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You are browsing the archive for The Geo Model Blog Archives - The Field.

April 5, 2022

Real sandbox model meets “numerical sandbox” model…an interesting comparison of dry granular media and discrete element simulation

By Philip S. Prince Back in February, I saw several references to the CDEM discrete element modeling tool on Twitter. One of the example simulations reminded me of a “real” sandbox model I made a couple of years ago while experimenting with different material properties. The two results are shown below, with the CDEM example on the left and the real sand model on the right. The CDEM example above …

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March 8, 2022

Lidar reveals geologic details of the “worst” coal mine in the Valley of Virginia

Despite its apparently good location, all was not well at the Altoona Mine. Coal seams in the mine were too distorted and mixed with surrounding rock to be easily extracted, leading to its ultimate failure. Early 20th century geologist Marius Campbell addresses this issue at length in the 1925 report The Valley Coal Fields of Virginia, twice calling Altoona’s location “the worst” in the general area and the obvious reason for the mine’s closure.

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February 14, 2022

The waddling boulder…a storm-induced trundle* event?

This was (and remains) the first and only boulder I have personally seen that has rolled or tumbled and come to rest recently enough for its track to be visible in the field. I thought the diagonal gouge marks were particularly interesting. For whatever reason, they caused me to visualize a slow, “waddling” rolling style like that of an American football or rugby ball rolling downhill.

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January 25, 2022

Two mappings of a folded thrust fault in the Appalachian Valley and Ridge, 100 years apart

These klippen are made even more interesting by the fact that they were mapped and correctly interpreted in 1924. Comparing these maps separated by 98 years and considerable changes in land use, geologic exposure, tectonic understanding, and imaging technology is very interesting to me. The same patterns and structural relationships are obviously present in both to a high level of detail, which is impressive given the much larger scale of the 1924 map project.

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December 3, 2021

“Squirrel tail” synclines in the Appalachian Valley and Ridge

I settled on “squirrel tails” because Bartholomew and Lewis’ cross sections of the features reminded me of how a squirrel drapes its tail over its body and head. I am not sure if this is an effective comparison or not, but the overall approach seems to have served humans well when it comes to mentally organizing patterns of stars in the night sky. This structural style came across my radar after I mapped a similar type of structure ~25 miles (40 km) to the southwest, near the town of Max Meadows itself.

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November 17, 2021

Another intersection of lidar and 19th-century observations at the Silas McDowell slide, Macon County, North Carolina

McDowell described the slide as a “violent shock” which opened a “chasm” that remained visible for many years after the initial event. The date of the slide is unknown, but it probably occurred during the 1850s.

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November 2, 2021

A mid-1800s description of landslide topography meets 21st century lidar at Split Mountain, Haywood County, North Carolina

The “mystery” of Split Mountain specifically refers to episodes of falling rock, formation of lumpy “hillocks” on previously smooth slopes, split and tilted trees, and cracked ground that gave the mountain its name in the mid-19th century. Interestingly, none of the features Clingman described are readily apparent today, allowing the mystery to persist.

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June 22, 2021

Low-displacement landslides explain unusual West Virginia landscape features visible in lidar imagery

Like so many older landslides in the Appalachians, the significance and cause of these features is unknown. Because they are so numerous and are only visible using lidar data acquired in 2016, they may represent an untapped resource of useful information about the recent history of Appalachian landscapes.

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April 6, 2021

Central peak formation in model impact craters

I produced the model impact crater with a combination of the same granular materials I use for tectonic models and a projectile fired from a powerful air rifle (a city-safe version of Gene Shoemaker’s approach). The model crater developed a nice central peak as well as terraced margins. The darker material is quartz sand, combined with a small amount of cornmeal to produce a minor amount of cohesion between sand grains. The white material comprising the central peak is glass microbeads.

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March 24, 2021

What does that landslide actually look like, part 2: an active landslide

As indicated in the previous post, lidar-derived imagery still needs ground-truthing to maximize its usefulness as a means of characterizing landslides and other slope failures. Last June, Ken Gillon and I visited the Rutherford County, North Carolina, landslide described below as part of our work with Appalachian Landslide Consultants, PLLC (ALC) on behalf of the North Carolina Geological Survey. This slide caught my eye in lidar hillshade imagery because it appeared to share characteristics with an active slide we had visited a few days before.

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