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You are browsing the archive for structural geology Archives - Page 2 of 6 - The Field.

March 10, 2020

A sandbox model without fault(s)?

Fold-thrust belts (both real and model, like this one) develop fault and fold patterns that reflect the properties of the rock (or sand-like materials) being deformed. The model section shown (shown here) is interesting because it results from shortening a granular layer sequence by 50% and does not show any major thrust fault structures that cut through all of the layers…

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March 9, 2020

‘Remarkable groove’ slides gold into Alaska

In the 160 miles between the towns of Eagle and Circle, a half-dozen gold-mining settlements — most of them ghosted out — were on the south bank of the Yukon River. Not one was on the north side. That seemed like more than a coincidence.

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February 27, 2020

Where did that boulder come from? A LiDAR perspective on a large Appalachian rockfall

I have always wondered about the possibility of finding the specific outcrop source of large boulders, which is very difficult in the field due to vegetation and continued evolution of the cliff line after a boulder falls off and makes its way downhill. Using LiDAR-derived hillshade imagery of a portion of the Blue Ridge Escarpment in western North Carolina, I recently came across a particularly large boulder that appears to be traceable to a scar on cliffs hundreds of feet further up the slope.

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February 17, 2020

Outcrop patterns in a fold-thrust belt analog model, round 1

The model shown here did not work out as planned because I shortened it too much, but the overall appearance is still cool and reflects local variations in the layer pack. In real fold-thrust belts, the local or regional variations in folding and faulting style also reflect the details of the layer sequence being folded and faulted, among many other conditions.

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February 10, 2020

The Pigeon River is perched, which is geologically bad news for it

At Canton, North Carolina, the headwaters of Hominy Creek, a French Broad River tributary, are VERY close to capturing the Pigeon River. In human terms, this is still probably a long way off, but it is most certainly geologically “imminent.”

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February 3, 2020

The mountain that has it all (at least it did in the pick-and-shovel days)

Back in 1830, The Catawba Iron and Coal Company got an outrageous deal on a plot of land at the foot of North Mountain in western Botetourt County, Virginia. Within about 1 square miles, coal, iron ore (oxide), and high-purity limestone could be mined, and thick layers of quartz pebble conglomerate could be quarried for much sought-after millstones.

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January 23, 2020

Denali Park Road failings and other stories

By the summer of 2020, a landslide will bury a portion of the road from the Denali National Park entrance to Wonder Lake. That’s the conclusion of Zena Robert, a UAF graduate student who visited the park in summer 2019. Last summer, she did a ground survey of giant blobs of frozen hillside that sometimes ooze over the 92-mile road, which workers built from 1923 to 1938.

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Discount inverted basin models: You get what you pay for (mostly)

A basic Google search of “inversion geology” will produce a tremendous number of results, including conceptual illustrations, analog model results, and actual cross sections generated from subsurface imaging and drilling exploration.

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January 6, 2020

Surface uplift and deep fault structure in sandbox models

A particularly interesting method of attempting to understanding deep fault geometry is using patterns of surface landscape evolution to identify the moving zone of uplift above a deep fault ramp. A useful analogy for this concept is to visualize sliding a spatula underneath a cooking egg.

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December 19, 2019

Spreading volcano follow-up: Cross sections showing normal faults and thrust faults

Geo Models: The GIF shows the results of about 15 minutes of deformation with fresh sealant straight out of the tube. The summit of the cone collapses into a graben, and the flanks of the cone spread outward, creating compression that generates thrust faults and folds.

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