The Geology Post! Grand Coulee Edition
Since one person liked the idea of a geology post, I made this long and rambly post laden with photos and links.
Okay, geology. I love geology, and took a bunch of classes in college. That said, I am terrible at identifying rocks, but I love them anyway. Geology is as close as we're going to get to a time machine to the far past. It's one age influencing another. The past shapes the present and the present changes the past. A humble stream bed, dry for eons, is all that's needed to divert a river and carve a canyon.
I'm particularly interested in the Channeled Scablands, aka most of Eastern Washington. They were carved by massive floods into layer after layer of flood basalt, and are pretty much as close as we'll get to certain Martian terrains here on earth. (1)
My favorite part is Glacial Lake Missoula, which was created when an ice age glacier dammed the Clark Fork River and flooded much of Western Montana's steep valleys. I like it because I like imagining myself underneath this huge, cold lake filled with icebergs whenever I visit my grandparents. I like imagining the whole system breathing as the water rises, breaks the ice dam, and pours out, rushing through the plains, pauses to pond behind the Wallula Gap, then rush through the gap and the Columbia Gorge, pause again in the Willamette Valley, and then rush on to the sea. Then the glacier kept moving forward, and the cycle started again.
A brief digression: Because of the way plate tectonics works, we should have a massive trench, a la Mariana, offshore, but we don't. Thank the Columbia for that, and those floods that shoved hundreds of square miles of topsoil into the sea. You may also notice that there isn't a delta like the Nile or Mississippi are so famous for. Deltas need a lot of slow, shallow water to form; the river has to dump its sediment over a wide area. But the Columbia doesn't get to meander across the gentle landscapes of Louisiana; it carved its way with brute force into solid basalt. You get a couple islands like the incredibly flat Puget Island, but that's it. All the sediment gets rolled over by the river and pushed out to sea like leaves before a pressure washer. There, it fills in our would-be trench, and creates one of the most dangerous sandbars in the world. (Shout out to the sixteen pilots qualified to navigate it!)
Back to Eastern Washington. Let's start with the oldest events first. Used to be, our coastline was around Idaho, but we had all these islands offshore--possibly a volcanic arc like Japan. Plate tectonics pushed those islands our way, and in time they docked. Roughly 100 million years ago, the Okanogan Subcontinent docked. It makes up Northeast Washington, and probably Southeast, though we can't tell because that area is covered in flood basalts. 50 million years ago, the North Cascades Subcontinent docked, and makes up Central Washington. Western Washington is mostly ocean floor that got uplifted during the docking, as well as trench stuffing. (Imagine stuffing a blanket between two couch cushions, but the blanket is sea floor, and the cushions are an oceanic plate on one side and a continent on the other, and and you've got trench stuffing.)
But most of that got covered up when, 17 million years ago, the lava floods came. Cracks opened up in Eastern Washington and Oregon that dumped out molten rock. Lots of it. There's one theory that says it was caused by an asteroid striking over the border between Oregon, Idaho, and Nevada, but I'm not sure that explains why there were many different eruptions over 10-15 million years. More likely, the Yellowstone Hotspot is responsible, as our crust slowly moved over it. Maybe it could be both, because asteroids are cool.
The series of flood basalts that make up the Grand Coulee are called the Grande Ronde basalts. They were the second series of floods, and came about 16.5-14.5 million years ago. It's a dense, dark basalt that doesn't weather easily, and when it does, it forms sharp cliffs. It has plenty of cracks, so it just breaks off, rather than rubbing away under wind and water.
This is a colonnade! It makes Eastern Washington possible, as well as the rather weak climax of Hellboy 2 which took place at the Giant's Causeway in Northern Ireland. Flood basalts cool into three layers, of which the colonnade is the most distinct. As it cools, it contracts and forms the distinct hexagon columns separated by what is known as columnar jointing. The jointing is what makes it so easy to break away and form sheer cliffs. This particular colonnade has a bend to it that was likely caused by pressure applied to the side, possibly from being on a slope.
On top of the colonnade is the entablature, which is more or less solid, and on top of that, are the vesicles, which is where all the gas settles at the top, and when the lava cools, it is filled with cavities called vugs. Sometimes, these fill up with silica-rich water and form agates and geodes. Othertimes, they house lichen and small porcelain frogs.
This is the underside of a colonnade. Since the vesicles are all bubbly, they erode the easiest, exposing the colonnade above. In this picture, it's easy to see the columns because a bunch of cliff swallows colonized it and pooped on everything. (This photo also shows the limitations of my cheap telephoto lens. Looking at the colony with my binoculars, which are the same magnification as my lens, showed the birds clearly.
After the flood basalts, along came the ice ages. Other stuff happened between then, like the eruptions of the Cascade volcanoes, but for this story, that's irrelevant.
The ice ages, like the flood basalts, came in multiple series. Glaciers poured slowly out of the north, turning Canada and much of northern America into the spitting image of Greenland. The farthest the ice got near the Grand Coulee is just to the west of the Grand Coulee Dam. There's an extensive geological structure called the Withrow Moiraine, a terminal moiraine which marks the point where the glacier ended, and dumped out sediment and meltwater. Cape Cod and Nantucket Island are great examples of ice age era terminal moiraines. I wanted to check out the moiraine, which consists of rolling hills and huge chunks of basalt stranded in fields, but I didn't have the time. The moiraine isn't strictly responsible for the coulees, but the ice that created it is.
It's all about the Columbia River. We don't really know where the river used to flow, but when the lava came, it pushed the river into its current place. Probably, if we cut into the mile or so of flood basalts, we might come upon a continuous line of pillow basalts(2) which would mark the point where the lava hit the water and cooled instantly. This is the sort of thing I like to think about: a flood of lava hits the water, and eventually, a river hundreds of miles long turns to steam. It probably sucked for all the rhinos and ground sloths on the south side of the river, but they, like the Blue Lake Rhino, probably died a quick death asphyxiated by gas or heat or something. Let's hope that. Those flows came at them around 5 km/h. Molten rock is kind of relentless. (3)
Anyway, enough sad dead animal stories. The Columbia River got pushed up to its current position, until the glaciers came and blocked it off. Poor river--liquid fire from the south, and ice from the north.
The collection of glaciers heading the Columbia's way is called the Okanogan Lobe of the Cordilleran Ice Sheet. (This is another reason I like geology. I like picturing the ice age as consisting of a giant ice amoeba stretching its lobes, slowing groping its way south.) At first, the river was diverted down the Moses Coulee. It's not as big as the Grand Coulee, but it's still spectacular, and has more of the giant ripple marks and flood bars visible from its time as a riverbed. The ice amoeba kept groping, and blocked off Moses Coulee, forcing the Columbia into what would become the Grand Coulee.
Prior to all this, plate tectonics were still pushing from the west, shoving up some mountains from the remains of the old North Cascade Subcontinent. This helped warp the flood basalts, creating a monocline that sloped to the southwest. When the water came, this slope helped pull the water along with even greater force.
At this point, the coulee wasn't really divided into Upper and Lower, but there was a huge waterfall at the north end of the coulee. As I mentioned above, basalt doesn't wear away smoothly and politely. The cracks that separate the columns (called joints) get easily pushed apart, knocking off boulders the size of houses. Underneath all that basalt, however, is the granite bedrock, which doesn't wear away so easily. Water cut cliffs hundred of feet high, and crashed right over. It dug huge plunge pools, and undercut the rock layers, so that the falls are slowly and steadily moving upstream, creating what's called a recessional gorge. Niagara Falls is an example, but Niagara is a trickle compared to the ice age falls in the coulees.
Eventually the northern falls eroded itself out of existence (the Grand Coulee Dam is built into the now-exposed bedrock.) There's still some remnants like Steamboat Rock that show what used to be. Down south was a different story. More erosion was happening, and the waterfall that no longer is cut open the Lower Grand Coulee.
Here's some of the bedrock, which I think is gneiss, which is granite which has been squooshed like silly putty. The above picture is about six feet high. I apologize for my lack of assistant, pen or the traditional rock hammer to use for scale.
On the gneiss were several thin layers of a thin, translucent green stone which undoubtedly had a lot of olivine in it. (If it's green, it's olivine.)
Dry Falls
Now, Dry Falls is a testament to the size and power of those falls. Three miles wide, and blah feet high, they were probably the biggest waterfalls in history. The plunge pools are still there, filled with water, as are a pile of basalt boulders which were probably either recently undercut rock, or erratics dumped there by glacial meltwater. In the above panorama, you can see the plunge pools, as well as a gap in the rock which shows a neighboring channel. Dry Falls went over several different scalloped ledges, carving out dividing ridges, again, just like Kasei Vallis Cataract and Niagara Falls. And here's Dry Falls from above.
View Larger Map
This panorama of Niagara Falls in winter is probably a good guess at what Dry Falls looked like when it was active back in the Ice Age.
Here are the house-sized boulders I spoke of. Battleship Rock is behind the boulder field, which divided the two channels, which are both visible.
Now, there might actually be water going over Dry Falls in this day and age, but we put in a dam just upstream to help regulate the flow of the Grand Coulee Dam. As a result, the Upper Coulee is filled by Banks Lake, which is very lovely and probably only covers up a few priceless Native American sites.
Lake Lenore Caves
The Lower Coulee also holds lakes, but smaller ones. They are highly alkaline and reportedly feel like soap. I wanted to experience this for myself, but getting up to the shoreline was difficult thanks to extensive reeds and a crusty layer of minerals around the shore that really didn't seem like they'd support my weight. So, I'll just assume that the people who named Soap Lake knew what they were talking about.
Above the lakes rise basalt terraces. When the floods came through, they carved away at the pre-fractured collonades, creating caves. Many of these caves provided temporary housing for Native Americans, who came there from their villages on the Columbia to gather sacred plants, and probably also enjoy the view.
Here's the view from above of the most spectacular cave. You can see what this really is, is a potcole carved by swirling eddies. if you zoom out, you can see the distinct scallops in the cliffs made by other eddies. They look kind of like this.
View Larger Map
Here's that cave from the outside:
And from the inside:
Looking across the coulee over one of the alkaline lakes (I believe this one is named...Alkaline Lake.) You can just barely see the white rim of minerals along the lakeshore. Note the slope in the layers, caused by the continued uplift of the North Cascade Subcontinent. I would also like to point out that close to where I took this picture, the trail rounded a cliff with literally a foot and a half of ledge to stand on.
The trails along these caves provide a great chance to get up close to the flood basalts. One of the great pleasures in my life is pressing my bare flesh against sun-baked basalt. look how smooth it is. I've put it a lot of my stories. I swear, sun-baked basalt is to me what big knuckles and hangnails are to Samuel R. Delany.
The biggest vug in that picture is less than a quarter of an inch wide. The elongated shape of the patch of vugs shows that there was a lava tube an inch or so across stretching through cooler lava. That's the path the gas took to the surface, and when if finally cooled completely in the tube, that's where it stayed.
This photo shows the contact point between the older vesicle layer and the newest colonnade. You can really see how foamy the rock is. The dark line marks the point of contact metamorphism, where hot lava affected the old rock. To the left, you can see a lighter structure which I'm pretty sure is the sediment that built up in the time between flows. It was basically fused sand.
Supposedly there's a trail that takes you over the cliffs to the East Lenore Coulee, which is basically a hidden mini-coulee, and sounds kind of magical. I didn't learn about it until after I got home, but it's one of many reasons I want to return and explore some more.
All images, except the Google Maps, are copyright Elizabeth Coleman, 2013, Creative Commons Attribution-NonCommercial-NoDerivitives.
1 Go check out this blog, where NASA interns explore the scablands with a hexacopter. It's worth it just for the hoverbot hexacopter.
2 Check out the entire Ice Age Floods blog, which has a lot more information and makes me jealous.
3 http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/description_columbia_plateau.html
Okay, geology. I love geology, and took a bunch of classes in college. That said, I am terrible at identifying rocks, but I love them anyway. Geology is as close as we're going to get to a time machine to the far past. It's one age influencing another. The past shapes the present and the present changes the past. A humble stream bed, dry for eons, is all that's needed to divert a river and carve a canyon.
I'm particularly interested in the Channeled Scablands, aka most of Eastern Washington. They were carved by massive floods into layer after layer of flood basalt, and are pretty much as close as we'll get to certain Martian terrains here on earth. (1)
My favorite part is Glacial Lake Missoula, which was created when an ice age glacier dammed the Clark Fork River and flooded much of Western Montana's steep valleys. I like it because I like imagining myself underneath this huge, cold lake filled with icebergs whenever I visit my grandparents. I like imagining the whole system breathing as the water rises, breaks the ice dam, and pours out, rushing through the plains, pauses to pond behind the Wallula Gap, then rush through the gap and the Columbia Gorge, pause again in the Willamette Valley, and then rush on to the sea. Then the glacier kept moving forward, and the cycle started again.
A brief digression: Because of the way plate tectonics works, we should have a massive trench, a la Mariana, offshore, but we don't. Thank the Columbia for that, and those floods that shoved hundreds of square miles of topsoil into the sea. You may also notice that there isn't a delta like the Nile or Mississippi are so famous for. Deltas need a lot of slow, shallow water to form; the river has to dump its sediment over a wide area. But the Columbia doesn't get to meander across the gentle landscapes of Louisiana; it carved its way with brute force into solid basalt. You get a couple islands like the incredibly flat Puget Island, but that's it. All the sediment gets rolled over by the river and pushed out to sea like leaves before a pressure washer. There, it fills in our would-be trench, and creates one of the most dangerous sandbars in the world. (Shout out to the sixteen pilots qualified to navigate it!)
Back to Eastern Washington. Let's start with the oldest events first. Used to be, our coastline was around Idaho, but we had all these islands offshore--possibly a volcanic arc like Japan. Plate tectonics pushed those islands our way, and in time they docked. Roughly 100 million years ago, the Okanogan Subcontinent docked. It makes up Northeast Washington, and probably Southeast, though we can't tell because that area is covered in flood basalts. 50 million years ago, the North Cascades Subcontinent docked, and makes up Central Washington. Western Washington is mostly ocean floor that got uplifted during the docking, as well as trench stuffing. (Imagine stuffing a blanket between two couch cushions, but the blanket is sea floor, and the cushions are an oceanic plate on one side and a continent on the other, and and you've got trench stuffing.)
But most of that got covered up when, 17 million years ago, the lava floods came. Cracks opened up in Eastern Washington and Oregon that dumped out molten rock. Lots of it. There's one theory that says it was caused by an asteroid striking over the border between Oregon, Idaho, and Nevada, but I'm not sure that explains why there were many different eruptions over 10-15 million years. More likely, the Yellowstone Hotspot is responsible, as our crust slowly moved over it. Maybe it could be both, because asteroids are cool.
The series of flood basalts that make up the Grand Coulee are called the Grande Ronde basalts. They were the second series of floods, and came about 16.5-14.5 million years ago. It's a dense, dark basalt that doesn't weather easily, and when it does, it forms sharp cliffs. It has plenty of cracks, so it just breaks off, rather than rubbing away under wind and water.
This is a colonnade! It makes Eastern Washington possible, as well as the rather weak climax of Hellboy 2 which took place at the Giant's Causeway in Northern Ireland. Flood basalts cool into three layers, of which the colonnade is the most distinct. As it cools, it contracts and forms the distinct hexagon columns separated by what is known as columnar jointing. The jointing is what makes it so easy to break away and form sheer cliffs. This particular colonnade has a bend to it that was likely caused by pressure applied to the side, possibly from being on a slope.
On top of the colonnade is the entablature, which is more or less solid, and on top of that, are the vesicles, which is where all the gas settles at the top, and when the lava cools, it is filled with cavities called vugs. Sometimes, these fill up with silica-rich water and form agates and geodes. Othertimes, they house lichen and small porcelain frogs.
This is the underside of a colonnade. Since the vesicles are all bubbly, they erode the easiest, exposing the colonnade above. In this picture, it's easy to see the columns because a bunch of cliff swallows colonized it and pooped on everything. (This photo also shows the limitations of my cheap telephoto lens. Looking at the colony with my binoculars, which are the same magnification as my lens, showed the birds clearly.
After the flood basalts, along came the ice ages. Other stuff happened between then, like the eruptions of the Cascade volcanoes, but for this story, that's irrelevant.
The ice ages, like the flood basalts, came in multiple series. Glaciers poured slowly out of the north, turning Canada and much of northern America into the spitting image of Greenland. The farthest the ice got near the Grand Coulee is just to the west of the Grand Coulee Dam. There's an extensive geological structure called the Withrow Moiraine, a terminal moiraine which marks the point where the glacier ended, and dumped out sediment and meltwater. Cape Cod and Nantucket Island are great examples of ice age era terminal moiraines. I wanted to check out the moiraine, which consists of rolling hills and huge chunks of basalt stranded in fields, but I didn't have the time. The moiraine isn't strictly responsible for the coulees, but the ice that created it is.
It's all about the Columbia River. We don't really know where the river used to flow, but when the lava came, it pushed the river into its current place. Probably, if we cut into the mile or so of flood basalts, we might come upon a continuous line of pillow basalts(2) which would mark the point where the lava hit the water and cooled instantly. This is the sort of thing I like to think about: a flood of lava hits the water, and eventually, a river hundreds of miles long turns to steam. It probably sucked for all the rhinos and ground sloths on the south side of the river, but they, like the Blue Lake Rhino, probably died a quick death asphyxiated by gas or heat or something. Let's hope that. Those flows came at them around 5 km/h. Molten rock is kind of relentless. (3)
Anyway, enough sad dead animal stories. The Columbia River got pushed up to its current position, until the glaciers came and blocked it off. Poor river--liquid fire from the south, and ice from the north.
The collection of glaciers heading the Columbia's way is called the Okanogan Lobe of the Cordilleran Ice Sheet. (This is another reason I like geology. I like picturing the ice age as consisting of a giant ice amoeba stretching its lobes, slowing groping its way south.) At first, the river was diverted down the Moses Coulee. It's not as big as the Grand Coulee, but it's still spectacular, and has more of the giant ripple marks and flood bars visible from its time as a riverbed. The ice amoeba kept groping, and blocked off Moses Coulee, forcing the Columbia into what would become the Grand Coulee.
Prior to all this, plate tectonics were still pushing from the west, shoving up some mountains from the remains of the old North Cascade Subcontinent. This helped warp the flood basalts, creating a monocline that sloped to the southwest. When the water came, this slope helped pull the water along with even greater force.
At this point, the coulee wasn't really divided into Upper and Lower, but there was a huge waterfall at the north end of the coulee. As I mentioned above, basalt doesn't wear away smoothly and politely. The cracks that separate the columns (called joints) get easily pushed apart, knocking off boulders the size of houses. Underneath all that basalt, however, is the granite bedrock, which doesn't wear away so easily. Water cut cliffs hundred of feet high, and crashed right over. It dug huge plunge pools, and undercut the rock layers, so that the falls are slowly and steadily moving upstream, creating what's called a recessional gorge. Niagara Falls is an example, but Niagara is a trickle compared to the ice age falls in the coulees.
Eventually the northern falls eroded itself out of existence (the Grand Coulee Dam is built into the now-exposed bedrock.) There's still some remnants like Steamboat Rock that show what used to be. Down south was a different story. More erosion was happening, and the waterfall that no longer is cut open the Lower Grand Coulee.
Here's some of the bedrock, which I think is gneiss, which is granite which has been squooshed like silly putty. The above picture is about six feet high. I apologize for my lack of assistant, pen or the traditional rock hammer to use for scale.
On the gneiss were several thin layers of a thin, translucent green stone which undoubtedly had a lot of olivine in it. (If it's green, it's olivine.)
Dry Falls
Now, Dry Falls is a testament to the size and power of those falls. Three miles wide, and blah feet high, they were probably the biggest waterfalls in history. The plunge pools are still there, filled with water, as are a pile of basalt boulders which were probably either recently undercut rock, or erratics dumped there by glacial meltwater. In the above panorama, you can see the plunge pools, as well as a gap in the rock which shows a neighboring channel. Dry Falls went over several different scalloped ledges, carving out dividing ridges, again, just like Kasei Vallis Cataract and Niagara Falls. And here's Dry Falls from above.
View Larger Map
This panorama of Niagara Falls in winter is probably a good guess at what Dry Falls looked like when it was active back in the Ice Age.
Here are the house-sized boulders I spoke of. Battleship Rock is behind the boulder field, which divided the two channels, which are both visible.
Now, there might actually be water going over Dry Falls in this day and age, but we put in a dam just upstream to help regulate the flow of the Grand Coulee Dam. As a result, the Upper Coulee is filled by Banks Lake, which is very lovely and probably only covers up a few priceless Native American sites.
Lake Lenore Caves
The Lower Coulee also holds lakes, but smaller ones. They are highly alkaline and reportedly feel like soap. I wanted to experience this for myself, but getting up to the shoreline was difficult thanks to extensive reeds and a crusty layer of minerals around the shore that really didn't seem like they'd support my weight. So, I'll just assume that the people who named Soap Lake knew what they were talking about.
Above the lakes rise basalt terraces. When the floods came through, they carved away at the pre-fractured collonades, creating caves. Many of these caves provided temporary housing for Native Americans, who came there from their villages on the Columbia to gather sacred plants, and probably also enjoy the view.
Here's the view from above of the most spectacular cave. You can see what this really is, is a potcole carved by swirling eddies. if you zoom out, you can see the distinct scallops in the cliffs made by other eddies. They look kind of like this.
View Larger Map
Here's that cave from the outside:
And from the inside:
Looking across the coulee over one of the alkaline lakes (I believe this one is named...Alkaline Lake.) You can just barely see the white rim of minerals along the lakeshore. Note the slope in the layers, caused by the continued uplift of the North Cascade Subcontinent. I would also like to point out that close to where I took this picture, the trail rounded a cliff with literally a foot and a half of ledge to stand on.
The trails along these caves provide a great chance to get up close to the flood basalts. One of the great pleasures in my life is pressing my bare flesh against sun-baked basalt. look how smooth it is. I've put it a lot of my stories. I swear, sun-baked basalt is to me what big knuckles and hangnails are to Samuel R. Delany.
The biggest vug in that picture is less than a quarter of an inch wide. The elongated shape of the patch of vugs shows that there was a lava tube an inch or so across stretching through cooler lava. That's the path the gas took to the surface, and when if finally cooled completely in the tube, that's where it stayed.
This photo shows the contact point between the older vesicle layer and the newest colonnade. You can really see how foamy the rock is. The dark line marks the point of contact metamorphism, where hot lava affected the old rock. To the left, you can see a lighter structure which I'm pretty sure is the sediment that built up in the time between flows. It was basically fused sand.
Supposedly there's a trail that takes you over the cliffs to the East Lenore Coulee, which is basically a hidden mini-coulee, and sounds kind of magical. I didn't learn about it until after I got home, but it's one of many reasons I want to return and explore some more.
All images, except the Google Maps, are copyright Elizabeth Coleman, 2013, Creative Commons Attribution-NonCommercial-NoDerivitives.
1 Go check out this blog, where NASA interns explore the scablands with a hexacopter. It's worth it just for the hoverbot hexacopter.
2 Check out the entire Ice Age Floods blog, which has a lot more information and makes me jealous.
3 http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/description_columbia_plateau.html