How is a cave formed?

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Postby George Dasher » May 8, 2006 10:41 am

Here's an Italian cartoon that tells all.

The picks are carbonic acid that are picked up in the soils--from decaying organic matter. And the packs with bricks are the loads of calcium carbonate.

Now to get the cartoon to load...

Image
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Postby hewhocaves » May 8, 2006 11:33 am

George Dasher wrote:My understanding is that the dissolution or calcium precipitation can occur anywhere in the vadose or phreatic zone, not just at or below the water table. Both can occur at the same time, and on different sides of the passage (depending on the CO2 concentrations). In addition, the dissolution and calcium precipitation can move upstream and downstream in the passage depending on the amount of groundwater flowing into the cave.

Some caves are vadose, some caves are phreatic, and some caves are both.

And some have nothing to do with water, but that is a different story.


agreed. but to 'dumb it down' to a five minute explanation, you have to cut corners somewhere, so i just go with the most comon places. like i said, it's becomes a good jumping off point for further discussions on the topic.
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Postby Teresa » May 9, 2006 10:22 am

hewhocaves wrote:agreed. but to 'dumb it down' to a five minute explanation, you have to cut corners somewhere, so i just go with the most comon places.


Here's the sweet and short, "Dumb it Down" explanation:

Rain falling down and going through the dirt picks up bubbles of carbon dioxide turning it into weak soda pop. Just as soda pop rots your teeth, this weakly acid rain rots limestone and dolomite, forming carbonate caves and karst.

In New Mexico and a few other locations, sulfur rich hot springs surged upward, dissolving similar caves in gypsum and limestone.

Sea caves are formed by wave action of the sea hollowing under cliffs.

Tectonic caves result from ground movement or erosion shifting huge rocks and boulders stacked against each other with spaces between.

When lava flows downhill, crusts over, then drains leaving a hollow tube behind you have lava tubes.

That should be about a 5 minute explanation, and covers all the major karst and pseudokarst groups. :banana:
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Postby hewhocaves » May 9, 2006 10:40 am

Teresa wrote:Rain falling down and going through the dirt picks up bubbles of carbon dioxide turning it into weak soda pop. Just as soda pop rots your teeth, this weakly acid rain rots limestone and dolomite, forming carbonate caves and karst.


cool! i like the soda pop reference! a lot! that's going right into the spiel!
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Postby bigalpha » May 9, 2006 11:16 am

That's about what I used when I worked at Dunbar - though I would use a little more detail. The soda reference makes more sense to "joe blow".
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Postby Vader » May 9, 2006 11:43 pm

hewhowcaves,

Thanks. I like the explanation.


Teresa,

That soda pop explanation is priceless.
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Postby graveleye » May 11, 2006 3:50 pm

It might be too much in depth, but the pre-history of how the limestone and sandstones formed, and subsequently uplifted plays a pretty large part of cave "pre-development". Of course, thats opening up a whole new bag of worms:)
Ask someone what time it is and get an explanation on how the clock works :grin:

/now I am going to brush my teeth :tonguecheek:
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Postby hewhocaves » May 11, 2006 4:43 pm

Of course you could just tell them that it's all Doozers.

Image

"Mokey, why do Doozers do what Doozers do?"
"Cause they do."

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Postby Mike Cato » May 12, 2006 3:21 pm

hewhocaves wrote:Of course you could just tell them that it's all Doozers.

Image

"Mokey, why do Doozers do what Doozers do?"
"Cause they do."

john


That's so cute, john. You've made my day. :grin:
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Postby hewhocaves » May 13, 2006 1:18 pm

like some people, i grew up with the fraggles (well, not physically, but they were on the tele.) something about massive, massive cave systems intrigued me even then :)

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Postby Amemeba » May 14, 2006 6:12 pm

Hey Flash, here is a simple recipe for making caves.

ground water + limestone + joint openings + flow + time = cave

Without input and discharge the cave would just be a wee crack.

These are the caves that made America great.
All other types of caves are "exotics". :-)
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Postby hydrology_joe » May 17, 2006 11:04 pm

Ya'll forgot mixing water corrosion...

Without getting too deep in aqueous geochemistry, I'll try to explain it simply. When the rain water percholates through the soil, it becomes slightly acidic... BUT when it encounters carbonates, it becomes saturated with calcite with respect to its pCO2 long before it gets into the bedrock and can create any cave passages. That calcite-saturated water then migrates deeper until it encounters the water table. The groundwater is also saturated with calcite with respect to its pCO2. When those two waters mix, the resulting chemistry is no longer saturated with calcite at the pCO2 and becomes corrosive. See the picture below for a graphical representation... Water A mixes with Water B. The resulting water is no longer saturated at its given pCO2 and is corrosive.

Image
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Postby Teresa » May 17, 2006 11:39 pm

Hydro_joe

We also neglected ceiling collapse, water abrasion of loosened particles and biological acidfication, hydraulic gradient, and evaporation. Plus a whole other bunch of variables...

Of course we did--because the question was: Keep it Simple, Make it Fun! (But tell no lies.)
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Postby hydrology_joe » May 18, 2006 8:07 am

Teresa wrote:Hydro_joe
We also neglected ceiling collapse, water abrasion of loosened particles and biological acidfication, hydraulic gradient, and evaporation. Plus a whole other bunch of variables...
Of course we did--because the question was: Keep it Simple, Make it Fun! (But tell no lies.)


In this case, the simple answer described previously in this thread is actually more applicable to the formation of epikarst, not cave passage formation. That is exactly why I provided the KISS description of mixing water corrosion.
What part of "Shall not be infringed" don't you understand?
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Postby Amemeba » May 18, 2006 10:33 pm

hydrology_joe wrote:
Teresa wrote:Hydro_joe
We also neglected ceiling collapse, water abrasion of loosened particles and biological acidfication, hydraulic gradient, and evaporation. Plus a whole other bunch of variables...
Of course we did--because the question was: Keep it Simple, Make it Fun! (But tell no lies.)


In this case, the simple answer described previously in this thread is actually more applicable to the formation of epikarst, not cave passage formation. That is exactly why I provided the KISS description of mixing water corrosion.


Wrongo, Hydro, "epikarst" is but an aspect of poor hydrologic circulation.

The dissolution effects of renewed acidity by a recharging liberation of CO2 through mixed waters is dwarfed by the effects of a time enhanced hydrologic flow. A directional flow through time is paramount to linear cave developement.

Ain't it the truth?
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