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All the Colors of the Lava Rainbow

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Over winter break last year, I went to one of the most spectacular caves I’ve ever been to. It was a short cave (just a couple hours’ trip,) but the features were unlike any I’d ever seen before. Outrageous oxidized flows and shiny, colorful glazes, stalactites, and runners – this little cave sure packed a big punch!

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This is a set of leeves (also called railroad tracks!) near a spot where the cave is sealed by lava, and the tube ends. You can see how, as the lava began to cool on the sides, narrowing the stream. The center lava tongue looks a little smoother, because it would have been flowing more than the outside edges. (Lava on the edges of a channel moves more slowly, because of friction. This is kind of like at a skating rink, where the uncoordinated people cling to the walls.)

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Looking back towards the collapse entrance, you can see the levees as they flow down the tube. There are also some really great benches on the wall: that’s where the passage seems to narrow at the bottom. These benches probably formed as the level of lava in the tube remained stable long enough for the lava on the edges to begin cooling onto the walls. It cools there first because the walls are cooler than the lava itself – relatively speaking. Additionally, you can see some great flow lines on the walls, showing intermediate levels of the flow.

You can see that, on the right side of the picture, the bench is wider. This is what’s called an apron: here, the tube is going around a bend there, slowing the flow, and allowing more lava to be deposited on the inside curve of the tube. On the opposite side of the curving tube there is frequently a cutbank:  on this side, the lava was flowing more quickly, and eroded away the tube wall, creating a recessed portion. (There’s a dude standing in the way of the cutbank here.)

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Looking to the side of our levee, we can see another segment of the tube. This section pinches off, but it did create a really nice “prow.” This forms when two different tubes converge, letting lava build up in the calm spot behind the intersection. This creates an upraised “V” that reminds some people of the prow of a ship. This one is pretty nifty, because we can see how the different levels of lava flow made different levels of the prow.

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After we crossed back through the collapse entrance, into the other side of the tube, things got really cool. I had never seen any colored lava flows in tube – this side passage was incredible!

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In this part of the passage, I count at least four different flows (or four significant changes in the same flow, to be more exact.) Initially, the tube was created by one flow, a dark brown, seen on the roof. Next, another flow of a more purple color moved through, creating a nice curb. After that, a third, orange flow came through the tube, and created those great levees, lining the floor of the passage with orange lava in the process.

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The next flow confuses me a bit, as I thought we were travelling down the tube, and this black lava appears to be travelling up the tube. As far as I know, there are three possible explanations for this: another side tube feeding into the main tube, lava from a different area surging back up the tube, or a large lava bubble over an older flow that was popped (either by natural causes or people stepping on it.)

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I think it’s the first cause (another side tube feeding into the main tube, now covered by rubble.) Just a couple meters further up the passage, we found this… mess. You can see possible evidence of smaller “tube-within-a-tubes”s in the center of the picture (the thing that looks like an “M.”) Just in the lower left corner, you can see some slabs of lava that could have been the tops of those tubes.

It looks as though the lava was pouring into this passage, creating a curb against the right wall, and eventually blocking the passage. The lava slopes down towards us, which makes me think that this is a side passage feeding into the main passage (that does not have this brightly oxidized lava.)

However, that tongue of dark lava is nowhere to be seen. While there is a lot of broken lava at this point, there isn’t enough at that point to indicate that a bubble of the orange lava could have covered the entire floor and then been cracked. If it was a later flow that surged back up this tube, it would have to have flowed from under this orange flow – perhaps through other mini-tubes, or through a “window’ into another now blocked level. That still seems unlikely to me, however.

I honestly was too overwhelmed by all the color to devote enough actual field study to this question. Next trip, I guess!

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After turning around, we got to travel through the same awesome passage. This picture really shows the low viscosity of the orange flow – the wall lining here is very thin. This is reminds me of flood marks in someone’s basement: the water (lava) rises, leaves marks behind, and then flows away.

Once out of the colorful side passage, and back in the main tube, there is no more colored lava of this variety. I also didn’t spend much time examining the interface between the colored lava and the regular lava – this is another question I’d like to investigate when I go back.

When we got back into the main passage, we saw some fantastic linings and runners, as well as something I like to call “ectoplasm lava”:

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Analyze your own lava tube:

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