Paineopticon posted:

Did everyone look at you weird when you started chewing it

I Greyhound posted:

Post your favorite geological event you wish you could have seen. Mine would be the collapse of Mt Manzama to firm the Crater Lake caldera.

I Greyhound posted:

Post your favorite geological event you wish you could have seen. Mine would be the collapse of Mt Manzama to firm the Crater Lake caldera.

CommunistPancake posted:

I'm reading T. Rex and the Crater of Doom by Walter Alvarez right now. It's a book about the research that went into proving the impact theory for the extinction of the dinosaurs, and the conflicts between this theory and gradualism. Pro read.

Paineopticon posted:

Did everyone look at you weird when you started chewing it

zedprime posted:

If you're a fast talker you can get geologists to stick anything in their mouth.

Picnic Princess posted:

Yeah, like the prof I was with. Granted, she did it first. And it can't hurt you, it was safe and really neat.

Picnic Princess posted:

There are riverbeds in Calgary with an exposed ash layer from that volcano, it's like an inch thick. It's really neat stuff too, it's silky feeling between your fingers because it's so fine, but if you chew it with your teeth it's super gritty because it's basically powdered glass.

Butt Wizard posted:

The TVZ is currently having a bit of an episode - no localised shaking, it's a bit all over the place. This poo poo happens pretty often and doesn't lead to any volcanic activity - if it happens and the lakeshore swells/the ground starts to lift, then we might have a problem. It's also worth remembering that there was localised tremors at Mt Doom and Ruapehu in the last month and nothing happened. Anyway, three days ago they were on the West side of Ruapehu. The last two days have been mostly on the South Western side of Lake Taupo.

This station seems to be picking up a lot of them. I can't rehost it or hotlink it because it's updated every four minutes - if you refresh the page you'll get the most recent readings. It reads from right to left, bottom to top.

http://images.geonet.org.nz/volcano/drums/latest/katz-seismic-drum.png

Bugsmasher posted:

I'd love to check this out and show my kids, can you give approximate locations to see it in Calgary?

Really liking this geology diversion on this thread, didn't expect it to be so drat fascinating.

NaDy posted:

Also what's insane is the fact that the eruption deposited an ash layer approximately 15 centimetres (6 inches) thick over THE WHOLE of South Asia.

Butt Wizard posted:

The TVZ is currently having a bit of an episode - no localised shaking, it's a bit all over the place. This poo poo happens pretty often and doesn't lead to any volcanic activity - if it happens and the lakeshore swells/the ground starts to lift, then we might have a problem. It's also worth remembering that there was localised tremors at Mt Doom and Ruapehu in the last month and nothing happened. Anyway, three days ago they were on the West side of Ruapehu. The last two days have been mostly on the South Western side of Lake Taupo.

This station seems to be picking up a lot of them. I can't rehost it or hotlink it because it's updated every four minutes - if you refresh the page you'll get the most recent readings. It reads from right to left, bottom to top.

http://images.geonet.org.nz/volcano/drums/latest/katz-seismic-drum.png

Outrail posted:

You seriously have a Mt Doom?

Jose posted:

I watched the Ueli Steck Eiger speed climb video. How do they film all of it? Or any climbing video really

The Light Eternal posted:

I saw him speak in December. He said the videos are staged. They fly him around with a helicopter and drop him in spots to film.

SaNChEzZ posted:

Does the helicopter crash that left 8 dead today count towards the death pool?

captainoblivious posted:

The Mount Saint Elias documentary was ok but man, the soundtrack was embarrassing.

ZombieLenin posted:

Geolgists, riddle me this... How did plate tectonics start

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why doesn't Venus have a magnetic field or plate tectonics

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how much heat does the earth have left?

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Why did Mars cool so fast?

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And what do you think of this plan to save us from doom?

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Lastly are you excited about the bore attempt to reach the mantle?

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PS no mountaineer worth his salt hasn't climbed these mountains.

Venusian Weasel posted:

Yellowstone is good times. Unless it's peak season. Then it's just a traffic jam.

Geology is a chaotic science. You can look at the general principles of how the Earth works, but in the end each geological feature is, by and large, going to be somewhat unique. For example, volcanoes have personalities. Mt. St. Helens erupts every couple decades, while nearby Mt. Hood and Mt. Rainier erupt much less frequently. It's all driving by subtle differences in what's going on in the subsurface that are difficult or even impossible to pick up on.

Yellowstone is a lot like that, too. It's got the classic hallmarks of how we think a hotspot should behave. A quick recap for non-geopeeps: Mantle plumes are thought to originate deep in the mantle, at least 600km below the crust, perhaps as deep as the core/mantle boundary. Hot rock works its way up to the surface, acquiring a shape a lot like a rising blob in a lava lamp - kind of a pancake-shaped head and a narrower tail. When the head hits the surface, we get a massive outpouring of lava, called a volcanic trap. Then as the plate moves, we see a series of eruptions that continue indefinitely as material in the plume's tail builds up under the surface until enough is there to cause an eruption.

As Leperflesh mentioned, Hawaii is a good example of a hotspot. Each volcanic island represents a vent or set of vents that have dumped lava out onto the surface until they've risen above sea level. The plate carries the vents away, the volcanoes slow down, and eventually activity switches to a new center. The volcanic traps that formed when the Hawaiian hotspot are long gone (you can follow the old seamounts right up to a subduction zone), but we see these in other parts of the world. The Tristian de Cuña hotspot in the central Atlantic has the rifted remnants of flood basalts on both Africa and South America. The La Reunion hotspot trails away from the Deccan Traps. So it is with Yellowstone.

Flood basalts in Washington and Oregon, forming the Columbia River Plateau, date to around 16-17 million years ago, and a string of calderas in the map Leperflesh posted trail away from it to Yellowstone. It seems like an open and shut case of a mantle plume and hotspot, right?

Well, in reality things are a little murkier than that. For one, the chemistry is really weird. The layers of the Earth are based partially on chemistry, specifically the amount of silica present. When the Earth formed, it formed from little metal silicate beads called chondrules. Given the intense amount of radioactive and impact energy in the early Solar System, the entire Earth was molten. Silica is relatively light, being a molecule of silicon and two atoms of oxygen, while nickel and iron are much denser. With the molten Earth, the two separated out, nickel and iron sinking to the core, silica floating to the top. The mantle is kind of an in-between state, and after the Earth cooled to the point it was no longer molten, plate tectonics has acted as sort of a distillery to remove silica from the mantle. So, we expect a silica-rich layer in the mantle near the oceanic crust, where partial melting has concentrated it a little more, then less and less silica as we go deeper in the mantle. There are a few irregularities stemming from mantle convection, but we don't need to really worry about them.

So anyway, chemistry: most hotspot eruptions, land or sea, erupt silica-poor basalt, which contain about 20-30% silica. Basalt is really runny, which is how you get shield volcanoes and cool stuff like ropy pahoehoe flows like in Hawaii. Helping make it even runnier is the fact that hot rock is like molasses, so the hotter it is the easier it flows. Since rock is a poor conductor of heat, and the deep mantle is a lot warmer than the upper mantle, hot spots are really hot. Something like 1200C, whereas basalt erupting from rift valleys are around 800-1000C. These factors mean that hotspot eruptions are really runny and not particularly explosive, even when they occur on land, like at the Anaheim hotspots in British Columbia. But Yellowstone has left a trail of calderas, large volcanic pits that come from magma chambers being exhausted and the overlying rock collapsing into them. That's a sign that the magma contains more silica, is colder, or some combination of the two. At Craters of the Moon, Idaho, which is still tapping into some remnant magma left behind by Yellowstone a couple million years ago, we see that the silica content for fresh basalt is somewhere around 55%, which is barely basalt at all. Recent eruptions of Yellowstone have produced enormous volumes of silica-rich ash, which is also very unhotspotlike.

Another thing is lithology, or the kinds of minerals we see in the rock. At Hawaii, we see little bits of rock that contain a mineral called spinel, which isn't stable at the surface or in the upper mantle - it comes from more than 400km below the surface! These rocks can be found with a little bit of searching in most hotspots, and if I parsed something my tectonics professor said once, we've found these little bits of rock from as far down as 800km. But again, at Yellowstone, we don't really see those.

Finally, the Yellowstone hotspot has been declining in activity for the last few million years. As we see elsewhere, hotspots can keep erupting for millions of years. Hawaii is at least 100 million years old, La Reunion 65. But Yellowstone is only 17 million years old.

Now the common model explains that away as hotspot magma pooling underneath the crust, melting that, and mixing a little bit with the crust before erupting, which both cools it and adds silica. But hotspots should be hot enough that the material should be neutrally buoyant all the way up to the surface. The decline in activity is attributed to moving under thicker crust, which would mean longer pooling times between eruptions. That said, it's a little bit of a mystery as to what's going on.

A couple years back, we had a guest lecturer at the department talking about a different way to explain what was going on. This was peer-reviewed in a relatively well-known geology journal, so it's probably not complete bullshit. His idea was that while Pangaea existed, there was a huge swath of oceanic crust in the Pacific Ocean (the Farallon plate, of which the Juan de Fuca and Nazca plates are remnants) that North America began to slide over when the supercontinent broke up. This large swath would have had a relatively powerful convective cell, since it had operated with little change for a hundred million years, plenty of time to become metastable. So as North America drifted westward over the Farallon plate and began pushing more and more of the plate under, the momentum of the convecting mantle began to be directed more and more towards the underside of the subducting oceanic crust. Eventually, the pressure built up to a point where it experienced a blowout just under the subduction zone, which in turn redirected the mantle towards the surface. Kind of a poor man's hotspot. Over time, the pressure would be relieved through the subducting blowout zone, leading to less volcanic activity as the zone got dragged deeper into the mantle.

Better, the new technique of mantle tomography sort of supports this interpretation. Think of it like a CT scan of the mantle. Earthquake waves travel more slowly through and are attenuated by hot rock, and travel more quickly and better through cold rock. With a sufficiently dense seismic network, we can trace waves all across the Earth and build up a picture of hot and cold zones in the mantle. Most hotspots have at least a warm signature (although the plume tails, being narrow, don't show up very well), but the Yellowstone hotspot only appears as a slightly warm spot in the upper mantle, originating in a gap in the comparatively cold oceanic crust.

This model does a decent job explaining some of those peculiarities in the Yellowstone hotspot I listed, but it's by no means definitive. It's kind of a special snowflake theory with no other definitive examples of that happening, but so it is with a lot of landforms in geology. At the very least you all have a decent understanding of how hotspots work now.

Also there's a lot of words to be said about the geology of the western US, "unique" being one, "clusterfuck" being another. It's a brave new world, but I really need some time to organize my thoughts on that one. I guess in the meantime I can post stories of why volcanologists are considered the crazy uncles of geology.

Edit: SAL postin in neogibbis

ZombieLenin posted:

quote:

How did plate tectonics start?

quote:

Lastly are you excited about the bore attempt to reach the mantle?

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PS no mountaineer worth his salt hasn't climbed these mountains.

OMGVBFLOL posted:

The first time someone sets foot on the summit of Olympus Mons, they will have flown and landed there directly. I doubt it'll ever be "climbed" in the sense we think of climbing mountains. It'd be like "climbing" from the Louisiana delta to Denver; just an enormously long overland trek with no discernable slope despite the elevation gain.

Bugsmasher posted:

I'd love to check this out and show my kids, can you give approximate locations to see it in Calgary?

Really liking this geology diversion on this thread, didn't expect it to be so drat fascinating.

I Own Soulz posted:

Isn't one of the biggest issues with drilling to the mantle that the rock starts to get almost plastic like because of the heat and you can't really drill it? I thought I'd read about that somewhere before.

Venusian Weasel posted:

It was a bigger problem for the Kola Superdeep Borehole. At the deepest parts of the hole (12,000 m) the holes would completely close back up in the day or two it would take to take to pull the drill back up, replace the bit, and slide it back down the hole.

quote:

A spotter at the top watched them descend and fly with their outstretched wingsuits. Once they fell out of site, Gauthier said, she heard a “pop-pop” sound from below. She had hoped it was the smacking sound of their chutes opening somewhere in the darkening depths of the valley. But daylight brought the confirmation that it was not.