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April 22, 2020
Listric normal faults with glass microbeads
Latest from from The Geo Models: Deformation associated with listric (downward flattening) normal faults produces very interesting patterns.
April 7, 2020
Interesting reverse faults in a simple extensional sandbox model
The different mechanical properties of the layers are apparent in the dip angles of the normal faults in the model. The master fault on the left side of the model (black line) is less steep in the weak microbeads, an expression of how their failure behavior differs from the stronger layers above and below.
March 25, 2020
Cracked mountaintops Part 2: Sinking summits?
Some upper Devonian sandstone mountains in the Virginia Valley and Ridge show evidence of deep-seated landsliding, resulting in the formation of a downthrown block (graben) along the summit ridge.
March 20, 2020
Cracked mountaintops of the Virginia Valley and Ridge
A newly-released LiDAR data set reveals impressive ridge-top cracks associated with large rock slides in the Virginia Valley and Ridge. While the cracks are easily visible with LiDAR hillshade imagery, they appear to be covered by normal forest vegetation and would probably look like elongated depressions in the forest.
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…
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.
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.
January 23, 2020
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.
January 13, 2020
An abandoned river valley and the “true depth” of Appalachia’s deepest river gorge
This post centers around an oddly meandering, dry valley 800 ft above the northwest wall of the gorge. It’s not much to look at in Google Earth imagery alone, but with enhanced maps and some understanding of how river gorges spread through topography, it gives great context for different ways of thinking about gorge development.
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.
