust so far inland?

Before we could find out, we needed to decide whether or not to make a run for the border. Glacier National Park is actually properly called Waterton-Glacier International Peace Park, as it shares a boundary with Waterton National Park in Alberta, Canada. You can drive to the border as we did here, or you can backpack through the park (and still go through customs, apparently).

We bravely set foot into the wild frontier of Canada, and also wondered who has the job of keeping that line clear through the miles of forest. It was one of the busiest border crossings I've ever seen, as there was at least one motorcycle that came through while we hung around.

Lots of flowers were out and about. Since we missed Logan Pass and the Going to the Sun Highway and the fields of glacier lilies often found there, I was glad to find a few along the highway near the border.

We reached a vista point for looking at Chief Mountain (9,080 ft; 2,768 m), one of the truly unique peaks in the region. Click on the panorama shot below to see just how isolated the mountain is. It is an eastern outlier of the Rocky Mountains, standing some 5,000 feet above the Great Plains. It is visible for miles, and is a sacred place to the local Native Americans. Half of the mountain lies within the boundaries of the Blackfeet Reservation, and the Blackfeet people claim jurisdiction over the entire region (a fact that I learned, admirably, from the visitor center for Glacier National Park).

I was briefly distracted by some beautiful Shooting Stars...

The unique shape of the mountain derives from its origin as a fault klippe, an erosional remnant of a thrust fault . It is one of the world's best examples of this type of feature. The rocks forming the plateau and summit are actually older than the softer Cretaceous sedimentary rocks below. The older rocks were pushed upwards from deep in the crust and then pushed over the younger rocks by intense compressional forces.

I wish I had a chalkboard to illustrate, but the wikipedia diagram will have to suffice in this instance!

From Wikipedia (http://en.wikipedia.org/wiki/File:Thrust_system_en.jpg)

Where did these compressional forces come from? Apparently, the subducting slab from way out west in Washington got trapped along the base of the crust and never plunged into the mantle until it was far inland. This caused a crumpling of the crust in late Cretaceous and early Cenozoic time (between about 100 and 50 million years), a series of related mountain-building events called the Sevier and Laramide Orogenies. At Glacier National Park, the fault zone is called the Lewis Thrust.

We then drove to Upper St. Mary Lake, for a look at the unique rocks of Glacier National Park (and one of the most iconic views in the national park system at Wild Goose Island Overlook, below). All of the rocks visible in the picture below are more than a billion years old, and sit on top of the much younger Cretaceous sedimentary rocks. This is another manifestation of the Lewis Overthrust that we first saw at Chief Mountain.

The glacial features are outstanding: U-shaped valleys, hanging valleys, truncated spurs, aretes, horns, cirques, moraine lakes, and the occasional surviving active glacier. The park once had around 150 glaciers. Today there are no more than 25. They are expected to be gone within twenty years. Ignorant politicians should be forced to stand at the base of one of these disappearing glaciers when they pontificate about how global warming is a hoax. They shouldn't hide in places like drought-stricken Oklahoma (where coincidentally they shouldn't be allowed to fly airplanes).

Picture by Susan Hayes

The slightly dipping layers making up much of the park are a series of sedimentary rocks called the Belt Supergroup. The rocks were deposited in fault-controlled basins at the edge of the ancestral North American continent over a billion years ago. It was a strange time in Earth history...no plants, no animals, just barren rock on land, and only bacteria and other single-celled organisms in the lakes and oceans. The only real fossils are layered mounds called stromatolites.

One of the most vivid layers was the dark red Grinnell Formation. There was no oxygen in the Earth's original atmosphere, but when photosynthesis evolved, oxygen was released. It immediately reacted with iron in the sediments, and the world turned rusty red. Although the rocks are from an alien time in our own history, they still contain recognizable features like the exquisitely preserved mudcracks seen below.

The group was fascinated by the outcrop (always a pleasing moment for a teacher, especially seven days into a trip!).

The group had the afternoon off, and most took off on hikes (and saw grizzlies and bighorn sheep). Others found a wi-fi signal in the wilderness, and did some homework (along with some laundry)...times have changed in the world of field-tripping!

I had a few moments in the late afternoon, so I went moose and grizzly hunting around the outlet of Upper St. Mary Lake. The rivers were swollen with snowmelt (flooding is still a problem across the northern tier of states). I didn't find any animals, but they no doubt noticed me crashing through the brush.

It was a beautiful evening, and I had a fine time photographing the lovely clouds that swirled above us. I realized with a start that we had reached the half-way point of our trip, and that the moment we turned our backs on the Canadian border, we were turning towards home. There were many wonders yet to come, though. Tomorrow we would cross part of the Great Plains, and make our way to Bozeman through the lands once trod by the dinosaurs.

Time and pressure....

A Convergence of Wonders: Day 6, In the Land of the Great Draining

The young man was stalking an elk along the shore of the huge lake where he had lived for much of his short life. Stepping quietly through the underbrush, he was sweating, not from the heat, but from exertion. There was no heat, even now in the height of summer. The ice lands lay just a few miles to the north, and the scattered low shrubs provided little shelter from the winds pouring off the frigid glacial slopes. He had been stooping for hours, staying out of sight of the animal. He carried no bow, no atlatl, for his culture knew nothing of these things. His weapon was a spear.

He was nearly close enough, and positioned himself for the attack. The elk looked up, startled, but the man had done nothing to reveal himself. The animal started bounding up the slope, and the man started running, hoping for a lucky throw, but he stopped, for now he heard what startled the animal. The ground was rumbling. The lake, he realized, was moving, and currents of muddy water were starting to tear at the banks. He watched, stunned, as the lake level started to drop. From his vantage point on the high ridge, he could see water surging through the gap in the hills, tearing away at the soil and rock. He could hear giant boulders bouncing in the depths.

In the next four days, the lake that he and his people had known for all of their lives simply disappeared. In its place were stinking mud-filled canyons and strange forests of dead trees and stumps that had been hidden by the lake's dark waters.

The elders had spoken of times like these, when the gods removed the lake as punishment for their indiscretions. The young man had no reason to disbelieve the stories, but neither had he ever thought that he would live to see the punishments carried out. His people prepared to migrate south in hopes of better hunting...

Before my archaeologist friends jump all over me, I can state that my story of people in Montana 15,000-20,000 years ago is based in no way on known archaeological data. It's just that I have read the story of the Spokane Floods from the point of view of imaginary witnesses downstream, but not from people who could have been living at the source of the great floods.

The story of J Harlan Bretz and the Spokane Floods is one of the legends of the geological sciences. Bretz had amassed a great deal of evidence supporting his contention that vast amounts of water had swept across Washington in a series of massive floods, but he could not pinpoint a source of the waters. Joseph Pardee, a U.S. Geological Survey scientist could. He had been studying odd terraces on the hills above Missoula Montana, and eventually outlined the boundaries of a huge lake in western Montana that had been hundreds of feet deep, with enough water to fill one of the Great Lakes. It was formed by a glacier that had blocked the westward drainage of the lake near Lake Pend Oreille in Idaho. The floods had come when the unstable dams had collapsed, sending cubic miles of water surging over the Columbia Plateau in Washington.

It was day 6 of our Pacific Northwest expedition, and after exploring the effects of the flood in Washington the previous day, we were having a look at the evidence for the presence of glacial Lake Missoula. Our day would end with our arrival at Glacier National Park.

We didn't stop there, but we couldn't help but pull off the highway and drive through the business district of Wallace, Idaho (below). If that elevated freeway looks somehow familiar, you have seen the movie Dante's Peak. Wallace was the stand-in for the town that was destroyed by the giant volcanic eruption while Pierce Brosnan ran around saving Linda Hamilton, and watching irritating grandma die in the acid lake. We looked and looked, but there just wasn't a huge volcano looming over the town...

The freeway is elevated because town residents fought to keep their historical district from being bulldozed for the highway. There isn't a lot of room in these narrow canyons. The towns grew along with logging and mining (this is a big silver and lead mining district), and there wasn't a lot of level ground to work with.

After stops at the Montana state border for a discussion of mining, and at St. Regis for a discussion of whether to have breakfast or lunch, we set off for the Camas Prairie, the setting for some of the most dramatic evidence of Lake Missoula and the Spokane Floods. The prairie is a bit unusual for western Montana due to a lack of forest cover. There are no through-going rivers to speak of, and a rain shadow effect that keeps precipitation low. The grasslands expose some fascinating features.

As we looked around, we could see that the valley floor was not flat, but had an undulating surface. The strange low hills are hard to visualize from ground level, but are linear ridges hundreds of feet long and as high as 35 feet. The ridges are around 300 feet apart from each other.

The drying grass highlights the ridges. The best view is from above (see this USGS page for a good shot), but we had a pretty good angle from near the top of Markle Pass. These ridges are ripple marks! Just like the kind you can see in the silt of any river. Of course, in a river the ripples may be an inch high, and on the Camas Prairie, the ripples are 30-35 feet high. How? In short, the ripple size is determined in large part by velocity. Water was moving over the surface of this prairie at speeds of 50-60 mph, in water that was hundreds of feet deep! It is astounding to stand at the crest of Markle Pass and imagine the scene during the collapse of the ice dam...

 Before we left, I couldn't help snapping a few pictures of the many flowers littering the valley...

 I figure the first is some kind of clover, but I don't know the other. ID is welcome!

As we headed towards Kalispell and Glacier National Park, we could see strand lines from glacial Lake Missoula on the surrounding hillsides. They are subtle in the picture below, but the horizontal benches record multiple shorelines as the lake level flucuated.

We arrived at the western edge of Glacier National Park late in the afternoon. The afternoon storm was breaking up over Lake McDonald, making a spectacular play of clouds and shadows (see the photo at the top of the page), but my attention was also drawn to the pebbles on the shore. The rocks are a literal rainbow of bright colors.

 There was also a real rainbow along the lakeshore...I love those things!

As the sun came out, we headed south towards Marias Pass, because the Going to the Sun Highway was still buried under as much as 35 feet of snow. It is expected to finally open next week, making it the latest opening ever. We finally arrived at our camp at Lake St. Mary late in the evening. There were a few changes to our camp protocol...we were in bear country now.

The next day we had to decide whether we would flee the country or not...