Potential of Antarctic Sea Level Rise (Barclay Kamp 1990)
Barclay Kamb's 1990 talk on Antarctic ice sheets and disintegration potentials, as was understood at the time. https://climatestate.com/2019/07/24/is-antarctic-ice-sheet-disintegrating-summary-1990/
Transcript
00:00:00You
00:00:30Good evening. My name is David Stevenson. I am Professor of Planetary Science and Chairman of the Division of Geological and Planetary Science, and I am here to introduce tonight's speaker.
00:00:46Before I do that, let me mention a couple of announcements. First, I was asked to tell you that malathion spraying will begin at 9 o'clock tonight, somewhat earlier than usual.
00:01:02I have no control over that. Second, I was asked to mention that following the lecture tonight, there will be no formal question and answer session. However, Barclay will stay around to answer informally any questions you may have, should you come up to the podium after the talk.
00:01:29Tonight's Watson lecture is to be given by Barclay Kamm, who is Professor of Geology and Geophysics here at Caltech. Barclay is the quintessential Caltecher. He was an undergraduate here at Caltech. He got his Ph.D. here at Caltech. He has spent his entire academic career here at Caltech.
00:01:55He was chairman of the Division of Geological and Planetary Sciences for 12 years. Most recently, he was provost and vice president of Caltech. I should mention at this point that the provost, at least in respect of academic affairs, is the person with real power here at Caltech because he is the one who controls the money.
00:02:20Throughout all this distinguished service, Barclay has also maintained an active research program, which is diverse in character, but has, for much of his academic career, concentrated on water ice, H2O in its solid form.
00:02:40For some reason, these studies have always seemed to be centered around water ice that has been traumatized one way or another, either by squeezing it to high pressures and studying how its structure has changed in the earlier part of his scientific career, and more recently, by studying large amounts of ice that are doing interesting things like surging or disintegrating or whatever.
00:03:06Tonight, he is going to pose and, we hope, answer the question, is the Antarctic ice sheet disintegrating? Barclay Kemp.
00:03:16This is the great frozen continent of Antarctica as seen in a satellite mosaic image.
00:03:37Antarctica is much in discussion and in the news nowadays. It just hit the cover story in Time Magazine this week with the subtitle, Is There Any Place Left on Earth Untouched by Man?
00:03:56This, of course, refers to the widespread concern about environmental issues in Antarctica, impact of various activities, potentiality for mineral and oil exploitation, and so on.
00:04:10I will not be addressing that subject, but still it's a subject of impact on Antarctica, and that is, with all of the thought and consideration of the CO2 increase in the atmosphere and the greenhouse effect that may result from that, the possibility has been raised that the Antarctic ice sheet may in some sense collapse or disintegrate or sometimes they say melt down.
00:04:37If it were to do that, it would have substantial consequences for human activity elsewhere on the Earth.
00:04:45Now, when we consider what might happen in Antarctica, we have to consider, in fact, that there are really two parts of Antarctica that aren't really all that similar.
00:04:57They are separated by the transantarctic mountains here that go from one side of the continent to the other.
00:05:02Over here, the large part is called East Antarctica, and it's covered almost entirely by the East Antarctic Ice Sheet, a continuous mass of ice, thousands of kilometers in extent.
00:05:15And this part then is called West Antarctica.
00:05:19This is the Antarctic Peninsula.
00:05:21From here you go on up to South America.
00:05:23From here you go on up to New Zealand.
00:05:27And the West Antarctic Ice Sheet is also quite large, a couple of thousand kilometers in dimension, but small compared to the East Antarctic Ice Sheet.
00:05:36If the East Antarctic Ice Sheet were to melt, the worldwide sea level would rise by 50 meters, and this would have very drastic effects on all coastal areas, inhabited coastal areas of the world.
00:05:51On the other hand, the puny West Antarctic Ice Sheet, if it were to melt, sea level would rise five meters.
00:05:58Now that's much less, but it still would have drastic consequences.
00:06:02Five meters is 17 feet or so, and that's quite a rise in sea level to have to handle.
00:06:09I won't be considering that, but I will be considering the possibility that the West Antarctic Ice Sheet could melt.
00:06:16Everybody agrees that the East Antarctic Ice Sheet is stable and is not subject to any rapid change,
00:06:24but the attention is focused on the West Antarctic Ice Sheet and the possibility that it could change.
00:06:30It could respond rather rapidly to changes imposed on it or also possibly to internal instabilities that exist within it.
00:06:39Now, in this next map here, this map shows the elevation of the surface of the ice or rock in Antarctica.
00:06:49You can see the East Antarctic Ice Sheet. These purple colors are high elevations.
00:06:54This is 4,000 meters here, so the East Antarctic Ice Sheet rises up to an elevation of 4,000 meters.
00:07:00Lots of it is above 3,000. At the South Pole here, you're just barely below 3,000.
00:07:05The small West Antarctic Ice Sheet rises to a maximum of 2,400 meters, and the average level is down around 1,000.
00:07:14So it's smaller, and it's lower, it's thinner, and so the effect is much less, as I just said.
00:07:21The effect of it is melting or collapsing or disintegrating.
00:07:26These two parts of the continent are different. Well, they're different in many ways.
00:07:31Geologically, they're very different, but I can't go into that.
00:07:35But glaciologically, there's a major distinction between the West Antarctic and East Antarctic Ice Sheets,
00:07:41not only in terms of size, but in terms of the nature of the bed.
00:07:47This is a plot of the elevation of the bed under the ice as it's been determined by various sounding methods.
00:07:56Here are the Transantarctic Mountains again.
00:07:58In East Antarctica, you see these colors yellow and shades of brown are elevations above sea level.
00:08:06So the bedrock in a good part of East Antarctica is above sea level.
00:08:10There are a few low spots, but by and large, it's at or near or above sea level.
00:08:15Whereas in the West Antarctic Ice Sheet, most of the bedrock is below sea level.
00:08:20Again, there are a few mountains sticking up, but most of it is below sea level.
00:08:23And if the ice were to melt away, you would have an island chain here
00:08:27and be able to sail through from the Ross Sea here to the Weddell Sea up here.
00:08:32And the fact that the base of the ice sheet is below sea level over much of its area
00:08:39first earns it the designation a marine ice sheet
00:08:43and also is recognized by glaciologists as a condition of potential instability.
00:08:48As the ice sheet tends to melt away, it tends to go afloat.
00:08:51And going afloat, it's no longer constrained,
00:08:55and so it tends to break up faster and faster in a kind of mode of instability.
00:08:59At least that's the hypothetical concept.
00:09:02Now, the going afloat is seen very clearly in this map here.
00:09:08The West Antarctic Ice Sheet, as it flows down toward the Ross Sea,
00:09:14goes afloat along this line here and becomes the Ross Ice Shelf.
00:09:17This whole area, the size of the state of Texas, is ice afloat.
00:09:22It's that marvelous thing that you've seen in the pictures with the huge cliff
00:09:26100 or 200 feet high here with ships beneath it
00:09:30as they came up against this so-called Great Barrier.
00:09:32That's the edge of the Ross Ice Shelf.
00:09:34And there's a similar large ice shelf, floating ice,
00:09:37here in the Ronnie and Filchner Ice Shelves.
00:09:40And so they represent the present state of going afloat
00:09:44of this West Antarctic Ice Sheet.
00:09:50Well, a new element has come into the picture.
00:09:55It has been suggested for a while, from time to time,
00:09:59that perhaps the West Antarctic Ice Sheet or the East Antarctic Ice Sheet
00:10:04might go into surge, meaning that it would move all of a sudden
00:10:09very much more rapidly, the way surging glaciers do in Alaska and elsewhere.
00:10:13And this would be a means for very rapid change
00:10:17and very, very rapid collapse or disintegration of the ice sheets.
00:10:21This is where I got interested in the subject
00:10:24because I've been working, as David said,
00:10:28on surging glaciers and the mechanism of surging.
00:10:31And you may remember those old-timers who've been here five years ago
00:10:35that I gave a talk in this lecture series
00:10:39on surging glaciers in Alaska at that time.
00:10:42So the idea that surging might somehow be involved,
00:10:46the phenomenon of surging might somehow be involved
00:10:48in the response of the West Antarctic or East Antarctic Ice Sheet
00:10:51sort of intrigued me.
00:10:54But that seemed kind of hypothetical.
00:10:57Well, how do you deal with that in this huge area?
00:11:00But then recently there have been some discoveries
00:11:02that made it seem as though maybe a surge-like phenomenon
00:11:04is actually going on right now.
00:11:06And that is the discovery of what are called the ice streams,
00:11:09the ice streams of the West Antarctic Ice Sheet.
00:11:12Now, if you have sharp eyes, you can read that it says right here
00:11:15Ice Stream B, or Ice Stream C, actually, Ice Stream B, and so on.
00:11:20These things have gotten onto maps now,
00:11:24although they're only recently discovered.
00:11:26There are other ice streams which flow out
00:11:29and feed the Rani Ice Shelf
00:11:32and feed these coastal parts of the West Antarctic Ice Shelf
00:11:35and also over here in the East Antarctic Ice Sheet.
00:11:38Now, an ice stream is just a very rapidly flowing current of ice.
00:11:43And we're going to be talking a lot about those
00:11:45because those are the things that I'm focusing on
00:11:47in my work in Antarctica.
00:11:50Here you see them shown more clearly,
00:11:53the various ice streams.
00:11:55None of them over here are shown
00:11:57because these are the ones that the work has been concentrated on.
00:12:00Now, how are these things recognized?
00:12:03Well, here's a rather faint picture.
00:12:05It's taken from a loft in an airplane about 20,000 feet.
00:12:09You're looking across the Ross Ice Shelf here,
00:12:12flat as a pancake,
00:12:14and in the distance are the Transantarctic Mountains.
00:12:17And in the foreground is this thing,
00:12:20kind of a swath cut across the terrain.
00:12:23This is the snake,
00:12:25and this is the snake that's in the ice.
00:12:28This is the snake.
00:12:30The pilots who flew over this country,
00:12:33landing parties here and there,
00:12:35saw these things and started giving them names,
00:12:38and they called this one the snake.
00:12:40It's a chaotic jumble of ice blocks,
00:12:43which I'll show you better views of in a minute.
00:12:46And it represents the edge of an ice stream.
00:12:50Now, in the next one,
00:12:52again, even more faintly in the distance
00:12:54are the Transantarctic Mountains
00:12:55and the Ross Ice Shelf between.
00:12:58And here's the snake again.
00:13:00And now, on the other side,
00:13:02over here is the dragon.
00:13:04Now, these two shear zones, or chaotic zones,
00:13:08are the edges of Ice Stream B.
00:13:10Ice Stream B is a great current of ice
00:13:12flowing parallel to these marks that you see here.
00:13:15It's about 50 miles wide or so,
00:13:18and flowing like this,
00:13:20past this ice in the ice sheet,
00:13:22which is relatively almost stationary.
00:13:24And this up here.
00:13:26So this is Ice Stream B,
00:13:28and it's the one that we've worked on,
00:13:30just a little bit of it.
00:13:32The thing extends, oh, three, four hundred miles
00:13:34back into the West Antarctic Ice Sheet.
00:13:39Here you see, flying over at a low elevation,
00:13:42100 feet or so above the ground,
00:13:44you see this chaotic jumble of ice blocks
00:13:47that constitutes the snake,
00:13:49or any of these chaotic shear margins
00:13:51of ice streams.
00:13:53It's as though somebody just took
00:13:55a huge egg beater or something
00:13:57and churned the whole area up.
00:14:01Here you see them then mapped
00:14:03as they've been recognized from,
00:14:05initially it was done from the presence
00:14:07of these shear margins,
00:14:09snake, dragon, etc.
00:14:11This would be the snake here,
00:14:13on this side of Ice Stream B,
00:14:15and this would be the dragon here.
00:14:17Actually, I misspoke when I called
00:14:19that other one the dragon.
00:14:21It's up here, and that's actually
00:14:23called Valhalla.
00:14:25Anyway.
00:14:28You see these ice streams are given
00:14:31these letter designations, A, B, C, D, E,
00:14:34and then there's actually an F over here,
00:14:36which is not shown on the map.
00:14:38This is the main U.S. base
00:14:40in Antarctica, McMurdo.
00:14:42We're going to be talking about work
00:14:44that we've been doing on this Ice Stream B,
00:14:47and particularly at this location
00:14:49where this dot is plotted here,
00:14:51there's a damp called Upstream B,
00:14:53which you will see presently.
00:14:55When I say we,
00:14:57I'm talking about my collaborators in this,
00:15:00Herman Engelhardt and Neil Humphrey
00:15:02and Mark Fonstock,
00:15:04as well as people from other institutions,
00:15:06but those are the people from Caltech
00:15:08and John Chadwick also
00:15:10who've been helping in this effort.
00:15:17Now, I'm going to show you
00:15:19some satellite images,
00:15:21which are evident from these
00:15:23recently obtained satellite images.
00:15:25You can see these features very clearly.
00:15:27This is upside down
00:15:29because I want up in this
00:15:31to be sort of generally south
00:15:33so that it will be similar to the map
00:15:35you were just looking at.
00:15:37This is Ice Stream B here.
00:15:39Actually, it consists of two branches,
00:15:41one called B1 here,
00:15:43one called B2 here.
00:15:45They come together flowing out this way,
00:15:47and what you were seeing before
00:15:49was right up in here.
00:15:51D and E.
00:15:53You'll notice that where the ice streams are,
00:15:55there's a kind of a chaos generally,
00:15:57a kind of a jumbling of the surface.
00:15:59This you don't see with the eye
00:16:01or with photography.
00:16:03It's some kind of a feature,
00:16:05very fine, delicate feature
00:16:07that satellite imagery reveals
00:16:09which ordinary senses do not reveal.
00:16:14One very interesting thing
00:16:16has emerged from this.
00:16:18Ice Stream C,
00:16:19which you notice looks somewhat less churned
00:16:21than the others,
00:16:23is very clearly an ice stream.
00:16:25It has a sheer margin and so on,
00:16:27but it's stopped.
00:16:29It's no longer moving
00:16:31or moving very slowly.
00:16:33This is an instance
00:16:35where you can see that,
00:16:37well, maybe this is a surge-like phenomenon.
00:16:39In surging of Alaskan glaciers,
00:16:41a glacier flows along slowly
00:16:43and then all of a sudden
00:16:45speeds up to very high speed
00:16:47and flows at a high speed for a while
00:16:49and then almost stops.
00:16:51And that's the case with Ice Stream C.
00:16:53Whereas Ice Stream B
00:16:55is moving along at high speed right now.
00:16:57There's this enlargement
00:16:59where you can see Ice Stream B
00:17:01closer up.
00:17:03Ice Stream C is over here.
00:17:05These are the sheer margins.
00:17:07They come through very black right in here.
00:17:09Our location where we're working
00:17:11is right here.
00:17:13This little lump here,
00:17:15it looks like an island
00:17:17and it is more or less an island.
00:17:19You can see the sides.
00:17:21Sometimes in maps
00:17:23they'll treat all of this
00:17:25as not part of the ice streams
00:17:27and these as two separate tributaries.
00:17:29Sometimes more and more
00:17:31now they're treating this like an island
00:17:33in the middle of a huge ice stream.
00:17:35Now,
00:17:37we know something now
00:17:39about the motions of these things.
00:17:41That's hard to find out
00:17:43because unlike in conventional glaciology,
00:17:45you know, when you're working
00:17:47with valley glaciers
00:17:49you can measure the motion with a spectrum.
00:17:51Here there's no fixed points.
00:17:53There's no rock showing,
00:17:55sticking up anywhere around here
00:17:57for hundreds of miles.
00:17:59Satellite geodesy
00:18:01or satellite navigation of high precision
00:18:03has made it possible
00:18:05to determine the motion
00:18:07in these ice streams.
00:18:09That's been done,
00:18:11most of it has been done
00:18:13by a group led by Professor Ian Willans
00:18:15at Ohio State University.
00:18:17What I'm going to show
00:18:19is here's a snake,
00:18:21here's Valhalla,
00:18:23here's the dragon
00:18:25and this one doesn't have a name.
00:18:27The unicorn we were just talking about,
00:18:29this piece that's not moving.
00:18:31And now in this map,
00:18:33here first of all is the scale of the map,
00:18:3550, 100 kilometers.
00:18:37And then these arrows show the motion
00:18:39but now they're on a different scale.
00:18:41This is a length representing
00:18:43500 meters per year.
00:18:45So here at upstream B
00:18:47where we're working
00:18:49is 800 meters per year.
00:18:51And down here farther downstream
00:18:53where that picture was taken
00:18:55I showed you the movement gets up
00:18:57close to 800 meters per year.
00:18:59And smaller movements
00:19:01as you go headward
00:19:03up toward the higher part
00:19:05of the West Antarctic Ice Sheet.
00:19:07Now outside the ice stream
00:19:09the movements are very small.
00:19:11They're actually shown
00:19:13on a different scale,
00:19:1510 times smaller.
00:19:17So these little arrows here
00:19:19and this is typically the contrast.
00:19:21Within the ice stream
00:19:23the ice is moving
00:19:25the order of one or two meters per day.
00:19:27Outside of the ice stream
00:19:29it's moving a few meters per year.
00:19:31It's a very tremendous contrast in motion.
00:19:34And again reminiscent of surging.
00:19:38Well, why is this happening?
00:19:41What is going on?
00:19:43That's what we're interested in finding out.
00:19:45That's what we're trying to do.
00:19:47Get some clues to the physical conditions
00:19:49that make it possible
00:19:51for such a stream to be moving
00:19:53at such high speed.
00:19:59Now just to illustrate
00:20:01and make clear one aspect of this
00:20:03I'm going to show you in the next slide
00:20:05a couple of cross-sections.
00:20:07One is drawn
00:20:09like we would cut a slice,
00:20:11a vertical slice
00:20:13along the length of Ice Stream B
00:20:15along the flow line
00:20:17and then on down to the edge
00:20:19of what I'm mapping out here
00:20:21goes across this thing
00:20:23called the Prairie Ice Rise
00:20:25and on down to the edge
00:20:27of the Ross Ice Shelf here.
00:20:29And then there will also be one
00:20:31through Ice Stream C
00:20:33which would come down
00:20:35something like this
00:20:37and fragments of one from Ice Stream D
00:20:39which would come down like this.
00:20:41And so this is just what these things
00:20:43look like in cross-section
00:20:45along a flow line.
00:20:47And here is Ice Stream B up here
00:20:49the cliff where it breaks off.
00:20:51And you can see the line
00:20:53where the West Antarctic Ice Sheet
00:20:56goes afloat right here
00:20:58some water under here.
00:21:00In this case it then collides
00:21:02with a bedrock high
00:21:04and rides over it
00:21:06and that produces the Prairie Ice Rise
00:21:08and then it goes floating on
00:21:10down to the edge.
00:21:12The place where we're working
00:21:14is up here at this camp
00:21:16called Upstream B.
00:21:17Upstream B up here is fairly similar
00:21:19although it doesn't intercept
00:21:21any bedrock high
00:21:23and produce an ice rise.
00:21:25Now the thing that's mainly significant
00:21:27and the reason I'm showing
00:21:29these cross-sections
00:21:31is that a thing that we devote
00:21:33a lot of attention to
00:21:35when we're thinking about
00:21:37glacier mechanics
00:21:39and why glaciers move fast
00:21:41and slow and whatever
00:21:43is that we want to relate
00:21:45the forces that are driving
00:21:47a glacier like this.
00:21:49Imagine in this mass here
00:21:51that we could consider
00:21:53gravity pushing on it
00:21:55and forcing it to the right.
00:21:57All the flow of ice
00:21:59is always taking place
00:22:01under the action of gravity
00:22:03and it's being pushed to the right.
00:22:05And then at the bottom
00:22:07its motion is being resisted
00:22:09by a kind of drag.
00:22:11So you have a shear
00:22:13as we would call it
00:22:15in other words a force
00:22:17by the bedrock underneath
00:22:19and that we call
00:22:21the basal shear stress
00:22:23and it is the quantity
00:22:25of primary concern
00:22:27in glacier motion
00:22:29because in glacier motion
00:22:31most of the action
00:22:33occurs at or near the bottom
00:22:35and it occurs under the action
00:22:37of this shear stress.
00:22:39The larger the shear stress
00:22:41the more things being forced to go
00:22:43and the faster it goes.
00:22:45Now when you look at glaciers
00:22:47what you find is
00:22:49that that shear stress
00:22:51which is something that has
00:22:53to be calculated by the way
00:22:55it isn't normally measured
00:22:57but it can be calculated
00:22:59from the action of gravity
00:23:01on the mass.
00:23:03It is about one bar
00:23:05which is a bar
00:23:07is essentially the same
00:23:09as an atmosphere
00:23:11which as you all know
00:23:13is 14.7 pounds per square inch.
00:23:15So that level of stress
00:23:17is what typifies
00:23:19the basal shear stress
00:23:21of glaciers throughout the world
00:23:23in Antarctica, in the Arctic,
00:23:25in Alaska, wherever.
00:23:27Now however
00:23:29in this region of the
00:23:31West Antarctic Ice Sheet
00:23:33it's very different.
00:23:35Up high up in here
00:23:37the shear stress is about
00:23:39a bar at the base
00:23:41but as you go down
00:23:43through this concave profile
00:23:45it gets less and less.
00:23:47As you go down the line
00:23:49it gets even lower
00:23:51and when it goes afloat
00:23:53the shear stress at the bottom
00:23:55is zero because water
00:23:57can support no shear stress.
00:23:59So one of the things
00:24:01that's been regarded as amazing
00:24:03and needing explanation
00:24:05and it's part of the
00:24:07ice stream phenomenon
00:24:09is how can it be
00:24:11that the shear stress
00:24:13gets so low here
00:24:15and yet the movement
00:24:17is as fast as you like
00:24:19because there's no
00:24:21resistance of the kind
00:24:23I'm talking about here.
00:24:25You're going to have
00:24:27trouble pushing it
00:24:29but in the normal
00:24:31situation of glacier mechanics
00:24:33to have a glacier
00:24:35with a basal shear stress
00:24:37of two-tenths of a bar
00:24:39moving 1.2 or 2 meters
00:24:41a day is just phenomenal.
00:24:43It represents a phenomenal
00:24:45state of affairs
00:24:47particularly over here.
00:24:49And you'll see the importance
00:24:51of that in relation to
00:24:53what we have been doing
00:24:55later on.
00:24:57Okay, now I want to
00:24:59jump to our area
00:25:01but first I want to
00:25:03give you some feeling
00:25:05for what Antarctica is like
00:25:07and that's part of the
00:25:08excuse for this talk.
00:25:10From the point of view
00:25:12of people at least
00:25:14doing science in Antarctica
00:25:15we come to McMurdo
00:25:16the main base here
00:25:18before we go on from that.
00:25:20And here is getting
00:25:21aboard the Hercules
00:25:23aircraft in Christchurch
00:25:25with the government issue
00:25:27Antarctic clothing
00:25:28that you have to have.
00:25:30Here's what it looks
00:25:31like inside and it so
00:25:32happens that this man
00:25:33here is Jim Zumberg
00:25:35who is the president
00:25:36of USC and he's also
00:25:37a well-known glaciologist.
00:25:39We happen to be
00:25:40sharing seat mates here
00:25:42and you can see how
00:25:43easy it is to look out
00:25:44for each other.
00:25:46Now here is landfall
00:25:48in Antarctica.
00:25:49This is Cape Adair
00:25:50and this is where
00:25:51Karsten Borchgravink
00:25:53the Norwegian expatriate
00:25:55Australian made the
00:25:57first overwintering in
00:25:58Antarctica.
00:25:59He and about ten men
00:26:01set up a little cabin
00:26:03here and spent the
00:26:04first winter that had
00:26:05ever been spent on the
00:26:06Antarctic mainland.
00:26:07This is the northern
00:26:08end of the transantarctic
00:26:09mountains here.
00:26:10This is sea ice of course.
00:26:12And now just a couple
00:26:13of shots of what you
00:26:15see as you go cruising
00:26:16down the transantarctic
00:26:17mountains.
00:26:18Mountains, mountains and
00:26:20mountains just swimming
00:26:21in ice.
00:26:23Huge glaciers pouring
00:26:24through.
00:26:27Another one.
00:26:28This is the Priestly
00:26:29Glacier, a very large
00:26:30impressive glacier coming
00:26:31down out of a polar,
00:26:33high polar plateau back
00:26:34up in here.
00:26:35This is sea ice.
00:26:36This is the ocean here.
00:26:38The Germans have a
00:26:39station right here now.
00:26:42And now here we arrive
00:26:43at McMurdo.
00:26:44This is the active
00:26:46volcano of Antarctica,
00:26:47Mount Erebus.
00:26:48You can't see the plume
00:26:49here, but in this little
00:26:51bit of rock sticking out
00:26:52from under the ice is
00:26:54where the U.S. has its
00:26:55station, the McMurdo
00:26:56station here.
00:26:57New Zealanders have a
00:26:58station over here.
00:27:01And here we come out.
00:27:04And this is another view
00:27:05of the airfield with
00:27:06Mount Erebus in the
00:27:07background and some
00:27:08unloading of the
00:27:09airplane.
00:27:12And now here we come
00:27:13into McMurdo.
00:27:14Here's the station back
00:27:15behind.
00:27:16And this little shack is
00:27:18the hut.
00:27:19It's called Scott's Hut
00:27:21and it was built by Scott
00:27:22and his party in 1902,
00:27:24the first men to come to
00:27:26this point of Antarctica
00:27:27and start their work,
00:27:29which included, of
00:27:30course, as you all know,
00:27:31trying to reach the South
00:27:32Pole ultimately.
00:27:35And inside the hut,
00:27:37some of the things they
00:27:38left behind are still
00:27:39lying around on this
00:27:40little box here.
00:27:44You can see some of
00:27:45their boots and gloves,
00:27:46the funny stuff that
00:27:47they wore back then,
00:27:49and a testimony to
00:27:51the climate.
00:27:52Here's a couple of
00:27:53carcasses of seals that
00:27:54they had in there to
00:27:55eat and they're still
00:27:56hanging there frozen
00:27:57and preserved like they
00:27:58were back in 1910 or
00:28:00whenever they got left
00:28:01there.
00:28:05Now, here's how it
00:28:06looked in 1902.
00:28:08This is copied from
00:28:09Scott's book, Voyage
00:28:10of the Discovery.
00:28:11This is the discovery,
00:28:12an anchor here,
00:28:13and here's the hut
00:28:15and some magnetic huts
00:28:16here.
00:28:17And in the background,
00:28:18well, here's a bay
00:28:20with sea ice,
00:28:21covered over with sea ice,
00:28:22and here's where our
00:28:23station, McMurdo,
00:28:24now is.
00:28:25And in the next slide,
00:28:26you'll see just the
00:28:27same view exactly.
00:28:28I reoccupied the same
00:28:29point so you could see
00:28:30how it's changed.
00:28:32Here's the hut
00:28:34and here is our
00:28:36station, McMurdo,
00:28:37with all the buildings
00:28:38and fuel tanks
00:28:39and everything.
00:28:43And in this somewhat
00:28:44wider view,
00:28:45you can see the bay
00:28:46better.
00:28:47You can see the ice
00:28:48dock.
00:28:49The ships come in.
00:28:50Later, the sea ice
00:28:51breaks out or ice
00:28:52breakers come in and
00:28:53break it out and the
00:28:54ships dock along by
00:28:55these poles you see
00:28:56here.
00:28:57This is built up
00:28:58artificially with ice
00:28:59to be thicker and they
00:29:00unload their cargo.
00:29:01And now from the,
00:29:02this is Observation
00:29:03Hill.
00:29:04I want to show you a
00:29:05view from the top of
00:29:06that.
00:29:07You can see the cross
00:29:08up here on top in
00:29:09memory of Scott and
00:29:10his party that
00:29:11perished on the way
00:29:12back from the pole.
00:29:13Here's Mount Erebus
00:29:14and the plume,
00:29:15volcanic plume from
00:29:16it.
00:29:17And from the top
00:29:18looking down,
00:29:19you see McMurdo
00:29:20Station.
00:29:21Here's the helicopter
00:29:22pad, helicopter
00:29:23sitting there.
00:29:25Scott's hut is out on
00:29:26the point right here
00:29:28and here's where
00:29:30we all eat.
00:29:31This is a huge
00:29:32mess hall and
00:29:33everything else.
00:29:34You can see lots of
00:29:35cargo spread
00:29:36around,
00:29:37stored,
00:29:38very neatly I might
00:29:39say.
00:29:40And the center,
00:29:41nerve center of this
00:29:42whole thing is right
00:29:43here.
00:29:44And there's Main
00:29:45Street.
00:29:46And the next slide,
00:29:47this is Main
00:29:48Street during a
00:29:49snowstorm.
00:29:50It's not very
00:29:51prepossessing but
00:29:52it's a very
00:29:53business-like
00:29:54operation.
00:29:55This is the
00:29:56firehouse right
00:29:57here.
00:29:58This is the
00:29:59infirmary.
00:30:00And the
00:30:01headquarters of the,
00:30:02where the National
00:30:03Science Foundation
00:30:04presides over all
00:30:05U.S.
00:30:06activities in
00:30:07Antarctica is right
00:30:08here.
00:30:09It's called the
00:30:10chalet.
00:30:11Whenever a question
00:30:12comes about,
00:30:13about what to do,
00:30:14they say,
00:30:15ask the chalet.
00:30:18Well,
00:30:19here's what we do
00:30:20mainly when we're
00:30:21there in McMurdo
00:30:22waiting a week or so
00:30:23as you always have to
00:30:24do before you can
00:30:25get out in the
00:30:26field.
00:30:27We're working on
00:30:28our equipment.
00:30:29All these crates are
00:30:30full of machines
00:30:31and you'll see them
00:30:32a bit later and
00:30:33our people are
00:30:34working on them.
00:30:35Another thing you
00:30:36have to do is go
00:30:37through survival
00:30:38training.
00:30:39They require that of
00:30:40all people coming to
00:30:41Antarctica and,
00:30:42for example,
00:30:43you have to fall into
00:30:44a crevasse and climb
00:30:45out and here this
00:30:46guy is about to
00:30:47descend this ice
00:30:48cliff on a rope,
00:30:49you can see,
00:30:50with a, with a
00:30:51rappel.
00:30:52So that's the kind
00:30:53of thing they have
00:30:54you do.
00:30:55And then you have
00:30:56to spend a night
00:30:57out and you dig
00:30:58yourself a snow
00:30:59cave.
00:31:00There's Neil here.
00:31:01Neil Humphreys is,
00:31:02he and I shared
00:31:03a snow cave.
00:31:04He's digging here
00:31:05and these two kids,
00:31:06this is Mark
00:31:07Fonstock, they're
00:31:08building an igloo
00:31:09over here.
00:31:10They're going to do
00:31:11that.
00:31:12You get your choice
00:31:13about how you're
00:31:14going to do this.
00:31:15Here you see what
00:31:16our snow cave looks
00:31:17like.
00:31:18Now actually where
00:31:19he's sleeping is way
00:31:20down below.
00:31:21You can't see but
00:31:22this is our little,
00:31:23we did a quite nice
00:31:24job I think, Neil
00:31:25and I don't even
00:31:26think.
00:31:27And here's a view
00:31:28out from there.
00:31:29This is the igloo
00:31:30and Mount Erebus
00:31:31in the background.
00:31:32You can sleep
00:31:33comfortably right
00:31:34there.
00:31:35It's a lot of fun
00:31:36actually.
00:31:37Now, I want to head
00:31:38out from McMurdo
00:31:39here on Ross Island
00:31:40to our camp over
00:31:41here but I can't
00:31:42resist the temptation
00:31:43to make a diversion
00:31:44to the South Pole
00:31:45partly because
00:31:46everybody that I've
00:31:47ever talked to about
00:31:48Antarctica, they say
00:31:49oh, did you get to
00:31:50the South Pole?
00:31:51What was it like?
00:31:52So we're going to do
00:31:53that.
00:31:54We're going to go to
00:31:55the South Pole.
00:31:56We're going to go
00:31:57to the South Pole
00:31:58and we're going to
00:31:59make a diversion
00:32:00to the South Pole
00:32:02and we follow the
00:32:03same routes more
00:32:04or less that Scott
00:32:05did.
00:32:06He went across the
00:32:07Ross Ice Shelf for
00:32:08hundreds of miles
00:32:09and then up the
00:32:10Beardmore Glacier
00:32:11and on to the Pole.
00:32:12Sounds easy.
00:32:13He had a lot of
00:32:14trouble.
00:32:15It's easy for us
00:32:16though if you've got
00:32:17a LC-130.
00:32:18So here's from the
00:32:19cockpit and this is
00:32:20the Ross Ice Shelf
00:32:21and we're just coming
00:32:22now to the
00:32:23Transantarctic Mountains
00:32:24and the glaciers,
00:32:25big glaciers are
00:32:26flowing into the
00:32:27right.
00:32:28Oh, on the
00:32:29other side
00:32:30of the mountains
00:32:31is East Antarctica
00:32:32and the Polar Plateau
00:32:33or the East
00:32:34Antarctic Ice Sheet.
00:32:35This is the
00:32:36Ross Ice Shelf.
00:32:37Everything is
00:32:38mantled with ice
00:32:39of course.
00:32:40This is the
00:32:41Lenox King Glacier,
00:32:42a relatively small
00:32:43glacier flowing
00:32:44through and over
00:32:45here is the
00:32:46Beardmore.
00:32:47We're coming up
00:32:48on it.
00:32:49And here you see
00:32:50the Beardmore Glacier
00:32:51pouring out of
00:32:52East Antarctica,
00:32:53out of the
00:32:54Polar Plateau
00:32:55and headed through
00:32:56the Transantarctic
00:32:57Mountains.
00:32:58And here it is
00:32:59just curving around.
00:33:00This is the
00:33:01highway to the
00:33:02pole as it has
00:33:03sometimes been
00:33:04called.
00:33:05Such a highway
00:33:06you might wonder
00:33:07with all these
00:33:08crevasses.
00:33:09But anyway,
00:33:10that's the
00:33:11Beardmore Glacier.
00:33:12And here we
00:33:13look down at
00:33:14miles and miles,
00:33:15actually 150
00:33:16miles on down
00:33:17to where it
00:33:18empties out
00:33:19into the
00:33:20Ross Ice Shelf.
00:33:21And this is
00:33:22where Scott and
00:33:23his party
00:33:24walked through
00:33:25here somewhere
00:33:26if they could
00:33:27pick their way
00:33:28through the
00:33:29mountains behind.
00:33:30And a few
00:33:31last remnants,
00:33:32none attacks
00:33:33are called,
00:33:34stick up.
00:33:35And you may see
00:33:36kind of a bluish
00:33:37tinge here.
00:33:38This is one of
00:33:39those blue ice
00:33:40areas which have
00:33:41proved to be
00:33:42of great value
00:33:43for collecting
00:33:44meteorites.
00:33:45The greatest
00:33:46collection of
00:33:47meteorites ever
00:33:48made since it
00:33:49began has been
00:33:50made from these
00:33:51blue ice areas
00:33:52in Antarctica.
00:33:53And then we
00:33:54head out over
00:33:55the featureless
00:33:56East Antarctic
00:33:57rift by magic.
00:33:58The South Pole
00:33:59appears beneath
00:34:00us.
00:34:01This is the
00:34:02runway.
00:34:03This is the
00:34:04glittering dome
00:34:05which is the
00:34:06center of the
00:34:07thing and various
00:34:08buildings for
00:34:09scientific work
00:34:10and supplies and
00:34:11so on.
00:34:12Here we are on
00:34:13the ground.
00:34:14They never
00:34:15shut off the
00:34:16engines.
00:34:17They don't
00:34:18trust them to
00:34:19start again.
00:34:20And this is
00:34:21the geodesic
00:34:22dome.
00:34:23And here you
00:34:24see just a
00:34:25little closer
00:34:26here is a fuel
00:34:27line.
00:34:28Always these
00:34:29aircraft coming
00:34:30into the pole
00:34:31they carry extra
00:34:32fuel and then
00:34:33they pump it off
00:34:34to fill the
00:34:35tanks at the
00:34:36South Pole.
00:34:37They use a lot
00:34:38of fuel for
00:34:39heating and
00:34:40whatnot there.
00:34:41And this is the
00:34:42entrance to the
00:34:43station.
00:34:44There's this big
00:34:45quonset-like
00:34:46thing which is
00:34:47where they keep
00:34:48supplies and have
00:34:49a lot of their
00:34:50equipment.
00:34:51Here is the
00:34:52entrance.
00:34:53It says the
00:34:54United States
00:34:55is under the
00:34:56geodesic dome.
00:34:57And in there
00:34:58they have their
00:34:59dining room and
00:35:00their quarters and
00:35:01library, scientific
00:35:02library and
00:35:03scientific equipment
00:35:04of all kinds.
00:35:05And here is the
00:35:06South Pole.
00:35:07With a few
00:35:08flags.
00:35:09It's always
00:35:10very gay like
00:35:11this.
00:35:12And since I
00:35:13was there in
00:35:14late December
00:35:15you wouldn't be
00:35:16at all surprised
00:35:17that Santa
00:35:18appeared.
00:35:19And here
00:35:20is the
00:35:21South Pole.
00:35:22And here
00:35:23is the
00:35:24South Pole.
00:35:25And
00:35:26Santa
00:35:27appeared.
00:35:28They have
00:35:29signs to all
00:35:30parts of the
00:35:31earth here.
00:35:32Now
00:35:33actually that
00:35:34isn't the
00:35:35South Pole.
00:35:36That's over
00:35:37here.
00:35:38That's what's
00:35:39called the
00:35:40ceremonial pole.
00:35:41They put it up
00:35:42there to be
00:35:43handy to the
00:35:44station.
00:35:45The distinguished
00:35:46visitors who
00:35:47come don't
00:35:48want to go
00:35:49walking out in
00:35:50the Sastrugi
00:35:51here so they
00:35:52go to the
00:35:53plain wooden
00:35:54pole and that
00:35:55is the actual
00:35:56South Pole.
00:35:57No joke.
00:35:58And this
00:35:59nine seems to
00:36:00be backwards
00:36:01here though.
00:36:02These are
00:36:03actually hours.
00:36:04They put
00:36:05these little
00:36:06pegs around
00:36:07here so you
00:36:08can stand at
00:36:09the South Pole
00:36:10and sight at
00:36:11the sun and
00:36:12you can tell
00:36:13what time it
00:36:14is.
00:36:15But there's a
00:36:16problem there.
00:36:17You think about
00:36:18that.
00:36:19What does it
00:36:20mean time of
00:36:21day at the
00:36:22South Pole?
00:36:23They have to
00:36:24move this every
00:36:25year because you
00:36:26see the ice is in
00:36:27motion.
00:36:28It moves ten
00:36:29meters a year at
00:36:30the South Pole so
00:36:31they have to
00:36:32figure out each
00:36:33year where they're
00:36:34going to put it
00:36:35down and get it
00:36:36back in the right
00:36:37place again.
00:36:38So it marches
00:36:39off away from
00:36:40the ceremonial
00:36:41pole behind.
00:36:42Here's a
00:36:43plane ready to
00:36:44go.
00:36:45This is where
00:36:46they sample the
00:36:47air for various
00:36:48chemical measurements.
00:36:49For example, a
00:36:50measurement of
00:36:51the temperature
00:36:52of the air
00:36:53at the South
00:36:54Pole.
00:36:55Now to the
00:36:56business here of
00:36:57what we're doing.
00:36:58We go over to
00:36:59Ice Stream B and
00:37:00the camp
00:37:01Upstream B here.
00:37:02And here we are.
00:37:03This is the snake.
00:37:04We're coming in
00:37:05to Ice Stream B.
00:37:06We're landing.
00:37:07And here is the
00:37:08main building.
00:37:09This Jamesway,
00:37:10it's called.
00:37:11It's kind of a
00:37:12Quonset hut made
00:37:13out of wood and
00:37:14fabric.
00:37:15All these antenna
00:37:16mass.
00:37:17One of our guys
00:37:18put the
00:37:19antenna
00:37:20flag of the
00:37:21great state of
00:37:22Alaska up
00:37:23here with a
00:37:24North Pole,
00:37:25North Star on
00:37:26it.
00:37:27That's still
00:37:28flying there a
00:37:29year later.
00:37:30And inside
00:37:31it's very cozy.
00:37:32Here you see
00:37:33the table set
00:37:34for Christmas
00:37:35dinner and
00:37:36our nice cook
00:37:37here and
00:37:38just what it
00:37:39looks like.
00:37:40And here's
00:37:41where we sleep
00:37:42in these tents
00:37:43here.
00:37:44They're called
00:37:45Scott Tents
00:37:46after Scott I
00:37:47guess.
00:37:48And the
00:37:49other
00:37:50side of
00:37:51the tent
00:37:52is a
00:37:53mess hall.
00:37:54And now
00:37:55here in this
00:37:56view,
00:37:57there's another
00:37:58Jamesway here.
00:37:59And then you
00:38:00see there's a
00:38:01couple of
00:38:02Jamesways here
00:38:03that are almost
00:38:04buried in the
00:38:05snow.
00:38:06They were put
00:38:07in there in
00:38:081983 when
00:38:09this camp was
00:38:10first established.
00:38:11And in the
00:38:12meantime,
00:38:13the blowing
00:38:14snow has
00:38:15built up to
00:38:16this level and
00:38:17they're almost
00:38:18gone.
00:38:19And here's
00:38:20the midnight
00:38:21sun over our
00:38:22camp.
00:38:23Now people
00:38:24often say,
00:38:25what's the weather
00:38:26like?
00:38:27Well, it's often
00:38:28good as you've
00:38:29been seeing.
00:38:30But then these
00:38:31clouds will come
00:38:32across like this
00:38:33and you get a
00:38:34whiteout.
00:38:35And man,
00:38:36you can fall down
00:38:37so fast when
00:38:38you go along
00:38:39in a big lump
00:38:40of ice you
00:38:41can't even see
00:38:42and trip right
00:38:43over it.
00:38:44And of course
00:38:45flying any
00:38:46aircraft is
00:38:47a little
00:38:48bit.
00:38:49Then the
00:38:50wind will blow
00:38:51and here you
00:38:52see the snow
00:38:53blowing.
00:38:54Not all that
00:38:55much.
00:38:56We had winds
00:38:57up to 25
00:38:58knots and the
00:38:59wind chill
00:39:00factor, you
00:39:01know, is quite
00:39:02noticeable.
00:39:03The temperatures
00:39:04range at times
00:39:05I've been there
00:39:06from, it's
00:39:07quite modest
00:39:08really, it's
00:39:09kind of a
00:39:10banana belt
00:39:11for Antarctica
00:39:12plus 5
00:39:13Fahrenheit to
00:39:14actually 33
00:39:15above freezing,
00:39:16so the snow
00:39:17melts but it
00:39:18still hit that
00:39:19point.
00:39:20And when
00:39:21this blows
00:39:22like this then
00:39:23you get dunes
00:39:24formed.
00:39:25Here, everywhere
00:39:26there's something
00:39:27that will influence
00:39:28the flow of the
00:39:29wind you get a
00:39:30big dune formed
00:39:31and some of
00:39:32these are quite
00:39:33spectacular.
00:39:34Here's one that
00:39:35formed behind
00:39:36this sled.
00:39:37This is a Nansen
00:39:38sled just next
00:39:39to my tent.
00:39:40This wasn't here
00:39:41the day before.
00:39:42And then the
00:39:43wind cuts the
00:39:44snow and it
00:39:45makes these
00:39:46famous features
00:39:47that are such an
00:39:48obstacle to travel
00:39:49in much of the
00:39:50Antarctic because
00:39:51they're such a rough
00:39:52surface.
00:39:53They're carved by
00:39:54the wind.
00:39:55Okay, now
00:39:56down to business.
00:39:57Here's our machine
00:39:58cargo.
00:39:59What are we here
00:40:00for?
00:40:01What are we going
00:40:02to do?
00:40:03Well, we're here
00:40:04to drill to the
00:40:05bottom of the ice
00:40:06sheet to try to
00:40:07find out what's
00:40:08going on near the
00:40:09bottom.
00:40:10And the equipment
00:40:11is in these boxes
00:40:12but I'll talk a
00:40:13little bit about
00:40:14how to observe
00:40:15and measure and
00:40:16then I'll show you
00:40:17a little bit about
00:40:18doing it.
00:40:19What are the
00:40:20possible explanations?
00:40:21There basically are
00:40:22three candidate
00:40:23explanations for how
00:40:24these ice streams
00:40:25move so fast.
00:40:26And the first
00:40:27one I've called
00:40:28here the
00:40:29superplasticity
00:40:30model.
00:40:31And the idea is
00:40:32well, there's some
00:40:33special property to
00:40:34the ice down in
00:40:35the basal region.
00:40:36Ordinary ice would
00:40:37flow in some way
00:40:38like this.
00:40:39This represents a
00:40:40vertical section
00:40:41through the ice
00:40:42and then the
00:40:43horizontal section
00:40:44through the ice
00:40:45and these vectors
00:40:46represent the
00:40:47motion that's
00:40:48taking place.
00:40:49And ice as we know
00:40:50it from other glaciers
00:40:51would deform in a
00:40:52certain way and it
00:40:53would deform a little
00:40:54along a line like
00:40:55this.
00:40:56But some extra
00:40:57strong deformation
00:40:58would be needed to
00:40:59allow it to move so
00:41:00fast as it does.
00:41:01And that peculiar
00:41:02property of the ice
00:41:03being unusually
00:41:04plastic is called
00:41:05just by a name
00:41:06superplasticity.
00:41:07And so to detect
00:41:08that what you would
00:41:09have to do is prove
00:41:10that the ice is
00:41:11superplastic.
00:41:12You would have to
00:41:13prove that the ice
00:41:14is not moving
00:41:15at the bottom
00:41:16but in a zone
00:41:17some thickness
00:41:18whatever it is
00:41:19above the bottom
00:41:20there's very rapid
00:41:21shear going on
00:41:22within the ice
00:41:23and then you would
00:41:24have to try to
00:41:25explain why the
00:41:26ice has changed
00:41:27its property so
00:41:28much and becomes
00:41:29going into
00:41:30the superplastic
00:41:31state.
00:41:32Okay, now another
00:41:33alternative arises
00:41:34from thinking that
00:41:35this phenomenon is
00:41:36something like
00:41:37surging in Alaska
00:41:38and so on.
00:41:39There we know
00:41:41that it is a
00:41:42property not of
00:41:43the ice but of
00:41:44the movement of
00:41:45the ice over its
00:41:46bed.
00:41:47And we call this
00:41:48basal sliding.
00:41:49When the ice is
00:41:50moving rapidly
00:41:51sliding over the
00:41:52bed we call that
00:41:53basal sliding.
00:41:54And it's something
00:41:55that you probably
00:41:56already recognize
00:41:57very clearly if
00:41:58you've ever been
00:41:59in New England
00:42:00or the Sierra
00:42:01or anywhere where
00:42:02there's been
00:42:03glaciation you've
00:42:04seen how the
00:42:05rocks have been
00:42:06scoured off and
00:42:07polished by the
00:42:08ice sliding over
00:42:09them.
00:42:10Now basal
00:42:11sliding can occur
00:42:12only if the ice
00:42:13reaches the melting
00:42:14point.
00:42:15If it's frozen to
00:42:16the bed there's no
00:42:17sliding.
00:42:18And so this would
00:42:19require the ice
00:42:20to be at the
00:42:21melting point at
00:42:22the base whereas
00:42:23we know at the top
00:42:24from shallow holes
00:42:25and so on that the
00:42:26temperature here of
00:42:27the ice is minus
00:42:2825 centigrade.
00:42:30So that requires
00:42:31something going on
00:42:32to get it to reach
00:42:33the melting point
00:42:34down at the base.
00:42:36Okay.
00:42:37Now very recently
00:42:38a third candidate
00:42:39explanation has
00:42:40surfaced.
00:42:41It comes about
00:42:42from some
00:42:43geophysicists at
00:42:44the University of
00:42:45Wisconsin led by
00:42:46Charles Bentley,
00:42:47Professor Charles
00:42:48Bentley.
00:42:49They scrutinized
00:42:50such diagrams.
00:42:51I will not take the
00:42:52time to try to
00:42:53explain this diagram
00:42:54but it's a stacked
00:42:55seismic record.
00:42:56And this is the
00:42:57reflection of the
00:42:58base of the ice.
00:42:59The top of the ice
00:43:00is clear up here
00:43:01and the bottom
00:43:02of the ice is
00:43:03clear up here.
00:43:04And from
00:43:05scrutinizing these
00:43:06little features
00:43:07that you see here
00:43:08and all this
00:43:09jumble of hash
00:43:10they decided that
00:43:11there was,
00:43:12that they could
00:43:13reach the conclusion
00:43:14that there was a
00:43:15layer of very
00:43:16special material
00:43:17of ground up
00:43:18rock,
00:43:19ground up by
00:43:20the glacier
00:43:21and they
00:43:22therefore called
00:43:23it till,
00:43:24glacial till,
00:43:25a layer of
00:43:26ground up rock
00:43:27between the
00:43:28base of the
00:43:29ice and the
00:43:30bedrock.
00:43:31Which the bedrock
00:43:32they saw as
00:43:34this stuff with
00:43:35these dipping
00:43:36lines here.
00:43:37They saw it as
00:43:38bedded sediments
00:43:39which had a dip.
00:43:40So that's,
00:43:41and their concept
00:43:42of how this till
00:43:43allowed this whole
00:43:44process to occur
00:43:45is shown over here
00:43:46that the till was
00:43:47deforming.
00:43:48It was like a
00:43:49lubricant.
00:43:50The ice was
00:43:51deforming but
00:43:52only a little.
00:43:53There was no
00:43:54basal shear zone
00:43:55in the ice
00:43:56but below the
00:43:57base of the ice
00:43:58there was a very
00:43:59great shear zone
00:44:00in the till.
00:44:01Shear meaning
00:44:02it's very fast
00:44:03and the velocity
00:44:04drops off away
00:44:05to zero at the
00:44:06bottom.
00:44:07Driven by the
00:44:08basal shear stress,
00:44:09the thing we talked
00:44:10about before.
00:44:11It's pushing it
00:44:12to the right
00:44:13and being resisted
00:44:14at the bottom.
00:44:15So this is the
00:44:16subglacial till
00:44:17deformation theory
00:44:18of how this
00:44:19would be happening.
00:44:20And you see all
00:44:21these three theories
00:44:22have to do with
00:44:23things going on
00:44:24at the bottom
00:44:25and you can
00:44:26walk around up
00:44:27here till the
00:44:28cows come home
00:44:29and you're never
00:44:30going to really
00:44:31have access to it
00:44:32and actually make
00:44:33some kind of
00:44:34measurements.
00:44:35Now of course
00:44:36they did by their
00:44:37indirect, they'd
00:44:38shoot off charges
00:44:39of dynamite and
00:44:40reflect the seismic
00:44:41waves down here
00:44:42and they thought
00:44:43they could make
00:44:44these interpretations
00:44:45but there's such a
00:44:46thing called the
00:44:47truth of the drill.
00:44:48Until you drill,
00:44:49you don't know
00:44:50whether the
00:44:51geophysicists are
00:44:52right or not.
00:44:53So anyway, that's
00:44:54what we do.
00:44:55And you'll see
00:44:56the details of it
00:44:57in a minute.
00:44:58So we pick a
00:44:59drill site over
00:45:00here and we
00:45:01use these
00:45:02machines to
00:45:03form a drilling
00:45:04rig here and
00:45:05what we do,
00:45:06basically what we
00:45:07do is produce
00:45:08hot water, pump
00:45:09it down a hose
00:45:10into a jet and
00:45:11use that jet to
00:45:12melt its way down
00:45:13into the ice.
00:45:14And the
00:45:15components of
00:45:16this thing,
00:45:17we're changing
00:45:18gears here,
00:45:19but the
00:45:20components are
00:45:21first, melting
00:45:22snow to form
00:45:23water, there's no
00:45:24liquid water
00:45:25available in
00:45:26these tubs here,
00:45:27sometimes you
00:45:28need antifreeze,
00:45:29and then pumps
00:45:30to pump it up
00:45:31to high pressure
00:45:32around 2,000 PSI
00:45:33is what we
00:45:34use.
00:45:35And then
00:45:36heaters to heat
00:45:37it up to about
00:45:38200 degrees
00:45:39Fahrenheit and
00:45:40then it goes
00:45:41into the
00:45:42hose, which
00:45:43the hose is in
00:45:44four separate
00:45:45pieces because
00:45:46that's as much
00:45:47as we can handle
00:45:48in one spool,
00:45:49so four pieces
00:45:50of 300 meters
00:45:51each.
00:45:52And here's
00:45:53Herman Englehart
00:45:54by the way,
00:45:55my colleague,
00:45:56and then here's
00:45:57the hot water
00:45:58coming through
00:45:59it into the
00:46:00derrick up
00:46:01and down
00:46:02into the ice
00:46:03where it is
00:46:04melting its way
00:46:05down through
00:46:06the ice at a
00:46:07speed as large
00:46:08as 100 meters
00:46:09an hour.
00:46:10We drill at
00:46:11speeds of 100
00:46:12down to 50
00:46:13or so.
00:46:14Well, it gets
00:46:15less the deeper
00:46:16you go because
00:46:17of loss of heat.
00:46:18Okay, now,
00:46:19what do we
00:46:20find out?
00:46:21Oh, well,
00:46:22sorry, here's
00:46:23the drill,
00:46:24and here you
00:46:25see the
00:46:26jet of hot
00:46:27water shooting
00:46:28out.
00:46:29So this is a
00:46:30little test of
00:46:31the drill on
00:46:32the surface.
00:46:33And here's
00:46:34another device.
00:46:35This is John
00:46:36Chadwick.
00:46:37He's testing
00:46:38the reamer,
00:46:39which we have
00:46:40to use to
00:46:41maintain the
00:46:42hole.
00:46:43Now, you see
00:46:44the ice is at
00:46:45minus 25,
00:46:46so you drill
00:46:47your hole,
00:46:48but it starts
00:46:49freezing in
00:46:50immediately,
00:46:51and if you
00:46:52don't keep
00:46:53going back in
00:46:54with the reamer
00:46:55and you try to
00:46:56get it to
00:46:57switch,
00:46:58and you'll see
00:46:59it did, and
00:47:00he got, for his
00:47:01trouble, bathed
00:47:02in hot water
00:47:03here, which his
00:47:04arctic clothing he
00:47:05didn't much like.
00:47:06But he's quite
00:47:07good-natured about
00:47:08it.
00:47:09Well, this one's
00:47:10upside down for
00:47:11some reason,
00:47:12but it simply
00:47:13is a shot.
00:47:14You can see
00:47:15lowering an
00:47:16instrument into
00:47:17the hole.
00:47:18This long
00:47:19aluminum tube
00:47:20is an instrument,
00:47:21which I won't
00:47:22try to explain
00:47:23here.
00:47:24But there are
00:47:25many that we
00:47:26lower into the
00:47:27hole trying to
00:47:28make observations
00:47:29and measurements.
00:47:30And now I'm
00:47:31going to discuss
00:47:32what we observe.
00:47:33The most
00:47:34striking thing we
00:47:35observe is the
00:47:36following.
00:47:37When we're
00:47:38drilling a bore
00:47:39hole, represented
00:47:40by this one here,
00:47:41this is, again, a
00:47:42section through the
00:47:43ice with the bed
00:47:44down here, and
00:47:45this is supposed to
00:47:46represent a bore
00:47:47hole with water
00:47:48in it.
00:47:49The water
00:47:50stands up at a
00:47:51level about 30
00:47:52meters below the
00:47:53base of the
00:47:54fern, what
00:47:55glaciologists call
00:47:56the fern.
00:47:57That's just old
00:47:58snow that's permeable
00:47:59so water can move
00:48:00around in it.
00:48:01Below the base
00:48:02of the fern is
00:48:03solid ice and water
00:48:04can't move through
00:48:05it.
00:48:06And so the water
00:48:07fills up to there
00:48:08and then it drains
00:48:09out in the fern and
00:48:10freezes.
00:48:11We actually pump
00:48:12water and recycle
00:48:13it from that level
00:48:14and we don't have
00:48:15to melt as much
00:48:16snow that way.
00:48:17When the bore
00:48:18hole reaches the
00:48:19bottom, within a
00:48:20few minutes, in
00:48:21most all cases,
00:48:22the water will
00:48:23reach the surface.
00:48:24In one case it did
00:48:25it only nine hours
00:48:26later, but in all
00:48:27other cases, these
00:48:28are the holes we've
00:48:29actually drilled,
00:48:30eight holes so far
00:48:31successfully, or at
00:48:32least at the time I
00:48:33left on December
00:48:3421st that was the
00:48:35case.
00:48:36And all of those,
00:48:37the level dropped
00:48:38down to about like
00:48:39this.
00:48:40And that has two
00:48:41important implications.
00:48:42First, it means the
00:48:43base of the glacier
00:48:44can accept water in
00:48:45some kind of a
00:48:46conduit system or
00:48:47pipe or whatever
00:48:48it's called.
00:48:49It's a
00:48:50conduit system.
00:48:51It's a conduit
00:48:52system or passageway
00:48:53system in which water
00:48:54can move.
00:48:55And this would only
00:48:56be true if it were at
00:48:57the melting point, if
00:48:58it were frozen,
00:48:59everything were frozen
00:49:00down there, the water
00:49:01couldn't penetrate and
00:49:02this level would not
00:49:03drop.
00:49:04So that's a proof if
00:49:05you need one and we
00:49:06want one, that the
00:49:07base is at the
00:49:08melting point.
00:49:09And then the other
00:49:10thing is that this
00:49:11level, 110 meters
00:49:12below the surface, is
00:49:13just slightly less
00:49:14than the pressure
00:49:15of the glacier
00:49:16itself.
00:49:17It's just slightly
00:49:18less than the
00:49:19pressure of the
00:49:20glacier.
00:49:21And the pressure
00:49:22represents a level
00:49:23such that the
00:49:24pressure of water at
00:49:25the bottom is just
00:49:26slightly less than
00:49:27what we call the
00:49:28overburden pressure of
00:49:29the ice.
00:49:30That's the pressure of
00:49:31the ice just due to
00:49:32the weight of the
00:49:33overlying ice.
00:49:34And if you want to
00:49:35think of that in
00:49:36mechanical terms, what
00:49:37it means, overburden
00:49:38pressure, suppose you
00:49:39could pump water into
00:49:40this well enough of
00:49:41it so that you could
00:49:42actually form a little
00:49:43blister down here and
00:49:44jack the ice up off
00:49:45its bed.
00:49:46Then you would be
00:49:47lifting the weight of
00:49:48the ice, which is the
00:49:50ice overburden
00:49:51pressure, and the
00:49:52water that you would
00:49:53have, the amount of
00:49:54water, the height of
00:49:55water you'd have to
00:49:56supply would be
00:49:57sufficient to generate
00:49:58that pressure.
00:49:59And the level at which
00:50:00water would stand up
00:50:01here then is what we
00:50:02call the flotation
00:50:03level, a level
00:50:04sufficient to float the
00:50:05glacier off its bed.
00:50:06And you see, there's
00:50:07just a few meters
00:50:08difference.
00:50:09You can see, the
00:50:10flotation level in
00:50:111988 when the
00:50:12borehole that we
00:50:13drilled, the boreholes
00:50:14were about 1,035
00:50:15meters deep, the
00:50:16flotation level was
00:50:17just at or slightly
00:50:18greater depth than
00:50:19that.
00:50:20And in 1989, this
00:50:21year, we drilled in a
00:50:22different spot.
00:50:23We had a somewhat
00:50:24deeper mass of ice
00:50:25because, of course, it
00:50:26isn't of constant
00:50:27thickness.
00:50:28And the flotation
00:50:29level was at this
00:50:30level and the levels
00:50:31to which the water
00:50:32dropped in our holes
00:50:33are shown here.
00:50:34Again, one of them
00:50:35right at flotation and
00:50:36two of them below
00:50:37flotation, a little
00:50:38bit.
00:50:39Now, the
00:50:40flotation level
00:50:41here, the flotation
00:50:42level at the
00:50:43bottom of the
00:50:44glacier, the
00:50:45flotation level
00:50:46at the top of the
00:50:47glacier.
00:50:48Now, this is
00:50:49mechanically very
00:50:50significant because it
00:50:51means that the ice
00:50:52can move very
00:50:53rapidly by basal
00:50:54sliding.
00:50:55Or, if there's any
00:50:56of that till at the
00:50:57bottom, its strength
00:50:58will be very low
00:50:59because of the effect
00:51:00of water pressure
00:51:01reducing the strength
00:51:02of a granular medium
00:51:03that would be high if
00:51:04it were not for the
00:51:05pressure of water in
00:51:06it.
00:51:07So that it basically
00:51:08means we have the
00:51:09kind of conditions
00:51:10down there that are
00:51:11required for rapid
00:51:12motion either by
00:51:13basal sliding or
00:51:14by sub-basal
00:51:15deformation.
00:51:16Now, we
00:51:17measure temperature
00:51:18in one of the
00:51:19holes.
00:51:20And here's
00:51:21temperature at minus
00:51:22degrees centigrade
00:51:23below freezing here
00:51:24at zero as a
00:51:25function of depth or
00:51:26height above the
00:51:27borehole.
00:51:28We couldn't, our
00:51:29transistors, our
00:51:30transducers failed in
00:51:31the bottom hundred
00:51:32meters.
00:51:33So we can't, we
00:51:34can only extrapolate.
00:51:35But you see it's
00:51:36heading towards zero.
00:51:37It's fairly
00:51:38close to zero.
00:51:39So we're
00:51:40measuring the
00:51:41temperature at
00:51:42zero.
00:51:43It's fairly
00:51:44compatible with the
00:51:45conclusion from the
00:51:46water that the base
00:51:47is at the melting
00:51:48point.
00:51:49This year we hope to
00:51:50carry this curve on
00:51:51down to the bed.
00:51:54Now, what does
00:51:55that mean?
00:51:56Well, here's an
00:51:57illustration of what
00:51:58goes on in determining
00:51:59the basal temperature.
00:52:00The heat is flowing
00:52:01up out of the earth,
00:52:02the geothermal heat,
00:52:03and the typical value.
00:52:04This hasn't been
00:52:05measured here, but
00:52:06it's typically about
00:52:07one heat flow unit
00:52:08where a heat flow
00:52:09unit is described
00:52:10here.
00:52:11Microcalories per
00:52:12square centimeter per
00:52:13second.
00:52:14And now we measure
00:52:15this curve here, and
00:52:16then we can therefore
00:52:17calculate how much
00:52:18heat is transported,
00:52:19is conducted up
00:52:20through the ice of
00:52:21known thermal
00:52:22conductivity.
00:52:23That's 1.9 heat flow
00:52:24units.
00:52:25So you can have a
00:52:26curve like this
00:52:27provided you supply an
00:52:28extra .9 heat flow
00:52:29units to add to the
00:52:30one and carry it on
00:52:31up through the ice.
00:52:32That will then be a
00:52:33valid temperature
00:52:34distribution.
00:52:35Now, in fact, when
00:52:36you calculate the
00:52:37temperature at
00:52:38zero, you can
00:52:39calculate the
00:52:40temperature at
00:52:41zero.
00:52:42When you calculate
00:52:43how much energy is
00:52:44dissipated in the
00:52:45sliding of the ice
00:52:46over its bed or the
00:52:47deformation of the
00:52:48till, it's the same
00:52:49amount of energy
00:52:50either way.
00:52:51It's dependent on the
00:52:52basal shear stress
00:52:53and the speed of
00:52:54motion.
00:52:55Then you find that
00:52:56that's 3.7 heat flow
00:52:57units, much more
00:52:58than enough to
00:52:59provide the .9
00:53:00that's needed.
00:53:01So that means this
00:53:02is a valid profile,
00:53:03and then the balance,
00:53:043.7 minus .9, is
00:53:05going to melt ice
00:53:06off the bottom of
00:53:07the ice sheet.
00:53:09And that water that's
00:53:10melted then in that
00:53:11way has to find its
00:53:12way under the ice
00:53:13stream and presumably
00:53:14ultimately to the
00:53:15Ross Ice Shelf.
00:53:16And the system of
00:53:17conduits through
00:53:18which it finds its
00:53:19way is the system
00:53:20that we're putting
00:53:21water into when we
00:53:22pump water into our
00:53:23borehole and it
00:53:24disappears into the
00:53:25bottom.
00:53:26This one managed to
00:53:27get in upside down
00:53:28too, but I don't think
00:53:29we need it.
00:53:30Now, if you look at
00:53:31the temperature
00:53:32distribution at
00:53:33zero, you can
00:53:34calculate the
00:53:35temperature at
00:53:36zero.
00:53:38Now, here we are
00:53:39going to lower a
00:53:40core in device to
00:53:41try to get a core of
00:53:42that supposed till
00:53:43that's down there.
00:53:46Well, it's no
00:53:47supposition.
00:53:48Here it is.
00:53:49We've got two meter
00:53:50core of it and
00:53:51actually a second two
00:53:52meter core of it
00:53:53thanks to the
00:53:54ingenuity of Neil
00:53:55here who built this
00:53:56device.
00:53:59Notice it's full of
00:54:00water.
00:54:01It's very slimy and
00:54:02pasty like putty.
00:54:05Notice how it just
00:54:06deformed as we put it
00:54:07out on the table
00:54:08here.
00:54:09These are centimeter
00:54:10marks.
00:54:13The other core,
00:54:14very deformed,
00:54:15very plastic.
00:54:18Here I'm
00:54:19scrutinizing it,
00:54:20trying to see any
00:54:21sign of internal
00:54:22structure, but there
00:54:23is none.
00:54:24It's just an
00:54:25anonymous material.
00:54:26Very much, it has
00:54:27many of the
00:54:28attributes of till
00:54:29as we know it from
00:54:30other circumstances.
00:54:31So we tend now to
00:54:32call this the till
00:54:33and say this thing
00:54:34really exists down
00:54:35in the basement of
00:54:36any geophysicist's
00:54:37imagination.
00:54:38Here's the core
00:54:39being cut up by
00:54:40Neil and bagged for
00:54:41transport.
00:54:42Notice how you can
00:54:43just cut it like
00:54:44butter with a knife
00:54:45here.
00:54:47It has, if you look at
00:54:48the distribution of
00:54:49particle sizes in it,
00:54:50I won't go into this
00:54:51in any detail, but
00:54:52it's very wide.
00:54:53It's much like other
00:54:54sediments in the U.S.
00:54:55that are recognized
00:54:56as tills.
00:55:01There are fossils in
00:55:02it.
00:55:03This is an example
00:55:04probably from a
00:55:05radiolarian.
00:55:06There are diatoms
00:55:07and they range in
00:55:08age from 50 million
00:55:09years to 2 million
00:55:10years old.
00:55:12This has been
00:55:13determined by a
00:55:14micropaleontologist at
00:55:15the University of
00:55:16Illinois, I'm sorry,
00:55:17of Indiana.
00:55:18That wide range of
00:55:19ages is a very
00:55:20strong indication
00:55:21that this material
00:55:22has come from a
00:55:23very diverse source
00:55:24and been mixed
00:55:25and has all kinds
00:55:26of implications
00:55:27in terms of
00:55:28history, the fact
00:55:29that those fossils
00:55:30are in this.
00:55:31The final thing that
00:55:32we did with the
00:55:33core on the spot,
00:55:34and we have a lot
00:55:35more of this to do
00:55:36now that we have
00:55:37it back here at
00:55:38Caltech, is to test
00:55:39its shear strength
00:55:40in this little gadget
00:55:41that we rigged up
00:55:42here, in which,
00:55:43well, this one's on
00:55:44its side, but here
00:55:45you can see the
00:55:46till bulging out
00:55:47and this is a
00:55:48shear box, as it's
00:55:49called.
00:55:50This side of it is
00:55:51pulled relative to
00:55:52that and you measure
00:55:53the shear stress
00:55:54of the material,
00:55:55shear stress
00:55:56of the material
00:55:57and the shear
00:55:58strength of the
00:55:59material.
00:56:01And now, what is
00:56:02involved here is
00:56:03the sort of thing
00:56:04we're trying to
00:56:05recognize and
00:56:06distinguish.
00:56:07If it were like a
00:56:08fluid, a viscous
00:56:09fluid, and we
00:56:10looked at the
00:56:11relation between
00:56:12the shear stress
00:56:13applied to it
00:56:14and the rate
00:56:15at which it
00:56:16deformed, the
00:56:17shear strain rate,
00:56:18it would be a
00:56:19linear relation.
00:56:20And that's what
00:56:21we call viscous
00:56:22flow, like any
00:56:23fluid, molasses
00:56:24or anything like
00:56:25that, honey would
00:56:26be linear.
00:56:27And so we
00:56:28looked at the
00:56:29relation between
00:56:30the shear stress
00:56:31and the shear
00:56:32strain rate.
00:56:33If we look at
00:56:34ice or some
00:56:35material like that,
00:56:36generally solids that
00:56:37are creeping, they're
00:56:38nonlinear.
00:56:39And so there's a
00:56:40curved relation like
00:56:41this, like in the
00:56:42case of a power,
00:56:43with a power of
00:56:44three, it would
00:56:45look like I've
00:56:46drawn here, which
00:56:47is typical of ice.
00:56:48So as the stress
00:56:49goes up, the thing
00:56:50flows very much
00:56:51faster.
00:56:52And then there's a
00:56:53limiting case where
00:56:54it becomes very
00:56:55nonlinear and
00:56:56essentially what
00:56:57happens is as you
00:56:58raise the stress on
00:56:59it, it doesn't
00:57:00deform at all.
00:57:01Then when it
00:57:02reaches a yield
00:57:03stress, it deforms
00:57:04arbitrarily large
00:57:05amount.
00:57:06And that's what we
00:57:07refer to as a
00:57:08plastic material.
00:57:09Now what we find is
00:57:10that this clay or
00:57:11this till is
00:57:12basically a plastic
00:57:13in its properties,
00:57:14at least at a crude
00:57:15level of determination.
00:57:16And that's shown by
00:57:17these data points
00:57:18here.
00:57:19Here we have
00:57:20applied shear
00:57:21stress and measured
00:57:22shear displacement
00:57:23rate in that little
00:57:24cell I was showing
00:57:25you.
00:57:26When you have a
00:57:28stress at this level
00:57:29and these are repeated
00:57:30trials on the same
00:57:31sample, jumping back
00:57:32and forth between a
00:57:33higher stress and a
00:57:34lower stress.
00:57:35At this level of
00:57:36stress, you get a
00:57:37creep when you apply
00:57:38the stress but it
00:57:39drops away to zero
00:57:40as time goes on.
00:57:41That's what these
00:57:42arrows mean.
00:57:43When you apply the
00:57:44stress at this level,
00:57:45sometimes it goes so
00:57:46fast initially you
00:57:47can't even determine
00:57:48or I couldn't even
00:57:49determine the rate.
00:57:50Sometimes it's a
00:57:51determinable rate but
00:57:52it then shoots on up
00:57:53and always off scale
00:57:54on this.
00:57:55So essentially you
00:57:56can see a little bit
00:57:57above this level, the
00:57:58thing just flows as
00:57:59much as you want.
00:58:00Below this level, it
00:58:01just doesn't flow or
00:58:02flow drops away to
00:58:03zero.
00:58:04That would be what we
00:58:05would say is
00:58:06appropriate for a
00:58:07plastic material with
00:58:08a well-defined yield
00:58:09stress.
00:58:10In this case, the
00:58:11yield stress is .02
00:58:12bars.
00:58:13In other samples, it
00:58:14ranged up as large as
00:58:15.04 bars and Neil did
00:58:16his own separate
00:58:17determinations of
00:58:18that.
00:58:19So that's a range
00:58:20between the both of
00:58:21us.
00:58:22What's so significant
00:58:23about that is this
00:58:24stuff is very weak.
00:58:25Remember I told you
00:58:26the basal shear stress
00:58:27was .02 of a bar.
00:58:28Well, now we're in a
00:58:29kind of a strange
00:58:30position.
00:58:31This stuff is so weak
00:58:32there's no problem at
00:58:33all causing the ice to
00:58:34move very fast by the
00:58:35deformation of it
00:58:36because it's so weak
00:58:37it'll deform readily
00:58:38out of stress ten times
00:58:39its value.
00:58:40The problem is that
00:58:41it's so weak that how
00:58:42are you going to
00:58:43support even that low
00:58:44shear stress of .02
00:58:45of a bar with
00:58:46something like
00:58:47.04 of a bar?
00:58:48Well, the problem is
00:58:49that the deformation
00:58:50is so weak that the
00:58:51deformation is so
00:58:52weak that the deformation
00:58:53of .02 of a bar with
00:58:54something that's only
00:58:55got .02 of a bar
00:58:56strength.
00:58:57Well, you could get
00:58:58into a long discussion
00:58:59about that and I won't
00:59:00but basically you can
00:59:01dream up other
00:59:02mechanisms, other ways
00:59:03of doing it or perhaps
00:59:04there's some pressure
00:59:05dependence of the
00:59:06property, say, because
00:59:07there is some confining
00:59:08pressure that is the
00:59:09water pressure is
00:59:10slightly below the
00:59:11overburdened pressure
00:59:12so there is some
00:59:13confinement and maybe
00:59:14there's enough
00:59:15friction to keep
00:59:16the ice from
00:59:17moving as fast as
00:59:18it can.
00:59:19So there's some
00:59:20confinement and maybe
00:59:21there's enough
00:59:22effect of that on the
00:59:23strength.
00:59:24This we have to do by
00:59:25more careful tests.
00:59:26Now, what does this
00:59:27all come down to?
00:59:28We can have the
00:59:29lights.
00:59:30Basically, what have
00:59:31we got, where have we
00:59:32got in all this?
00:59:33We've managed to show
00:59:34that the base is at the
00:59:35melting point.
00:59:36Oh, incidentally, the
00:59:37cores were not frozen.
00:59:38That's the best
00:59:39indication that the
00:59:40base is not, is at the
00:59:41melting point because
00:59:42if the core were not,
00:59:43when the core comes
00:59:44up unfrozen, that's
00:59:45by definition
00:59:46the melting point
00:59:47of the ice.
00:59:48So we've managed to
00:59:49show that the base
00:59:50is at the melting
00:59:51point.
00:59:52If the core is not
00:59:53frozen, that's by
00:59:54definition at the
00:59:55melting point or
00:59:56certainly not frozen.
00:59:57Okay.
00:59:58So we have the base
00:59:59at melting.
01:00:00We have a high
01:00:01water pressure,
01:00:02almost equal to
01:00:03overburden.
01:00:04Those are the
01:00:05conditions required for
01:00:06rapid basal sliding or
01:00:07rapid sub-basal
01:00:08deformation.
01:00:09We have a till there.
01:00:10It's very weak.
01:00:11And so all these
01:00:12things add up to
01:00:13basically the concept
01:00:14of the till deformation
01:00:15model, the
01:00:16deformation model
01:00:17that we've
01:00:18developed.
01:00:20The till deformation
01:00:21model being seemingly
01:00:22a good model.
01:00:23Geophysicists win
01:00:24in this case.
01:00:25The only place where
01:00:26they fall down a bit
01:00:27is that they assumed
01:00:28in their modeling of
01:00:29this that the stuff
01:00:30would be linearly
01:00:31viscous.
01:00:32And as you saw,
01:00:33it's anything but
01:00:34that.
01:00:35But that's kind of a
01:00:36detail, a refinement
01:00:37of the thing.
01:00:38Now, what does
01:00:39this all mean?
01:00:40Is the ice sheet
01:00:41at the melting point
01:00:42at the melting point
01:00:43at the melting point
01:00:44at the melting point
01:00:45at the melting point
01:00:46at the melting point
01:00:47at the melting point
01:00:48is the ice sheet
01:00:49disintegrating?
01:00:51Or what have we
01:00:52learned about it
01:00:53that's relevant to that?
01:00:54Well,
01:00:56we
01:00:58basically what
01:00:59we're doing is
01:01:00getting some
01:01:01physical information
01:01:02that may help us
01:01:03decide how
01:01:05physical parameters
01:01:06control the motion
01:01:07of this ice
01:01:08stream.
01:01:09And once we
01:01:10have a clear
01:01:11picture of
01:01:12what this material
01:01:13the till is,
01:01:14if the till is
01:01:15controlling the
01:01:16motion and what
01:01:17properties are, we can then address the question,
01:01:20how could it respond to changes in the physical situation
01:01:24of the ice stream if that changed, say,
01:01:26due to climatic change?
01:01:29We haven't got to that point yet.
01:01:31But what you can, among the various thoughts
01:01:33you can have about this, is one that I think
01:01:36is fairly striking is this.
01:01:39What controls the strength of that teal
01:01:42and the rate of its deformation?
01:01:45Well, it seems clear that the biggest control on it
01:01:48is the water pressure.
01:01:49If the water pressure is increased,
01:01:51it's going to become weaker.
01:01:52It's going to flow faster and vice versa.
01:01:55Well, what controls the water pressure?
01:01:57This is much like the story in surging.
01:01:59We ask the same questions because we
01:02:00have a similar situation.
01:02:02In this case, what controls the water pressure?
01:02:05Well, the only evident thing is the basal melting,
01:02:08which we were talking about.
01:02:09Remember the heat coming up and the heat generated
01:02:11at the bottom, melting ice off the bottom of the ice stream
01:02:15producing water.
01:02:16That water has to move through this conduit system.
01:02:18And through that process of water being generated,
01:02:21transported, a distribution of pressure
01:02:25has to be achieved to make that flow possible.
01:02:29Now, think.
01:02:32If you had the thing moving along
01:02:33in a certain situation in equilibrium
01:02:37and you pushed it faster, you caused
01:02:40it to go a little faster somehow,
01:02:41just a little perturbation, you would
01:02:43increase the melting rate.
01:02:45Because the melting rate is directly
01:02:47proportional to the rate of sliding
01:02:50because the generation of heat, which
01:02:52is produced by the sliding of the mass at this shear stress,
01:02:55is directly proportional to the rate of sliding.
01:02:59So you would increase the melting rate.
01:03:02You would, therefore, I think, increase the basal water
01:03:05pressure because you're going to have to have a higher
01:03:07pressure there to get that extra water generated out
01:03:11of the system and prevent it from accumulating.
01:03:15If the pressure went up, then the till would get weaker.
01:03:18It would slide faster.
01:03:20Then more heat would be generated and so on.
01:03:22So you see, you have there an instability, potentially.
01:03:26And now, what is really going on?
01:03:29What determines the level at which it actually
01:03:31moves, the 1.2 meter a day at upstream B and so on?
01:03:37Is it really stable?
01:03:39Not too sure about that because ice stream C is stopped.
01:03:41That's making a manifestation there
01:03:43is kind of instability, a kind of a start and stop
01:03:45instability.
01:03:47What kind of speed could it actually reach?
01:03:51Well, you think about surging.
01:03:54One meter a day is pretty puny for a surge velocity.
01:03:58We readily had, in our glacier in Alaska, 10 meters a day.
01:04:00And in some parts, we had up to 60, 65 meters a day.
01:04:04And surging speeds of 100 a day are known.
01:04:07Are those possible in the Antarctic ice sheet?
01:04:11It reminds me of one day on a glacier in Alaska.
01:04:14I was in my sleeping bag trying to go to sleep.
01:04:17And suddenly, there was a great shaking.
01:04:19The glacier was surging underneath.
01:04:21There was a great shaking.
01:04:22I thought, is this it?
01:04:23Is this thing really taking off?
01:04:25Is this what it feels like to be in a real surge
01:04:27and it's starting to shake?
01:04:30I rushed out of the tent, and I heard rocks
01:04:32roaring down the mountainside.
01:04:33I realized it was an earthquake.
01:04:35It wasn't the glacier taking off like a galloping.
01:04:39Well, it was galloping, but it didn't gallop that hard.
01:04:42So we don't know.
01:04:44But this is the kind of question we would ask.
01:04:46How do we figure out what kind of speed
01:04:47is ultimately attainable?
01:04:49And this bears on what sort of disintegration
01:04:54could really possibly take place.
01:04:56If you could have an instability like that,
01:04:59that the thing would go faster and faster,
01:05:01and suppose you could have a speed of 100 meters a day.
01:05:05You can move the ice out of the West Antioch Ice Sheet
01:05:07remarkably fast that way.
01:05:09You could get rid of that ice in the order of decades
01:05:12if you could have speeds that fast.
01:05:14On the other hand, at a speed of a meter a day,
01:05:16it's going to take hundreds or thousands of years
01:05:18to get it out.
01:05:19And so the conclusion about, is there
01:05:22a threat of any kind due to possible disintegration
01:05:24is much dependent on those potentialities, which
01:05:27we can't say really what they are
01:05:30or what the conclusions are.
01:05:31But we can point to them and can say the kind of data
01:05:34that we're trying to get is at least bearing on them.
01:05:43And what is the answer to the question?
01:05:45Is the Antarctic Ice Sheet disintegrating?
01:05:49Well, I would say no.
01:05:50I mean, not obviously disintegrating.
01:05:52It's certainly doing some rather remarkable things
01:05:57in these ice streams.
01:05:58But it doesn't constitute a disintegration yet,
01:06:00whatever that exactly means.
01:06:02Certainly, the fact that ice stream C has stopped
01:06:05already shows it's a whole thing is not just running away,
01:06:07something like that.
01:06:10Could it disintegrate in the future?
01:06:12Well, I must say I'm somewhat skeptical of wild things.
01:06:16But at least the kind of question,
01:06:18the kind of way you could approach the question
01:06:20of its possible disintegration, I
01:06:21think, is seen in these kind of attempts
01:06:23that we're making to understand what's going on.
01:06:30So thank you for your attention.
01:06:33Thank you, Barclay. I would just like to remind you about the next Watson lecture, which is
01:06:54two weeks from tonight, January 24th, to be given by Kip Thorne and has the intriguing
01:06:59title, Wormholes Through Hyperspace and Travel Through Time. If any of you have questions,
01:07:07please come up and Barclay will be glad to answer them. Thanks, Barclay.
01:07:37Thank you.