Ventifacts are such a broad subject! I'm having a hard time finding the first words to write. I'd like to show you the pictures right now, but there are so many things to address before that can happen.
If you are a person who came a long distance, possibly from a galaxy far far away, you came here to learn about such all-important things as what exactly ventifacts are, who created them and why. You might also be angling to learn where you can find a few neat pieces for your personal collection (of memories).
Calm down, they're just rocks!
What are ventifacts and who created them?
Ventifacts are rocks that have been smoothed and shaped over time by wind and ice crystals.
Coachella Valley field trip video
They are an everyday sight in most deserts of the world, the tundra biome, and have been identified on Mars.
Ventifacts are formed by sand-blasting, which is an effective means of erosion, both in nature and as a way for cleaning buildings and surfaces in preparation for painting. Sand-blasting was first discovered in a geological context in 1855 when geologists described wind-eroded features in the Coachella Valley of southern California in a study of aeolian processes.
The term ventifact means "wind-made." It was coined in 1911 by a British geologist when he was performing field work in arid regions of Africa and Asia. The terms describes any wind-modified object and does not apply exclusively to erosion by wind-blown sand.
Ventifacts can be recognized by many features, ranging from wind-cut faces - called facets, - polished or etched surfaces, to features such as pits, flutes, and grooves. They come in many sizes from grains a few millimeters across to huge rocks over 3 m long.
Where can I find ventifacts?
You can find ventifacts where aeolian processes have been occurring, such as in arid regions, glacial plains, or along coastlines.
They are more easily formed given a moderate but steady supply of sand and silt particles for abrasion, strong enough winds to move them, and vegetation that does not impede the wind-blown particles before they could affect the rock surface.
Glacial plains are especially well-suited to produce ventifacts as evidenced by a multitude of them in parts of Antarctica and Iceland.
Since these conditions can also be found on Mars, you should expect a big ventifact population, even though they might not be easily recognized from where we are.
Ventifacts are widespread in the deserts of North America. They have formed on the slopes of desert lakes that are almost always dry except after exceptional rainfall. Much of their basin is covered by a veneer of wind-blown sand.
When windﬂow approaches a hill, airstream compression accelerates it and increases the speed and volume of sediment transport. A back-ﬂow eddy is created on the lee slope.
The actual speed-up increases the volume of sand transport and causes ventifacts to form on dune and hill slopes.
In the picture, there is a strong northwest wind that develops ventifacts over 2/3 of the slope while the weak but also accelerated southeast wind forms ventifacts only near the crest. The intensity of ventifaction - meaning the depth and width of grooves - correlates well to wind velocity up the slope.
Below is a map of North American deserts.
Ventifacts are of many different shapes, including prolate, oblate, pyramidal, triaxial ellipsoidal, or irregular forms. Wind-cut surfaces are either curved or flat (facets), and edges are either angular or rounded. Since multiple facets are not uncommon a hierarchy of terms has been suggested to describe facet arrangements - einkanter, zweikanter, driekanter, etc., meaning one, two, or three corners, etc. In fact, ventifacts can have up to 20 facets.
Why do multiple facets develop?
They can be a result of a variety of circumstances such as multiple wind directions, shifting of the rock to present new surfaces to abrasion, as well as complex patterns of air flow and abrasion by suspended particles.
Ventifact morphology is a useful way to map active wind patterns from currently active ventifacts and paleowinds from fossil ventifacts. The main facet usually faces the prevailing wind and pits are commonplace on these surfaces.
However, the use of a single ventifact to identify wind directions is inaccurate, because ventifacts tend to shift orientation over time. It is necessary to map a large number of ventifacts to determine wind patterns that corroborate the measurements of the active winds.
In order to calculate wind abrasion rates, researchers always need to look at three principal factors:
- wind frequency including strengths and durations,
- particle characteristics such as velocity, flux, etc.,
- susceptibilities to abrasion for a variety of ventifacts.
Pretty pictures of ventifacts from around the worldClick thumbnail to view full-size
Ventifact Beauty Contest
Welcome to the first ever Ventifact Beauty Contest!
Now that you know everything that you never wanted about these fantastic creatures, it's time to get to the main attraction of this hub.
Although beauty contests often incorporate personality, talent, and answers to judges' questions as judged criteria, we decided against bothering with all that and are focusing solely on the physical beauty of our contestants.
So lets get down to voting for the most beautiful, most stunning ventifacts of the world! Here are your contestants:
Select this year's Ventifact Beauty Queen!See results without voting
Thanks for the hub idea, Ardie!
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