by johnnydeep » Wed Mar 10, 2021 4:50 pm
Chris Peterson wrote: ↑Wed Mar 10, 2021 4:38 pm
Sam Waldon wrote: ↑Wed Mar 10, 2021 4:11 pm
Refer to photo Flat Rock 3 in alter-ego's thread comment. It illustrates the triangular shape I mentioned. I can understand flat or rounded shapes resulting from sedimentation or erosion, but why the sharp angular shapes among them?
Angular rock shapes, facets, and pits are all indications that we're looking at ventifacts, rocks ablated by blowing sand particles.
Cool! I wouldn't have thought it possible for wind to form a pyramidal shape, but it apparently happens. From the link to Dreikanter -
https://en.wikipedia.org/wiki/Dreikanter:
A Dreikanter is a type of ventifact that typically forms in desert or periglacial environments due to the abrasive action of blowing sand.[1][2]
Dreikanters exhibit a characteristic pyramidal shape with three wind-abrased facets. The word Dreikanter is German for "three-edged."[3]
Similarly, a zweikanter ("two-edged") has two wind facets, an einkanter ("one-edged"), has only one wind facet. [4]
Most places on the planet have several weathering processes acting at the same time, so finding good examples of Dreikanters is often difficult. Antarctica is a good location for finding such ventifacts since wind is usually the only active weathering agent. Many specimens in the Northeastern United States were formed during the Pleistocene era when the absence of vegetation made for little cover from wind-blown sediment.[5]
..
Formation
In areas where there is a prevailing wind, sand and debris cause a rock face to become flattened and polished. This changes the mass distribution of the rock, and may cause it to turn another surface toward the wind. If this process continues undisturbed, the resulting rock will have three distinct flattened and polished faces.[7] Dreikanters generally form in dry, arid environments from hard rocks.[7]
[quote="Chris Peterson" post_id=311522 time=1615394325 user_id=117706]
[quote="Sam Waldon" post_id=311521 time=1615392660]
Refer to photo Flat Rock 3 in alter-ego's thread comment. It illustrates the triangular shape I mentioned. I can understand flat or rounded shapes resulting from sedimentation or erosion, but why the sharp angular shapes among them?
[/quote]
Angular rock shapes, facets, and pits are all indications that we're looking at ventifacts, rocks ablated by blowing sand particles.
[/quote]
Cool! I wouldn't have thought it possible for wind to form a pyramidal shape, but it apparently happens. From the link to Dreikanter - https://en.wikipedia.org/wiki/Dreikanter:
[quote]A Dreikanter is a type of ventifact that typically forms in desert or periglacial environments due to the abrasive action of blowing sand.[1][2]
Dreikanters exhibit a characteristic pyramidal shape with three wind-abrased facets. The word Dreikanter is German for "three-edged."[3]
Similarly, a zweikanter ("two-edged") has two wind facets, an einkanter ("one-edged"), has only one wind facet. [4]
Most places on the planet have several weathering processes acting at the same time, so finding good examples of Dreikanters is often difficult. Antarctica is a good location for finding such ventifacts since wind is usually the only active weathering agent. Many specimens in the Northeastern United States were formed during the Pleistocene era when the absence of vegetation made for little cover from wind-blown sediment.[5]
..
[b][size=150]Formation[/size][/b]
In areas where there is a prevailing wind, sand and debris cause a rock face to become flattened and polished. This changes the mass distribution of the rock, and may cause it to turn another surface toward the wind. If this process continues undisturbed, the resulting rock will have three distinct flattened and polished faces.[7] Dreikanters generally form in dry, arid environments from hard rocks.[7][/quote]