There's still some geology left for me this semester - this coming Monday I get to start cutting my thin section from the kimberlite I picked up at Green Mountain. Eventually the thin section will be made in to a slide and I'll be doing a petrographic analysis, taking a photo micrograph of it, and writing a paper. Which is fine. Kimberlite is super cool.
But the field component is definitely done. This last trip was another jaunt down to New Mexico, this time over by Los Alamos. We spent most of our time between the Bandelier National Monument and the Valles Caldera. It's a very cool area. Our reason for being at Bandelier was to look at the Bandelier Tuff, as well as some other volcanic rocks in the area. The tuff was produced by the Valles Caldera blowing out about 1.2 million years ago.
The tuff starts pretty far away from the Caldera, as you might expect from the sort of massive volcanic explosion that would come from a caldera-forming eruption. At the first place where we examined it, I think we were at least 20 km away from the Bandelier National Monument, and the tuff and pumice layers were about 50 feet thick. The layering of the rocks in the area moving toward the caldera are pretty interesting. There are alternating layers of fairly unconsolidated pumice, tuff, ignimbrite. The tuff is basically pumice that has been partially welded back together by heat, and contains some phenocrysts. Sometimes the extremely well-welded ash units look eerily like basalt flows from a distance, which is very cool. By the time we got in to Bandelier National Monument to see the cliff dwellings, the tuff was about 500 feet thick.
The tuff and pumice makes for some pretty bizarre rocks. You normally expect rocks to be heavy, but the pumice feels almost as if it's made of styrofoam. The cliff dwellings were actually cut in to the tuff layer, which is only slightly heavier and more solid than the pumice itself.
We also drove in to the caldera, which is a stunning area. It's basically a massive, rolling plain covered with grass, which is surrounded entirely by a ring of large hills. The plain itself is dotted with smaller hills, which are actually obsidian domes that have formed at one time or another since the caldera collapsed. The biggest of the hills within the caldera is the resurgent dome. I do have some pictures (still need to pull them and the ones from the previous field trip off my camera) but for now, here's a couple nice shots from Wikimedia Commons:
One of the domes in the Caldera
A couple more domes, during the winter
The pictures really can't give you an idea of the scale of the place. You'll just have to go there yourself, some day. Also, if you want a piece of Bandelier Tuff for yourself, you obviously cannot collect in the national park. However, there are several road cuts outside of the national monument where you can pull over and pick up large pieces of pumice and tuff, as well as some where you can find obsidian-like extrusions. It's some very cool stuff.
Not far outside the caldera itself, there's a picnic area where you can catch a trail up on to Battleship rock, which is made of ash deposits. The trail up to the rock is pretty tough. It gave my knees hell going back down particularly. But you do get a fantastic view from the top.
Also at that picnic area, you can catch a trail to the McCauley Warm Springs. It's about a five mile round trip, and if you have knee problems like I do, I'd really recommend some walking sticks for this one. They make progress faster and much less painful. It's a tough enough hike that there weren't too many people in and out of the area, even on a beautiful and warm Sunday. The Springs themselves aren't what you would expect. They're meteoric hot springs, which basically means that rain water gets down in to the magmatically active zone via fissures and then is expelled to the surface. This means that they're not too mineralogically strange - and don't smell like sulfur, for example. (There are other sulfur-rich springs in the area which are hydrothermal in nature.) They're also not as hot as you'd think - they're more "warm" springs than hot springs. The temperature was like being in a very pleasant swimming pool, which is more remarkable than it seemed at the time considering that temperatures were getting down below 40 degrees F at night in the area. There's a lot of algae growing in them, but the water's warm enough that they certainly don't smell like an active breeding ground for cyanobacteria. So it was a nice little excursion and a nice soak. There are also a lot of little fish that live in the springs. My feet got gently nibbled at a lot, which felt very ticklish and was quite amusing. I recommend having a beer (if you're old enough) while relaxing in the springs.
Overall, an amazing experience courtesy of Giant Geological Features That Could Kill Us All.
Wednesday, September 30, 2009
Wednesday, September 23, 2009
ESLI
This week, I come bearing a link: The Earth Science Literacy Initiative
I hadn't actually heard of this before. My mom got a copy of their flier when she was on a tour, and then handed it off to me. It is one densely packed little folded piece of paper. One thing I did notice right away, though - Dr. Budd's involved! He's in the Geology department at CU, and was my teacher for general geology and for intro to field.
Really, I feel like I'm randomly running in to Dr. Budd a lot these days. I also randomly met him at the AAPG conference that was in Denver over the summer and we chatted a little, mostly just saying hello. I'm glad to see that he's so out there and involved in promoting public education, though. I already respected Dr. Budd and thought he was an excellent teacher, but this bumps him up even further in my esteem.
It looks like the PDF on the site is basically a copy of the flier, so I definitely recommend taking a look at it. The PDF sure has it all... not just lot of information focused on Earth sciences, but a blurb right up front about the scientific method. Best quote:
Well said indeed.
The other thing that really struck me about how they're laying this out is that they break the basis for the study of geology (and other earth sciences) down in to nine simple "Big Ideas." Now, each of these ideas have a bunch of sub-points that elaborate and illustrate, but the big ideas in and of themselves are, I think, a very sound framework for the things everyone should know and understand about our field of science. Things that I would, given the opportunity, write on Ray Comfort or Ken Ham's arms in permanent ink. For all the good that would do. But anyway, the idea seems to be to promote the big ideas and the supporting concepts to give a much clearer framework for what earth science education standards should be, particularly for K-12 in both schools and text books.
The site even notes that we should be worrying about how scientifically illiterate the population is. There's been a lot said about the battles in biology in regards to trying desperately to keep religion out of the science class room. And those are big, important battles. But I think it's sometimes easy to forget that earth sciences are in the cross-hairs of the dogmatic opponents of science, considering one of our most important concepts is that our dynamic planet is quite old. I'm very glad to see steps being taken to promote earth science before it gets in to the dire straits biology is in. (Though we may already be there, and we're just not seeing it reported. It's a worrying thought.)
Getting a unified document about earth science literacy is a very good first step. I suppose that promoting it is the next step. And then...?
I hadn't actually heard of this before. My mom got a copy of their flier when she was on a tour, and then handed it off to me. It is one densely packed little folded piece of paper. One thing I did notice right away, though - Dr. Budd's involved! He's in the Geology department at CU, and was my teacher for general geology and for intro to field.
Really, I feel like I'm randomly running in to Dr. Budd a lot these days. I also randomly met him at the AAPG conference that was in Denver over the summer and we chatted a little, mostly just saying hello. I'm glad to see that he's so out there and involved in promoting public education, though. I already respected Dr. Budd and thought he was an excellent teacher, but this bumps him up even further in my esteem.
It looks like the PDF on the site is basically a copy of the flier, so I definitely recommend taking a look at it. The PDF sure has it all... not just lot of information focused on Earth sciences, but a blurb right up front about the scientific method. Best quote:
The power of the scientific process is seen in its relentless march toward better explanations of how the laws of the universe operate.
Well said indeed.
The other thing that really struck me about how they're laying this out is that they break the basis for the study of geology (and other earth sciences) down in to nine simple "Big Ideas." Now, each of these ideas have a bunch of sub-points that elaborate and illustrate, but the big ideas in and of themselves are, I think, a very sound framework for the things everyone should know and understand about our field of science. Things that I would, given the opportunity, write on Ray Comfort or Ken Ham's arms in permanent ink. For all the good that would do. But anyway, the idea seems to be to promote the big ideas and the supporting concepts to give a much clearer framework for what earth science education standards should be, particularly for K-12 in both schools and text books.
Big Idea 1: Earth scientists use repeatable observations and testable ideas to understand and explain our planet.
Big Idea 2: The Earth is 4.6 billion years old.
Big Idea 3: Earth is a complex system of interacting rock, water, air, and life.
Big Idea 4: Earth is continuously changing.
Big Idea 5: Earth is the water planet.
Big Idea 6: Life evolves on a dynamic Earth and continuously modifies Earth.
Big Idea 7: Humans depend on Earth for resources.
Big Idea 8: Natural hazards pose risks to humans.
Big Idea 9: Humans significantly alter the Earth.
The site even notes that we should be worrying about how scientifically illiterate the population is. There's been a lot said about the battles in biology in regards to trying desperately to keep religion out of the science class room. And those are big, important battles. But I think it's sometimes easy to forget that earth sciences are in the cross-hairs of the dogmatic opponents of science, considering one of our most important concepts is that our dynamic planet is quite old. I'm very glad to see steps being taken to promote earth science before it gets in to the dire straits biology is in. (Though we may already be there, and we're just not seeing it reported. It's a worrying thought.)
Getting a unified document about earth science literacy is a very good first step. I suppose that promoting it is the next step. And then...?
Tuesday, September 15, 2009
Backyard Geology: Capulin Volcano
Four days in a row of hiking (since even though we came back on Sunday, we did another hike on Monday) have just about destroyed me. I'm limping around like an old lady today. Lots of very, very cool stuff was seen on the field trip. Yes, I took many pictures. No, I haven't uploaded them yet. I'm working on it, though. And there's lots of very amazing geology stuff to write about. I may never catch up, considering that school has apparently slowed me to a one-post-a-week crawl.
For the three day trip, we spent most of our time in the Raton Volcanic Field down in New Mexico, though on Sunday we did head back in to Colorado for the Spanish Peaks. (Which are a whole other cool thing to write about.) The Raton Volcanic Field (RVF from here on out) was and still is caused by the rifting near the Rio Grande River, where there's hot, plastic mantle (asthenosphere) welling up to within 30 kilometers of the surface, which on a continent is a Very Big Deal. Normally, the asthenosphere minds its own business and stays at a depth of 100-200 km. At the Rio Grande Rift, it's poking its steaming head above the Moho, which means there's a lot of very hot rock where it really has no business being, and that makes for a lot of volcanic activity.
The RVF actually isn't in the Rift Valley itself; it stands on the margins. The area is very topographically interesting; generally you have a lot of rolling plains there, but there are also stair-step like mesas and very prominent hills poking up from the landscape. Each of these prominent, conical hills is an extinct volcano. The mesas are caused by basalt lava flows that came from the volcano. So the basic process of the RVF is that a volcano pops up in a valley (where the crust has thinned a bit due to the rifting to the west), puts out a lava flow or two, there's more rifting and a new valley created, and then the process repeats.
Now, most of the volcanoes in the RVF (with such prominent exceptions as Sierra Grande, which is a shield volcano) are cinder cones. Many of them are now covered with vegetation of some type, but I did see some prominent and presumably younger (since they still had their very distinctive shape) cinder cones that were completely naked. Naked cinder cones tend to erode down very quickly, since they're basically made of layers of ash and other pyroclastic debris that aren't well consolidated. As far as volcanoes go, cinder cones are fairly well understood. There are a lot of active cinder cones today, and one in Mexico even started its formation a little more than 60 years ago: Paricutin.
Capulin Volcano is one of the RVF cinder cones. It's relatively young, between 58 and 62 thousand years old, and it is rather well vegetated. The vegetation layer has helped preserve the volcano's shape, so it's very distinct and pretty. The volcano itself is a national monument, and there are several extremely nice trails. One goes around the volcano's rim, another goes down in to it, so you can look at the blocked-off vent that spewed all the ash and debris, and a third goes out on to the lava flow at the volcano's feet. As is common, Capulin did put out a basaltic lava flow, but not from its central vent as we've come to expect from the normal images of composite and shield volcanoes. Since cinder cones are structurally weak due to their composition, most develop a vent at their base and that's where the lava comes out.
Other than the simple OH MY GOSH COOL of begin able to walk on and down in to a volcano, there's some very nifty geological stuff to be seen. At several of the road cuts on the volcano, you can see the layers of ash that make up the cone. They come in a lot of different colors and are fairly distinct. You can also see volcanic "bombs" all over the place. These are chunks of magma that got spewed into the air and solidified in distinct chunks. As you look over the lava flow at Capulin's feet, there are several visible tumuli, which are dome-like features where hot lava welled up through the cooler, thin crust on the lava flow surface. Also, in the fields that cover most of the lava flow now, you can still see the ghost of pressure ridges, which are ripples preserved in the flow. These are also caused by the movement of hot lava under the cooler surface, causing deformation.
All this cool volcano stuff, and it's only a four hour drive or so from Denver! I do have some pictures of Capulin that will hopefully be posted soon, but they're not going to do the volcano much justice. Soon after we left, it started raining and then rained extremely hard for the next eight hours. So as you can imagine, while we were at Capulin it was extremely overcast. (And also shockingly cold.)
For the three day trip, we spent most of our time in the Raton Volcanic Field down in New Mexico, though on Sunday we did head back in to Colorado for the Spanish Peaks. (Which are a whole other cool thing to write about.) The Raton Volcanic Field (RVF from here on out) was and still is caused by the rifting near the Rio Grande River, where there's hot, plastic mantle (asthenosphere) welling up to within 30 kilometers of the surface, which on a continent is a Very Big Deal. Normally, the asthenosphere minds its own business and stays at a depth of 100-200 km. At the Rio Grande Rift, it's poking its steaming head above the Moho, which means there's a lot of very hot rock where it really has no business being, and that makes for a lot of volcanic activity.
The RVF actually isn't in the Rift Valley itself; it stands on the margins. The area is very topographically interesting; generally you have a lot of rolling plains there, but there are also stair-step like mesas and very prominent hills poking up from the landscape. Each of these prominent, conical hills is an extinct volcano. The mesas are caused by basalt lava flows that came from the volcano. So the basic process of the RVF is that a volcano pops up in a valley (where the crust has thinned a bit due to the rifting to the west), puts out a lava flow or two, there's more rifting and a new valley created, and then the process repeats.
Now, most of the volcanoes in the RVF (with such prominent exceptions as Sierra Grande, which is a shield volcano) are cinder cones. Many of them are now covered with vegetation of some type, but I did see some prominent and presumably younger (since they still had their very distinctive shape) cinder cones that were completely naked. Naked cinder cones tend to erode down very quickly, since they're basically made of layers of ash and other pyroclastic debris that aren't well consolidated. As far as volcanoes go, cinder cones are fairly well understood. There are a lot of active cinder cones today, and one in Mexico even started its formation a little more than 60 years ago: Paricutin.
Capulin Volcano is one of the RVF cinder cones. It's relatively young, between 58 and 62 thousand years old, and it is rather well vegetated. The vegetation layer has helped preserve the volcano's shape, so it's very distinct and pretty. The volcano itself is a national monument, and there are several extremely nice trails. One goes around the volcano's rim, another goes down in to it, so you can look at the blocked-off vent that spewed all the ash and debris, and a third goes out on to the lava flow at the volcano's feet. As is common, Capulin did put out a basaltic lava flow, but not from its central vent as we've come to expect from the normal images of composite and shield volcanoes. Since cinder cones are structurally weak due to their composition, most develop a vent at their base and that's where the lava comes out.
Other than the simple OH MY GOSH COOL of begin able to walk on and down in to a volcano, there's some very nifty geological stuff to be seen. At several of the road cuts on the volcano, you can see the layers of ash that make up the cone. They come in a lot of different colors and are fairly distinct. You can also see volcanic "bombs" all over the place. These are chunks of magma that got spewed into the air and solidified in distinct chunks. As you look over the lava flow at Capulin's feet, there are several visible tumuli, which are dome-like features where hot lava welled up through the cooler, thin crust on the lava flow surface. Also, in the fields that cover most of the lava flow now, you can still see the ghost of pressure ridges, which are ripples preserved in the flow. These are also caused by the movement of hot lava under the cooler surface, causing deformation.
All this cool volcano stuff, and it's only a four hour drive or so from Denver! I do have some pictures of Capulin that will hopefully be posted soon, but they're not going to do the volcano much justice. Soon after we left, it started raining and then rained extremely hard for the next eight hours. So as you can imagine, while we were at Capulin it was extremely overcast. (And also shockingly cold.)
Tuesday, September 08, 2009
Sinkholes and Giant Rats
Okay, they're not actually related. Just a couple of nifty links for today - I got something of a late start this morning because the cat that I'm cat-sitting had a pee accident. The result was a lot of frantic squirting of Nature's Miracle and me getting out of the house close to an hour late.
I do have another backyard geology post to write up, possibly two since I've now been to both Sugar Loaf Mountain (the Colorado iteration of it at least) and several outcrops of the Iron Dike. I'm hoping to get that done tomorrow. Also, this weekend is the first of our two long field trips for my class this semester. We'll be down in New Mexico to look at the volcanic fields that sit on the eastern side of the Rio Grande Rift. (Yes indeed, the United States actually IS slowly pulling apart at Texas, and it has nothing to do with politics.) I'm making it my business to take my camera with plenty of batteries, so barring a complete senior moment, there will be pictures!
Cool link #1: Giant rat found in 'lost volcano'
A BBC camera crew finds a new species of rat in a crater left by an extinct volcano in Papua New Guinea. I hope that I get to see the BBC special at some point, since the area looks very interesting. The crater itself is about 4 kilometers wide and 1 kilometer deep. This sounds pretty big at first blush, but it's really not. The crater was formed by the Mount Bosavi cone collapsing at some point in its history, so the crater is much bigger than it would have been during the volcano's active life. To also give you some perspective, a really big volcanic crater - a caldera - would be something like the Yellowstone Caldera, which is 72 kilometers across at its widest.
Cool Link #2: Florida Sinkhole Database
We don't get much in the way of sinkholes in Colorado, since we don't have the immense quantities of near surface limestone that Florida and a lot of areas in the southeastern United States have. I find Karst topography, which is what you get when limestone erodes below the surface and eventually causes collapses, very interesting because it's something that I just don't get to see very often.
I do have another backyard geology post to write up, possibly two since I've now been to both Sugar Loaf Mountain (the Colorado iteration of it at least) and several outcrops of the Iron Dike. I'm hoping to get that done tomorrow. Also, this weekend is the first of our two long field trips for my class this semester. We'll be down in New Mexico to look at the volcanic fields that sit on the eastern side of the Rio Grande Rift. (Yes indeed, the United States actually IS slowly pulling apart at Texas, and it has nothing to do with politics.) I'm making it my business to take my camera with plenty of batteries, so barring a complete senior moment, there will be pictures!
Cool link #1: Giant rat found in 'lost volcano'
A BBC camera crew finds a new species of rat in a crater left by an extinct volcano in Papua New Guinea. I hope that I get to see the BBC special at some point, since the area looks very interesting. The crater itself is about 4 kilometers wide and 1 kilometer deep. This sounds pretty big at first blush, but it's really not. The crater was formed by the Mount Bosavi cone collapsing at some point in its history, so the crater is much bigger than it would have been during the volcano's active life. To also give you some perspective, a really big volcanic crater - a caldera - would be something like the Yellowstone Caldera, which is 72 kilometers across at its widest.
Cool Link #2: Florida Sinkhole Database
We don't get much in the way of sinkholes in Colorado, since we don't have the immense quantities of near surface limestone that Florida and a lot of areas in the southeastern United States have. I find Karst topography, which is what you get when limestone erodes below the surface and eventually causes collapses, very interesting because it's something that I just don't get to see very often.
Tuesday, September 01, 2009
Backyard Geology: The Green Mountain Kimberlite
Unfortunately, I can't provide very good directions to this one, and there's a good reason for it. We drove up to Green Mountain (near Boulder, Colorado), got on one of the trails, and then at a random time just sort of bombed off into the underbrush. It involved going down and back up an extremely steep stream valley where there wasn't even the hint of a track. Steep, like I'm clinging to trees to keep myself from tumbling down the slope steep. It was a very, very, very rough hike for someone with bad knees and an often embarrassing lack of balance. It's only about a mile and a half, but it feels much, much longer.
About the best I can do right now is give you the lat/lon of the outcrop: 39º59.431'N, 105º18.09'W. These coordinates should have about a 20 foot accuracy if you believe the claims of the GPS unit's manufacturers.
That said, the hike is very, very worth it. Big important note, though: the kimberlite is in park land. I honestly have no idea what trouble if any there could have been for us going off trail the way we did, but I know for certain that you're not supposed to bring in a rock hammer and whack samples off the outcrop.
The kimberlite itself is very interesting. It intrudes through the Boulder Creek granodiorite, which is a holocrystalline intrusive rock with large crystals of quartz, feldspar, and mafic minerals. If you run across Boulder Creek outcrops, they have a distinctive "salt and pepper" appearance. In comparison, the kimberlite is a porphyritic extrusive rock where the ground mass is extremely dark. The samples we found contained large garnets, ilminites, and olivines. The weathered surface of the kimberlite is gray rather than black, with the chemically altered phenocrysts much more obvious by color difference.
The outcrop is mid to upper slope and stands out fairly well from the landscape. There are no trees growing in it. The outcrop itself is about 100 feet in diameter, though on the down slope it elongates into a teardrop-like shape due to the erosion of the slope.
So, a tough hike, but very cool rocks.
Kimberlite is actually one of my favorite igneous rocks, mostly because it's very cool to look at in thin section. Much of the fine-grained ground mass in kimberlite isn't actually silicate minerals - it's calcite. This makes it incredibly colorful when looked at with crossed polars.
The story behind kimberlites is also very cool. They are effectively volcanic dikes, but rather unusual ones. Kimberlitic magma is produced when there's a critical mass of volatiles in an area of the mantle, normally carbon dioxide and water. (The large amount of carbon dioxide present is the reason kimberlites contain so much calcite.) The volatiles lower the melting point of the surrounding mantle material, and with the sudden pressure on a body of volatile-filled magma, the results are explosive. The magma exits the mantle upward and comes exploding out of the crust, in some cases at the speed of sound. This incredibly explosive, violent eruption of magma under high pressure is what gives kimberlites their characteristic carrot or funnel-like shape.
Also, since the eruption of a kimberlite is so violent, they often carry significant chunks of everything they went through to get to the surface. This includes pieces of mantle peridotite - most of what we know about the mantle composition came from samples brought up in kimberlites. In certain areas, this also means that the kimberlite brings up pieces of old continental crust - most importantly, pieces of the remaining cratons from the Archean. And these craton bits are where diamonds come from. Kimberlites can be small (like the one on Green Mountain) or enormous, like the ones that are mined for diamonds in Africa.
And the best part? Technically speaking, we could get another one erupting out of the ground at any time. There's no way of knowing. There's just something cool about that thought, though I wouldn't want to be standing on top of one when it made its appearance.
About the best I can do right now is give you the lat/lon of the outcrop: 39º59.431'N, 105º18.09'W. These coordinates should have about a 20 foot accuracy if you believe the claims of the GPS unit's manufacturers.
That said, the hike is very, very worth it. Big important note, though: the kimberlite is in park land. I honestly have no idea what trouble if any there could have been for us going off trail the way we did, but I know for certain that you're not supposed to bring in a rock hammer and whack samples off the outcrop.
The kimberlite itself is very interesting. It intrudes through the Boulder Creek granodiorite, which is a holocrystalline intrusive rock with large crystals of quartz, feldspar, and mafic minerals. If you run across Boulder Creek outcrops, they have a distinctive "salt and pepper" appearance. In comparison, the kimberlite is a porphyritic extrusive rock where the ground mass is extremely dark. The samples we found contained large garnets, ilminites, and olivines. The weathered surface of the kimberlite is gray rather than black, with the chemically altered phenocrysts much more obvious by color difference.
The outcrop is mid to upper slope and stands out fairly well from the landscape. There are no trees growing in it. The outcrop itself is about 100 feet in diameter, though on the down slope it elongates into a teardrop-like shape due to the erosion of the slope.
So, a tough hike, but very cool rocks.
Kimberlite is actually one of my favorite igneous rocks, mostly because it's very cool to look at in thin section. Much of the fine-grained ground mass in kimberlite isn't actually silicate minerals - it's calcite. This makes it incredibly colorful when looked at with crossed polars.
The story behind kimberlites is also very cool. They are effectively volcanic dikes, but rather unusual ones. Kimberlitic magma is produced when there's a critical mass of volatiles in an area of the mantle, normally carbon dioxide and water. (The large amount of carbon dioxide present is the reason kimberlites contain so much calcite.) The volatiles lower the melting point of the surrounding mantle material, and with the sudden pressure on a body of volatile-filled magma, the results are explosive. The magma exits the mantle upward and comes exploding out of the crust, in some cases at the speed of sound. This incredibly explosive, violent eruption of magma under high pressure is what gives kimberlites their characteristic carrot or funnel-like shape.
Also, since the eruption of a kimberlite is so violent, they often carry significant chunks of everything they went through to get to the surface. This includes pieces of mantle peridotite - most of what we know about the mantle composition came from samples brought up in kimberlites. In certain areas, this also means that the kimberlite brings up pieces of old continental crust - most importantly, pieces of the remaining cratons from the Archean. And these craton bits are where diamonds come from. Kimberlites can be small (like the one on Green Mountain) or enormous, like the ones that are mined for diamonds in Africa.
And the best part? Technically speaking, we could get another one erupting out of the ground at any time. There's no way of knowing. There's just something cool about that thought, though I wouldn't want to be standing on top of one when it made its appearance.
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