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18 December 2022
Another track left by huge sandstone boulders visible with lidar, Big South Fork National River, Kentucky
An interesting aspect of the boulders is that very few have been known to slide or roll into place since folks started recording such things, and they very, very rarely show visible tracks or paths downslope in lidar-derived imagery. The question of how the boulders got to their resting place is legitimate (more on this below), but sometimes, lidar serves up a nice answer, as in the case of the two huge (115 ft or 35 m long) McCreary County, Kentucky, boulders shown below. The boulders and their track are highlighted in the lower image for comparison to the bare lidar.
2 December 2022
What’s under that anticline? Fold-thrust belt interpretation ideas from geologic sandbox models
Complex structures like this are common in Earth’s sedimentary fold-thrust belts and are tough to fully interpret without seismic surveys or drilling through them, but field- and concept-based information can be gathered to at least give some idea of what might be beneath an anticline like this one. I offer up a few of my own thoughts here, and there are undoubtedly many other possible strategies.
1 November 2022
Blowout landslides, part 2: Material movement, and did anything actually “blow out?”
So, what actually happens when these slides occur? I have not personally witnessed one, but I think that a look at details of failure surface shape and the behavior of saturated soil during failure can be used to figure out why blowouts appear to “blow out” instead of just slide. Lack of disturbance of the slopes below blowouts was remarked upon by both Eisenlohr (1952) and Hack and Goodlett (1960), with Hack and Goodlett going to the length of determining just how small of a sapling tree could survive a blowout strike in their study area.
29 October 2022
“Blowout” landslides and the lidar signature of extreme Appalachian rainfall events
On the night of June 27, 1995, the Albemarle County, Virginia, mountainside shown below received an exceptional amount of rainfall. No one knows how much, but a nearby rain gage recorded ~ 11 inches (28 cm) of rainfall with only 2 hours…the rain event continued for several more hours. Unsurprisingly, a tremendous number of landslides resulted. The slides are clearly visible in this lidar hillshade image, and those marked with yellow arrows are of particular interest in the context of the storm’s outrageous precipitation rate and total, which likely reached 30 inches (76 cm).
23 October 2022
Sandbox models with high-displacement thrust faults compared to features of some Canadian Rockies sections
Sandbox models don’t always produce the geometry the modeler wants, but with properly scaled materials, a “failed” model run can still produce worthy analog structures. I recently came up short on attempts to model some details of the southern Appalachian Valley and Ridge, instead producing structures reminiscent of some well-known Canadian Rockies sections. Were the model a real thrust belt, drilling through the first anticline of the upper thrust sheet, through the thrust, and into the upturned footwall beds might be interesting, whether you’re into exploration or carbon storage. A hypothetical well is shown here…
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 …
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.
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 …
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.
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.
2 February 2022
Fun with ice physics in the cryosphere
By Ned Rozell A recent winter storm that featured a heavy rainfall caused hardships for many animals of Interior Alaska, but some people found the event fascinating. Two men who live up here and study the cryosphere — the frozen and snow-covered portion of the Earth’s surface — squinted for a closer look at what the storm threw at us. When the snow-rain-snow storm began just after Christmas 2021, Matthew …
31 January 2022
Midwinter rain-on-snow a game changer
By Ned Rozell A few hours of a December day may affect living things for years to come in the middle of Alaska. On Dec. 26, more than an inch of rain fell over a wide swath of the state. Much of the backcountry of Interior Alaska now has an ice sheet beneath a foot of fluffy snow. With half of the seven-month winter yet to come, things look grim …
The porcupine’s winter in slow-motion
By Ned Rozell While running through Bicentennial Park in Anchorage, biologist Jessy Coltrane spotted a porcupine in a birch tree. On her runs on days following, she saw it again and again, in good weather and bad. Over time, she knew which Alaska creature she wanted to study. “I thought, ‘Oh my god, how does he do it? How does this animal make it through winter?’” Coltrane said years ago …
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.
10 January 2022
Is this the steepest river in the Appalachian Mountains?
Topographic superlatives are almost always a bit arbitrary, and comparing river steepness is about as arbitrary as it gets. How long of a stretch of river needs to be considered? How big does a stream need to be in order to be considered a “river?” Since a vertical waterfall is the maximum steepness possible, is the biggest river with a freefalling waterfall the winner? How tall does the waterfall have to be? These questions all have merit…
4 January 2022
Thirty years on semi-solid ground
By Ned Rozell At the end of this month, Vladimir Romanovsky will retire after 30 years as a professor and permafrost scientist at the University of Alaska Fairbanks’ Geophysical Institute. This comes at a time when people — finally — no longer squint at him with a puzzled look when he mentions what he studies. Permafrost is ground that has remained frozen through the heat of at least two summers. …
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.
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.
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.
13 July 2021
The peak of summer warmth is near
By Ned Rozell You may not notice it as you scooped fish out of the Copper River or rode your bike through the tawny light of 10 p.m., but Alaska is about to make a left turn toward winter. Much of the state will soon reach the average yearly date when the air won’t get any warmer. In Fairbanks, on July 19 the average daily temperature based on about a …
