Why China's Largest Volcano Is So Unusual

[Music] this is mount peck 2 also known as chiang mai mountain by the chinese it lays here in northeast asia on the border between china and north korea although few outside the region even though it exists the enormous strata volcano is one of the largest and most dangerous volcanoes on earth its massive caldera which today is partially filled by an equally massive crater lake has an area of almost 20 square kilometers that's more than five times larger than the caldera of mount st helens the eruption that shaped the caldera around 1 000 years ago is considered to be the second largest volcanic eruption in the last 5 000 years classified as a 7 or super colossal eruption on the volcanic explosivity index it ejected more than 100 cubic kilometers of material enough material to bury even villages more than 1200 kilometers away in northern japan under a thick layer of ash and yet despite its size and its destructive pest mountain peck 2 was for the longest time and to some degree still is today a mystery even for the scientists that have studied it the volcano remained a conundrum only until very recently nobody could explain why exactly here in a tectonic sense in the middle of nowhere one of the largest volcanoes on earth exists to understand why mount peck 2 is so unique we first have to understand what makes ordinary volcanoes well ordinary take a look at this map it is a map of all the active volcanoes in the pacific most of them run along clearly visible lines almost like a string of pearls why this is becomes clear when you lay a map of the tectonic plates over it almost all volcanoes are found along plate boundaries more specifically along subduction zones so zones where two plates collide and the denser oceanic plates are pushed under the continental plates here in japan for instance where the pacific plate is being subducted beneath the okosuke and the philippine seaplate and where the philippine sea plate is in turn being subducted beneath the eurasian plate as a consequence of these complex subduction zones japan is one of the most volcanically active regions in the world in total the small island nation has over 100 active volcanoes the fuel of this subduction zone volcanism is slightly ironically water oceanic crust holds huge amounts of water stored in hydrous minerals which form when crust interacts with seawater as the subducting slab descends into the mantle it encounters greater and greater temperatures and pressures this ultimately at depths of around 120 kilometers or 75 miles causes the rock to change its chemical composition and release the water that was trapped in the crust into the mantle above water added to the hot solid mantle lowers its melting point because the water molecules weaken the crystalline structure of the rock much in the same way that salt weakens the crystalline structure of ice the magma produced this way then rises up into the overriding plate collects in magma chambers and eventually causes volcanic eruptions on the surface and so a volcanic arc that runs parallel to the subduction zones is created along the plate boundaries a similar pattern can be found all around the pacific ocean like here in indonesia or in chile in fact almost 80 percent of all active volcanoes on earth run along the numerous subduction zones in the pacific which is why the region is commonly referred to as the ring of fire we already know this since the 1960s when the model of continental drift first proposed by alfred wegener in 1912 was finally proven and together with the model of seafloor spreading combined into the theory of plate tectonics there was only one problem there were still a few volcanoes that didn't conform to this theory volcanoes that were seemingly sprinkled across the globe at random like here in hawaii some 3 800 kilometers or 2 400 miles away from the next plate boundary or in yellowstone chiang bai mountain which sits more than a thousand kilometers northwest of the japan trench is another one of these weird interpolated volcanoes to explain this kind of volcanism a new model was needed an important clue to solve this mystery could be found on the ocean floor in the north pacific if you follow the line of islands that make up the hawaiian archipelago northwest you could find a series of volcanic structures that once form very similar islands before millions of years of erosion reduce them to a series of atolls and sea mounts this so-called hawaiian emperor chain contains more than 80 individual structures like this stretching nearly 6 000 kilometers or 3 900 miles across the ocean floor on first glance you might come to the conclusion that the source of hawaii's volcanism must be moving from northwest to southeast like a giant marker drawing a line across the pacific plate however you can also explain this line in a different way the same pattern would be produced if instead the oceanic floor is moving to this realization came the canadian geologist john wilson 2 in the 60s the movement of the pacific plate from southeast to northwest above a stationary source of magma would also produce this image and sure enough this is exactly the current path of the plate such volcanism that isn't influenced by plate tectonics would need to have a much deeper origin than other volcanoes this idea was then developed into the mantle plume model it explained these volcanoes as hot spots that are fed by enormous upwellings of hot mantle rock that rise to the surface from the depths of earth's mantle driven by heat exchange across the core mantle boundary 2 900 kilometers or 1800 miles below the surface and while it would take a few more decades before technology had advanced to the point that it could actually prove what wilson had only hypothesized based on a few pieces of evidence there was finally an explanation for intra-plate volcanism with this the puzzle surrounding the source of the mysterious volcanoes in places such as hawaii yellowstone and northeast asia seemed to be solved there was only one slight issue mount peck 2 is not such a hot spot but scientists wouldn't realize this until the end of the 20th century one reason the mountain has remained elusive for such a long time certainly has to do with its location it not only lays in a very remote region of asia it also sits at the border of two countries that lived in almost complete isolation for much of the 20th century it was only once china started to open up more and more to the outside world in the 80s and 90s and began to promote scientific research that gathering information about the solitary giant became less of a political impossibility still it wasn't until the end of the 90s that the first permanent seismographs were installed on the chinese side of the mountain and this was hugely important because seismographs had become perhaps the most essential tool for studying the geology of earth's interior that's because of one clever invention seismic tomography in the 1970s computed tomography or ct scans revolutionized medicine by giving doctors the ability to look into their patients bodies without having to make any cuts and that way look for tumors fractures infections and a variety of other problems and diseases safely and effectively geologists realize that they can adopt this technology for themselves to finally reveal what's going on hundreds or even thousands of kilometers below our feet the seismic waves produced by earthquakes move at different speeds depending on the temperature density water content and state of the rocks they travel through you can measure the arrival times of these waves at various points on the surface to map out the interior of our planet this allowed scientists to quite literally cut open the earth and see what's inside like medicine before this technology revolutionized earth science finally it was possible to see processes that were long hypothesized like the subduction of plates into the mantle the formation of new ocean floor through upwellings of hot mantle material below mid ocean ridges and of course plumes that rise up from the core mantle boundary and feed hot spots such as hawaii and yellowstone and so for a brief moment in time we had an explanation and explanation for every form of volcanism on the planet all three forms subduction-induced volcanism mid-ocean ridge volcanism and mantle plumes were supported by evidence and seemed to explain every volcano or volcanic structure on the planet that was until the first tomographic models of mount changbai appeared in the late 90s and early 2000s what they showed was significantly different from what images of hawaii or yellowstone showed there wasn't the prominent low velocity anomaly extending all the way down to the core mantle boundary instead the anomaly seemed to end roughly 400 kilometers or 250 miles below the surface which is deep much deeper than the source of any volcano near subduction zones but not nearly as deep as the 2900 kilometers or 1800 miles geologists had expected not only that but below the low velocity anomaly there was a distinct high velocity anomaly that showed up in the images at depths of about 600 kilometers or 380 miles right here it showed what appeared to be a large barrier of unusually cold material this puzzled the geological community once again there was a form of intra-plate volcanism that couldn't be explained that wasn't a typical hot spot like previously thought one of the largest volcanoes on earth suddenly didn't seem to fit into any existing category it was a completely new kind of volcano to understand what's going on here we first have to understand this zone curiously the cold anomaly observed here sits right inside the so-called mantle transition zone this is the known transition zone between the lower and upper mantle here the pressure is great enough that it changes the internal arrangement of the atoms by forcing the rock into a much denser more compact crystalline structure this results in a sudden quite significant jump in viscosity in the zone because of this the mantle transition zone acts as a sort of barrier in the mantle which at least partially separates the processes in the upper and lower mantle from one another geologists quickly realized that the distinct anomaly of cold material in this zone can only be a piece of ancient crust expanding the image further to the east quickly reveals which plate it is it appears that the pacific plate after subducting into the mantle bends horizontally and becomes stagnant in the mantle transition zone right below mount pek 2. this wasn't even that surprising ever since we began to understand more about the interior of our planet and its layers it has been speculated that slabs after their subduction would become stagnant here in fact there was a fierce debate going on in the geological community with one side arguing that the convection processes in the upper and lower mantle are separated from one another and that slabs after their subduction becomes stagnant in the boundary layer while the other side argued for whole mantle convection and subducting slabs sinking all the way to the bottom of the mantle forming a graveyard of slabs on top of earth's core but before you think clearly the first group had it right here's an image of the subduction zone just a few hundred kilometers to the south here you can clearly see the pacific slab penetrating the mantle transition zone and sinking into the lower mantle likewise global seismic tomography models have revealed an entire catalog of roughly 100 old slabs that have penetrated deep into the mantle so clearly it's not as simple as picking one model over the other that aside there was also the question how a stagnant slab could even produce volcanism so far away from the subduction zone earthquakes provided an important clue most earthquakes on earth occur just like volcanoes near plate boundaries where the crust is bent and deformed by the collision of the plates but seismographs in asia also frequently pick up strong earthquakes deep below mount chiang bai 600 kilometers or 380 miles below the surface remember this chart it'll be important later here our story takes a bit of a turn because at the start of the 20th century earthquakes became the center of discussion for a different reason in 2002 the newly established tiansher volcano observatory started to pick up a worrying increase in seismic activity 5 kilometers or 3 miles below the mountain over the next year the number of earthquakes increased from an average of 10 per month to over a hundred in some months even over 200 signaling that an outbreak might be imminent if we look at mount chiang bai's eruptive history we can see that it can be broadly divided into three evolutionary stages the volcanic activity started around 20 to 30 million years ago as part of the large-scale interplayed volcanism that took place in northeast asia since the late jurassic period around 2.5 million years ago partial melting in the mantle below the volcano increased significantly and resulted in the eruption of extensive amounts of basaltic lavas which even today cover an area of around ten thousand square kilometers or four thousand square miles with an enormous shield like plateau the largest in the region due to the enormous weight of this plateau the rise of the magma below was eventually slowed down so much that it began to collect in a shallower magma chamber before erupting to the surface this was actually very important as the extra time changed the chemical composition of the melt due to contamination from the crust and the deposition or removal of certain minerals in the magma as a result the lava that erupted onto the surface became a lot more viscous which led to the formation of a volcanic cone on top of the basalt plateau this second phase lasted from around 1 million to 4 000 years ago and by the end of it had produced a cone roughly 4 kilometers or 13 000 feet high the last stage the explosive stage then resulted in the almost complete destruction of this cone which brings us back to the millennium's eruption of 946 this enormous eruption blew off the entire top half of the volcano creating the caldera that we see today if you imagine the amount of material that must have existed between the two kilometer high surface of heaven lake that partially fills the caldera today and the once four kilometer high summit of the volcanic cone it's not difficult to see that the millennium eruption must have been one of the most catastrophic eruptions in human history it produced a plume of smoke and ash that shot an estimated 25 kilometers or 15 miles into the stratosphere and ultimately covered more than 350 000 square kilometers between northern korea and the kuril trench in 5 to 10 centimeters or 2 to 4 inches of ash that's an area larger than the entire korean peninsula the total amount of ash dispersed by the eruption would have been enough to bury the whole of new york city under almost 150 meters or 500 feet of ash additionally pyroclastic flows avalanches of superheated gas and debris filled valleys and canyons as far as 50 kilometers or 30 miles in every direction burning an area the size of tokyo in the process at the time the area around the mountain and northeast asia in general were not particularly densely populated but today more than 1.5 million people live within the immediate danger zone of the volcano and almost a billion people live within the potential fallout zone within this 1500 kilometer radius you can find many of the largest cities in the world such as seoul pyongyang tokyo osaka beijing and shanghai if only one or two of these mega cities would be buried in volcanic ash from a similarly strong eruption the damages caused by that could easily make it one of the most costly natural disasters in history but in mid-2005 the mountain went silent again the seismic activity went back to its pre-2002 levels and has remained that low ever since making an eruption within the next few years unlikely at least at the present day but what these years have shown us is that the volcano is very much active and will likely erupt again at some point in the future this ignited the scientific interest in the volcano and resulted in a flood of new research primarily from china mountain pectus sudden unrest even got the normally very reclusive north korean government worried to the point that they started to reach out to the west and eventually even invited a team of scientists to the country to study the volcano together with their north korean colleagues the group collected data took rock samples and installed a set of seismographs to monitor the mountain the first results of this unique collaboration were published in 2016. [Music] with all the new research that has been done over the last 10 to 20 years we now have a pretty good understanding of what causes this unusual form of volcanism using the latest seismic tomography models created taking nearly 80 000 earthquakes recorded by over 3 000 seismic stations we can now map the mantle below northeast asia with never seen before clarity from here we can create a schematic 3d model of the main features that drive the volcanism under chiang mai mountain let's start with the most obvious one the pacific plate as you can see a huge portion of the slab has become horizontal and stagnant under northeast asia after subducting at a roughly 30 degree angle below the island of japan in the process it has trapped much of the upper mantle in the region between the crust and itself creating what geologists have termed a big mantle wedge under the korean peninsula and east china also of note is this gap roughly at 35 degrees northern latitude here the pacific plate is visibly being torn apart at depths of around 300 kilometers or 190 miles with the southern part descending at a much steeper 70 degree angle and subsequently penetrating the lower mantle the length of the western edge of the stagnant slab which is much longer than the corresponding part of the subduction zone indicates that these two pieces were once joined together before they were ripped apart likely as a result of the huge forces generated by the differences in the subduction rate direction and angle focusing on the mantle below mount peck 2 reveals a prominent low velocity anomaly of partially molten rock that sits on top of the stagnant slab and has a diameter of roughly 100 kilometers or 60 miles it can be described as a plume that rises from the mantle transition zone this is an important distinction because unlike normal mantle plumes that are relatively unaffected by the tectonic processes near the surface this plume seems to be the direct result of these processes namely the subduction and stagnation of the pacific plate furthermore the source of its buoyancy also seems to be different while normal mantle plumes rise as a result of heat exchange between the lower mantle and the much hotter core this plume is not significantly hotter than the surrounding mantle instead its buoyancy seems to mainly be caused by water electrical conductivity studies have shown that the mantle transition between northeast asia holds huge amounts of water 5 to 10 times more than you would normally find here this water was likely trapped here by more than 100 million years of continuous subduction and dehydration of the ocean floor along the eastern seaboard of asia deep earthquakes in the stagnant slab seem to indicate that these dehydration processes are still going on today here's where the chart from earlier comes in as you can see earthquakes occur pretty much everywhere in the downgoing slab but they seem to pick up again in magnitude and quantity once we get to this point the mantle transition zone below chiang mai mountain where we can see a visible cluster of deep earthquakes these earthquakes may reflect the reactivation of faults deep in the slab caused by the horizontal bending of the plate near the japan trench many normal faulting earthquakes occur in the outer rise portion because of the upward bending of the oceanic lithosphere before the plate subduction a large amount of seawater may enter into the deep portion of the pacific plate through these normal faults as the stress regime changes from extension to compression during the subduction the normal faults are closed and thus a large amount of water could be preserved deep within the slab while dehydration processes of the overlying crust cause the commonly observed arc volcanism the water stored deep within the slab is brought down to the mantle transition zone here the stress regime once again changes because of the huge resistance at the bottom of this zone as the slab bends and deforms the preserved faults are reactivated which allows for dehydration processes deep within the slab how these dehydration processes look like in detail is however still subject to debate the extreme temperatures and pressures as well as the unique minerals found in this zone make it difficult to predict how exactly the water interacts with the surrounding mantle one thing however has become clear over the last couple of years the mantle transition zone below northeast asia and likely elsewhere in the world is an enormous water reservoir and likely plays a critical role in global water recycling processes thanks to the minerals in this zone that are particularly good at incorporating water into their structure the mantle transition zone may hold more water than all the oceans combined below chiang bhai mountain in particular it seems the water content has reached a critical amount enough that the hydrous mantle becomes buoyant and starts to rise into the upper mantle here it accumulates on top of the mantle transition zone and forms a hydrous plume convection processes in the big mantle wedge caused by the fast subduction of the pacific slab likely further aid the plume's rise and the reduction in pressure ultimately causes dehydration melting of the wet mantle rocks the result is a continuous wet and hot upwelling right below northeast asia so to summarize mountain peck 2 is not a traditional hot spot but a sort of back arc volcano caused by a hydras plume that rises from the mantle transition zone and that is fueled by the subduction and stagnation of the pacific slab under northeast asia detailed tomographic images of the other volcanic fields in the region show similar structures below them indicating that they were the result of similar subduction related processes in fact it seems the entirety of east china and the korean peninsula were heavily shaped by these mechanisms if you map the western edge of the pacific slab you can find it lines up perfectly with the so-called north-south gravity linument an important geophysical boundary in east china where the surface topography visibly changes you can see it quite clearly on this height map when you cross this boundary from west to east the thickness of the continental plate dramatically decreases from around 100 kilometers or 60 miles to about 50 kilometers or 30 miles the result is a significant reduction in surface elevation in northeast asia that this boundary lines up so well with the pacific plate below is no coincidence evidence suggests that the entire region was the result of millions of years of lithospheric destruction from below caused by the continuous subduction in the subduction related melting and upwelling of mantle material [Music] the result of these processes was extensive large-scale volcanism and the formation of interplayed volcanoes in northeast asia of which chiang mai mountain is currently the largest and most active of [Music] while this might seem like a story about this one very unique volcano in a remote corner of asia it's actually much more than that what the geodynamics of northeast asia have shown us over the last 20 years is that the mantle transition zone plays a key role in continental magnetism and that the importance of water in these processes has been significantly underestimated in the past and this has historically not just happened here in asia wet upwellings related to the subduction and stagnation of oceanic crust in the mantle transition zone may in fact provide a possible explanation for much of the terrestrial interplay volcanism that has happened around the globe geochemical analyses even suggest similar processes are likely linked to the formation of continental flood basalts which represent the largest volcanic events in earth's history these cataclysmic eruptions that covered areas of hundreds of thousands to more than a million square kilometers in lava are important points in our geological history points that mark the rifting and breakup of continents or catastrophic mass extinctions conventionally the formation of these provinces was like their oceanic counterparts attributed to the initial arrival of plumes from the core mantle boundary but the chemical composition of continental flood basalts is often distinct hydrous melt that seems to have originated from recycled oceanic crust could for instance be identified in the siberian traps and the central atlantic magmatic province which instead implies a subduction related origin this means chiang mai mountain is not an isolated case instead it has become an important window into processes that likely have in the past albeit on a much larger scale not just played a key role in the formation and breakup of continents but also severely impacted the course of evolution on a global scale [Music] [Music] you

Channel: Deep Dive

Views: 2,349,511

Rating: 4.925096 out of 5

Keywords: volcano, geology, plate tectonics, mantle plumes, volcanoes, eruption, largest volcanoes, hawaii, hawaii volcano, largest eruption, Mount St. Helens, Yellowstone Volcano, Changbai Mountain, Mount Paektu, Mount Baektu, Paektusan, Paektu, China's Largest volcano, Korea's largest volcano, Millenium Eruption, Weird Volcanoes, Why Chinas volcano is so unusual, Strange Volcano, Lava, Magma, Science, Volcano Science, infographic, motiongraphic, animation, documentary

Id: 3C2HVOB-g5s

Length: 27min 2sec (1622 seconds)

Published: Tue Nov 17 2020

Reddit Comments

[u/da_guru]

That was an excellent documentary, thanks for sharing and are there more like this?

[u/28757b2]

Very nice Saturday morning breakfast for the brain.

[u/Briggtion]

Excellent video. This video deserves more views. I'm sure if the creator makes a few more one will get picked up by the algorithm and ignite the channel

[u/Yetisquatcher]

The video is incredible! Compelling writing, interesting topic, great research, and effective use of animation. It's such high quality, that I have a hard time believing that one person, or even a small group, had the means to put together a 30 minute documentary for youtube. I would not be at all surprised to find out that this video is a front for a big media company looking to break into youtube.