this post was submitted on 01 May 2024
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Big volcanoes look like this
(Mount Rainier, Washington)
The BIGGEST volcanoes look like this
Or this
Notice how they don’t have that nice big pretty volcano cone shape? It just looks like some drunk geologists scribbled on a map and drew circles around a low lying area with a lake or two in it and called it a “volcano” or a “volcanic zone”.
The reason though is that the BIGGEST and most destructive volcanic eruptions tend to happen with lava/magma that doesn’t flow very well and like when you get a stuffed nose, everything gets blocked up. Like many of us, these volcanos don’t solve the problem and go take a decongestant or blow their nose, they just sit there sniveling and stewing, failing to release the pressure that keeps building and building and building.
These eruptions are called felsic eruptions (the opposite of mafic, goopy eruptions you have seen footage of from Hawaii where the lava comes out like a fluid). An immense amount of gas is released by magma as it becomes exposed to the surface (which then we call it “lava”) as the gas is no longer kept in the magma at immense pressures. The magma can’t flow and “pass the gas” so to speak so a plug forms and what you get is a terrifyingly big pressure cooker that just builds and builds like that person on the plane next to you that just keeps sniffing and sniffing and never blowing their nose.
When the built up pressure finally overcomes the plug, the resulting explosion is so catastrophic it doesn’t leave a clean volcano shape. What you are left with is an uneven low topography dotted with lakes that marks the site of an incomprehensibly large explosion, hence the topography of Yellowstone, Wyoming and the Taupo Volcanic Zone on the North Island of New Zealand.
TIME FOR SOME STATS THAT WILL BREAK YOUR BRAIN
"The Taupō Volcanic Zone has produced in the last 350,000 years over 3,900 cubic kilometres (940 cu mi) material, more than anywhere else on Earth, from over 300 silicic eruptions [my edit: "Felsic" means "has lots of silica/silicic (silicic? seriously wikipedia?) and wants to form minerals high in silica like quartz and feldspar"], with 12 of these eruptions being caldera-forming. Detailed stratigraphy in the zone is only available from the Ōkataina Rotoiti eruption but including this event, the zone has been more productive than any other rhyolite predominant volcanic area [my edit: Rhyolite is a record of catastrophe, it is a Felsic, silica-rich igneous rock like Granite except it cooled FAST at the surface instead of in big underground "batholiths" (that make up a good portion of the Canadian Shield and the NE of the US among other places) where the minerals had time to grow into big pretty crystals, same ingredients as Granite but with much more exciting baking instructions] over the last 50,000 odd years at 12.8 km3 (3.1 cu mi) per thousand years. Comparison of large events in the Taupō volcanic zone over the last 1.6 million years at 3.8 km3 (0.91 cu mi) per thousand years versus with Yellowstone Caldera's 2.1 million year productivity at 3.0 km3 (0.72 cu mi) per thousand years favours Taupo...
...The last major eruption from Lake Taupō, the Hatepe eruption, occurred in 232 CE. It is believed to have first emptied the lake, then followed that feat with a pyroclastic flow that covered about 20,000 km2 (7,700 sq mi) of land with volcanic ash. A total of 120 km3 (29 cu mi) of material expressed as dense-rock equivalent (DRE) is believed to have been ejected, and over 30 km3 (7.2 cu mi) of material is estimated to have been ejected in just a few minutes."...
^https://en.wikipedia.org/wiki/Taup%C5%8D_Volcanic_Zone
..."The main extremely violent pyroclastic flow travelled at close to the speed of sound and devastated the surrounding area, climbing over 1,500 m (4,900 ft) to overtop the nearby Kaimanawa Ranges and Mount Tongariro, and covering the land within 80 km (50 mi) with ignimbrite [my edit: the name for pyroclastic flow deposits, i.e. pumice and ash, that kind of thing]. Only Ruapehu was high enough to divert the flow. The power of the pyroclastic flow was so strong that in some places it eroded more material off the ground surface than it replaced with ignimbrite. There is evidence that it occurred on an autumn afternoon and its energy release was about 150 megatons of TNT equivalent. The eruption column penetrated the stratosphere as revealed by deposits in ice core samples in Greenland and Antarctica."
^https://en.wikipedia.org/wiki/Taup%C5%8D_Volcanic_Zone
why the did I make this stupid meme in feet instead of metric, I am such an asshole -facepalm
Ohhh, I had no idea there were different kinds of volcanoes but it does make sense in hindsight.
Well, I guess this might have been covered in primary or secondary education at some point but it's been about 3000 years since my last geography class
yo geolooggggyyyyyyy (lots of good brain food I promise)
There is a wonderful diverse world of volcanic eruptions! One thing you might not have thought about is how glaciers often form at the top of large cone volcanoes and the way the lava erupting interacts with a large volume of ice can shape the eruption significantly. One of the biggest results are lahars, like muddy, liquidy avalanches but even faster and deadlier.
https://www.usgs.gov/media/images/d-claw-computer-simulation-landslide-begins-mount-rainiers-west-flank-tahoma-glacier
https://www.usgs.gov/programs/VHP/lahars-move-rapidly-down-valleys-rivers-concrete
To give you a good point of reference though, one thing that links all volcanic eruptions and is a good axis for comparison between different eruptions and volcanoes is that all magma pretty much comes up from the interior of the earth to the near surface starting at the same chemical composition (called "mafic" it sounds like "basic"). Mafic minerals are heavy, dense and tend to be dark colored when viewed in a hand specimen, a common mafic rock is Basalt. Most of the oceanic crust is basalt.
Available Wherever You Get Your Bottoms Of Oceans
Felsic minerals tend to be light both in mass and in coloring, a comon felsic rock is Granite.
Looks like your mom's countertop, I remember it well how perfectly the skin of her naked legs complemented the gorgeously polished crystal textures of quartz, potassium feldspar (K-feldspar), sodic plagioclase feldspar, hornblende amphibole, and mica
This is a graph of Viscosity, the more Viscous the Magma the less ability it has to flow like a liquid (and thus the more likely a plug is likely to form inside a volcano). It is also more difficult for lower temperature magma to flow, and Felsic lava is almost always lower temperature (cooling had to occur to become Felsic in the first place so).
https://en.wikipedia.org/wiki/Magma
Here is something to ground these two ends of what probably seems like an arbitrary spectrum to focus on, the Oceanic Crust (i.e. the bottom of the ocean) on this planet is overwhelmingly made up of mafic rocks (i.e. Basalt) and large amounts of felsic rocks only really form on continental plates where there is the space and depth of rock to house massive chambers of magma, especially since Oceanic Plates are always getting subducted and recycled unlike Continental Plates (and thus the magma might be subducted & recycled before it could even begin the process of becoming significantly felsic). This axis of chemistry is critical to Geologists because it points directly to some of the biggest trends of geology on the planet and a related fact I might as well drop here is that because of these dynamics Continental Plates (i.e. basically the continents) can be orders of magnitude older (on the order of 1 billion years or older, the earth is only 4 or so billion years old) than oceanic crust which tends to be younger than 200 million years old (and often is much younger).
On Continental Plates if magma feeds into large underground chambers (batholiths) and is allowed to cool slowly then certain minerals will begin to form and precipitate out like snow that layers up on the bottom of the chamber. The specifics of what minerals these are depends on how long, how hot, how much pressure and other factors but you can vaguely think of it as a process of distillation where magma progresses from the original "mafic" composition to a "felsic" one as the high temperature mafic minerals crystallize out leaving behind a progressively more felsic magma mixture. The felsic minerals don't crystallize out until the magma has significantly cooled and thus if the magma chamber undergoing this process is integrated into an eruption, it can become extremely explosive and destructive.
https://opentextbc.ca/geology/chapter/4-2-magma-composition-and-eruption-style/
Half Dome in Yosemite California is such a trip because it is so clearly what we imagine in geology when we talk about a really big underground chamber of magma (after it has cooled into rock obv), Half Dome just looks like exactly how you would imagine it if you dug up an old magma chamber and cracked in half with a suitably large hammer
Huh, interesting. I didn't expect to learn about volcanoes today but here I am! Thank you for the explanation