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Basalt Monocline and Ice-age Grand Coulee

Basalt Monocline and Ice-age Grand Coulee
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Grand Coulee

During multiple ice ages, enormous glacial rivers swept through central Washington and neighboring areas, gouging out enormous and smaller channels, canyons, and coulees (known collectively as scablands). Over 13,000 years ago, floods carved the Grand Coulee when a glacial lobe dammed the Columbia River where the Grand Coulee Dam stands now, forcing the water to re-route (Amara and Neff 2008:17-18).

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Banks Lake of Grand Coulee by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.Banks Lake is a human-made reservoir that fills a portion of the Grand Coulee upstream (S-SW) of Grand Coulee Dam. Although the dam was completed in 1941,  it is in the same spot that blocked, then re-routed the Columbia River over 13,000 years ago, carving out the Grand Coulee in the first place. While south of Banks Lake, the tilted rock is from a monocline; underneath Banks Lake and the dam itself, the tilted rock formed from landslides. Blocks of basalt slid in a rotational curve at their bases, called rotational slides (Amara and Neff 2008:13, 17-19, Diagram 4). Banks Lake is a human-made reservoir that fills a portion of the Grand Coulee upstream (S-SW) of Grand Coulee Dam. Although the dam was completed in 1941, it is in the same spot that blocked, then re-routed the Columbia River over 13,000 years ago, carving out the Grand Coulee in the first place. While south of Banks Lake, the tilted rock is from a monocline; underneath Banks Lake and the dam itself, the tilted rock formed from landslides. Blocks of basalt slid in a rotational curve at their bases, called rotational slides (Amara and Neff 2008:13, 17-19, Diagram 4).

This mass of water, icebergs, and debris poured into an area called the Coulee Monocline. The visible basalts of this monocline are Wanapum basalts, which formed from lava smothering the landscape between 15.6 and 14.5 million years ago (Bjornstad et al. 1997:211, Fig. 2). However, these lavas covered other magma; and, in turn, were blanketed by still more basalt flows. The entire process occurred between 17.5 and 6 million years ago. Amara and Neff (2008:23) suggest that the monocline, which is a sideways “S”-shaped warped landform, resulted from “deep-seated faulting and settling of the basalt lava flows in response to the thousands of feet of lava that erupted onto the earth’s crust from the earth’s interior.”

To give you a better picture of a monocline, this is the sideways "S", kind of flattened out. The cracks are at bends . The bends endure the greatest strains and stresses. Therefore, they break apart the most.

To give you a better picture of a monocline, this is the sideways “S”, kind of flattened out. The cracks are at bends . The bends endure the greatest strains and stresses. Therefore, they break apart the most.

This portion of the Association of Women Geoscientists (Pacific Northwest Chapter) field trip I took on Saturday, August 13, 2013, led by geoscientist Mark Amara, focuses on the Grand Coulee glacial floods and the Coulee Monocline.

Definition of Coulee

Before I go any farther, let me pull the definition of coulee from the post of the first portion of the field trip: Basalts and Ice-age Floods of Grant County, Washington.:

“A long, dry, steep-walled, trench-like gorge or valley representing an abandoned river channel. In south central Washington, the term coulee is mostly used for an abandoned ice-age flood channel,” (Ice Age Flood Institute 2002-2011).

Dry Falls with Pothole

The first of these Dry Falls slides appears in part one of the field trip, Basalts and Ice-age Floods of Grant County, Washington, but the following one would seem incomplete with out it. It is a dramatic element of the Grand Coulee. Besides, it’s a pretty view.

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Dry Lake by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.When they flowed over basalt rock 14,000 years ago, these falls dwarfed Niagara. They spanned 3.5 miles and plummeted 350 feet. The water may have been 300 feet deep before cascading over the cliffs. The water originated from an ice dam break, which released glacial Lake Missoula to pour over central Washington. The gargantuan glacial river carried huge icebergs and boulders, as as sands, mud, and gravel. All these scoured the landscape (Amara and Neff 2008). When they flowed over basalt rock 14,000 years ago, these falls dwarfed Niagara. They spanned 3.5 miles and plummeted 350 feet. The water may have been 300 feet deep before cascading over the cliffs. The water originated from an ice dam break, which released glacial Lake Missoula to pour over central Washington. The gargantuan glacial river carried huge icebergs and boulders, as as sands, mud, and gravel. All these scoured the landscape (Amara and Neff 2008).

Pothole

The next slide is the reason for the previous slide: the pothole. Potholes (also known as kettles) are circular depressions carved by violently swirling vortices called kolks (Bjornstad 2008:17). These underwater whirlwinds occur in extremely abundant, powerful water. The pothole pictured below is located just downstream from Dry Falls, over which abundant, violently quick-moving water flowed.

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Dry Lake Falls Pothole by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.The small, circular lake at the top right of the photograph appears to be a pothole (or kettle). The larger lake at left lies at the base of Dry Falls. The small, circular lake at the top right of the photograph appears to be a pothole (or kettle). The larger lake at left lies at the base of Dry Falls.

Park Lake: Monocline Excavation and Revealed Buried Water Deposit

This stop (at Milepost 92 on State Highway 17), revealed three great views. These views revealed three items: the Grand Coulee floods, the Coulee Monocline, and a possible lake deposit.

Park Lake: The Grand Coulee Floods

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Park Lake with Coulee Monocline by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.The floods through the Grand Coulee tore at the weak points in the basalt, exposing vertical cliffs. Weak points of a monocline are at the bends, so you see the vertical standing cliffs. The islands within Park Lake have tilted tops. These are portions of the monocline's midsection. The floods through the Grand Coulee tore at the weak points in the basalt, exposing vertical cliffs. Weak points of a monocline are at the bends, so you see the vertical standing cliffs. The islands within Park Lake have tilted tops. These are portions of the monocline’s midsection.

Park Lake: the Unbent Basalt

This view is from across the chasm from the monocline. The view shows two portions of the Wanapum Formation. It serves as scale for the photograph following this one. It also is a nice example of a cataract.

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Wanapum Basalts Cataract by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.This view of the Wanapum Basalts is from the Coulee Monocline across Park Lake. These are cataracts. Cataracts are the vertical walls formed when rapid erosion cuts away at the weak rock below the columns (Bjornstad 2008:19). This view of the Wanapum Basalts is from the Coulee Monocline across Park Lake. These are cataracts. Cataracts are the vertical walls formed when rapid erosion cuts away at the weak rock below the columns (Bjornstad 2008:19).

Park Lake: The Possible Lake

On the our side of the lake, the cut on the other side of the road is formed by the upper portion of the Coulee Monocline. You can see a slight tilt, indicating that it dipped downwards towards the lake in the canyon, but also to the right (north) a bit. The long white line shows this dip.

The long white line divides the base of one flow from the top of another (one field trip companion suggested that the above flow was the Roza Member of the Wanapum Formation, due to its blocky features).

The white line may be the remnants of a lake that the Roza (?) Member buried. The white color, its texture, and other attributes suggest diatomaceous earth. Diatoms form in shallow water bodies, such as clear, fresh water lakes that were common in the region when the basalt flowed (Bjornstad 2008:183).

Definition of a Diatomaceous Earth and Diatoms

Diatomaceous earth is formed from tiny skeletons formed of silica. Diatoms, which grow in fresh water lakes, are single-celled plants that excrete the tiny skeletons (Bjornstad 2008:183).

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Coulee Monocline and Diatomaceous Earth by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.The white line in this photos tell us two bits of info right away. 1). The monocline is already tilting, not only towards the canyon, but a little to the right (north); and 2). The upper basalt may have covered a fresh water lake, because the white may be composed of diatomaceous earth. The white line in this photos tell us two bits of info right away. 1). The monocline is already tilting, not only towards the canyon, but a little to the right (north); and 2). The upper basalt may have covered a fresh water lake, because the white may be composed of diatomaceous earth.

Lake Lenore: Coulee Monocline

We could really see the monocline better from the Lake Lenore Caves park (near Milepost 85 on State Route 17). I understand that the caves themselves are very interesting, but the sun was waning. Below are a couple pictures of the Coulee Monocline.

Lake Lenore: Island with Central Portion of Coulee Monocline’s Tilt

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Coulee Monocline Tilted Island by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.This is one of several islands visible from the Lake Lenore Caves park. The center of the middle portion of the tilt suffers fewer stresses and strains from the bending process. This may be why there are so many surviving islands. This is one of several islands visible from the Lake Lenore Caves park. The center of the middle portion of the tilt suffers fewer stresses and strains from the bending process. This may be why there are so many surviving islands.

Lake Lenore: Surviving Part of Upper Bend in Coulee Monocline

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Coulee Monocline Upper Bend by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.At the top of the cliff on the right, you can see where the basalt top changes from an almost horizontal level to a slope downwards toward the canyon. This is the upper part of the monocline bend, which is a weak point in the structure. At the top of the cliff on the right, you can see where the basalt top changes from an almost horizontal level to a slope downwards toward the canyon. This is the upper part of the monocline bend, which is a weak point in the structure.

Soap Lake

The last (and most southerly) of the chain of lakes within the Grand Coulee, Soap Lake’s waters feel slippery and watery, hence the name. It lies in a topographic basin, deeply eroded in basalt (Amara and Neff 2008:31).

High concentrations of sodium carbonate salts, some of which line the lakeshore like bubbles, cause the soapy feel. Other minerals, including lithium, copper, tungsten, titanium, vanadium, and iron, fill the lake as well. A thick bed of clay blankets the lake bottom’s cobbles and gravels. The only life in the lake is brine shrimp, and the lake’s pH reading is 9 (7 is neutral [Amara and Neff 2008:31]).

All this attracts tourists as a health destination. Before tourism, Native Americans used it. In fact, they called the lake, “Smokiam.” This means healing waters (Amara and Neff 2008:31).

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Soap Lake by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.Although its deep clay deposits and rich concentration of minerals doesn't draw huge crowds to Soap Lake, some tourists still visit to "bathe in its foaming waters and use the mud as a poultice (Amara and Neff 2008:31)." Although its deep clay deposits and rich concentration of minerals doesn’t draw huge crowds to Soap Lake, some tourists still visit to “bathe in its foaming waters and use the mud as a poultice (Amara and Neff 2008:31).”

Ephrata Boulder Fields

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Ephrata Boulder Fields by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.At the boulder fields in between Soap Lake and Ephrata, the flood waters through the Grand Coulee slowed down. The decrease caused the boulders to drop from the bedload. As a result, huge boulders, mostly basalt ripped from their foundations upstream, rest on a huge expanse here. Gravel bars are in the distance, showing where the floods slowed down further. However, they are hard to see in a photo, so you are getting the boulder fields. At the boulder fields in between Soap Lake and Ephrata, the flood waters through the Grand Coulee slowed down. The decrease caused the boulders to drop from the bedload. As a result, huge boulders, mostly basalt ripped from their foundations upstream, rest on a huge expanse here. Gravel bars are in the distance, showing where the floods slowed down further. However, they are hard to see in a photo, so you are getting the boulder fields.

Link to Part One of Field Trip

First Portion of Basalts and Ice-age Floods Field Trip: Basalts and Ice Age Floods of Grant Co, Washington

References

Amara, Mark S. and George E. Neff
2008 Banks Lake to Soap Lake. In Geologic Road Trips in Grant County, Washington. Moses Lake Museum and Art Center, Moses Lake, Washington.

Bjornstad, Bruce
2008 On the Trail of the Ice Age Floods: A Geological Field Guide to the Mid-Columbia Basin. Keokee Books, Sandpoint, Idaho.

Bjornstad, Bruce N., R. Scott Babcock, and George V. Last
2007 Flood Basalts and Ice Age Floods: Repeated Late Cenozoic Cataclysms of Southeastern Washington. In Floods, Faults, and Fire: Geological Field trips in Washington State and Southwest British Columbia, Stilling, Pete and David S. Tucker, editors. In The Geological Society of America: Field Guide 9, 2007. The Geological Society of America, Inc., Boulder, Colorado.

Ice Age Floods Institute
2002-2011 Glossary of Technical Terms Related to the Ice Age Floods. Within Ice Age Floods Institute website. Electronic document, http://www.iceagefloodsinstitute.org/glossary.html, accessed April 24, 2013.

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Balsalt Monocline and Ice-age Grand Coulee by Shari Maria Silverman is licensed under a Creative Commons Attribution 3.0 Unported License.


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6 Comments

  1. I love those photos of major strucures and erosional remnants. About 15 years ago a woman wrote a book called, “Legend and Landform.” It related a dozen or so native American legends with geological accounts that tend to back up the legends. The book was fairly elementary, and it looks like you are going much further with this type of work. This is important work that needs to continue as long as the ancient legends are out there. I could point out a few more from Massachusetts, Including Walden Pond (legend mentioned in Thoreau’s book, “Walden”). Myths and legends relating to real geological events can be handed down for thousands of years!

    • I will definitely look up those sources. They both sound great. I have a lot of family in the Boston area, so I’d like to know those as well. Part of my work as a geoarchaeologist, and even in straight-up archaeology, was to relate landform stories to the region. I live in Puget Sound now, where there are a lot of great resources. One that is readily available and one of my favorite books is “Native Seattle: Histories from the Crossing Over Place,” by Coll Thrush. When I lived in northern Idaho, I was really fascinated by Lake Pend Oreille. There’s a legend of a giant monster there. I wonder where it originated. Native Americans have stories of monsters in lakes in the Pacific Northwest/Rocky Mountain interior, but Scots also settled that locale early on. Very cool. Thanks!

      • The legend in Thoreau’s book, “Walden” is about the origin of the pond. I think is is in the chapter called, “The Ponds,” but I am going by memory as I no longer have a copy of the book. The legend goes like this (from memory): “Where the pond is now was once a great hill, which rose as high into the heavens as the pond now sinks deep into the earth. Some squaws atop the hill were fighting and using profanity. The Great Spirit was offended and caused the hill to shake and cave in on itself. The only person to escape was an Indian princess named ‘Walden.’ ” It is easy to recognize the striking similarity between this legend and the geological explanation for he origin of kettle hole ponds. The ice block responsible for the pond would have been covered with till, resembling a more permanent hill. The melting would of course have been gradual, but no doubt noticeable over the course of a lifetime. What is a good legend without a little exaggeration?

        I used to think I was nuts for even making that connection the first time I read “Walden” as a Teenager (more than 50 years ago, I hat to admit). But then in 1992 Bob Oldale of the USGS wrote a popular book called, “Cape Cod and the Islands, THE GEOLOGIC STORY.” On page 65 Bob talks about how this may well be a legend handed down for about ten thousand years. I call the author Bob because this is what I always called him–I worked for the USGS as a summer geologic field assistant back in 1966, and Bob was one of the geologists that I worked with the Copley Square, Boston office and several field sites.

        Another legend that comes to mind invokes a possible Native American observation of Glacial Lake Hitchcock in the Connecticut River Valley of western Mass. “A great beaver lived in a great lake. He ran out of food and attacked man. The beaver was chased from Mt. toby and jumped into the lake.. The Great Spirit changed the beaver into stone. Mt. Sugarloaf was the head, the Pocumtuc Range to the north was the body, and the low hills near the Deerfield River were the tail. I got this account from reading, “Dinosaurs, dunes and drifting continents,” which was self- published by Richard Little, a geologist who taught at Greenfield Community College. It is still readily available in the Northampton area, and is updated from time to time.

        I hope this is helpful to you, and would be willing to help get this out in better form if you would like. I think your blog is really great. Currently living in France, but I go back to New England once per year or so.

        Warm regards from Mussidan, France (Bordeaux area),
        Richard Heeley

        • Thank you for the legends! I absolutely love them. I’ll be sure to share them with my family, who love that kind of stuff also. We’re all pretty familiar with those in the Pacific Northwest, but I don’t think many are familiar with the New England ones.

          Very groovy about France. I’ve never been, but reading about Carnac in the library of my high school job (I worked in a planetarium) got me interested in astro-archaeology. This led to geoarchaeology. I don’t know if the moon-calendar theory has been debunked (Wikipedia didn’t mention it), but it really impressed me that people could figure out astronomical features and movements without the theory and technogadgets we have today. They must have been very smart and open-minded.

          Thank you for the kind words about the blog. It is a work in progress.

          Shari

  2. I enjoyed this article & the photos very much. Very informative. Thank you.

    • Thanks! It was a fun trip.

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