I think I'm the first Tuzo Wilson
lecture introducer who didn't ever know
or meet Tuzo Wilson my impressions of him are therefore entirely based on his work
what's written in textbooks and what
people say about him one thing I've
noticed is that as soon as you bring up
the name to Tuzo Wilson to someone in the
department who knew him their face
immediately lightens up and they want to
tell you stories about him about their
interactions with him I think this is
truly revealing of the impact he had on
our community not only scientifically
but also personally and I don't think
one can ask for much more out of life as
a professor in scientist in honor of 20
Wilson the Department of Physics created
the J Tuzo Wilson professorship in
geophysics in 1995 the position is
appointed for five years to a prominent
U of T professor who has made
significant contributions to the field
of geophysics this year marks the
incoming of professor Stephen Morris as
the new J Tuzo professor having
succeeded Nigel Edwards after his term
the first year of the term is marked by
having the two so Wilson professor give
the Tuzo Wilson lecture and I'm
therefore happy to introduce professor
Stephen Morris as this year's lecture I
first met Stephen when I was an
undergraduate student in physics here he
gave a guest lecture to my third year
lab class on something called spiral
defect chaos at the time I thought there
is no way something there is no way
something that cool actually exists
during that lecture not only did he
demonstrate it that it does exist but
that you can build a tabletop experiment
to show it Stephens work covers a vast
array of physics topics with the
underlying theme of pattern formation a
quick glance at his website will
delivered project topics such as the
fluid mechanical sewing machine the
shape of icicles washboard Road and a
supernova in a jar he received his PhD
from U of T in 1991 and it's been a
professor here since 1993 he was awarded
the Faculty of Arts and Sciences
outstanding teaching award in 2004 and
was named a fellow of the american
physical society in 2012 you've probably
seen him in his work
on the discovery channel YouTube or
Flickr where he regularly demonstrates
exciting physics phenomena to a broad
audience today we are going to hear
about his work on an amazing geological
pattern known as the Giant's Causeway
please join me in welcoming professor
Stephen Morris thank you thank you don't
clap I haven't said anything yet we're
feeding back sound booth oh wait I could
turn this on it's great to be here I
actually did meet to the Wilson once
back when I was a graduate student we
used to have a graduate student only
seminar series on Friday afternoons at
four o'clock because we knew that no
professors would ever come at Friday
afternoon four o'clock and we had two
cases of beer that we kept on the front
counter and the speaker was allowed to
start drinking the beer while they gave
their talk and everyone else had to wait
until he's finished speaking and
somebody had the waggish idea to invite
to the Wilson to give graduate student
seminar at age 84 85 something like that
and I vividly remember standing at the
front of the room and making a little
speech appointing to the Wilson as
honorary graduate student for the day he
gota so he would be qualified to give
the rider student seminar and then I
handed him his beer that was the one
unfortunately the one and only time I
ever met him and he gave a very spirited
talk on plate tectonics and I wish I'd
taken a picture or something in those
days when didn't take pictures if you
told me then that I would be standing
here giving the j-20 Wilson
professorship lecture I'd simply
wouldn't have believed it it's
unbelievable so I'll tell you another
little story about my interaction with
to zone
I'm going to tell you about rocks okay
it's useful to remember that geophysics
is ultimately about rocks in this era of
wonderful satellite data and Planetary
geophysics it's nice to know that just
plain old garden variety rocks are still
interesting these are just not a old
rocks of course these are probably the
most famous rocks in the history of
geology this is the Giant's Causeway in
Northern Ireland and this is a tabletop
experiment which I will show you a
little bit later and I hope I can
convince you that there's some
connections between these two things I
wanted to show you the book that got me
into this field okay it's called the how
and why wonder book of our earth and it
was published in nineteen sixty and I
must have received it around the time i
was born in nineteen fifty-nine know i
have to receive it soon after because i
don't remember any of the words of this
book but I remember every single picture
in this book so I believe I received
this book as a kid before i could read
and who could not be fascinated by a
cover like this it's got everything
right it's good it's got cracks so
subliminally i think i saw this it has
always been in the back of my mind but
if you go to page 19 of this book and I
vividly remember these pictures there
are these fascinating things like here's
us right here's the geologic time scale
and there's this funny picture with the
blob between the two continents here and
if you read the section here called what
was the earth like long ago it talks
about that we've studied fossil clues
and we've discovered that at one time a
bridge of land probably connected
northern Europe with green land and
another such land brim extended between
spain in the united states and at still
another stage africa australia and south
america were all part of the same
massive land and forests of fern trees
grew across water today thousands of
miles of open water and you know they're
here it is these are there's the lost
continent there and of course this is
what 20 Wilson did ferocity he
eliminated those thousands of miles of
fern trees by the simple expedient of
putting this one up against that one and
having it having the ocean disappear in
between and so this was nineteen sixty
within about 10 or 15 years of this
book's publication this became a chuckle
I dia
but that's sort of where I came in i
guess i don't i don't remember these
words but I sure remember these pictures
and I remember the lost continent of
Lemuria where the Linear's come from
it's in the middle of the Indian Ocean
it's not really there but anyway I gave
this book to my kids but I don't think
they actually anyway so I'm going to
talk about the work of several people
almost everything I'm going to tell you
about is was the thesis work of Lucas
going who's now a group leader in at the
Max Planck of suiting in in gooding in
and my summer student marry me tomorrow
is made interesting film which I'll show
you and myself and we had some
theoretical help from mahato van from
Harvard and mahana vans great tech
ability is to make complicated things
really really simple so he gave us the
courage if you like to to believe that
we'd actually had a very very simple
argument for the I'll give you about
about these columns and here's Lucas at
work on whose thesis he's wearing a life
jacket because if he falls off here
he'll land in the surf and he's wearing
climbing boots and a hat because if you
fall off your bang his head and he is
actually climbing a not the Giant's
Causeway but another place that I'll
tell you so here's the probably the most
famous picture people see above the
Giant's Causeway if you go there how
many people have been there with you
okay it's a world heritage site it's on
the north coast of Ireland and it
basically faces north it's at the bottom
of a huge cliff and it's a huge array of
spectacular least weirdly or ordered
rock columns and they all fit together
like pencils and they're mostly
hexagonal but they're not all hexagonal
but if people often say they're all
hexagonal and there's thousands and
thousands of them and they're sort of in
the surf and it's a very dramatic kind
of sort of place the real trick when you
go there is to take a picture with no
people in it because as a world heritage
site it's crawling with tourists all the
time and so I had to wait for a
gentleman to walk down behind that
little mound before I took this picture
scientifically also it goes back right
to the very beginning of science in fact
not just the name geology but really to
the beginning of science it was first
reported to the Royal Society in 1693
and I can tell you that because you can
download the paper okay
it's on jstor it's published in
philosophical transactions of the royal
society and it's written by Sir RB SRS
in those lovely far-off days gentlemen
scientists were so chummy that they
didn't even have to put their names on
their publications and for a long time
we had no idea who sir RBS RS was and
eventually it was tracked down his name
is Sir Richard bulkley Scottish Royal
Society is what it actually stands for
and I like a good gentleman he didn't he
personally go to the Giant's Causeway
because that was not what gentlemen did
at the time he reports the tales of
travellers so first he tries to convince
the the editor that I showed you a
pardon I was very exact and getting it
from a person that was Ray compost and
perhaps puritas a scholar a Master of
Arts from Cambridge so in those days
gentlemen especially gentlemen who were
interested in geology or geography they
didn't go away from their comfortable
armchairs they they sent men out into
the to bring back a rock or maybe two to
send back a verbal report and so the the
idea that that geologists or people of
that sort should be interested in
actually going to the field took 100 100
more than 100 years to become common as
far as they were concerned you know the
Giant's Causeway was a thing that they
could trust if they knew if they trusted
the reports from the travelers that's
all they needed as far as data today
this formation is called kilometer
joints and giant's causeway is by no
means unique in fact it's found all over
the world I'll show you a few examples
the word joint does not mean what people
in my generation think it means it means
a crack which does not slip okay so it's
just a crack that opens so kilometer
joints refers to the fact that these
things are formed by a cracking process
basically and I'll describe this in gory
detail but a lava flow came down some
tens of meters or 60 million years ago
and as it cooled it cracked in this
straight into this strange pattern so
here's a picture of the Giant's Causeway
taken from the top of the cliff and you
can't really see it but there's
thousands of these little uh mostly
hexagonal things all over here little
mound that I showed you is just this
little bump here and I will draw your
attention to this wall here it's sort of
a ramp with a wall on the other side and
if i should say it's very difficult to
get a sin
some of this thing without being there
and walking around it's almost
impossible to take a picture of lots of
joints at once without going to the top
of the cliff but this this picture was
taken at a very clever fashion can
anyone guess it looks like a drone
picture right and indeed if you put
Giant's Causeway drone in you can find
beautiful videos but this was made any
even cleverer fashioned from a kite okay
so this guy Nick Russell went to the
Giant's Causeway and took a number of
wonderful pictures by kite so this is
very very good illustration because you
can see what you would see sort of
walking around here's a person from
scale these things are mostly hexagonal
some of them are extremely exciting
here's a very good one up here and some
of them are really rather far from being
hexagonal here's a kind of you know
block shape would hear these little
things are actually puddles and so some
of them dome up and some of them dumb
down and I'm not going to talk about
that that's called the ball and socket
joint I'm talking about the cracks that
separate the little tiles from each
other that's those are the things that
that are the subject of the top and
there's thousands of thousands of these
columns at the causeway so here's a
picture taken from the cliff a little
bit farther east and here's that wall
that I pointed out to you before and
here's the actual causeway and I will
spare you the story of the Giants okay
there every tourist is told a
complicated story of a battle between a
Scottish giant and they ended Irish
giant and it's really hilarious but
that's of course not actually how they
form so to get back to the history the
reason that that outcropping there is so
famous is that it prominently appears in
this picture which is the one of the
first accurate illustrations of a
geological topic ever made in fact the
picture that precedes this was actually
commissioned by the Royal Society was
the first effort by anyone to draw a
realistic picture of a geological of
formation for the purposes of learning
something about science and this is like
the second one and some people believe
that Susannah Drury who's a no-name
artist no one knows anything about her
some believe she used a camera obscura
to make this picture it's so realistic
but or she also had to populate it with
little groups of happy sort of a
landscape figures in order to kind of
make it a friendly scene and one of the
reasons it's extremely influential in
famous was because it was quickly
engraved actually some years but it was
engraved
this engraving and it's interesting to
see what the engraver thought was
important and you know what they left
out so if you look at the details you
can see the rocks move around a little
bit between the two pictures and the
people are looking at different
directions but after it was engraved in
1744 it was published a little bit later
in the the famous encyclopedia put
together by d0 and Dalembert and it was
a result of this very wide dissemination
of this picture of the Giant's Causeway
that it became a famous sort of uncanny
thing that had to be explained and it
was only after seeing pictures like this
that people began to realize that there
were other at places where the rocks
were were broken into these amazing
columns there some in the center of
France for example and that began the
the kind of you know the widespread
understanding that this was an
interesting place it was a little bit of
a tourist trap before that but after
this it became a major tourist trap so
it's been a tourist traps in for 300 250
years or whatever okay so uh here is my
friend Bob and Bob made you you're going
to hear more about him later but here he
is sitting on top of that very crapping
that I showed you a minute ago he didn't
actually climb up there he actually went
up the back which is much easier to do
so the Giant's Causeway is by far the
most famous example of kilometer
jointing but probably the second most
famous example is an island near mall in
the Irish in the Inner Hebrides of
Scotland which is just across the Irish
Sea from from Northern Ireland where
giant's causeway is and it's called
stafa and staff is an ancient word
meanings stave like a post for your
house and the staff ax is if anything
way more spectacular than the Giant's
Causeway you don't need to wander around
on it to appreciate it you can see it
from a boat and it has this spectacular
colonnade which is like a layer cake of
beautiful order ordered columns and
these are actual people for scale
they're not 17th century tourists
they're real tourists okay and you can
see the very very very regular columns
to know their dr. Johnson the Samuel
Johnson actually managed to in the 18th
century to visit both stafa and the
giant's causeway and he Fame
ashley said of the Giant's Causeway that
it was worth seeing but not worth
traveling to see so which is a nice put
down a very British sort of thing the
reason why you may have heard of Staffa
is because just to the right of the
picture I just showed you is a
spectacular wave cave which is dug into
the columns by wave action in its
Fingal's cave and of course it's famous
because it was visited by Mendelssohn
who actually didn't get out of his boat
but he went he went to there and was so
impressed by the sites that we wrote a
part of the Hebridean overture which is
called Fingal's cave and was you or
musically inclined can you know whistle
it to yourself and your head and your
head I don't really know what it sounds
like but Fingal's cave brings in Bob
Mayhew because Bob Mayhew is a spelunker
and at the time I met him he had a
permit from the Scottish National Trust
who owns staff are now to survey the
caves of staff and as you'll see there
quite a few caves and so he got
interested in kilometer joints and we
started working a little bit on
kilometres to go if you go inside
Fingal's cave you can kind of walk right
in and there's a beautiful sort of
pathway on the stones here it's an
unbelievable sight it's at the waves
roar right back and they crash right at
the back of the cave and then they roll
back out again and the far side of
Fingal's cave looks like this it was
described in the 19th century as a kind
of natural cathedral and it fitted in
perfectly with the with the kind of
natural theology of the day how could
such a beautiful piece of work not be in
all the work of the creator's these
there's no scale in here but these
things are about half a meter in size
here by the way is an engraving of
Fingal's cave which shows you that some
engravers are much more careful about
their engravings and authors and this is
a not particularly realistic picture of
the girls okay now kilometer joints a
reason that giant's causeway is famous
is partly just because Englishmen
visited it once you start looking for
them you find them all over the world
pretty much wherever there's any kind of
volcanic activity and there's a few
other places where it which are rather
famous or perhaps infamous for having
kilometer joints and for being uncanny
as a result and one of them is the
devil's tower in Wyoming famously these
right of the UFO landings in Close
Encounters of the Third Kind and these
joints are enormous there are several
meters in diameter and people like to
climb them in the fact it's quite a cop
quite a popular thing is to climb
kilometer joints another place which is
in California is called The Devil's
Postpile you'll notice that the devil
has been very very active in making
these things they're always either
described as being built by giants or
Devils or something like that i like to
say this is this reflects the theorists
early ideas about how they were formed
okay this one is just near a Yosemite in
California and it's a National Monument
so you can drive up to them and go and
visit they don't let you climb up this
rubble here and touch them but you can
you can look at the name very recently
however kilometer joints were discovered
in an even more interesting place which
is on Mars in a place called Marty
marked ivalice I'm not sure how you
pronounce it but it's a huge crater and
the idea is it's at some pat some past
time there was a lava flow on Mars which
became kilometer and then it was
excavated by a huge impact crater and if
you if i zoom up on this little area
down here you can be fairly convinced
that these look like roughly corner
joints and as I will describe in a few
minutes water is involved in the
formation of kilometer joints so the
idea that these really are normal
kilometer joints on Mars is quite
exciting because it's partly evidence
that there was water on Mars yet more
evidence or primordial water on Mars
these are deep under the ground so they
don't have to be water now at the time
of their formation for some reason
things that happen on Mars are suddenly
vastly more interesting than things that
happen on the earth I'm not sure why
that is but that's that's how it is so
I'm going to tell you I'm going to
answer i hope some of the more obvious
questions how do these crazy things form
and what sets their size and i will
argue that the size the question of what
sets the size of the columns is really
the important question and then i will
hope to convince you what sort of
tabletop experiment could possibly shed
light on such questions now the
geologists have been spending several
centuries working on this problem and I
will not I will not describe all of the
false starts and all the wrong theories
but this is the current understanding of
how kilometer joints form according to
the standard textbook geology
um the columns are actually carved out
if you take lava and it's it's red hot
and it cools it will shrink and as it
cools and shrinks it develops stresses
just like mud develop stresses and those
stresses can become large enough to
break it so as thick as the lava begins
to cool from the outside in the outside
gets cool against uh it's stressed and
it cracks just like mud and then as time
goes on those cracks penetrate farther
and farther into the lava flow and after
a while they've penetrated very far into
the flow and they get so far that it
actually would take centuries for the
heat to escape by diffusion alone but
what happens is that water gets down in
these cracks and boils down where
they're hot and that carries out the
heat and that is such an efficient way
to remove heat from the flow that that
determines the heat transfer fairly soon
after the cracks begin to penetrate the
flow so what happens is the crack a
crack network develops on the surface of
the flow just like a mud crack network
and then as the crack network advances
it extracts heat from the flow mostly by
boiling water up through the cracks and
then a region down near the crack-tip
seeeeee advances into the flow and and
down here it's too hot for water to
exist and the heat travels down the heat
normal heat conduction until it can find
some water to boil off and be carried
out and the one important fact is that
these cracks do not advance slowly they
actually advance and little brittle
advances little crack son crack motions
and those crack tips advance suddenly
asynchronously on different tracks like
this okay so up here it's basically all
cold down here it's all warm and
everything happens in its own between
those two and as each little crack
advances it leaves a mark on the side of
the column and these marks are called
striae I hope I'm pronouncing that right
that's how I say it anyway and so if you
look at a reasonably fresh column you
can see its limits marked on the side by
these little horizontal lines and this
represents a fracture advanced jump jump
jump jump jump and sometimes that rather
narrow like this so I don't have a scale
here that's a piece of grass and there's
Lucas for scale and you see these ones
are very broad okay now the reason you
don't see these at the Giant's Causeway
is simply that it's been exposed for so
long
and it's all weathered off so you nobody
noticed them on the Giants cause but you
have to see the amount of fresh exposure
of kilometer joints and there is no
better place to find a fresh exposure of
plumber joints then Iceland so here is a
picture sent to me by one of my flickr
buddies and it shows spectacular stria
on the side of a relatively fresh set of
columns in Iceland and these little like
stacked books or something but each of
these things represents a sudden
fracture advance and you notice they
don't quite line up with each other they
make a kind of wrinkly pattern on the on
the surface and those are the stri and
those are important to the story okay so
as the thing is cracking in advancing it
turns out after a while it this region
where all the action is happening has
some kind of scale L where all the
stresses are causing the fractures and
above that it's cold and below that is
hot and that little slab advances into
the flow at a constant speed and it
advances at a constant speed because the
water carries the heat to the surface
and it doesn't matter how far the
service is a way it's so efficient to
carrying the heat out that it carries
the heat out and just and just this
thing slowly moves through the lava flow
carving out the columns as it goes and
once it gets to the all the way to the
end the whole thing cools down and
become solid and eventually it gets
eroded or something removes the top off
it and then you know you see it as an
outcropping like the Giant's Causeway so
before we talk about how that happens in
kilometer joins it's wise to go back and
discuss some mud physics I'm very
interested in mud okay my kids know that
every time we go out for a walk and I
see mud I look at the cracks very
carefully okay so it turns out that it's
actually rather tricky to get hexagonal
or nearly hexagonal mud cracks everybody
says all bike racks are all hexagonal
but that's not true in fact they are
mostly square and they're mostly bounded
by t-shaped junctions and not y-shaped
junctions at all so I want to make a
distinction between sequential fracture
and iterated fracture networks this is a
network of cracks and these things by
the way are called peds that's a great
scrabble word right a ped a pet is a
little lump of mud okay see the
wonderful technical terms that we have
so is sequential fracture what happens
is you give your your whole layer is is
drying in this case and not cooling as
it dries it shrinks stresses develop it
cracked and then you get primary cracks
which things like this one and then
later there's a secondary crack and the
secondary cracks feel a difference
they're steered by the stress field of
the first crack and if they approach it
crack they'll turn and they'll hit it at
90 degrees and you can show that this is
this is the direction that it should go
to to maximize the release of strain in
the material locally and that gives rise
to this naturally to this t-junction so
after you've cracked this thing for a
long time it naturally a heads toward a
pattern which is mostly T junctures so
that brings us to the film and I believe
this is in fact the world premiere of
marry me demos movie which is watching
mud dry ready roll there's the primary
cracks notice the secretary cracks come
in very quickly they meet the primary
cracks at 90 degrees after a while the
action slows down considerably nothing
interesting happens and there might be
some tertiary cracks there's a few
little ones the end so let's marry is
sitting right over here I'll point my
laser their shoes so this is the pattern
that you get at the end and you might
say well why doesn't it just keep going
it turns out that the scale of these
cracks the typical spacing of the cracks
is related to the thickness of the layer
if I make the layer thicker the cracks
will be farther apart and there's a
scaling relationship between those two
but if you look at this for a while you
see they're mostly really they are very
square there's a few junctions that look
a little bit y ish but almost all of
them are quite quite t-shaped in fact
there's a kind of incipient why okay so
if we what we did is we were scientists
right we can't just look at it we
trained a computer to recognize the
shapes of the peds and decide what sides
they had and what their angles were and
so on and this was done a long time ago
but basically most of them are four
sided after this kind of process there's
a few three side and a few five-sided
but there's relatively few hexagons okay
that number of hexagons is actually
pretty small
and if you look at the distribution of
the angles that the things make it's
enormously peaked at 90 degrees there's
virtually nothing at 120 degrees no y
junction basically so the question is
you know how do we ever get hexagons if
I can't make them by a cracking process
which obeys the normal statistics of
cracking why how can I ever get them
well it turns out you can get them not
sequentially but iteratively first you
make a crack network which has T
junctions and square pads and then you
wet it or you cool it or are you you
warm it up in cooler or you do something
to repeat the cracking process and you
sequentially crack it over and over
again and it turns out that that makes
it move from T junctions and squares to
Y junctions and hexagons and here's how
it works and this is a beautiful table
top experiment which I have to say I'm
very proud of because I didn't think of
it Lucas my student thought of it
completely on his own and did the
experiment and it's very simple you
start with a layer of mud and you let it
crack and you get you know a network
with T junctions like this one and then
you just spritz it with water until this
nice and wet and then you crack it again
and he's very patient young man if he
did it for 25 iterations it takes many
hours to crack and what you see is this
is the primary crack and this is the
secondary crack on this t-junction but
the next time it cracks it cracks in
nearly the same place but in a different
order so here's the first crack in this
iteration whoop and here's the second
one dude right and then on the third
generation or maybe this is some other
generation the first one went this may
rip and then the second one came in that
way so after a long time the cracks
approach each junction from random
directions and that removes the
asymmetry of the t and all the
directions are equivalent so it becomes
a why and in fact it moves just a tiny
bit in order to accommodate that so this
one move from from there to there to
become something like a wide junction
and if you look at the statistics you
see that does go from a peak at 90
degrees over to a peak at 120 degrees
now this does sometimes happen in
natural mud but it has to be natural mud
that cracks it gets rained on and cracks
and gets rained on again and a great
place to do that to find such bud is in
a Death Valley
and I've never been to death valley but
Bernie Haleh has been a Death Valley
Andy took a Swiss Army knife with them
and and this is actually a natural mud
crack pattern which has a lot of
hexagonal joints a lot of hexagonal peds
and why junctions and it also something
else which tells you that it's iterated
and that is that the met the Centers of
these things are mounted up a little bit
and that's because every time the cracks
opened a little bit of stuff technically
known as schmutz falls into the cracks
and then when the cracks close up they
push the center up you see and they open
and close many times and they leave her
the center up like this and that means
the cracks are found in little Valley so
you can see here's a little wide
Junction that didn't reopen on the last
cycle and here's another one you see so
if you see this and you see hexagons
like this it's not because it cracked
that way once it cracked that way after
many iterations and there are other
systems in nature where this happens and
Lucas had the good fortune to go to the
Dry Valleys of Antarctica which contrary
to your picture of Antarctica are not
covered with snow they get very little
rain very little snow this is just a
little tiny dusting of snow and what you
get is what's called pattern ground or
polygonal terrain and this is caused by
the freeze-thaw cycle rather than drying
and cracking it's got something to do
with the fact that water expanded it
freezes and contracts when it thaws and
those levering motions make cracks and
those cracks open and close every year
and these this terrain is tens of
thousands maybe even hundreds of
thousands of years old and after many
many iterations the same kind of process
occurs why junctions emerge and
hexagonal not called Ted's now hexagonal
tiles are really want to call them up
here and what do you know they're on
Mars too okay now these ones those ones
I just showed you a few meters across
these ones are a few hundreds of meters
across but it's believed that patterns
like this on Mars are evidence for marsh
and permafrost like behavior and whether
it's actually water ice or some mixture
of carbon dioxide ice and water ice is a
complicated question but it's believed
that these crack networks on Mars are
also dominated by too many why chuckles
here's a hexagon and this is evidence
for a freeze-thaw cycle on Mars an even
more bizarre place where you might find
such a process is on the snout of a Nile
crocodile it turns out
that all the body scales of crocodiles
are the same from crocodile to crocodile
and they're guided by the DNA and the
and the usual developmental mechanisms
but the snout scales of a Nile crocodile
I love saying that the snow scales are
different for every specimen and that's
because during embryonic development
they have some kind of crunchy layer
develops it as the animal grows it
cracks and it's believed that there's a
kind of iterated cracking pattern going
on there and people who analyze the
joint network on the Nile crocodile in
this paper and they claim that it that
it evolves in a way that's similar to be
so the thing that I have been describing
okay so what does this have to do with
columnar joint how does it work well the
things I've been telling you up about
now occur in a single layer where you
repeatedly crack it in kilometer joints
that layer is not repeatedly cracked but
it moves and the cracks advance and so
this is a paper by aidan in the graph
where they found a place in Hawaii which
I really mean to go to where you can see
the bottom of the lava flow right here
and in fact the lava flow cool downward
the heat went down into the ground here
and the cracks move upward in this
picture and what you see is that there's
a lot of cracks initially and a lot of
them stop there's also a lot of key
junctions initially so there's a lot of
T junk is at the base of the flow and as
you look just a few meters up you find
they very quickly turn into y junctions
and this announcer this is some kind
intermediate thing and they very quickly
turn into mostly y junction so after
just a few meters the columns which
develop from these cracks are mostly
hexagonal and they have wide junctions
instead of T junctions and this this
formation is called the lower colonnade
and typically the most beautiful
kilometer joints you get don't form from
the cracks coming down from the top but
they form from the cracks coming up from
the bottom so for example on Staffa this
is the great colonnade of Staffa you see
here's the grand colonnade and the
cooling Direction is actually the
correct direction is actually upward and
the cooling direction heat runs downward
and up here you have something called
the entablature which is a very
disordered looking mass of very small
columns but it's very disordered this
rock is actually exactly the same as
that rock what happens is the horizontal
flow cools from both directions and the
bottom cool is by losing heat into the
ground very slowly and that develops the
beautiful columns down here
and the top is cooled much more rapidly
because it's exposed to the rain and so
on and it it cools much faster and that
produces this disordered thing called
the colonnade if you look very closely
and I'm perhaps I'm a true believer but
if you look very closely you can see it
kind of wrinkling down here and it's not
as it's not as smooth as it is up here
that's the little region where the
columns adopt the hexagonal and why
junction II sort of shape and after that
they just sail along this little thing
here which looks like a garage is
actually oh this is an ash layer which
is believed to have been there before
out when he'll have I came down and this
little cave here is called boat cave and
one of Bob Mayhew's great discoveries
and very brave thing was he went into
boat cave at low tide and established
that it connected to the other side of
the island got out again before the tide
came back on that's why he's a spelunker
okay and I'm not so what Aidan and de
Graaff did was they used the stria and
what are called the hackle patterns on
the sky or plumose patterns if you look
very closely on fresh stria you can
deduce how a crack front zipped around
on these as it as it moved very quickly
you can see the pattern left behind and
he established that various crack
directions are possible so for example
here's one where a crack came in and one
went out and woman out that way here's
one where one went in and one went in
and one came out and you know all but
all the combinations are possible so as
the columns are carved by the advancing
cracks asynchronously they approach the
junctions at random directions just like
in the mud and that does the same job it
turns the T junctions into y junctions
and that gives you the hexagonal columns
ok it's time to release the cornstarch
ok the experiment i'm going to describe
is something that you can do in your
kitchen or you can almost do in your
kitchen and i encourage you to try it
we've done it many many times it's very
cheap you can go by ordinary cornstarch
and all you do is wet it and then dry it
out and it cracks and it makes beautiful
columns these columns were just a few
millimeters across it what you do is you
take cornstarch and you make a thick
layer of it not a thin layer like I was
showing you before but it layer that
several centimeters thick these are
centimeters and then you dry it just
with a hot light it takes a long time
maybe days and then when you break it
open at the end you'll see the whole
inside of it is beautifully organized
due to these cracks and the services
look just like the surface of the
Giant's Causeway now I didn't discover
this this this idea was brought to my
attention by a paper by Mueller from the
1990s which was brought to my attention
by a Pierrot ban who's sitting in the
audience somewhere so everything you're
hearing about is basically because of
one conversation i had with care in
which he told me about this paper and we
realized that we could we could do this
experiment in a more careful way and
learn more about it and so we thought if
you read Mueller's paper he doesn't cite
anyone for this idea so he it sounds
like it was his idea but it turns out
that it's really really an old idea it
it's mentioned the fact that that starch
cracks in two columns is actually
mentioned by thomas henry huxley okay
who is used to be called Darwin's
bulldog he was a famous kind of public
scientist of the 19th century and he
wrote a book called physio physiography
which is unfort of an unfortunate
neologism that did not survive but it's
basically the founding textbook of
physical geography and in it he
discusses volcanoes and lava in all
sorts of landforms and here on page 204
he says oh you can find that you know
even volcanic outbursts in England hero
and especially in the county and trim
where the remarkable scenery the Giant's
Causeway is due to the fact that some of
the old lava has split up in two columns
not altogether unlike those into into
which a massive start splits during
drying and he says no similar evidence
of volcanic action can be found in
Scotland and blah blah blah blah he
doesn't say anything else okay this is
extremely frustrating how did he know
that starch does this how many people
knew this how come nobody did this
experiment before as far as we know
Muller is the first person to publish a
scientific paper exploiting the fact
that Huxley news since 1881 so you are
going to go back and buy Huxley's book
and look for good ideas that nobody's
bothered to follow up on okay so here's
the experiment that you can do in your
kitchen almost it's extremely high-tech
what you do is you get a beaker you fill
it with Canada brand cornstarch and
water about 5050 you put it on a scale
and you point hot lights on and you go
away for a week and you come back when
it's dry it out you analyze
is the cracked the Sarge did you get if
you do that we call that an uncontrolled
experiment we measure the weight of the
starch which tells you how much water
there is in it as a function of the time
but we don't do anything else if you
really want to make the Giant's Causeway
with starch you have to control the rate
at which it dries so then we very
cleverly get the computer to read the
mass on the balance and then we feedback
control the lights to change the amount
of heat we're putting on them to control
the rate at which it dries that's an
experiment that you can't do in your
kitchen but you know maybe you have a
more high-tech kitchen go for it and the
next high-tech thing is you take your
your twenty cents or the cornstarch and
you find somebody at the hospital for
sick children who has a fantastic
scanner and you put it in there and you
make a 3d x-ray tomography scan of it
this is a place called the mouse Imaging
Center and they have a this is a 40
micron resolution x-ray scan and you get
a 3d information about where the cracks
are inside you can also do this the hard
way by shaving the thing off and taking
pictures of it destroying the sample as
you do that but it's far more fun to
take it over to the hospital and just
scan it takes a very short time ok so
this is an uncontrolled run and what you
see is the it look like columns on one
end are small and the columns on the
other end it kind of large and so what
happens in an uncontrolled run is that
the scale of the column slowly grows and
the rate at which the mass decreases
slowly slows down and slows down ok cuz
it's harder and harder to get the water
out of the starch / as time goes on and
that causes the columns to get large and
I'll explain that so here's a movie
where we sweep forward using the x-ray
scan in the direction of cracking so
this is sort of what the correct network
looks like as it advances through the
starch okay we're not doing this in real
time but we're doing it after the fact
so I want you to focus your out your eye
on one of the columns and you'll see
that often a joint will stop or even
three at hold y junction will disappear
and a column will suddenly find out that
it's too big like here's one and you'll
see that it shrinks quickly down to be
closer to its neighbors inside here's a
big one that just formed you see it's
shrinking down and you can study the
statistics of how the how the Y
junctions appear from T junctions you do
everything you want this is exactly what
you cannot do with it outcropping like
the Giant's Causeway they
will not let you tear it apart or x-ray
the gigantic cliff but you can look at
every detail of the ordering process in
this experiment if you do a controlled
experiment that is to say you keep the
rate of drying constants of the rate at
which water is leaving the sample per
unit time is kept constant then you get
very regular looking columns and this is
our little giants causeway and in the
drive the big difference of course is
that this only takes a week lava takes
centuries or tens of years or centuries
to finish cooling and these are
millimeters instead of meters so it's a
tabletop experiment okay so it starts
really like bath salt or really like
lava or is it just a coincidence that
they look similar one way to test the
idea that they really are similar and
there many other ways but the simplest
way is simply to compare the statistics
do they statistically look similar and
you know does the ordering process make
sense ironically one of the only ways to
get statistics on kilometer joints is to
use the data of a pirate by the name of
with the unlikely name of o'reilly ok
and it turns out that O'Reilly had a
kind of crackpot theory so the Giant's
Causeway in the 19th century but the
good thing about O'Reilly was that he
was he was a data man ok he spent three
years at the Giant's Causeway surveying
about 200 joints and he measured the
length and the angles of every single
one of those 200 joints and he made this
map and it's only a few meters wide and
if you know before or five meters long
and he and his paper is full of crackpot
ideas and a great big data table ok so
ever since then it's basically O'Reilly
data that the best data around for
looking at the statistics of the
kilometer joints and that's from 1879
and what we did was we took a Riley's
map and we colorized it ok using
computer of software which O'Reilly was
not able to use this map is in black and
white it's actually colored in sort of
India ink or something like that and the
green ones here are hexagons in the
sense that they have six sides and some
of them are quite perfect pretty close
to being ideal hexagons there's one and
there's another one but many of them are
very you know very unexcited this one
has six sides but one of them is really
short and there's another short really
short one over there the sort of mustard
color ones are five sided and these are
seven sided so this is a common thing a
Penta heptad defect if these things were
to exchange one side they both the
hexagons and that would be a
ordered area but you see their areas
where lots of hexagons appear but
they're also areas where there's not
very many hexagons and in fact only
about half of the columns are six sided
and a very small fraction llamar really
ideal hexagons are really close to being
you know regular looking hexagons and
there's quite a few funny ones these are
eight sided ones and the red ones are
squares that is to say four-sided ones
and they turn out to be important in our
story so what we did was we simply
compare the statistics of the cornstarch
experiment as a function of time or as a
function of depth with the values that
we get from O'Reilly map and what we
find is for various statistics I won't
tell you what they all are but this is
the standard deviation of the angle
distribution this is the fraction of
angles close to 120 degrees and the
dotted lines are the Giant's Causeway
values and the symbols are the the depth
it or if you like the time that the
cracks advanced into the start sample
and what you find is that the Giant's
Causeway is pretty far from being
ideally ordered there's a pretty broad
distribution given by these dotted lines
but the starch starts out more
disordered than that it starts out more
like a mud crack pattern than that and
then it evolves toward the Giant's
Causeway values and it basically
plateaus at those values and so it does
not continue to become perfectly ordered
it's not getting more and more ordered
it orders for a while until it reaches
roughly the statistical ordering of the
Giant's Causeway and then it sticks
there but it does not become static it
actually remains dynamic columns you
know appear and disappear and edges move
around it's just that it stops
statistically involved so this is what I
call residual disorder and it's actually
I believe intrinsic to the dynamics of
this process it's not a mistake it's
really a feature it's real it's a real
thing about the system now one thing
that O'Reilly didn't tell us he told us
everything about these columns more than
you'd ever want to know about these
columns but he didn't tell us where they
are okay he had no way to survey the
Giant's Causeway to say where the
columns were so back in 2006 i went to
the Giant's Causeway with my friend Bob
and his wife Eleanor these are the
spelunkers a bob was actually the
president of the Grampian spelunking
society and Alastair Kennedy is actually
a history graduate student acts like
he's a geography graduate student at the
time and he wrote a thesis
on the history of the geography of the
Giant's Causeway and it's very
interesting read but we decided that we
would find these columns so Bob
laminated some maps because of course
that the Giant's Causeway it's raining
all the time okay and then we went on a
search to find these things there's
fifty thousand columns we're looking for
202 can how hard can it be right so we
lit upon the following algorithm squares
are real easy to see with your eye
because you can't tell the hexagon from
a heptagon but you can tell square and
there's only a handful of squares and
here the red ones are the squares so we
walked along more or less in a row until
Elinor saw a square as you said and then
you took the map but you kind of went is
that the square and sure enough she we
found square number hundred twenty-one
and there is the eight-sided one it's
rather rare for a square to be next to
an eight-sided one and sure enough there
is number 131 and number hundred
twenty-one and the most uncanny thing
happened then you're holding them out
you see the thing right elderly feet and
all sudden everything around you sort of
locks in too because you can see it all
on the map and then just by taking a few
paces you could walk across the map and
then the map runs out okay so we ran
around taking pictures of hundreds of
these well almost every one of these
columns using little fridge magnet
numbers to try and put the numbers on
them and this little tape shows the
outline of the o'reilly mapped area
gives you some idea how small it is
based on the on the whole it's not in a
secret place it seemed to kind of
obvious place if you're going to the
Giant's Causeway I'll tell you how to
find it i'll give you the map and you
can have a fun day looking for for the
famous column number 123 okay so why are
they hex aguilar or at least mostly or a
half hexagonal anyway where is this come
from well where it does not come from is
the one that everybody thinks it is
everyone thinks oh it must be the
hexagons are perfect ideal shapes in
some way after all they tile the plane
perfectly there must be some optimum
perfect tiling which they which the
process somehow approaches okay this is
a completely wrong idea because this is
a non equilibrium a wide open problem
wide open thermodynamic problem there's
no need for this thing to to approach
some kind of ideal best possible
configuration it would be equivalent to
saying all the weather you know it keeps
changing every day why doesn't it
settle down you know can it find the
optimum perfect weather and just stay
there and you know that's ridiculous
it's never going to settle down okay the
same with the thing with this problem
each of these each of these cracks
basically responds asynchronously all by
itself to local information it uses the
stress and the energy released locally
to decide whether to crack or not to
crack and then it goes for it right and
then it stops and then somewhere else
another crack stars and they respond to
each other's stress field asynchronously
through long-range interactions like
this and they're not conspiring okay
this is a perfect example of how
globally order can emerge from local
rules okay this is a big theme in
nonlinear science birds fly in beautiful
flock formations not because it is a
chief bird that tells them all where to
go each bird responds to its neighboring
birds in a simple way and the whole
flock dynamics emerges from those
interactions each bird doesn't know what
the whole flock is doing here the cracks
don't know that they're part of a
hexagonal lattice and they'll care
either all they do is they do what they
do and this thing emerges it's an
emergent property there's another fact
which is that as I showed you the
t-junction is involved into why
junctions and big columns shrinking area
and small ones grow and you can
understand this because if two cracks
are too far apart they'll attract each
other okay and they'll try to eat that
big column up if they're too close
together the ones that are on the other
sides will pull the stresses will be in
such a direction that they can get more
energy and they can crack better by
going in that direction so there's a
tendency for big ones to get smaller and
smaller ones to get bigger and you saw
that in the movie and the and what
happens really is they all approach a
certain scale the network is not random
because the polygons are very closing
area they're actually pretty disordered
in terms of number of sides but an area
and the uncanny thing about them is not
that they're all regular but the fact
that they're all the same size and in
fact there's a theorem which I won't go
into details but it actually requires a
disordered tiling of the plane with
random numbers of edges and vertices as
long as all the vertices vertices as
long as all the joint connections are Y
junctions and each of each tile shares
one edge each two tiles share a single
edge you can show
very simple argument which I won't give
you that the average number of nearest
neighbors even such a lattice has to be
6 so it's not completely crazy that a
random tiling of the plane would end up
with an average number of six now this
is not random mainly not because they're
uncannily regular hexagons but because
they have an uncanny regularity of area
and its really the area or they like the
average separation of the cracks which
is which is regular here and the six
cider that almost excited this kind of
emerges from from this so now I'm going
to give you the argument we can
understand this by analyzing the
similarity between the starch experiment
and data taken at various locations
including stafa by Lucas the basic idea
is the following both starch and bath
salt form under constant flux conditions
if I take out a certain amount of energy
per unit time a constant amount then it
follows that the average position of the
cracks or the position of that active
front has to move at constant speed
because it releases a certain amount of
energy period of time which is
constantly if you take out that amount
it moves at that speed similarly in the
water in the drying experiment we take
out a certain amount of water printing
the time at a constant rate and the
cracks advance on average a certain
depth that result of that so the flux is
proportional to the velocity of the
average velocity of the crack network
advancing and this follows from
conservation of energy now this is where
mojada van comes in because he realized
that if there is diffusion happening in
the system in both water and heat
diffuse around in the vicinity of the
crack tips then there's a length that
comes out just magically from the ratio
of the diffusion constant and the flux
it's actually technically known as the
mullins two critical length and it
appears in other physics problems
there's really only one length in the
problem is what it boils down to and
this is actually scales the thickness of
that active zone so what that means is
if I take out a lot of heat or a lot of
water then the active zone has to become
thinner ok so if J is Big D's a constant
of the material and L has to get smaller
and this is what sets the scale of the
columns ultimately
a more technical way of putting that is
to say that there's a dimensionless
number that's a number whose quantities
when you put them in there have have no
length or meters or anything to them
it's the velocity of the crack advance
times the scale of the columns divided
by the diffusion constant of either heat
or water and that's called the peclet
number and it's named after a 19th
century scientist and what we should
find is that all kilometer joints should
grow near no matter whether they're in
starch or basalt they should grow at a
value of the peclet number which is the
same it's universal okay and i'll show
you in a moment we find that that value
is about point two now if the peclet
number were really really large that
would mean that the cracks were
advancing so fast that there was no time
for the heat or water to diffuse around
to smooth out the temperature or
humidity field if the peclet number was
really really small that meant that the
humidity field are the water or the
temperature field had let plenty of time
to smooth out and the cracks wouldn't
have any stress to drive them so it
turns out that this peclet number has to
be somewhere near one for this process
to work okay if the cracks outran the
temperature or if they were too slow
compared to the temperature they
wouldn't develop the stresses to move so
we know from general ideas that it has
to be near one but the basic idea is
that the scale is some dimensionless
value of this con quantity and it will
show you that that turns out to
empirically to be point2 now this is
beautiful because we can do everything
in the starch experiment role that we
can measure the size of the cause we can
control the rate at which they advance
we can control everything and measure
everything so we can test this idea
here's the fracture spacing in
millimeters this is the typical diameter
of a column it's only a few millimeters
and here is the fracture velocity we can
infer this from the drying rate we can
measure the fracture velocity we can
measure the drying rate we can make a
connection between those two and the
data are are the experiments and some of
them are control that some of them are
uncontrolled and you can do use either
one and the lies here are and we also
know the diffusion constant of the water
because it is separate experiment we can
measure the diffusivity of the water so
we know everything and if that fear of
that theory that I just showed you is
correct then these that should fall on
it on one of these lines here which are
lines of constant clay number so you see
roughly they do there's actually a
little bit of hysteresis which is did
sting which I won't go into but
somewhere between point one and point
two point three
you get this inverse relationship the
faster you make the the column you pass
you make the fractures go the smaller
the columns you get now we the kicker is
that we can also do this in the bath
salt and this is considerably more
difficult what you have to do is put
your climbing gear on and go up the
cliff and measure as many of the stria
widths as you can and we have a very
large database of striae widths on
various columns all over the world and
it turns out that the ratio of the
height of Australia to the width of the
column is a constant so big columns have
wide stria small columns have narrow
strife and it turns out from that single
number we can deduce the cooling rate of
the fracture of the lava and from that
we can deduce the average speed using
some physics of the cooling of allah we
could use the average speed of the crack
advance and that's what this value is
here and then we could also of course
measure the spacing of the of the joints
and that space and goes all up to 3
meters here so these are really big ones
ok and it turns out that the data is a
little noisier because we don't know the
diffusivity as well we don't know d that
well but using data from the giant got
from the Giant's Causeway actually but
from stafa and from various roadside
places in BC and from places in the
Columbia bass hall in Oregon you can get
the data and they really do have this
inverse relationship there's a lot of
scatter but you can argue that they
basically have the same roughly the same
peclet number as the starched so this
establishes the origin of the of the
thing it's very very simple that active
zone which is moving in and carving out
the things it's just like a layer of mud
if it's thin then the cracks are close
together if it's thick then the cracks
are farther apart what determines its
thickness its velocity dependent it's a
rate dependent process the faster you
cool the fact the thinner the thing has
to be to have the right peclet number ok
then it gets the closer the cracks are
together and the smaller the columns are
it's that simple it's very simple it's
just like a mud crack product except
that its velocity dependent in the
thickness ok and this follows from such
basic physics and it took mojada van who
is a very very good theorists to get to
to basically convince us that this
argument was really all we were saying
with our complicated mathematics and
boils all down to that one little
formula that I should that's the last
equation
okay and we I know this was a good idea
because we send it to nature and it was
immediately rejected ok I spent about a
month trying to come up with that first
sentence for the nature article the
Giants caused me the most famous site in
the world a world heritage site it's got
to go to nature they rejected it ok
insufficient general interest so then of
course we sent it to science and it was
immediately rejected so we set it to the
place you send papers after they're
rejected by nature and science which is
post nature and science or papers not
accepted by science which which is
actually called the proceedings of the
national academy of sciences of the
united states of america and not only
did we get it in there but we got the
cover picture ok and this is a tumbled
millimeter scale basalt analog flow of
ordinary cornstarch and it's on the
cover of the magazine ok so i've told
you what we know now i'm going to tell
you a few things by way of closing to
tell you a few things that we really
don't know we don't understand one of
the most is a remarkable thing that we
discovered our Lucas and I I actually
notice that many years ago when i
visited the devils postpile and I've
kept it in the back of my mind for about
20 years I got to remember figured out
why this happens but Lucas eventually
you documented it more in the field
there are places and this is one called
Frenchman's Cooley in and I think it's
in Washington or Oregon and the columns
here actually undulate they kind of do
this ok so the cracks here are actually
unstable 22 meandering they're not just
cracking straight they actually
undulated and these cracks are actually
these meanders are actually much larger
than a stri a sword it's not just single
stryer making ins and outs here it's
mini stri about 10 and so the column
scale this column size can also become
unstable and this is a very powerful
piece of evidence that this is a highly
non equilibrium process as you drive it
harder it's unstable to motion ok that's
a settle down at all and that actually
carves out these amazing undulatory
columns and the rock climbers love these
things and this rock climbing route at
the Frenchman's Cooley for some rock
climber s reason is called party in your
pants I'm not sure what it's called that
but I suppose that's rock climbing humor
kind but anyway you see here is these
beautiful under undulations here an even
more spectacular example which I really
really want to visit is in on the near
the north coast of turkey called boya
bat and this shows you the power of
wikipedia just by surfing Wikipedia
looking for pictures of Colombo joints i
discovered this place and look at that
okay these columns are not just doing
this they're doing this okay and these
are the two modes of oscillation of
neighboring cracks in thin layers it's
known that they can either go together
or they can go up anti-phase like this
okay so somehow there's an instability
of the crack network if you push it hard
enough and it's not just carbs Collins
but it carves wavy or unusual ettore
columns okay well I more or less reach
the end I would draw your attention
those of you who are lucky enough to be
american physical society members next
month i tried real hard to get it to
give out this month but it's not going
to come out next month we have a cover
article about all this in physics today
that wonderful trade rag of our field
and this is my picture of the Giant's
Causeway eight columns and this is
coming next month in in physics today
suzhou says be quiet so I'm finished
thank you very much for your attention
