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I was at a cave tour with family, and there were stalagmites and stalactites in an early room. The guide said "These took thousands of years to form." Then lat

I was at a cave tour with family, and there were stalagmites and stalactites in an early room. The guide said "These took thousands of years to form." Then later in the tour, there was a super thick layer of rock formations coating (layered mind you) a large section, it looked nearly identical to the stalagmites and stalacties from before, and the guide said "This all formed in a few months from a rush of hot mineral rich water from a broken geyser." The guide seemed to realize how these two notions completed conflicted in the story telling, got all flummoxed, tried to justify the difference in time claims (no one even questioned the guide) and then awkwardly stopped talking and continued the tour. I think there is a reasonable possibility we may be wrong about the timing of at least some rock formations...

nkrisc 9y ago
> it looked nearly identical to the stalagmites and stalacties From casual observation, perhaps. But how about upon close scrutiny?
- RobertRoberts 9y ago
  Who knows, I got the impression from the guide it was exactly the same kind of rock. It was even named by the guide, but this is from memory, and the guide could have been wrong.
jofer 9y ago
The key in that case would be composition. Gyeser deposits are typically silica, and even when they're carbonate, they have a very distinct composition. Also, I doubt what you saw was related to a geyser. It's not impossible, but I can't think of anywhere with volcanic activity and large caves formed in carbonates. More likely, you were in the Carlsbad area, in which case you have some massive gypsum formations that are related to acidic waters formed by bacteria decomposing hydrocarbons. They form relatively rapidly (and the acidic waters formed the huge caverns). However, they're a completely different chemical composition than the stalactites just beside them (Gymsum vs calcite -- basically, gypsum has sulfur, which isn't in the rock around it, while calcite is what the "native" rock is made of).
- RobertRoberts 9y ago
  Sure, "broken geyser" is what I had in memory, you are probably right about it being just "volcanic activity". :P It was in the black hills, SD. I am not sure of the rock formation material, but I really go the impression it was the exact same kind of rock, which is why it seemed so contradictory. Maybe it was the guides first few days on the job and they were incorrect? The cave was already formed, and the water coming into the cave caused all the formations. Could the waters have been of a different chemical formation? Seems like a reasonable explanation.
- RobertRoberts 9y ago
  Sorry for the second reply, but just for the technically curious, I found photos: The government site says these stones are calcite, flowstone, round bubbly rocks. (formed in a same/similar manner as stalagmites?) Almost all the rocks in this cave are calcite. (I looked through a number of them on this site) [0] This appears to be the thick layer of rock that I was told formed rather quickly. [1] This is a clear picture, and it looks like large crystal growth? Which would explain the difference from slow stalagmite/stalactite growth? [3] A detailed description, I honestly don't get all the chemistry/geology enough, but I have to trust they are being consistent. :P [4] [0] https://www.usgs.gov/media/images/flowstone-formations-jewel-cave https://www.usgs.gov/media/images/flowstone-formations-jewel... [1] https://www.usgs.gov/media/images/cross-section-calcite-crystal-covering-jewel-cave https://www.usgs.gov/media/images/cross-section-calcite-crys... [3] https://media-cdn.tripadvisor.com/media/photo-s/04/53/d9/bd/jewel-cave-national-monument.jpg https://media-cdn.tripadvisor.com/media/photo-s/04/53/d9/bd/... [4] https://www.nps.gov/jeca/learn/nature/geology-of-jewel-cave.htm https://www.nps.gov/jeca/learn/nature/geology-of-jewel-cave....
  - jofer 9y ago
    Oh, yeah! Jewel Cave is a bit unique in this regard. There's a lot of sparry calcite (large, well-formed crystals) inside the cave. The difference is in the size and shape of the crystals. Large crystals like that can only form when they have lots of room to grow (i.e. when everything is underwater). Those formed while the cave was flooded with water that was over-saturated with calcium carbonate. The rate of growth of a calcite crystal is a lot faster (inches per decade) under those conditions. The speleothems that are forming today grow slower (inches per century) because they're precipitating from a very thin layer/drip of water that only becomes saturated when it starts to evaporate or flow differently. Both processes are very rapid in geologic terms, but there's a significant difference in rate between the two.
deleted 9y ago
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coliveira 9y ago
Not all stalagmites are made of the same material. The guide most probably knew this, and you should have asked to get a correct explanation.
- RobertRoberts 9y ago
  Nah, it was too awkward. The guide wasn't very old, and could have made an error. Of course it could have been different material, but the cave is still there. http://www.blackhillsbadlands.com/business/jewel-cave-national-monument http://www.blackhillsbadlands.com/business/jewel-cave-nation...

nkrisc 9y ago

> it looked nearly identical to the stalagmites and stalacties From casual observation, perhaps. But how about upon close scrutiny?

RobertRoberts 9y ago
Who knows, I got the impression from the guide it was exactly the same kind of rock. It was even named by the guide, but this is from memory, and the guide could have been wrong.

jofer 9y ago

The key in that case would be composition. Gyeser deposits are typically silica, and even when they're carbonate, they have a very distinct composition. Also, I doubt what you saw was related to a geyser. It's not impossible, but I can't think of anywhere with volcanic activity and large caves formed in carbonates. More likely, you were in the Carlsbad area, in which case you have some massive gypsum formations that are related to acidic waters formed by bacteria decomposing hydrocarbons. They form relatively rapidly (and the acidic waters formed the huge caverns). However, they're a completely different chemical composition than the stalactites just beside them (Gymsum vs calcite -- basically, gypsum has sulfur, which isn't in the rock around it, while calcite is what the "native" rock is made of).

RobertRoberts 9y ago
Sure, "broken geyser" is what I had in memory, you are probably right about it being just "volcanic activity". :P It was in the black hills, SD. I am not sure of the rock formation material, but I really go the impression it was the exact same kind of rock, which is why it seemed so contradictory. Maybe it was the guides first few days on the job and they were incorrect? The cave was already formed, and the water coming into the cave caused all the formations. Could the waters have been of a different chemical formation? Seems like a reasonable explanation.
RobertRoberts 9y ago
Sorry for the second reply, but just for the technically curious, I found photos: The government site says these stones are calcite, flowstone, round bubbly rocks. (formed in a same/similar manner as stalagmites?) Almost all the rocks in this cave are calcite. (I looked through a number of them on this site) [0] This appears to be the thick layer of rock that I was told formed rather quickly. [1] This is a clear picture, and it looks like large crystal growth? Which would explain the difference from slow stalagmite/stalactite growth? [3] A detailed description, I honestly don't get all the chemistry/geology enough, but I have to trust they are being consistent. :P [4] [0] https://www.usgs.gov/media/images/flowstone-formations-jewel-cave https://www.usgs.gov/media/images/flowstone-formations-jewel... [1] https://www.usgs.gov/media/images/cross-section-calcite-crystal-covering-jewel-cave https://www.usgs.gov/media/images/cross-section-calcite-crys... [3] https://media-cdn.tripadvisor.com/media/photo-s/04/53/d9/bd/jewel-cave-national-monument.jpg https://media-cdn.tripadvisor.com/media/photo-s/04/53/d9/bd/... [4] https://www.nps.gov/jeca/learn/nature/geology-of-jewel-cave.htm https://www.nps.gov/jeca/learn/nature/geology-of-jewel-cave....
- jofer 9y ago
  Oh, yeah! Jewel Cave is a bit unique in this regard. There's a lot of sparry calcite (large, well-formed crystals) inside the cave. The difference is in the size and shape of the crystals. Large crystals like that can only form when they have lots of room to grow (i.e. when everything is underwater). Those formed while the cave was flooded with water that was over-saturated with calcium carbonate. The rate of growth of a calcite crystal is a lot faster (inches per decade) under those conditions. The speleothems that are forming today grow slower (inches per century) because they're precipitating from a very thin layer/drip of water that only becomes saturated when it starts to evaporate or flow differently. Both processes are very rapid in geologic terms, but there's a significant difference in rate between the two.

deleted 9y ago

[deleted]

coliveira 9y ago

Not all stalagmites are made of the same material. The guide most probably knew this, and you should have asked to get a correct explanation.

RobertRoberts 9y ago
Nah, it was too awkward. The guide wasn't very old, and could have made an error. Of course it could have been different material, but the cave is still there. http://www.blackhillsbadlands.com/business/jewel-cave-national-monument http://www.blackhillsbadlands.com/business/jewel-cave-nation...