I’m Not Just Going to Show You All My Faults

Spot the Fault

After a short climb along a rocky, thickly wooded path, the professor and his students round a corner and find themselves upon a promontory overlooking a seemingly endless, lush forest. The landscape is emerald green, rippled and textured where the underlying landscape rises and falls beneath the roots of the tallest trees. The forest canopy climbs up all but the highest and most jagged peaks of the mountains beyond.

Once all of the students have arrived at the top of the hill and gathered around him, the professor takes a deep breath, looks out at the splendor of the surrounding landscape and proclaims, “We have got to get rid of all of this vegetation!”

That’s just the life of a geologist for you. We love living things (really, we do) but dense forests or thickly carpeted prairie can severely obscure the underlying landscape and make the job of an Earth scientist very difficult. That’s the reason one of my old professors once described the western Columbia River Gorge to me as a “green hell.”

Case in point: The image above has a potentially dangerous, recently active, surface fault in it. Look really closely. Can you see it?
No, you can’t. And neither could Oregon geologists until just a couple of weeks ago, when they examined the results of recent LIDAR mapping along the flanks of Mount Hood.

LIDAR is an acronym for “Light Detection and Ranging,” a technology that utilizes laser pulses to map landscapes in such a way that overlying vegetation can be ignored. The result is a highly detailed terrain map that scientists can use to understand the dynamics of the land.

What scientists saw when they mapped the north side of Mount Hood near the town of Parkdale (an area called Blue Ridge) was this:

Blue Ridge Fault

It’s faint in this image, but you can surely see it. Just like a pencil tracing, there along the red arrows is a fault line. It crosses and, in fact, interrupts an old glacial moraine that was deposited at the end of the last ice age, so from that information alone we know that the fault has ben active in the last 12,000 years.

So, does this fault pose any danger to area residents? Likely, it does, but geologists are in the process of determining for sure. In order to do so, they’re digging a trench to expose some of the underlying strata. You can see the site plan here along with some more detailed images of the vicinity.

The project should only take a couple of weeks, so we may have some more information soon. I’m anxious to know what the researchers learn.


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