You will find these rocky columnar cliffs in Eastern and Central Oregon, but what exactly happened to form these unique structures? In this podcast, we talk with our resident rock doctor, Dr. Kim Ely.
Transcript
Dirty Freehub 0:05
This is the Connection, a dirty three hub podcast connecting gravel cyclists to where they ride through short stories about culture, history, people, places and lands.
Dirty Freehub 0:21
Our rock doctor, Kim Ely, has her Ph.D. in geology, investigating the evolution of volcanic arcs north of Australia. She now works in the field in plant ecology, studying tropical in Arctic ecosystems. Okay, Rock Doctor, I’m really excited for this topic on basalt rocks. So let’s kick it off. Thanks for joining Kim.
Dr. Kim Ely aka “The Rock Doctor” 0:42
And thanks for inviting me to chat some more about volcanoes and the geology of Oregon.
Dirty Freehub 0:47
Absolutely. Any time. So what causes these cliff formations story?
Dr. Kim Ely aka “The Rock Doctor” 0:52
This cliff started about 17 million years ago, which is older than what’s of the the current cascade range volcanoes that a lot of people are familiar with. And around this time, enormous amounts of basalt lava started to erupt in eastern Oregon. This event was quite different to the types of eruptions that did occur from the volcanoes that we’re familiar with. Instead of erupting from volcanic cones, this lava came out of fissures, which are giant cracks in the earth, some of them maybe over 100 miles long. And all these fissures were clustered around sort of present day Oregon, Idaho border. And then these eruptions, well, they went on for maybe about 14 million years that were extremely active for about a million years, sending lava flowing over most of eastern Oregon, eastern Washington and parts of Idaho. Some of the individual flows have been tracked to be over 300 miles long. And they flowed all the way west along the Columbia River Valley through to the ocean. And these rocks can still be seen as the spectacular rock stacks of the Oregon coast. So this type of volcanic feature with these massive volumes of basalt is known as a continental flood basalt. The flowing lava filled up valleys and then flooded across the landscape with successive flows layering on top of each other up to a thickness of around 15,000 feet. If we spread this lava across the whole country, this would have formed a layer of basalt over 45 feet thick over the 48 states. So it’s just. Wow, enormous. That is huge.
Dirty Freehub 2:33
I did not realize how big that was.
Dr. Kim Ely aka “The Rock Doctor” 2:36
The other feature about what we see today in the cliffs is this fact that they look columnar like they’re made up of all these columns jammed together. So the way that they are formed is, you know, how when most things cool they shrink. And basalt was no different to that. So a thin layer of basalt can just shrink down from the top like a failed baked cake that collapses when you take it out of the oven. But a really thick layer can’t do that. Is it still got hot lava that’s cooling, trapped in between rigid surfaces above and below. So when this happens, the basalt starts to shrink in from the sides. And some tricky physics and thermodynamics dictates that this occurs around spaced cooling centers. And each of these center points becomes a middle of a column and then rocks. Some rocks in particular like to be orderly and the columns form as these cracks between each column extend from the top of the flow all the way down to the bottom.
Dirty Freehub 3:37
That’s wild. So what is the basalt rock and how is it different than other types of rocks?
Dr. Kim Ely aka “The Rock Doctor” 3:42
Yeah. Okay, so basalt is a fine grained volcanic rock and its most one most common volcanic rock types. We call these rocks igneous rocks, and they are basically formed from molten magma. It’s coming from the center of the earth. Bessel in particular is what we call an extractive igneous rock, meaning it was erupted onto the surface as flowing lava and then cooled relatively quickly. And this results in a fine grained texture of the rock with interlocking crystals. In comparison, this is different to an igneous, intrusive rock such as granite, where the magma is in place deep below the surface of the earth, and it can take millions of years to cool. And this allows large crystals to form within the rock. A great place to see minerals in granite is in people’s smoothly polished kitchen countertops, but basalt and granite also different in terms of their composition. They have different proportions of elements, including silicon, iron and magnesium. And this means that the Mint types that crystallize are also different in their talk and relative abundance. But you don’t need a fancy microscope to see this due to the different minerals. Fresh basalt is almost black in color, whereas granite too often light gray or even pink.
Dirty Freehub 4:58
Why are these cliffs so vertical in? How do they erode over time?
Dr. Kim Ely aka “The Rock Doctor” 5:03
Well, the sick basalt flows are really strong and really resistant to weathering and erosion landscape with a variety of other rocks such as sandstones and mud stones. The vessel will often be the last to erode. But even a vessel, cliff, can’t hold itself up over thin air. So when a cliff gets undercut by a river at the base of a valley, the cliff will collapse, retreating away from the center of the valley. And while basalt is overall very strong, all of those vertical columns create weaknesses as the edge of each column is defined by a narrow crack. The geologists call these joints. These vertical weaknesses guide how the cliff erodes. When you have vertical joints, you will get vertical cliffs, and if you walk or ride along these valleys, you can see the result of this cliff collapse process in the form of giant piles of basalt blocks, often still with the column shapes evident.
Dirty Freehub 5:57
So no wonder why people use granite so such a strong structure. Are these types of cliffs unique to Oregon?
Dr. Kim Ely aka “The Rock Doctor” 6:04
Actually know this is a fairly common common landform in many places around the world where there are large basalt flows. These continental flood basalts have occurred in places in India, in Siberia, and in Africa, a bunch of other places, and these types of cliffs and sometimes even more spectacular examples of these type of clips also form in a closely related rock type called dollarized. Oh, and notably is common in Tasmania, in Australia, which I know is one of duty free house favorite places.
Dirty Freehub 6:38
Oh, it certainly is. Yeah. I really like the analogy of the cake that you had with the rocks was a very.
Dr. Kim Ely aka “The Rock Doctor” 6:43
Good visual for it. It’s what it really looks like and you get the cake appearance in the layers, definitely the surfaces of each floor can, has a bit of time elapsed between the flows, you get a bit of a weathering on each flow and so that enables it to look distinct when you see it in a definitely.
Dirty Freehub 7:02
I’ve even seen some of the ones along alongside the water. I don’t know if it’s what like just erosion over time or the plates are actually shifting, but they’re quite horizontal like layers to like this looks like they’re coming out of the ground.
Dr. Kim Ely aka “The Rock Doctor” 7:16
Yeah. Yeah. So if you get thin flow, you won’t get columns and you want the when you see horizontal layers in basalt, there will be contacts between the separate flow layers, whereas the vertical structures generally from that columns forming from the shrinking process within the flow as it cools.
Dirty Freehub 7:39
Well thanks for the chat are for our rock Doctor. Is there anything else you like to add?
Dr. Kim Ely aka “The Rock Doctor” 7:45
No. You’re welcome. Great to talk to you again, Kira.
Dirty Freehub 7:47
Yeah, good to talk with you, Kim. Thanks again.
Dirty Freehub 7:51
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