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This is geology B with Oliver's 
trampled. 

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After a decade of vigorous 
debate, the mantle plume 

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hypothesis first proposed in a 
paper by Jason Morgan in 1971. 

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Became the widely accepted 
explanation for the existence of

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volcanoes located far away from 
plate, boundaries. 

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Plumes are posited to be 
upwellings of hotter than 

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average mantle arising from a 
great depth. 

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Most probably from the very 
bottom of the mantle where it 

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meets the Earth's core Hawaii, 
and other mid-ocean islands are 

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pointed to as the classic 
examples of plume induced or so 

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called, Hot Spot volcanoes. 
However, even as the plume 

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hypothesis has become more and 
more entrenched, the evidence 

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for them remains inconclusive. 
Of and seismic tomography has 

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yet to attain the resolution 
needed to detect them in the 

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lower mantle. 
Jillian. 

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Folger is Emeritus, professor of
geophysics at Durham University,

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she is a leading. 
Exponent of the plate theory for

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volcanism in which the theory of
plate. 

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Tectonics is able to account for
all of the Earth's volcanism 

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dispensing with the need for 
additional hypotheses, including

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mantle plumes Julian Folger. 
Welcome to geology B. 

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Thank you, Oliver and thank you 
for doing this podcast. 

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Can you remind me what it was 
exactly that led Jason Morgan 

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another's to propose the 
existence of mantle plumes. 

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Well during the 60s, when plate 
tectonics was developed, it 

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became immediately clear to 
scientists that most volcanism 

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on Earth was immediately 
explained as occurring at plate 

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boundaries. 
So much of this was occurring 

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along mid-ocean ridges, where 
the plates are moving apart, and

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some was occurring behind 
subduction zones, Island arcs. 

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But then there was Hawaii, it 
was smack in the middle of the 

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biggest plate on Earth and it 
was as far away from any plate 

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boundary as you could possibly 
get anywhere on the surface of 

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the Earth, and it's a huge and 
very productive cluster of 

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volcanoes. 
So this was kind of a glaring 

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exception. 
Shun to the general rule and it 

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needed. 
Some kind of explanation. 

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Did you espouse the mantle plume
hypothesis? 

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When you started your career as 
a research, geologist guilty, 

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your honor When I Was An 
undergraduate. 

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And after again, it was 
presented to me by all my 

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colleagues and teachers and 
mentors. 

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As though, this was just a fact,
and this is well established as 

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plate. 
Tectonics of, which were very 

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confident. 
Of course. 

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But I never questioned them for 
plumes and in the first part of 

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my teaching career, as a 
lecturer at Durham University, I

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taught the undergraduates the 
mantle plume hypothesis and I 

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taught them that the Hawaii. 
Emperor seamount chain, Bend was

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due to a change in the direction
of the Pacific Plate and we all 

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assumed that this was correct. 
It wasn't till I looked into it 

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that I started to find that. 
Not everything was quite as 

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clear and straightforward. 
So we'd all been led to believe,

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was that something in particular
that brought on your misgivings 

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about the existence of plumes? 
What triggered me? 

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Really. 
And this was a kind of cathartic

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experience. 
I did a large seismic tomography

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experiment covering the whole of
Iceland's. 

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I worked with Jason Morgan at 
Princeton in the u.s.a., we 

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covered the island of Iceland 
with very modern Broadband 

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seismic stations and we gathered
a lot of seismic data, Data. 

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And we performed an inversion, 
to study, the three-dimensional 

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structure, down to about 600 
kilometers. 

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And what we saw there wasn't 
consistent with what we 

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expected, a mantle plume to look
like. 

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So I took these results to an 
International Conference in San 

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Francisco in 1999, and I 
discussed it with colleagues 

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there. 
And one colleague that I said 

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earlier, this month of plume is 
From what we expected, as a 

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different kind of mantle plume. 
And he said, well, maybe there 

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isn't a mantle plume there and I
was completely poleaxed by this,

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incredible suggestion. 
It hadn't occurred to me ever 

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before that. 
Such a thing could be so and I 

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just started asking questions. 
What about this? 

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What about that, what about the 
other and that just led me into 

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a 10-year long roller coaster 
ride where I realized that we 

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had to just drop all these 
assumptions. 

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We just hadn't been. 
I'm thinking what we were doing 

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was the conclusion that I came 
out with? 

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But surely since that 1990s, 
Iceland study of yours, there 

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have been a ton of other studies
that support the existence of 

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mantle plumes. 
There's a difference between 

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being consistent with a 
hypothesis and requiring it. 

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So many things could be claimed 
to be consistent with a mantle 

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plume hypothesis, but on the 
other hand, if there are half a 

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dozen other, Yes, and you've had
to change the plume. 

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Hypothesis beyond all 
recognition to cram your foot 

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into the glass slipper that 
wasn't made for it. 

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Then we have to really think 
what we're doing. 

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So what exactly are the 
geological features that would 

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provide conclusive evidence of 
the existence of a mantle plume 

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in the early days of the 
development of mantle plumes 

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dot-org, the website that really
hosts The debate regarding the 

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existence of mantle plumes, I 
thought it would be helpful to 

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decide exactly what a mantle 
plume was because there are so 

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many different variants. 
So I reached out to Professor, 

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Ian, Campbell of the Australian 
National University, Professor 

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Campbell as well. 
Known for his work simulating, 

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plumes in large tanks. 
Full of fluid in his laboratory 

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there. 
And I asked him what he can. 

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So that the plume hypothesis to 
predict what are the 

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predictions. 
If we go to study an area, what 

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should we look for? 
And what things should we expect

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to observe, a scientific 
hypothesis should be forward? 

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Predictive he very obligingly 
clarified. 

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That in his view, there were 
five primary predictions that we

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should look for if we're testing
for the existence of a mantle 

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plume. 
So the first one is that when 

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the mantle plume, First Rises 
up, through the mantle and it 

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reaches the base of the 
lithosphere. 

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It domes the lithosphere up so 
we should see kilometer scale, 

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lithospheric, uplift on a scale 
of some hundreds of kilometers 

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broad. 
That's the first one following 

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this uplift. 
We should see the outpouring of 

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a flood Basalt. 
For example, the Deccan traps, 

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something like that. 
The third thing is that there 

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should be a tail, a plume tail 
stretching, I'm from the surface

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down to the core-mantle boundary
and hopefully we should be able 

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to image this with methods such 
as seismic tomography. 

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The fourth prediction is that 
this plume along with its tail 

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is fixed relative to the Earth's
geomagnetic pole. 

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In other words, the tectonic 
plates which are moving relative

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to the geomagnetic pole. 
These tectonic plates are moving

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over the fixed plume and they 
should carry away with them. 

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A chain of extinct, volcanoes of
volcano erupts, it's carried 

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away. 
The next one, erupts that's 

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carried away. 
So a plume region should have a 

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Time Progressive trail of 
volcanism and the fifth 

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expectation is that there should
be evidence that the source of 

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the eruptive was hot. 
It was some 200 degrees hotter 

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than say, mid-ocean ridge Basalt
sources. 

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So those are the five 
predictions. 

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Uplift flood Basalt tail down to
the core mantle boundary Time 

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Progressive trial and high 
temperature. 

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And how did these stack up in 
Hawaii? 

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In Hawaii, the emperor chain, 
the oldest part of the a chain 

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is, right? 
At the far north of the Pacific 

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Ocean, and it's right by the 
Aleutian trench. 

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So anything older than about 80 
million years, has gone down the

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Aleutian trench. 
So if there was initially 

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uplift, And a flood Basalt, then
there's no evidence for it. 

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People have looked at the 
chemical composition of lavas in

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Kamchatka to try to see if 
there's some geochemical 

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signature of a subducted flood 
Basalt. 

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But they have not so far found 
any such evidence. 

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So, basically, there's no 
evidence for the first two 

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predictions. 
So then there's the plume tail 

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down to the core-mantle 
boundary, and there have been a 

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number of Of studies of this. 
And although almost every study 

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has reported some evidence that 
supports that, the problem is 

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every study, sees it in a 
different place or going down to

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a different depth or tilting in 
a different direction. 

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So, there's no repeatability 
between the studies. 

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It's very unfortunate that 
Hawaii is right in the very 

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middle of the Pacific and 
there's a relatively small 

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amount of land. 
Mass there, because it makes it 

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very difficult to do seismic 
experiments, and it would be a 

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lot easier if Hawaii was in the 
middle of a continent. 

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And we could spread out 
seismometers over a very broad 

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area. 
So that's the status of the 

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third prediction, the fourth 
prediction of a Time Progressive

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Trail. 
This is spectacularly, well, 

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reproduced the Hawaiian seamount
chain, and north of that. 

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The emperor seamount chain 
space. 

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Secular Lee time Progressive but
unfortunately, there's a sting 

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in the tail there and that is 
that the time progression, 

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doesn't match the motion of the 
Pacific Plate. 

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This is very curious. 
When the emperor chain was in 

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place, this is roughly between 
80 million years and 45 million 

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years ago. 
The Pacific Plate was 

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approximately stationary and the
locus of volcanism migrated 

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across Ross the stationary plate
at approximately Bend time, 

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that's about 45 million years 
say the Pacific Plate, began to 

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move and then the locus of 
volcanism stopped. 

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So the whole chain is indeed 
time Progressive, but not 

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because the Pacific Plate was 
carrying the volcanoes away. 

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It's just for some reason, this 
volcanic, Locus, this active 

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volcanic, Locus wants to move 
relative to the Plate. 

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And if the Pacific Plate is 
moving, it will stop. 

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And if the Pacific Plate stops, 
it moves. 

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So this is just the biggest 
puzzle in. 

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Geology really to move on to the
fifth prediction which is high 

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temperature. 
This prediction is fulfilled at 

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Hawaii. 
There is pretty unequivocal 

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evidence that the source of 
Magma's at Hawaii is hotter than

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at Mid. 
Ocean ridges. 

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So there we have it. 
One out of five in earlier, 

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geology, B podcasts, Barbara 
Romano, it's talked about the 

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large low Shear velocity 
provinces seen clearly in the 

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tomography and Alan McNamara 
showed fluid. 

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Dynamical models that seem to 
predict the existence of such 

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regions. 
Surely those are real. 

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The lsv peas are of course real 
but the Question is, what are 

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they? 
They were originally noticed to 

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have low seismic wave speeds and
they were nicknamed the super 

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plumes but it was immediately 
discovered that instead of being

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hot and buoyant they're dense 
and probably not hot at all. 

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They were quickly renamed 
seismic piles because they're 

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basically piles of dense 
material sitting on the 

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core-mantle boundary And it was 
quickly, hypothesized that 

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instead of generating plumes 
themselves, the plumes were 

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generated outside the LLS VPS 
and that they trickled up the 

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edges of the ls VPS and Rose up 
to the surface around their 

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edges. 
As you say, we can really only 

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see seismic wave velocity from 
the seismic data. 

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So what are the factors that 
affect seismic wave speed many 

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workers? 
Tomb, that the speed at which 

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seismic waves travel can be 
considered to be a proxy of 

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temperature. 
Well, this is not the case. 

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There are three things that can 
affect seismic wave speeds and 

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in order of their strength, if 
you like the first one, is the 

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presence of partial melt. 
If we have a trace of partial 

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melt, this can drop seismic wave
speeds enormously without any 

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change in. 
Temperature. 

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So that is the strongest effect.
Partial melt the second most 

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strong effect, which can lower 
weight, the seismic waves boots 

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00:14:15,300 --> 00:14:17,700
or indeed, raise them is 
composition. 

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So if you're in a region where 
you feel you can, absolutely 

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rule out, partial melt 
explaining your observations, 

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then the next thing to ask 
yourself is, could there be 

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geochemical variations, 
petrological variations in the 

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material down there. 
Only if that can be rolled out, 

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00:14:36,100 --> 00:14:38,100
should we really turn to 
temperature? 

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Because temperature is by far 
the weakest effect on seismic 

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00:14:42,100 --> 00:14:45,500
wave speeds. 
So if you go out and do an 

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00:14:45,500 --> 00:14:49,000
experiment and then you measure 
the three dimensional variation,

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for example in the S wave speed 
of seismic waves, you have one 

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variable there and you have 
three possible ways of 

229
00:14:57,600 --> 00:15:00,700
explaining it or indeed, a 
combination of those three. 

230
00:15:01,400 --> 00:15:06,800
So it really is not robust. 
Interpretation to assume that a 

231
00:15:06,800 --> 00:15:09,300
seismic tomography. 
Image is a proxy for 

232
00:15:09,300 --> 00:15:13,500
temperature. 
Okay, that's enough on plumes. 

233
00:15:14,200 --> 00:15:19,100
Tell us about the alternative 
hypothesis, which is called the 

234
00:15:19,100 --> 00:15:23,300
plate hypothesis. 
So the plate hypothesis suggests

235
00:15:23,300 --> 00:15:27,400
that the stress field in the 
lithosphere is variable, both 

236
00:15:27,400 --> 00:15:32,400
horizontally, and vertically, 
and that volcanism occurs away 

237
00:15:32,400 --> 00:15:36,000
from plate boundaries where the 
lithosphere is in extension. 

238
00:15:36,800 --> 00:15:40,000
Where the lithosphere is in 
extension, it can allow 

239
00:15:40,200 --> 00:15:44,700
pre-existing Melt to leak up 
either from the lower crust or 

240
00:15:44,700 --> 00:15:48,200
the mantle. 
And if the lithosphere goes into

241
00:15:48,200 --> 00:15:51,800
extension, to the extent, that 
it may even Rift all the way 

242
00:15:51,800 --> 00:15:55,000
through, for example, when we 
have supercontinent break up, 

243
00:15:55,400 --> 00:15:59,000
then you could have 
asthenosphere rising up, maybe 

244
00:15:59,000 --> 00:16:02,900
one or two hundred kilometers in
height and then you could boost,

245
00:16:03,300 --> 00:16:06,700
whatever. 
Pre-existing melt there is with 

246
00:16:06,700 --> 00:16:09,800
decompression, upwelling mantle 
melting. 

247
00:16:11,100 --> 00:16:15,200
So this is the plate hypothesis.
It's basically an extension of 

248
00:16:15,200 --> 00:16:20,400
the existing plate tectonic 
hypothesis, except it's really 

249
00:16:20,400 --> 00:16:26,000
saying that the Earth is not 
either 100% rigid plates and 

250
00:16:26,000 --> 00:16:30,100
narrow plate boundaries, but the
Interiors of the plates also 

251
00:16:30,100 --> 00:16:34,800
have variable stress and in some
places they're extending and 

252
00:16:34,800 --> 00:16:40,900
there can be leakage of melt in 
those areas to so the neat. 

253
00:16:41,100 --> 00:16:44,200
Thing about the plate hypothesis
really is that? 

254
00:16:44,300 --> 00:16:47,300
As you said in your 
introduction, it means that all 

255
00:16:47,300 --> 00:16:51,600
the volcanism on Earth and 
earthquakes can be explained by 

256
00:16:51,600 --> 00:16:55,300
one hypothesis. 
The the plate tectonic 

257
00:16:55,300 --> 00:16:59,700
hypothesis in its relaxed mode. 
If you like, and we don't need 

258
00:16:59,700 --> 00:17:04,000
to completely separate 
hypotheses with this volcanism 

259
00:17:04,000 --> 00:17:07,099
explained by plate tectonics and
that volcanism needing a 

260
00:17:07,099 --> 00:17:10,400
completely separate, unrelated 
hypothesis for it. 

261
00:17:10,400 --> 00:17:13,800
And then, All these volcanic 
regions, which might be half and

262
00:17:13,800 --> 00:17:17,800
half, causing us headaches in 
between, it's like a unifying 

263
00:17:17,800 --> 00:17:21,700
hypothesis if you like. 
So, according to the play type 

264
00:17:21,700 --> 00:17:25,400
offices, we would expect to see 
evidence of extension in the 

265
00:17:25,400 --> 00:17:29,200
lithosphere. 
Whenever volcanism has occurred,

266
00:17:29,200 --> 00:17:33,000
or is currently occurring away 
from a plate, boundary. 

267
00:17:33,500 --> 00:17:35,900
Yes, that's correct. 
Okay. 

268
00:17:35,900 --> 00:17:39,600
Let's see whether we can test 
the predictions of the play type

269
00:17:39,600 --> 00:17:43,900
officers. 
You're an expert on Iceland and 

270
00:17:44,100 --> 00:17:47,500
that's where you initially found
the evidence for plumes lacking,

271
00:17:48,000 --> 00:17:51,500
even though it's on a mid-ocean 
spreading Ridge at the edge of a

272
00:17:51,500 --> 00:17:53,800
plate. 
The fact that there's enough 

273
00:17:53,800 --> 00:17:57,700
magma generated there to form 
land in contrast to the rest of 

274
00:17:57,700 --> 00:18:02,400
the Mid-Atlantic Ridge, requires
some explanation, which of 

275
00:18:02,400 --> 00:18:05,600
course, the plume theorist 
provide by positing a plume 

276
00:18:05,600 --> 00:18:08,300
under Iceland. 
The observations can't be 

277
00:18:08,300 --> 00:18:12,900
explained by this the crust is 
30, E km thick is even as much 

278
00:18:12,900 --> 00:18:19,600
as 40 km thick in some places. 
And if this was all Plum juice, 

279
00:18:19,900 --> 00:18:25,000
if this was a stack of basaltic 
material Iceland should stand 

280
00:18:25,000 --> 00:18:29,000
for kilometers high. 
But Iceland doesn't stand for 

281
00:18:29,000 --> 00:18:31,700
kilometers. 
High is stands approximately one

282
00:18:31,700 --> 00:18:36,300
kilometer High and the only way 
of explaining this is that the 

283
00:18:36,400 --> 00:18:41,400
lower crust under Iceland the 
bottom 20 or 30, What is the 

284
00:18:41,400 --> 00:18:46,900
crust in Iceland is much denser 
than we would expect if it was 

285
00:18:47,000 --> 00:18:52,700
basaltic and really the only way
that can be explained is if it's

286
00:18:52,700 --> 00:18:56,800
largely Continental, this again 
is like, heresy. 

287
00:18:56,800 --> 00:18:59,600
Oh my God, you know, people will
say that I haven't read anything

288
00:18:59,600 --> 00:19:03,800
for the last 50 years because 
this was initially suggested 40 

289
00:19:03,800 --> 00:19:08,500
or 50 years ago, by Russian 
seismologists, everything 

290
00:19:08,500 --> 00:19:13,200
essentially can be explained by 
this, Adding the thermal field. 

291
00:19:13,800 --> 00:19:18,200
So although this sounds 
completely turned upside down. 

292
00:19:18,200 --> 00:19:23,700
I am virtually 100% certain that
the majority of the crust 

293
00:19:23,700 --> 00:19:27,200
beneath Iceland is largely 
continental. 

294
00:19:27,600 --> 00:19:31,200
And that what we're looking at 
in Iceland is basically a 

295
00:19:31,200 --> 00:19:36,400
volcanic passive margin in 
formation and the reason there's

296
00:19:36,400 --> 00:19:39,900
a volcanic passive margin in 
formation there is because 

297
00:19:39,900 --> 00:19:43,100
there's a micro-continent under 
Iceland. 

298
00:19:43,500 --> 00:19:47,500
I didn't quite understand how if
Iceland was made entirely out of

299
00:19:47,500 --> 00:19:51,500
Basalt that came out of a mantle
plume, it would have to be 4 

300
00:19:51,500 --> 00:19:56,000
kilometers high, but if it's got
Continental material underneath 

301
00:19:56,000 --> 00:19:59,300
it, which I thought was lighter 
than Basalt. 

302
00:19:59,300 --> 00:20:03,600
Anyway, it might only have to be
one kilometer, which is what it 

303
00:20:03,600 --> 00:20:05,200
is. 
How does that work? 

304
00:20:05,300 --> 00:20:11,500
Look, if the lower crust 
contains a lot of Continental 

305
00:20:11,600 --> 00:20:16,300
mid and lower crustal material, 
then it will have a higher 

306
00:20:16,300 --> 00:20:21,400
density than if it was just 
unusually thick Oceanic layer 3 

307
00:20:21,500 --> 00:20:25,400
and it will have the correct 
seismic velocity, so the seismic

308
00:20:25,400 --> 00:20:29,200
velocity of the lower crust 
under Iceland is approximately 

309
00:20:29,200 --> 00:20:32,000
7.3, which is consistent with 
crust. 

310
00:20:32,200 --> 00:20:36,900
But the density is close to the 
mantle This can be explained by 

311
00:20:36,900 --> 00:20:39,900
Deep crustal. 
Continental petrology is ultra 

312
00:20:39,900 --> 00:20:44,500
basic petrology she's but it 
can't be explained by Oceanic 

313
00:20:44,500 --> 00:20:49,100
type basaltic petrology. 
She's you mentioned are volcanic

314
00:20:49,200 --> 00:20:53,100
passive margin in Iceland, 
what's that? 

315
00:20:53,900 --> 00:20:55,900
Well it's easiest to give an 
example of that. 

316
00:20:55,900 --> 00:21:01,400
And this is what lies along the 
coastline of Norway and the east

317
00:21:01,400 --> 00:21:05,500
coast of Greenland. 
It's essentially stretched T', 

318
00:21:05,700 --> 00:21:10,800
continental crust which is 
capped with lava flows which 

319
00:21:10,800 --> 00:21:15,300
were produced in great volume 
when the Atlantic Ocean first 

320
00:21:15,300 --> 00:21:18,800
opened up. 
So I suppose this picture of a 

321
00:21:18,800 --> 00:21:23,500
rifting extending 
micro-continent forming a 

322
00:21:23,800 --> 00:21:27,700
passive. 
Volcanic margin is consistent 

323
00:21:27,800 --> 00:21:30,600
with the plate. 
Hypothesis for Iceland. 

324
00:21:31,400 --> 00:21:35,500
What about Hawaii then, which is
exhibit a for the plume 

325
00:21:35,500 --> 00:21:39,000
hypothesis? 
Can we see extension there? 

326
00:21:39,000 --> 00:21:41,300
That would be predicted by the 
plates. 

327
00:21:41,300 --> 00:21:47,200
Hypothesis, Hawaii is not only a
massive challenge to either 

328
00:21:47,200 --> 00:21:50,900
falsifying or verifying the 
plume hypothesis because of its 

329
00:21:50,900 --> 00:21:53,500
great remoteness. 
And the fact that a lot of 

330
00:21:53,500 --> 00:21:58,300
evidence would like to see is 
either very difficult to find or

331
00:21:58,300 --> 00:22:03,400
it's gone, but the same goes As 
for the point hypothesis, as you

332
00:22:03,400 --> 00:22:06,900
rightly point out, we would 
expect to see substantial 

333
00:22:06,900 --> 00:22:10,500
evidence of extension there. 
But we're not really in a 

334
00:22:10,508 --> 00:22:13,800
position to be able to find that
as yet. 

335
00:22:14,700 --> 00:22:19,900
So Hawaii is a tremendous 
challenge for both hypotheses 

336
00:22:20,000 --> 00:22:22,300
and it's just something that's 
going to be sorted out in the 

337
00:22:22,300 --> 00:22:25,400
future and I hope that happens 
quickly enough that I'm still 

338
00:22:25,400 --> 00:22:30,300
alive to see what happens. 
Do we have any independent line 

339
00:22:30,300 --> 00:22:33,700
of reasoning to That the 
lithosphere around Hawaii might 

340
00:22:33,700 --> 00:22:38,000
be extending there have been 
some studies done where people 

341
00:22:38,000 --> 00:22:41,700
have calculated the stress field
in the Pacific Plate. 

342
00:22:42,000 --> 00:22:47,600
Simply put the Pacific Plate, 
covers one third of the surface 

343
00:22:47,600 --> 00:22:50,700
of the planet. 
It's absolutely huge. 

344
00:22:51,200 --> 00:22:55,300
It is shaped roughly like the 
continent of Africa. 

345
00:22:55,400 --> 00:22:59,700
So it has a big gap, bulge to 
the West, which is the Western 

346
00:22:59,700 --> 00:23:03,500
Pacific and then, there's The 
part of the East, which is 

347
00:23:03,500 --> 00:23:07,200
bordered by the East Pacific 
Rise and the South Pacific 

348
00:23:07,200 --> 00:23:11,200
spreading Ridge and the part to 
the east. 

349
00:23:11,700 --> 00:23:15,600
As I say, it's got a spreading 
Ridge along most of its length. 

350
00:23:15,600 --> 00:23:18,400
And then there's the San Andreas
fault Zone, and then there's 

351
00:23:18,400 --> 00:23:20,900
more spreading in the Northeast 
Pacific. 

352
00:23:21,300 --> 00:23:24,300
So, that part of the Pacific is,
got a lot of spreading Ridge on 

353
00:23:24,300 --> 00:23:26,700
it. 
The West Pacific. 

354
00:23:26,700 --> 00:23:31,300
On the other hand is surrounded 
on three sides by subduction. 

355
00:23:31,400 --> 00:23:34,500
Bones. 
So there's a strong slab, pull 

356
00:23:34,500 --> 00:23:39,400
Force to the north down, the 
Aleutian trench to the west and 

357
00:23:39,400 --> 00:23:45,600
1/8 China, and to the South. 
So the Western Pacific is in 

358
00:23:45,600 --> 00:23:49,300
more extension. 
If you like due to being largely

359
00:23:49,300 --> 00:23:53,200
surrounded by subduction zones 
where as the East Pacific has 

360
00:23:53,200 --> 00:23:57,500
got more spreading Ridge so it's
subject to Less in the way of 

361
00:23:57,500 --> 00:24:01,200
extensional stresses. 
So these two parts of the 

362
00:24:01,400 --> 00:24:04,200
Pacifica really under the 
influence of very different 

363
00:24:04,200 --> 00:24:11,200
stress fields and Hawaii lies 
exactly on the border between 

364
00:24:11,200 --> 00:24:16,400
the East and West Pacific. 
So one kind of Smoking Gun if 

365
00:24:16,400 --> 00:24:23,000
you like, is that this volcanic 
region is active exactly where 

366
00:24:23,600 --> 00:24:27,000
Pacific Plate material is 
drifting from the Eastern 

367
00:24:27,500 --> 00:24:30,600
Pacific. 
Stress regime into the Western 

368
00:24:30,600 --> 00:24:34,500
Pacific. 
Stress regime, and people have 

369
00:24:34,800 --> 00:24:39,300
modeled this, some colleagues 
have done relatively simple 

370
00:24:39,600 --> 00:24:45,300
models of the stress field due 
to Thermal contraction to 

371
00:24:45,300 --> 00:24:47,500
Thermal effects cooling 
contraction. 

372
00:24:48,000 --> 00:24:53,000
And also due to these slab 
forces, there have been some 

373
00:24:53,000 --> 00:24:57,000
promising results, which 
suggests that there are regions 

374
00:24:57,000 --> 00:24:59,700
of extension smack in the middle
of the plate there. 

375
00:25:00,200 --> 00:25:03,000
And that this comes about About 
because of the variation is 

376
00:25:03,000 --> 00:25:05,900
Tresses, I've described this 
work. 

377
00:25:05,900 --> 00:25:10,900
Really needs to be done to the 
utmost accuracy that we can has 

378
00:25:10,900 --> 00:25:15,700
probably our best shot while we 
wait for seafloor geodesy to 

379
00:25:15,800 --> 00:25:19,100
become more mature. 
What about the other mid-ocean 

380
00:25:19,100 --> 00:25:22,300
volcanoes are there? 
Reasons to Suppose there might 

381
00:25:22,300 --> 00:25:26,100
be extension going on there as 
well Tristan da cunha for 

382
00:25:26,100 --> 00:25:29,200
example that might be an 
interesting place to look at as 

383
00:25:29,200 --> 00:25:31,200
been a lot of work done there, 
true? 

384
00:25:31,400 --> 00:25:34,900
The colonel is a relatively 
small island in the middle of a 

385
00:25:34,900 --> 00:25:37,900
very broad, scattering of 
seamounts. 

386
00:25:38,300 --> 00:25:42,400
In the Atlantic Ocean, we have a
lot of major active fracture 

387
00:25:42,400 --> 00:25:44,800
zones. 
We have a lot of scattered 

388
00:25:44,900 --> 00:25:49,100
continental crust. 
It's clear that there's a lot of

389
00:25:49,200 --> 00:25:53,300
Continental fragments there and 
the volcanism their, the 

390
00:25:53,300 --> 00:25:57,200
scattered volcanism is probably 
greatly influenced by the 

391
00:25:57,200 --> 00:26:00,800
inhomogeneous structure of the 
Atlantic in that region. 

392
00:26:01,400 --> 00:26:04,500
Which is bringing about 
differential movements. 

393
00:26:04,700 --> 00:26:08,200
The plate is not stable 
basically, okay? 

394
00:26:08,200 --> 00:26:13,400
So it's a complicated picture 
which may be consistent with the

395
00:26:13,500 --> 00:26:16,900
plate hypothesis. 
How does the plate hypothesis 

396
00:26:16,900 --> 00:26:20,800
address the volcanism in the 
middle of continental plates 

397
00:26:21,000 --> 00:26:23,300
such as Yellowstone in North 
America? 

398
00:26:24,400 --> 00:26:31,000
The plates are not fully rigid. 
As was initially proposed in the

399
00:26:31,000 --> 00:26:34,900
plate, tectonic hypothesis. 
But we now know that the plates 

400
00:26:34,900 --> 00:26:38,800
are deformable to some extent. 
We have features like the East 

401
00:26:38,800 --> 00:26:43,200
African Rift Zone, we have the 
Rhine graben and we also have 

402
00:26:43,200 --> 00:26:47,400
the Yellowstone area in North 
America and the Basin and Range 

403
00:26:47,400 --> 00:26:51,000
Province, for example. 
So these are regions inside the 

404
00:26:51,008 --> 00:26:56,400
plate which are deforming and in
To some extent and Volcanic 

405
00:26:56,400 --> 00:27:00,600
regions like Yellowstone, and 
the other volcanism more, 

406
00:27:00,600 --> 00:27:03,000
southerly and the Basin and 
Range Province. 

407
00:27:03,300 --> 00:27:08,100
This, I would attribute to 
defamations internally in the 

408
00:27:08,100 --> 00:27:10,700
plate. 
The one thing about Yellowstone 

409
00:27:10,700 --> 00:27:15,200
that is heavily emphasized, is 
that there is a Time Progressive

410
00:27:15,200 --> 00:27:20,500
volcanic Trail. 
So this time Progressive 

411
00:27:20,600 --> 00:27:24,200
volcanism along the Eastern 
Snake River plain is in The 

412
00:27:24,200 --> 00:27:29,400
great solicit calderas under the
Eastern State River plain there.

413
00:27:29,900 --> 00:27:34,100
The basaltic volcanism in that 
region is not time progressed if

414
00:27:34,100 --> 00:27:39,000
it's the solicit volcanism which
obviously comes from melting of 

415
00:27:39,000 --> 00:27:42,800
the lower crust. 
So I thought to myself, well, if

416
00:27:42,800 --> 00:27:46,200
this part of the volcanism is 
time Progressive than the plate,

417
00:27:46,200 --> 00:27:50,000
hypothesis predicts that 
extension must be time 

418
00:27:50,000 --> 00:27:55,600
Progressive So I just pulled up 
Google and started to type in 

419
00:27:55,700 --> 00:27:58,800
time Progressive volcanism in 
the Basin and Range Province. 

420
00:27:59,200 --> 00:28:03,300
And within five minutes I had 
found Papers written by 

421
00:28:03,300 --> 00:28:08,600
structural geologists who 
proposed that the activity of 

422
00:28:09,000 --> 00:28:12,800
large normal faults in the 
northern Basin and Range 

423
00:28:12,800 --> 00:28:16,300
Province was time. 
Progressive along the Eastern 

424
00:28:16,300 --> 00:28:19,800
Snake River, plain all the 
information is out there. 

425
00:28:19,800 --> 00:28:23,500
It just has not been Protected 
in terms of the plate 

426
00:28:23,500 --> 00:28:26,700
hypothesis. 
How long do you think it'll be 

427
00:28:26,700 --> 00:28:29,900
before observations will be good
enough to provide a rigorous 

428
00:28:29,900 --> 00:28:31,700
test of the plate? 
Hypothesis? 

429
00:28:32,400 --> 00:28:36,100
I think we have enough 
observations on the table 

430
00:28:36,100 --> 00:28:38,800
already, one. 
Excellent thing about the plume 

431
00:28:38,800 --> 00:28:44,500
hypothesis is that it certainly 
has inspired and in gendered and

432
00:28:44,500 --> 00:28:48,700
Justified a tremendous lot of 
research into very interesting 

433
00:28:48,700 --> 00:28:53,900
places like the Galapagos like 
Easter, Ireland reunions Tristan

434
00:28:53,900 --> 00:28:55,700
da cunha. 
The only thing that's really 

435
00:28:55,700 --> 00:28:58,600
lacking is for people to come 
along and say, okay, I'm going 

436
00:28:58,600 --> 00:29:01,900
to look at hotspots such and 
such and I'm going to gather 

437
00:29:01,900 --> 00:29:04,100
together all the data that we've
got so far. 

438
00:29:04,400 --> 00:29:07,500
I'm going to see how this fits 
into the plate hypothesis. 

439
00:29:07,900 --> 00:29:11,600
And then this will show what 
gaps there are in. 

440
00:29:11,600 --> 00:29:14,600
Testing the plate hypothesis and
maybe we can propose an 

441
00:29:14,600 --> 00:29:18,800
experiment to fill in that Gap. 
Julian Folger. 

442
00:29:19,000 --> 00:29:21,800
Thank you very much. 
It was a great pleasure. sir 

443
00:29:21,800 --> 00:29:25,100
Oliver, it's been tremendous, 
fun, talking to you for more 

444
00:29:25,100 --> 00:29:29,300
about geology, b, as well as 
pictures and illustrations, that

445
00:29:29,300 --> 00:29:33,600
support this podcast, you can go
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