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Outdoor (out of cave) flowstone.

PostPosted: Apr 6, 2007 7:01 pm
by GypsumWolf
When me and some people were looking for a cave we found
two (disappearing and reappearing) streams on the mountain
with flowstone. Here are two images:



PostPosted: Apr 6, 2007 7:47 pm
by mabercrombie
I think its called travertine when it is outside. I know where that stream is and its pretty amazing.

PostPosted: Apr 7, 2007 10:11 am
by graveleye
is it underneath an overhang or right out in the open? That's interesting!

PostPosted: Apr 7, 2007 10:32 am
by Teresa
Google tufa. This stuff is moderately common in some regions, especially at waterfalls, cliff seeps, road cuts (drops where underground water was intersected by blasting) or anywhere calcite rich water undergoes offgassing.

It usually is not as fine grained as cave travertine. Another place where this stuff is rampant is Mammoth Hot Springs in Yellowstone-- in other parts of the park, the rock accumulations are sinter or geyserite (cooled silica) but Mammoth Hot Springs is calcium carbonate.

Virginia has some thermal/non-thermal tufa, where hot and cold spring waters mix. It's also found on rocks below calcareous fens. Tufa growth is often accelerated by algae changing the water gas composition.

If you want to see tufa on steroids, go to Turner Falls near Davis Oklahoma. There is a 79 ft high waterfall draped with the stuff.

Once you become sensitized to this stuff,you will find it anywhere carbonate rocks and water are found.

PostPosted: Apr 7, 2007 11:14 am
by Caverdale
Google "Havasu Falls", located on an Indian reservation in the Grand Canyon, and take a gander at the cascades of rimstone dams downstream.

PostPosted: Apr 7, 2007 3:28 pm
by GypsumWolf
graveleye wrote:is it underneath an overhang or right out in the open? That's interesting!

It is right out in the open. No cliff, no overhang, no nothing like that.

PostPosted: Apr 7, 2007 4:11 pm
by Teresa
So...but Wildwolf showed us the mechanism in his photos-- the offgassing in the little waterfalls.

It doesn't take much of a drop to be a waterfall if you are a dissolved CO2 molecule.

Yippie!!! Fizz!!!

PostPosted: Apr 7, 2007 4:40 pm
by Dane
This is also widespread at the waterfalls at the end of Pocket Trail down at Crockford Pigeon Mtn WMA.
(at the end of the "butterfly boardwalk")
There is formations on the wall of the waterfall, and butterscotch flowstone beneath the where the waterfall lands and flows.

PostPosted: Apr 7, 2007 4:59 pm
by GypsumWolf
Teresa wrote:So...but Wildwolf showed us the mechanism in his photos-- the offgassing in the little waterfalls.

It doesn't take much of a drop to be a waterfall if you are a dissolved CO2 molecule.

Yippie!!! Fizz!!!

It does not have to be a waterfall because there is more of this up beyond this little falls.

My idea on this is that rain water goes through the soil (yes... just like how things are formed in a cave) then gets into the underground stream and then comes back out of the ground and deposits the minerals on the surface. (This stream comes from under the ground a little ways up the stream bed.)

PostPosted: Apr 7, 2007 5:00 pm
by Evan G
Teresa wrote:Google tufa

[center] That's a lot of tufa!:shock:[/center]

I thought the stuff was called travertine? What's the difference?

Mmm, I see:

Would someone turn on their light, because I'm blind over here!

PostPosted: Apr 7, 2007 8:56 pm
by Teresa
You are spot on. All it takes for the calcite to come out of solution is the normal rough and tumble of water running downhill, though the steeper the drop, the more rock gets bounced out of solution faster. Algae pulling CO2 out of the water can make calcite deposit faster. We're talking FAST. I've seen living moss being coated by tufa--weeks to months, not years to centuries of a stalactite dripping.

Wikipedia isn't quite right when it tries to make it sound like tufa forms primarily in lakes, and travertine only in streams. It's more a quality of the stone--just like in a cave you can have very hard, compact and finely crystalline flowstone, (travertine) and you can have punky flowstone incorporating mud, airbubbles, sticks, and so forth. It literally looks very close to those 'punk' sticks which come with 4th of July fireworks (though harder, of course.)
Tufa is more like the punky flowstone, or the calcite that deposits in bathtubs, sinks, and hot water heaters in hard water regions. There are also regional names, like marl, calcareous limestone, and a few more.

A couple of good references (if you are really into this) and by NSS people to boot are:

Ford, T.D., and Pedley, H.M. 1996. A review of tufa and travertine deposits of the world. Elsevier, Earth-Science Reviews, Vol. 41. p. 117-175.

Herman, J. S., and D. A. Hubbard, eds. Travertine-Marl: Stream Deposits in Virginia. 1990. Va. Div. Mineral Resources Pub 101, Dept. of Mines, Minerals and Energy, Div. of Mineral Resources, Charlottesville, Va. 184 p.

I prefer to use travertine for hard, pretty, highly crystalline banded water-laid calcium carbonate like show cave trinkets are made out of, tufa for the gray-green stuff like Wildwolf's photo, (and which I studied for about 5 years) and marl for what forms around my faucets.

Hope this helps.

PostPosted: Apr 7, 2007 9:15 pm
by Evan G
Very interesting Teresa, thank you that did help! Marl is a new one to me. Very interesting! Thanks a google!

PostPosted: Apr 7, 2007 9:50 pm
by Dane
Well Teresa, based on your description, I would characterize what I "tried" to describe down at Pigeon Mtn (I REALLY need to start using the preview!!!) as -
Tufa on the wall behind the waterfall (it looked like drapery you would see in a cave, but it looked "old" and gray, and not quite as smooth), and travertine for the flowstone where the waterfall lands and flows - it looked just like butterscotch you would see inside the cave.

PostPosted: Apr 8, 2007 3:28 am
by Bruce Rogers

One may usefully define marl as a clay-rich, freshwater, bedded limestone usually deposited in lakes and thus is not really tufa (or travertine). Marl deposits in the more arid Western States are often up to 30% clay (and often times silt as well).

Marls in the Death Valley area are interbedded with Ice Age fresh water lake bed sediments largely made of siltstone. The siltstone is removed by the cyclical formation and destruction of soil pipe caves. The marl beds provides a temporary ground armor for the pipes to form under so the entire hillside doesn't simply erode away.

Also realize that surface tufa or travetine may not be calcite. Dolomite (calcium-magnesium double carbonate), siderite (iron carbonate), aragonite, and other minerals such as goethite (iron oxide commonly called "rust"), sulfate minerals such as mirabilite and thenardite (both sodium sulfate minerals) and several different silica minerals as Teresa posted, also commonly form in surface deposits.

Bruce Rogers, Earth scientist on a good day.

PostPosted: Apr 8, 2007 11:37 am
by Teresa
I'm not doubting Bruce's explanation, and I'm glad he chimed in. Non-geologists might find this amazing, but you know--one could study calcium carbonate chemistry, crystallization and dissolution for an entire lifetime, and still not cover half of the information out there!

As to the whole marl question: I found in reading about freshwater surface calcium carbonate that each region seems to use that word to define different sorts of rock and deposition methods-- the same with tufa, which often has quite a bit of mud or clay, and some iron mixed in, too. The Glossary of Geology from the AGI isn't much help, either, as it includes Bruce's definition, and others as well. And don't even get us started on caliche!

One of the interesting things on my study site was, even though the parent rock was secondary (reimmersion-formed) dolomite after limestone, magnesium remained constant in the water along the stream, as it lost calcium carbonate.

When geologists explain about calcite and dolomite to laypeople they usually leave out 98% of the story--long ago I figured out that these separate rocks of calcite, dolomite, sandstone and shale are all just one long, intertwined, intergraded *thing* called sedimentary rock, and sometimes the breakpoints are fairly arbitrary.

I did not do a crystal study to determine if the crusts were aragonite or calcite, as I was studying the rate of deposition, but made the assumption since most of the active cave deposits around here are known to be calcite (not aragonite) such would be the case in the surface deposits as well. I did the whole computer speciation thing, but since aragonite and calcite are just crystal forms, not different chemistry, it didn't tell me anything.