Friday, July 26, 2019

Northern Arizona Argillite

Many years ago, I visited the ancestral mine of the Northern Arizona argillite.

Monday, July 22, 2019

UPDATE: The July 2019 Ridgecrest Earthquakes - Odd Indeed But Not Surprising

July 22 UPDATE: The Los Angeles Times has published striking images of the fault ruptures across the Ridgecrest area in stunning before and after photos. Check out the images here.

July 8 Posting

I grew up in southern California and earthquakes have been a part of my life since I felt my very first one in the 1960s. My family still lives there and as a geologist I always remind them to be mindful of the tectonic "gold mine" they sit on top of. I guess geologists may be the only ones (besides home repair stores) that think of earthquakes in not strictly negative terms.

I happened to be in southern California at my cousin's wedding when the June 1992 Landers earthquake hit and when it rattled the windows and sloshed the pool water outside our hotel room, the person laying next to me asked what was happening and then what we should do. The only thing I could think of (naturally) was "earthquake" and "just lay here and enjoy it."

So when I heard about the July 4th earthquake that ruptured the ground near Ridgecrest California, I couldn't wait to see the first images (below).

Photo showing how the pavement cracked during the rupture event, produced during the July 4 M 6.4 quake. Look closely at the painted lines. (Photo courtesy of Emily Guerin/LAList)

This is a view looking straight down on one of the ruptures. Note that no matter which side of the crack you stand on, when you look to the other side across the crack, the line shifts to the left. This is called left-lateral displacement. (Photo courtesy of Emily Guerin/LAList)

Additional ruptures from the July 4th earthquake near Ridgecrest.

When I saw these photos, they caused me to ponder this event more closely knowing that the famous San Andreas system of faults has right-lateral displacement. This breakage didn't seem to follow that pattern. However, there is another fault that abuts the San Andreas in a perpendicular fashion and I immediately thought of it as a possible fault for this earthquake - the Garlock Fault.  (Photo courtesy of Emily Guerin/LAList).

Map used from the California Seismic Safety Commission showing the Garlock Fault system and its relationship to the San Andreas system.

As it turns out, this July 4 event happened just to the north of the Garlock Fault, on a previously unknown fault (but the offset was in the same sense as the Garlock - left lateral). It's likely that the break on this event was related to the larger Garlock Fault system.

Then on July 5, another large quake, this time registering 7.1 occurred on a fault perpendicular to the fault that slipped on previous days quake. And this rupture curiously showed right-lateral displacement (see photos below).

Note here that no matter which side of the fault you are standing, when you look across to the other side the displacement is to the right. (Photo by Beth Hadden)

Aerial view of the same area (Photo by Brian Olsen).

A really good article on LiveScience about the displacements and the faults can be found here.

I often get hopeful when news organizations announce an upcoming story about these earthquake events. But invariably, these stories turn into human interest pieces that really have nothing to do with geology, the crust or how brittle substances behave under stress. I guess most people wouldn't care about that. But then, maybe they should label their stories, "How People Are Affected and Are Reacting to the Recent California Earthquakes."

The asthenosphere, a portion of the upper mantle that is hot and pliable - all while remaining a solid - churns slowly beneath the brittle lithosphere that we all live on. As the asthenosphere slowly creeps, the brittle lithosphere must respond to the tugging motion from below. Occasionally, the brittle lithosphere cracks under stress and a rupture and earthquake occur.

I often use an example that many people can visualize - imaging holding a Snickers candy bar with both hands and moving your hands in the opposite direction. Then look at the chocolate covering the candy bar and watch how subparallel cracks grow as the bar is progressively deformed. The picture above is a great example of this as well!

The "Big One" is coming for southern California. But engineers and geologist have been preparing for it and there may be no better place to experience a big jolt, except for other First World, quake-prone areas like Japan, China and Chile. Quakes rarely kill or injure people but falling objects do. My initial response to my bedmate in the 1992 Landers quake may have been cute in some sense, but it was potentially quite dangerous had we been nearer to the epicenter. When you feel it start to shake, look around and head away from anything that can fall on you. And then, sit back and feel the rumble of a force much greater than us mere humans.

Saturday, July 20, 2019

Thrust Faults, Landslides, and Glaciers - Geologic Gems of Jasper and Banff National Parks, Alberta Canada

We finally started toward the Canadian Rockies from Whitefish Montana. Note that geologically, the rocks in Glacier National Park, USA are considered part of the Canadian Rockies. The map above shows this. Taken from Handbook of the Canadian Rockies, by Ben Gadd.

At the international boundary near Eureka, Montana there are many glacial drumlins. This is the "toe" or downstream end of an elongate drumlin - the head was located across the boundary in Canada.

This is the Rocky Mountain Trench, a geologic feature that can be seen from space that trends from Flathead Lake in Montana to the northern Canadian Rockies. It is a long, linear valley about 1,000 miles long and from 2 to 10 miles wide. Although overprinted with glacial scouring, its origin is still debated although it must be fault related. We drove through the trench from Whitefish to Radium Hot Springs in British Columbia.

This is Columbia Lake within the Rocky Mountain Trench near the small village of Canal Flats, BC. This lake is the headwaters of the mighty Columbia River. The Kootenay River is located just 1.2 miles south of this lake and Canal Flats lies between the two.

The drainage pattern here is extremely interesting! The entire Columbia drainage is highlighted in light blue and the Kootenay is in red. Columbia Lake in dark blue and Canal Flats is orange square.  Be sure to read this link to learn more about this juxtaposition of the two rivers.

After crossing the Kootenay River drainage and across the Continental Divide into Alberta, we entered the heart of the Rockies. This is Castle Mountain near Lake Louise. The upper cliffs are composed of Cambrian-age limestone and shale that are age equivalent of the Burgess Shale farther west (behind the photographer). The Castle Mountain Thrust fault has put these rocks on top of younger late Paleozoic to Mesozoic sediments. The thrust fault can be seen conveniently at about tree-line in the photo.

Lake Louise from the 7th floor of the Fairmont Lake Louise Hotel.

Famous Lake Louise... had a zillion people on it even in the light rain. And...

...doesn't really compare to the view of Peyto Lake seen from above along the Icefields Parkway.

The blue color is due to the suspended glacial flour (ground up sediment). The lake was named after Bill Peyto who was an early trail guide in the Rockies.

The Athabasca Glacier spills off of the Snow Dome plateau. It is famous for its Snowcoach trips onto the ice. The glacier is also famous for its phenomenal retreat since the beginning of the 20th century. At that time, the glaciers edge was located where the highway is today and the retreat since then is about 1.5 miles.

A view of Snow Dome, which serves as a Triple Divide, forming the headwaters for the Athabasca River (Arctic Ocean), the Blueberry River and Columbia River (Pacific Ocean) and the Saskatchewan River (Atlantic Ocean and Hudson's Bay).

Maligne Canyon cuts through the Devonian Palliser Formation.

The canyon is dramatic in its rapid fall through the slot canyon.

Slow time exposure of the falls in Maligne Canyon.

Maligne Lake near the town of Jasper.

Spirit Island on Maligne Lake.

On the way down the lake we were told of a large, prehistoric (but post-glacial) landslide on the east side of the lake. You can see the scar from this slide through the trees.

House-size boulders not only lined the east shore of the lake but were seen on the western shore as well (behind the photographer). For a birds-eye view of the slide, see this graphic.

A black bear (Ursus americanus) came into view as we drove down the valley. It is estimated that there are over 400,000 individual black bears in Canada.

He then crossed the road looking bit sheepish. Black bears are most closely related to the grizzly bear and polar bears and diverged from a common ancestor about 5 million years ago.

The town of Jasper and the Athabasca River as seen from the Jasper Sky Tram. The blue lakes likely occupy oxbows along the river.

A geologists paradise - upturned strata! This is along the Icefield Parkway.

Our trip included a stroll out on the glass covered Skywalk above the Suwampta River.

The woman. on the left is afraid of heights but made it a point to overcome this fear.

A view out onto the horseshoe.

As it is with the glass Skywalk at Hualapai, Grand Canyon, folks are initially all gaga about the glass structure. But ultimately the gimmick gives way to what can be observed from the "teaser." Here, we can see that the Suwampta River is slicing its way through about 200 feet of loose chaotic debris. Note the very large, angular boulders on top of the debris. Hmm?

Further downstream,  I noticed these little waterfalls spilling over a cliff into the river. The falls are issuing directly from the ground where the debris is in direct contact with in-place, bedded limestone. The lightbulb went off - the water must be traveling through the subsurface in very porous rock and is ultimately forced to the surface where it encounters the solid limestone bed.

The larger view reveals the story! A very large series of landslides let loose from the mountains on the skyline, damming the Suwampta River. The former course of the river lies beneath the lower forested terrace. Once a reservoir formed upstream from the landslide, water spilled from its lowest rim and began to excavate the canyon. Evidence for multiple slides comes from the coloring seen in the loose material within the gorge - note the gold-colored band in the middle, covered by exclusively gray material on top Looking to the saddle in the upper right, we can see oxidized beds as the source of the middle slide and gray limestone to its left as the source of the upper debris.

The Saskatchewan River flows lazily from Howes Pass to the Alberta prairies (right to left in this view). Not strictly a drainage divide sat this location, Howes Pass was named by David Thompson in 1807 as a way toward the Columbia River.

Bow Lake along the Icefields Parkway.

The town of Banff from the Banff Gondola. Cascade Mountain rises 9,836 feet above the town to the north.

A thrust fault likely underlies this valley west of Cascade Mountain.

Highly contorted bedding near Banff.

Wide-angle view with Cascade Mountain (left), Lake Minnewanka (background), and Tunnel Mountain between the two and the Bow River.

What a wonderful trip with a wonderful group of people. Thank you Canada!

Wednesday, July 17, 2019

Waterton (Canada) and Glacier (USA) National Parks

We drove south out of Calgary on Highway 2 to Pincher Creek on our way to Waterton National Park.

There are fields and fields of canola growing everywhere on the southwestern Alberta prairies.

Finally, the Rockies come into view.

It's the heart of summer here with flowers everywhere. Note the low gap in the mountains (top center) - that is the valley of Waterton Lake.

Waterton Lake was carved by Pleistocene glaciers and the international boundary runs across this view about halfway up the lake. The village of Waterton can be seen to the right.

The lake is held back by a terminal moraine, seen on the left. I am standing on the moraine in front of the Prince of Wales Hotel. Waterton Lake is about 300 feet deep.

Barron Falls in the village of Waterton.

After leaving Waterton, we crossed the international boundary within Glacier National Park and soon saw one of the parks biggest features - Chief Mountain. The upper cliff is composed of Proterozoic sedimentary rocks about 700 million years old that have been thrust eastward (toward the photographer) about 50 miles. It all happened in the subsurface around 100 million years ago and subsequent erosion has removed about 2 miles of material, leaving Chief Mountain standing tall.

In the opposite direction lie the Great Plains, so called now that this is the United States. I find these wide open spaces to be just a bit more satisfying than the forested mountains in the other direction (although I like them both). I do like to see a long way.

Chief Mountain and the Montana sky.

We stayed in St. Mary on the Blackfoot Indian Reservation and adjacent to the Park. Looking west, we can see where the Lewis Thrust has placed much older Proterozoic sedimentary rock (dark gray) on top of light-colored Cretaceous limestone. Chief Mountain lies behind this wall to the north.

The U-shaped valleys of the Rocky Mountain front near St. Mary, Montana.

The Blackfoot tribe has established a nature walk with wonderful metal artworks near St. Mary and a metal tipi can be seen in the middle distance.

A huge lenticular cloud formed over us while we were taking in the view.

Zoom shot looking west up to Fusillade Peak at the head of Lake St. Mary.

A closer view of Fusillade Peak from a boat on Lake St. Mary. Note the bedding in the strata. These rocks belong to the Belt Group and specifically the upper snowless peak is part of the Snowslip Formation (tidally-dominated shale and sand), while the lower, snow-clad rocks are part of the Helena Formation (shallow marine limestone).

Crown Island is a much photographed feature on Lake St. Mary. Little Chief Mountain is on the left.

Near Logan Pass on the Continental Divide. Just to the left off of the photograph is a triple divide where water flows to the Missouri River via Cut Bank Creek and the Marias River; to the Columbia River via Pacific Creek and the Flathead River; and the Saskatchewan River via Hudson Bay Creek and the St. Mary River. Three drainages on their way to the Gulf of Mexico, the Pacific, and Hudson's Bay and the Atlantic.

At Logan Pass I noticed this limestone algal mound, which is a buildup of algae within the Helena Formation.

Close-up of the mounded laminae that formed when algae grew upwards through fine-grained lime mud.

Two mounds can be seen here in front of the Visitor Center. No one seemed to notice these gems and there was no sign announcing their presence.

The weather is always "iffy" up north but it was dramatic.

The famous red busses in front of the Lake McDonald Lodge.

The interior lobby of the Lake McDonald Lodge.

Kayakers on Lake McDonald, a glacially carved body of water.