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Archive for July, 2012

This final post of my Columns “Week” comes from an outcrop on I-84 along the Columbia River in northeastern Oregon. Technically this outcrop is in Washington, but since I took this picture from the Oregon side, and I am now a resident of Oregon, I am going to claim it as ours. This stretch of interstate is full of excellent examples of columnar jointing from the basalt flows that cover most of the state, and is a beautiful drive.

Becoming a bad habit for me is that this picture was taken from a moving car, and suffers from the slightest bit of blurriness and lack of good scale.

Even with the photographic flaws, I think it is apparent that there is some interesting distortion going on in these columns. Below, I highlighted the edges of most of the columns.

What stands out most to me about this outcrop is the change in direction of the narrow columns. Admittedly there is a high amount of fracturing going on, but the most apparent columns seem to diverge and converge in places.

Another interesting aspect of this place is the presence of what could be more, larger columns above the distorted, narrow ones. Here they are highlighted in yellow.

This gives me the sense that there are two separate flows existing here. A quick amount of research leads me to believe the lower flow could be the Middle Miocene Wanapum basalt (15.0 Ma), and the upper flow could be the  slightly younger Saddle Mountains basalt (13.5 Р6.0 Ma). Of course, to get a good grasp on the difference I would need to get my nose to the outcrop and take a better look.

If these are two separate flows, here is another annotated picture showing the contact between the two in blue.

Maybe I will find time to head back and get a closer look.

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The next post in my Columns “Week” series is an outcrop I saw along I-5 just north of Eugene back in March, and came away with an immediate impression. I was sick at the time, but still knew exactly what it was I was looking at as we drove past at 65 mph. Since coming back, this outcrop has become a bit more confusing to me. Not because I disagree with my initial impression, but because it has been explained to me as something else and I still agree with my first thought. Hopefully today I can get some input that will shine light on the situation to me.

Enough talk! Here is the outcrop in question:

This outcrop is located on the eastern side of I-5 with no safe place to park and walk up to, so these pictures are taken from across the interstate just off of Coburn Road near the McKenzie River.

Clearly there are some distorted basalt columns here, that is not in question. But, my initial impression was that these columns were distorted due to a lobate cooling front, and it has been explained to me (by very reputable sources) as a dike rolling into a sill. To help visualize my thought process, here is an annotated picture of the outcrop with the progressive cooling front in orange, and the direction of cooling shown with a red arrow. Also, a second picture with a passing tractor trailer to give a relative sense of scale.

Here is another angle of the outcrop where in my hypothesis the cooling front would be moving from the upper left of the picture towards the lower right.

Another interesting aspect of this outcrop is that the basalt can be seen overlying Oligocene aged marine sediments of siltstone and sandstone. Here is a picture of the contact between the two with another less than desirable “passing truck” for sense of scale.

Does anyone have a counter hypothesis? I would love to have a discussion on what I may not be seeing at this outcrop.

For good measure, here is a picture of the entire outcrop taken from a northern angle (again with cars for scale).

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I have recently transplanted myself in the Pacific Northwest, specifically the city of Eugene, OR. It has only been a couple of weeks, but I am already making myself right at home with the food, people and most importantly the geology. While I still have a lot to learn in terms of the local geology, what I have seen so far has prompted me to declare my own personal “Columns Week” on this blog. I have set aside three Oregon outcrops to discuss throughout the week, starting off with one suggested to me by Lockwood DeWitt at Skinner’s Butte.

Located on the northern side of town west of the campus, and just a short bike ride from my place, this outcrop shows some of the most spectacular basalt columns I have come across. I have been to Giant’s Causeway in Northern Ireland, and I think these ones belong in the same category.

The columns to the right are so well preserved!

Photo by V. Malinay

Photo by V. Malinay

If you click on the image for the larger version, you can see the arrest lines.

Special thanks to Lockwood DeWitt for bringing these to my attention, and also the guy climbing for the sense of scale.

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