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29 July 2022

This North Carolina boulder carved a satisfying track as it slid downhill, and you can see it with lidar imagery

By Philip S. Prince A few weeks ago, after years of “lidar surfing,” I finally encountered an Appalachian boulder that left clear evidence of its sliding path down a mountainside. Large boulders are common throughout all of topographically rugged Appalachia, but they typically reveal little or no evidence about their paths from upslope sources to their current resting places. This Macon County, North Carolina, boulder is a rare exception, as …

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5 July 2022

Lidar imagery reveals interesting details of debris flow movement in the eastern Blue Ridge Mountains of North Carolina

Lidar imagery provides a way to track downslope material movement of old flows that is otherwise difficult or impossible to see in the field, which is particularly significant in forested Appalachia. This post highlights some interesting debris flow styles and paths now hidden by vegetation in Pisgah National Forest in Transylvania County, North Carolina. The age of these failures is unknown, but they likely occurred in 1916 during an extreme tropical precipitation event in the area.

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5 April 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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8 March 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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14 February 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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25 January 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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3 December 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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17 November 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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2 November 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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22 June 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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6 April 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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24 March 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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1 March 2021

What does that landslide actually look like?

We have no constraints on the age of the slides, but they may reflect logging history in the area. The majority of these slopes were heavily and continuously logged during the past ~150 years, with logging in this area clearly occurring within the past 50 years. The slides may have developed after clear-cuts, with the rapid return of vegetation common in the region quickly making the area look less disturbed than it really is.

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24 February 2021

Lidar-derived imagery of 1949 debris flows on North Fork Mountain, Grant County, West Virginia

Debris flow events present a significant hazard to life and property in all parts of the Appalachians. The 1949 event that created the features shown here caused 8 fatalities and displaced a tremendous number of residents. Detailed mapping…along with analysis of detailed surface imagery, can greatly enhance understanding of where debris flows begin and where they travel. This understanding, in turn, can potentially reduce the human impact of these particularly dynamic and mobile slope failure events.

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11 January 2021

The Ray Sponaugle well: A 13,000-ft lesson in Appalachian Valley and Ridge structure

“To the surprise of the drillers and geologists involved with the project, the well bore never got anywhere close to the Cambrian quartzite. At 10,000 ft (3,010 m) below the surface, the well passed through a thrust fault and entered a tight, nearly recumbent syncline cored by the same Ordovician shale unit into which drilling began.”

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4 December 2020

Lidar hillshade imagery hints at the location of a future coal spoil landslide

A coal spoil landslide in southeastern Wise County, Virginia, appears traceable to a faint scarp visible in the spoil pile in a 2017 lidar dataset. The slide pre-dates October 2019 Google Earth imagery and post-dates the 2017 lidar data acquisition.

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15 October 2020

Normal fault, reverse fault, or both?

The new model, whose color scheme is admittedly quite shocking (think Pepto-Bismol bottle), is shown… The interesting fault is at the center of the image. The fault is traced in black in the lower image, with arrows indicating movement sense.

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5 October 2020

Interesting “sideways” movement of a large sandstone blockslide

A large sandstone blockslide in Highland County, Virginia presents an unusual appearance in LiDAR hillshade imagery–it appears to have moved sideways across a slope instead of directly down the slope.

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24 September 2020

LiDAR reveals the cloth-like appearance of a “wrinkled” translational landslide

The Virginia Valley and Ridge hosts plenty of amazing landslide features, but this wrinkled translational slide in Botetourt County, Virginia is particuarly eye-catching. It reminds me of the wrinkling that might occur in a thin layer of cloth pushed along a smooth surface–something like pushing a napkin or tablecloth along a tabletop.

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14 September 2020

The interesting geologic setting of Thomas Cole’s “The Oxbow”

New from The Geo Models blog: “Earlier this year, I became aware of the longer, geographically-specific title and learned that the painting does portray a real location with a particularly interesting geologic context…. Cole’s vantage point on Mt. Holyoke is east-northeast.

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