Why China's Largest Volcano Is So Unusual
Summary
TLDRMount Paektu, located on the border between China and North Korea, is an enormous stratovolcano with a massive caldera and lake. It's known for its super colossal eruption around 1000 years ago, yet it remained a mystery for scientists due to its remote location and political isolation. Recent research using seismic tomography reveals it's not a typical hot spot but a 'hydrus plume' volcano, fueled by subduction and stagnation of the Pacific plate. This discovery sheds light on the role of water in global volcanic activities and challenges conventional theories of plate tectonics.
Takeaways
- 🗻 Mount Paektu, also known as Mount Chiang Mai, is a massive stratovolcano located at the border between China and North Korea in Northeast Asia.
- 🌋 It has one of the largest calderas on Earth, formed by a super colossal eruption around 1000 years ago, which ejected over 100 cubic kilometers of material.
- 🌎 The volcano's existence was a mystery for a long time, as its location does not align with typical tectonic plate boundaries where most volcanoes are found.
- 🌏 Volcanoes are usually found along subduction zones where oceanic plates are pushed under continental plates, but Mount Paektu does not fit this pattern.
- 🔍 The theory of plate tectonics, which explains most volcanic activity, could not initially account for Mount Paektu's existence.
- 🌋 The discovery of the 'Hawaiian Emperor Chain' led to the Mantle Plume Model, which suggested that some volcanoes are fed by hot mantle rock rising from deep within the Earth's mantle.
- 🔬 Seismic tomography, a technique similar to medical CT scans, allowed scientists to visualize the Earth's interior and better understand the processes occurring beneath the surface.
- 🌏 The tomography models of Mount Paektu showed an anomaly in the mantle transition zone, indicating a piece of ancient crust that had become stagnant after subduction.
- 🌋 The volcano is not a typical hot spot but is instead fueled by a 'hydras plume' rising from the mantle transition zone due to the subduction and stagnation of the Pacific Plate.
- 🌐 The geological processes beneath Mount Paektu have implications for understanding the formation and breakup of continents and the role of water in these processes on a global scale.
Q & A
What is Mount Peck 2 also known as?
-Mount Peck 2 is also known as Chiang Mai Mountain by the Chinese.
Where is Mount Peck 2 located?
-Mount Peck 2 is located in Northeast Asia on the border between China and North Korea.
What is the significance of Mount Peck 2's caldera?
-Mount Peck 2's caldera is significant because it is one of the largest on Earth, with an area of almost 20 square kilometers, and it was formed by a massive eruption around 1,000 years ago.
How does the eruption of Mount Peck 2 compare to other volcanic eruptions?
-The eruption of Mount Peck 2 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.
Why was Mount Peck 2 a mystery to scientists?
-Mount Peck 2 was a mystery because its location in the middle of nowhere, far from typical plate boundaries, did not fit the conventional models of volcano formation.
What is the 'Ring of Fire' and how is it related to volcanoes?
-The 'Ring of Fire' is a region around the Pacific Ocean where almost 80 percent of all active volcanoes on Earth are found along numerous subduction zones.
How does the movement of tectonic plates relate to the formation of volcanoes?
-The movement of tectonic plates, specifically at subduction zones where plates collide and one is pushed under the other, is a primary cause of volcano formation due to the release of water from the subducting plate into the mantle.
What is the mantle plume model and how does it explain volcanism?
-The mantle plume model explains certain types of intra-plate volcanism as hot spots fed by enormous upwellings of hot mantle rock that rise to the surface from deep within Earth's mantle.
What is the relationship between Mount Peck 2 and the Pacific Plate?
-Mount Peck 2 is related to the Pacific Plate through the subduction and stagnation of the plate under Northeast Asia, which is believed to be the source of its unique form of volcanism.
How does the water content in the mantle transition zone contribute to the formation of Mount Peck 2?
-The water content in the mantle transition zone, which is significantly higher than normal due to subduction processes, contributes to the formation of Mount Peck 2 by making the mantle buoyant and causing it to rise, leading to melting and volcanic activity.
What is the potential impact of a future eruption of Mount Peck 2?
-A future eruption of Mount Peck 2 could have catastrophic consequences due to its size and the proximity of densely populated areas, potentially causing billions of dollars in damage and affecting the lives of millions of people.
Outlines
🌋 Mount Peck 2: The Enigma of a Colossal Volcano
Mount Peck 2, also known as Chiang Mai Mountain, is a massive stratovolcano located on the border between China and North Korea in Northeast Asia. Despite its enormous size and potential danger, it was relatively unknown until recent times. The volcano's caldera, partially filled by a large crater lake, is significantly larger than that of Mount St. Helens. The volcano's last major eruption around 1000 years ago was one of the largest in the last 5000 years. However, the reason for its existence in a tectonic sense was a mystery until recently. Unlike most volcanoes, which are found along plate boundaries, Mount Peck 2 does not fit this pattern, making it a geological conundrum.
🌏 Unraveling the Mystery of Mount Peck 2
To understand Mount Peck 2's uniqueness, the video script explains the ordinary volcanoes' formation along plate boundaries, particularly at subduction zones. It describes how water released from subducting oceanic plates fuels volcanic activity, as seen in Japan's numerous volcanoes. The script then contrasts this with 'hotspot' volcanoes like those in Hawaii and Yellowstone, which are not located at plate boundaries and are thought to be fed by mantle plumes originating deep within the Earth. The revelation that Mount Peck 2 does not fit either category, and its location's political isolation, contributed to the delay in understanding its geological processes.
🔍 Seismic Tomography and the Discovery of a New Volcano Type
The script details the use of seismic tomography to study the Earth's interior, allowing scientists to visualize what's happening deep below the surface. This technology helped to explain the existence of hotspot volcanoes like those in Hawaii and Yellowstone. However, when applied to Mount Peck 2, the results were unexpected. Instead of a deep mantle plume, the tomography revealed a shallower low-velocity anomaly, not typical of hotspots. This finding, along with the discovery of a cold material anomaly at about 600 kilometers depth, puzzled the geological community and suggested a new type of intra-plate volcanism.
🌌 The Mantle Transition Zone and Stagnant Slab Hypothesis
The script discusses the discovery of a cold anomaly within the mantle transition zone beneath Mount Peck 2, which is believed to be a piece of ancient crust from the Pacific Plate that has become stagnant after subducting. This finding challenges the previous understanding of whole mantle convection and suggests that some subducted slabs can become trapped in the mantle transition zone. The script also describes the increase in seismic activity beneath the mountain, which raised concerns about a potential eruption and led to increased scientific scrutiny.
🌄 The Explosive History and Future Threat of Mount Peck 2
The script outlines the three evolutionary stages of Mount Peck 2's volcanic activity, starting with extensive basaltic lava eruptions millions of years ago, followed by the formation of a volcanic cone, and culminating in a massive explosive eruption around the year 946. This eruption had catastrophic effects, covering a vast area in ash and causing pyroclastic flows that burned areas equivalent to the size of Tokyo. The script highlights the potential risks of future eruptions, given the volcano's proximity to densely populated areas and the possibility of it causing one of the most costly natural disasters in history.
💧 The Role of Water in the Formation of Mount Peck 2
The script explains the latest understanding of Mount Peck 2's volcanism, which is driven by a 'hydrus plume' fueled by the subduction and stagnation of the Pacific Plate. This process is distinct from typical mantle plumes, as it is influenced by tectonic processes near the surface and is likely caused by water trapped in the mantle transition zone due to continuous subduction. The script also suggests that the mantle transition zone may hold more water than all the oceans combined, indicating its critical role in global water recycling processes.
🌐 Global Implications of the Northeast Asia Geodynamics
The final paragraph discusses the broader implications of the geological findings in Northeast Asia. It suggests that similar processes related to the subduction and stagnation of oceanic crust in the mantle transition zone may explain much of the terrestrial interplay volcanism around the globe. The script also links these processes to the formation of continental flood basalts, which are significant events in Earth's history, potentially influencing the formation and breakup of continents and the course of evolution.
Mindmap
Keywords
💡Mount Peck 2
💡Caldera
💡Volcanic Explosivity Index (VEI)
💡Tectonic Plates
💡Subduction Zones
💡Mantle Plume
💡Seismic Tomography
💡Mantle Transition Zone
💡Stagnant Slab
💡Intra-plate Volcanism
💡Hydrous Mantle
Highlights
Mount Peck 2, also known as Chiang Mai Mountain, is one of the largest and most dangerous volcanoes on Earth.
The volcano's caldera is more than five times larger than Mount St. Helens' caldera.
Mount Peck 2's last eruption was the second largest volcanic eruption in the last 5,000 years.
The volcano's location in northeast Asia on the border between China and North Korea makes it difficult to study.
Ordinary volcanoes are typically found along plate boundaries and subduction zones.
The Pacific Ring of Fire is home to almost 80% of all active volcanoes on Earth.
Volcanoes like Mount Peck 2 that don't conform to the plate tectonics theory were a mystery for a long time.
The mantle plume model was developed to explain intra-plate volcanism.
Mount Peck 2 does not fit the typical hot spot model, challenging the existing theories.
Seismic tomography has revolutionized the study of Earth's interior, similar to how CT scans revolutionized medicine.
The discovery of a cold material anomaly in the mantle transition zone under Mount Peck 2 was puzzling.
The Pacific plate's subduction and stagnation under Mount Peck 2 could be the cause of its unique volcanism.
Mount Peck 2's explosive eruption around the year 946 was one of the most catastrophic in human history.
The potential fallout zone of Mount Peck 2 includes many of the world's largest cities.
Recent research has shown that Mount Peck 2 is not a traditional hot spot but a back arc volcano.
The mantle transition zone under northeast Asia is a significant water reservoir and plays a key role in global water recycling.
Mount Peck 2 and similar volcanoes in the region are the result of subduction-related processes.
The geodynamics of northeast Asia have implications for the formation and breakup of continents and the course of evolution.
Transcripts
[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
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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
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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
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you
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