lavacicles

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lavacicles

Postby karstcreature » Nov 21, 2006 2:45 pm

Hey all,

I have a question about lava tubes-

I believe the standard explanation for lavacicles is that they formed when the lava was still molten, dripping...etc. etc...

I'm wondering if some drippy-looking formations in lava tubes could actually be calcareous but through mineral leaching/dyeing actually appear to be of the same igneous rock as the cave(tube) itself...this wouldn't explain the differences in their structure and form but then again why do we rarely ever see calcite formations in lava tubes anyway??

thanks
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Re: lavacicles

Postby Squirrel Girl » Nov 21, 2006 3:17 pm

I've seen calcite formations in a lava tube in Arizona. But, indeed they are somewhat rare. I think the reason is that in limestone caves, the bedrock is made of calcium carbonate. That is pretty darn soluble, so there is a lot of calcium available to make the calcite stal, and there's a lot of CO2 around, as well.

In lava tubes, basalt is fairly rich in calcium in the feldspar that is a major component of the rock. But feldspar doesn't dissolve very much. When it weathers, it alters to clay and most of the calcium stays put.

I hope this helps.
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Postby Squirrel Girl » Nov 21, 2006 3:20 pm

Oh, yeah, one more thing. It's certainly possible that there could be basalt-stained formations. But generally (always exceptions), calcareous stal are some of the most recent deposits, so they would be less likely to have a later staining event.

In limestone caves, you could have flooding that covers stal with mud, but that's unlikely to occur in lava tubes.
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Postby karstcreature » Nov 21, 2006 8:31 pm

So staining events usually occur separately from initial deposition?

all those formations I chopped were the same color throughout...

HAHA just kidding...thanks for the response...
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Postby Squirrel Girl » Nov 21, 2006 8:45 pm

karstcreature wrote:So staining events usually occur separately from initial deposition?

all those formations I chopped were the same color throughout...

HAHA just kidding...thanks for the response...
Ya had me there for a sec!

You were the one who initially wrote:
karstcreature wrote:I'm wondering if some drippy-looking formations in lava tubes could actually be calcareous but through mineral leaching/dyeing actually appear to be of the same igneous rock as the cave(tube) itself
I *assumed* when you wrote "dyeing to appear igneous" you meant staining on the outside. That's why I wrote my answer the way I did.

Nevertheless, certainly you can get organic material or iron oxides, etc. that stain the calcite during growth. But I think empiric evidence shows that it just doesn't happen often in lava tubes. If you look at lavasicles closely, they are not quite the same shape as stalactites.
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Postby David_Weaver » Nov 22, 2006 3:41 pm

Karst Creature

My experience with lava tubes is limited to a pre-convention trip to some Mount Adams lava tubes last summer. My understanding of lavacicles is they are extruded into an existing lava tube from a pool of molten lava above the tube. The pool is flowing or under pressure and injects lava into the tube through a crack or weak spot in the ceiling. You can see a picture of a lavacicle below. (It always reminds me of the toothpaste tube after the kids brush their teeth.)

Image

Lava tubes can also contain solution formations, similar to those we see in limestone/marble caves. These formations originate the same as in carbonate caves. Groundwater dissolves the minerals, carries them into the cave, and precipitates the minerals when the water evaporates. The bedrock around lava tubes contains different minerals than the limestone and marble bedrock surrounding carbonate caves. Consequently, the minerals are different and the formations appear different. The minerals tend to be more silicate based than carbonate based. (Think Opal) Aluminum is also a typical component of these minerals.

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Postby Dave Bunnell » Nov 23, 2006 1:09 am

For details on these and other lava tube formations, check out the Virtual Lava Tube section of the Virtual Cave:

http://www.goodearthgraphics.com/virtual_tube/virtube.html

Lavacicles come in two major flavors, the tubular type, which can be straight or vermiform as in David's picture above, and the sharkstooth type, which are more pendant-like.

The tubular type form from gas pushing molten lava out of the matrix of the semi-molten ceiling, whereas the sharkstooth type form from repeated flows of lava that well up and coat projections on the ceiling, building up the stal in thin layers.

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Postby Squirrel Girl » Nov 24, 2006 7:47 am

David_Weaver wrote:Lava tubes can also contain solution formations, similar to those we see in limestone/marble caves. These formations originate the same as in carbonate caves. Groundwater dissolves the minerals, carries them into the cave, and precipitates the minerals when the water evaporates. The bedrock around lava tubes contains different minerals than the limestone and marble bedrock surrounding carbonate caves. Consequently, the minerals are different and the formations appear different. The minerals tend to be more silicate based than carbonate based. (Think Opal) Aluminum is also a typical component of these minerals.

Keep in mind that the bedrock that surrounds limestone caves forms in seawater, not so dissimilar in conditions to where the caves are. Lava, however, originated ten/hundred/more? miles underground at significantly higher temps and pressures. That the lava extruded onto the earth's surface is somewhat irrelevant. It just happened to be the place where the crystallized/vitrified (i.e., cooled and hardened). The minerals that were contained in the melt are very unhappy, thermodynamically speaking, at or near the earth's surface. In generally, all aluminosilcates are (clays being a notable exception). As noted by David, opal can form at surface Ts and Ps, but in reality it isn't extensively formed. I'd have to review my thermodyanmics to remember the whys and wherefores. FYI - there's no aluminium in opal.
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Postby bigalpha » Nov 24, 2006 1:39 pm

Squirrel Girl wrote:

FYI - there's no aluminium in opal.[/quote]

+1

Opal is merely a hydrous chert. That's why if you go to a rock show, they always have opal in water. If opal sits out too long, the water can actually evaporate out of the rock.
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Re: lavacicles

Postby ggpab » Nov 24, 2006 2:34 pm

karstcreature wrote:
why do we rarely ever see calcite formations in lava tubes anyway??

thanks


Hydrogeology is also a big factor. Even in Ca rich lavas, for calcite decorations to form you have to have a hydrological drive:
1/ to get the dissolution in the first place and enough water so that it infiltrates
If you go to the Canary islands for example, there is such limited rainfall (off top of head - << 400 mm/year) that is surprising there are any fresh groundwater resources at all.

2/ suitable flow paths.
You can have extremely high porosity in lava (from all the little gas bubbles) but in general it is very low permeability since the bubbles are like in an Aero bar. They are all closed off from each other It is therefore often very difficult for water to flow freely through these rocks, except in good fractures which may form as vulcanism continues or the whole lava field slumps.

That being said - again thinking of the lava tubes in the Canaries, I was really impressed by the number of lone little apparently calcite splems in the lava tubes. While some were aligned along fractures, not all of them were.

Cheers
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Postby knotty » Feb 5, 2007 11:05 am

What causes the different colors in lava? Some of the caves here in Idaho have as many as 7 different colors(7 different flows). Eache flow has there own color. The color is brightes on the surface or glaze but there is color all through the porus section as well.
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Postby hewhocaves » Feb 5, 2007 2:44 pm

knotty wrote:What causes the different colors in lava? Some of the caves here in Idaho have as many as 7 different colors(7 different flows). Eache flow has there own color. The color is brightes on the surface or glaze but there is color all through the porus section as well.


offhand, i'd have to say that the chemical // mineral composition has to do a lot with it. ah, here we are:

http://vulcan.wr.usgs.gov/Volcanoes/Ida ... _moon.html

Initially these eruptions are very violent and produce a lava known as rhyolite. Huge calderas of up to 30 miles in diameter are formed when these devastating eruptions take place. Later a more fluid lava known as basalt flows onto the surface and covers the rhyolitic flows. Yellowstone National Park, the area where the hot spot is believed to be located at this time, is the place where catastrophic rhyolitic eruptions last occurred 600,000 years ago. Craters of the Moon represents the second stage of the eruptions where fluid basaltic lava covered the landscape as recently as 2,000 years ago.


rhyolite is a extrusive (quickly cooling version of granite - essentially a light color) basalt is darker.

as for why the mineral composition varied - the off-the-cuff reaction is that its near a subduction zone (to the west) and so the magma coming upwards is essentially the melted continental plate which would have quite a vareity of elements associated with it. However, there is probably a more specific / altenate explanation to it involving the Yellowstone hot spot. but regardless, the point is that there was a mix of materials which changed over time forming the different colors.
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Postby bigalpha » Feb 5, 2007 3:53 pm

What kind of colors are associated with the different lava flows?
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Postby BenC » Feb 5, 2007 4:34 pm

knotty wrote:
What causes the different colors in lava? Some of the caves here in Idaho have as many as 7 different colors(7 different flows). Eache flow has there own color. The color is brightes on the surface or glaze but there is color all through the porus section as well.

I think We're getting into Bowens Reaction theory.
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lavatubes pictures

Postby mgala » Feb 5, 2007 4:54 pm

BTW, we've just put some pictures from kazumura and kipuka kanochina on our site:

http://speleo.pl/galeria_flash.php?album=60&lang=en
look at our cave pictures
at http://speleo.pl
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