Glaciers of Antarctica
And the effects on Climatic Change. Ice Streams The ice cap does not slowly flow radially outward in all directions. In places a deeper channel has been worn down and ice, say 10,000ft thick will flow a lot faster than ice 4,000ft thick. From the air the boundaries of the ice stream or "channel glacier" can be plainly seen. The biggest is the Lambert Glacier which flows to the sea over in the Australian sector, it is up to 80 km wide and flows near the sea at a rate of about 1 km per year into the Amery Ice shelf at Prydz Bay. In actual fact, the Lambert appears to consist of a series of ice streams which flow into a tectonic depression and become channelled into an outlet glacier which forms a large ice-shelf where it enters a widening bay. The Ross Ice shelf is largely built from several ice-streams flowing out of the West-Antarctic Ice Sheet, (WAIS) , as well as by Outlet Glaciers flowing through the mountains from the EAIS. |__| Satellite view of the Lambert Glacier (to come later.)
Outlet Glaciers The Antarctic Ice cap has existed for at least 25 million years which is about the same age as the Victoria Mountains which form an almost impenetrable dam to ice flowing towards the Pacific. However at intervals ice has a some time risen high enough to top the mountain range and begin flowing down eastwards towards the Ross Ice shelf. As a channel was worn deeper, the ice flow increased, even so the ice is still backed up an average altitude of 9 - 10,000 feet on the west of the ranges. These massive glaciers draining enormous amounts of ice to the sea or to the Ross Ice-shelf are called "Outlet Glaciers". To the north of McMurdo the Drygalski, the David, Mawson and Mackay Glaciers are outlet type. To the south are the Ferrar, the Skelton, Mulock, Darwin, Barne, Shackleton, Beardmore, Liv, Axel Heiberg, Reedy and others less well known. The Shackleton and Barne (= Byrd) are up to 20 miles wide and we first saw them when on an aerial photographic mission in late 1955. Members of Scott’s Expeditions had seen the gaps in the mountains but were too far off to see the glaciers and so named the gaps "Inlets", eg the "Barne Inlet". I simply wrote in "Glacier" on the old 1903 maps and crossed out "Inlet", so "Skelton Inlet" became "Skelton Glacier" and so on for the Mulock, Barne, Shackelton (= "Nimrod"), etc. Charles Swithinbank and others have since measured their flow rates and more recently flow rates have been measured by satellite. Up to 800m a year flow is seen in the Byrd Glacier. More detail will be added later.
Mountain Glaciers Glaciers smaller than the outlets arise within the mountains themselves from a combination of snowfall and windblown drift. They arise in a snow-collecting basin or neve, flow down a rock-walled valley and may flow into the sea, into another glacier or into the Ross Ice-shelf.
<< Notice the sharp inter-cirque ridges extending down to the snow, evidently the ice level has not been higher for tens of thousands of years, nor has there been any retreat though possibly there has been a slight advance.
From the lower slopes of Round Mtn, Upper Taylor Glacier. Wright Valley to North, ie, middle right. Wall-sided Glaciers
These do not really occur anywhere in the world except in the Dry Valleys and in similar valleys in Northern Ellesmere Land and Northern Greenland. Small mountain glaciers flow into dry valleys which were once occupied by an Outlet glacier but down which ice no longer flows because of "ice capture" by a bigger nearby outlet, or because of mountain uplift. The tributary reaches the floor of the dry valley, and with no walls to contain it, expands outwards in an "expanded foot". Dirt bands near the base are formed by sub-glacial till being brought to the surface along shear surfaces, the ice being under "compressive" flow. Reflection of heat from bare rock causes accelerated melting especially near the base, so the expanded foot terminates in steep cliffs or "wall sides". The Commonwealth Glacier in the Wright valley is a classic example. Wright & Priestley first defined them after the 1910-12 Scott Expedition. Probable annual layers can be seen in the ice face but discontinuities must occur at the shear zones. |__| Commonwealth Glacier seen from the air (to come later.)
Piedmont Glaciers
"Piedmont" means "Mountain-foot" or, "At the foot of the Mountains". All the way from southern McMurdo Sound to Terra Nova Bay there is a coastal plain half a dozen miles wide, only a hundred feet or so high at the coast and sloping up gently west till it abuts onto the lower slopes of the Victoria Mountains, which shoot up to 3-6000 ft. This coastal plain is covered by a thinnish slab of ice which moves very little but is cut through at intervals by the outlet and mountain glaciers which reach the sea. The origins of these ‘Piedmont Glaciers" is rather uncertain. Being close to the open sea all summer they get quite a heavy local snowfall which does not extend into the Dry Valleys. It may be that over the centuries the Piedmonts have worn the coastal rocks down into a low plain. On the other hand it may be structural, the Royal Society Range and the Victoria Mts in general are block-faulted parallel to the coast. Are the piedmonts a down-thrown block on which ice accumulates? Unless we can match a rock type in the piedmonts with one occurring in the coastal ranges we cannot prove either, and the rocks are a folded complex of schists and granites with no marker horizons. Another possibility is that the piedmonts are a former raised beach dating from an early inter-glacial period. Sastrugi
Occasionally when out on the Barrier or up on the Ice Cap one may get a few inches of snow. If it is not blowing already it soon will, and the lighter snow lifts a few inches or feet above the ground and is whirled away. This is called "drift". The heavier snow heaps up into crecent-shaped barchan dunes just like sand dunes with the horns pointed downwind. The wind packs them hard and they form an icy crust and your nice travelling surface has been transformed into a series of hummocks over which sno-cats etc crash and sledges bang and as there is no more fine powdery snow, there is no more drift. But the wind will pick up small ice fragments and carry them along and these begin cutting into the "barchan"-like drift accumulations. After a few days they will have cut channels through them. Up on the ice-cap this becomes extreme and channels several feet deep are cut through the hummocks. As the "drift-chiselling" is more active low down, the hummocks become under cut, until they can look like upturned canoes on pedestals, and may stand 4-5 feet above the channels the wind and drift has cut. It is impossible to sledge or drive across "sastrugi" like these and one is forced to turn and travel along the line of the channels. Once on the ice cap we had to travel for three days to the south-west when we wanted to go south-east. Eventually we came out of them, or we may have ended up in Vostok!
Crevasses Ice can never flow as a sheet. It seldom flows faster than a few feet per day and it can slowly bend but under tension will usually crack. These cracks are called "crevasses". If ice flows down a rock-walled valley as a glacier it will flow faster on top than at the bottom and faster in the middle than at the sides. This develops tensions which cause a chevron pattern of crevasses to form, the most crevasse-free place being in the middle of the glacier. Along the edges near the rock, crevasses may gape 20 feet wide and occur every fifty yards or so. An almost stagnant glacier may have almost no crevasses at all. If the gradient in a glacier sharply steepens as the ice flows over a hard band of rock, there will be gaping crevasses at right angles to the path of flow, especially near the break in slope at the top. Even if buried in snow, again you know they will be there. Only a complete fool would ever drive a vehicle over a sudden drop in the surface of a glacier.
Wind-drifted snow may partly fill them, or form a lid which can be inches to feet thick. A sharp jab with an ice axe will often go right through. Very large crevasses may be 20 – 50 feet wide and be lidded, the lid being a sagging bridge of triangular shape, sometime so solid you can walk over and not know they are there. A tractor or vehicle may cause it to fall in. Don't believe the clever remarks about the low ground pressure of Sno-cats. Six tons on a crevasses lid is exactly six tons extra weight!
Few things cause shortness of breath more effectively than the feeling of a leg suddenly going through and you find one foot is resting on several hundred feet of air. Where a glacier is forced to turn round a bend big pressure ridges form on the inside of the bend and very large crevasses on the outside of the bend. They may be buried under snow cover, but you know they are there so always walk with a rope on, they can be 2-300 feet deep. Again only a congenital idiot would select a route around the outside of a bend. This hole occurred on a flat slab of grounded ice several miles across on the edge of the Ross Shelf. It hadn't orta a been there! It was worse than sneaky, it was plain deceitful but it got us!.
Crevasses have a special vindictiveness all of their own. They can be there, buried under 3 feet of soft snow, on a flat area without a sign of a hump or anything to cause them. They have been sitting there for hundreds of years just waiting for some amiable idiot to come wandering past or driving over! To the experienced eye, a crack in the snow an inch wide 50 yards to one side means, "I am about to step over a buried crevasse maybe 3 feet wide.!" [Prod! Prod!] "Ah! Thought so!"
In bad country one man leads prodding the snow. Your best man comes second, when he see the first man suddenly drop, he gives a heave on the rope. Result? The first man finds himself sitting on the lip of a crevasses with his feet dangling and no harm done. The third man is there just in case the second man is a bit slow, pulling someone up who has gone down 6 -10 feet and is swinging in the air, takes two men. I have done it only once, the lead man was a bit too cocky and was insisting there was no danger so I gave him four feet of slack and waved him on. He went through and down out of sight within a dozen yards! Windslab snow is a crust with nothing but very soft snow beneath. If you or the dogs step on it, or the sledge goes over it, it may give a "woof" and an area a hundred yards across may settle by 6 inches or so. The dogs panic and leap to one side, they think it is a crevasse, and the driver's heart does some odd things at times!
Ice Tongues When an outlet or mountain glacier reaches the sea, it parts from the land and floats pushing out a tongue a mile or two long, sometimes 10 or 20 miles. Eventually, tide flow, currents or storms will cause it to break off and float away as a "tongue berg". "The Ice Tongue" on Ross Id flows down a channel into the sea and has broken off twice since 1912, as has the Mackay Tongue. The Mawson Tongue is very long but has broken off at least once. |__| Ice tongue at Terranova Bay, (but no re-entrants?? To come.)
Ice Bergs
Tabular Bergs
The face of the B -15A mass, freshly broken from the face of the barrier. Ice Shelves The edge of the Ice shelf (actually of the tabular berg "B -16"). Some new ice forming where the immense berg has split. Imagine the fate of a vessel taken into such a "lead" if the two halves moved together again! Beaufort Id in distance.
Ice shelves are thick floating ice masses attached to the continent and occurring in protected bays and bights in the land. In a bay pack ice may persist over several years and become bay ice and accumulate snowfall to become an ice shelf. However the larger Ice shelves have a great deal of ice contributed from outlet and mountain glacier tongues and the persistent bay ice between them plus accumulated snowfall. One wonders why the whole Weddell Sea is not one enormous ice shelf, as the southern Ross Sea is, but it is not quite enclosed enough and some pretty stiff ocean currents sweep round it in a clockwise direction, continuously breaking the ice up.
By now there must be a great deal of data on the thickness of the Ross Ice shelf at the southern end against the land, compared to the northern limit between Cape Crozier and Bay of Whales. In summer, warmer water flows under it with each tide, and there must be considerable bottom melting. We hope to get the latest thickness data and melting data and add it here. As yet the front of the Ross Ice shelf, while it calves off enormous bergs periodically, has not changed much since first seen by the "Erebus" and "Terror" in 1845. The surface of the Ross Ice Shelf is not flat but has swells and rises. At one point the horizon may only be miles away and one cannot see a thing. Then imperceptibly one climbs up out of the depression, to see the tops of mountains standing up perhaps a hundred miles away. |__| The Bay of Whales. Here the shelf is thinned because of the existence of a rock knoll upstream called Roosevelt Island which tends to part the ice to two streams which coalesce again but form a semipermanent bay in the ice (to come.) The Melting of Ice Shelves The popular press and other attention getters are currently prone to dropping remarks such as "Rising world temperatures may result in the melting of Ice Shelves and the West Antarctic Ice Sheet bringing catastrophic rises in sea level, which may cover the floor of you sea-side holiday home!" etc. Some refer to the complete submergence of New York and places like Holland and Pacific Islands. Pacific Islands of course have had no trouble in keeping above sea level in spite of the rise of >100m since the last glacial period 10,000 years ago, but coral is now having a hard time due to factors like people fishing among reefs by tossing in hand-grenades or poison. This may be seen in the dead coral in islands off Lombok in Indonesia. A great deal of coral is dying in the Pacific, eg in the Tonga Group and Great Barrier Reef due to the "Crown of Thorns" starfish which is exploding in numbers because their natural enemies the Helmet Shellfish and Giant Triton is being exterminated by people selling their shells to tourists. Excessively hot summers are also blamed but corals have stood up to higher temperatures before this. However, without actively-growing coral, Pacific atolls may indeed be in trouble. Ice shelves have a precarious existence with the inflow of glacier ice and accumulated snow having to match the loss along the frontal face by calving of icebergs. In cold winters ice may be frozen onto their lower surfaces, in a warm summer with seawater flowing in under them with the tides, there is some thinning due to melting of the lower surface. This is partly counterbalanced by the fact that water is heaviest at 4ºC so that any surface water that warms up to 4ºC promptly sinks to the bottom. I have never lowered a thermometer to the bottom of the Tongan Trench at 32,000ft depth, but I know what the temperature is, it is VERY close to 4ºC. Curiously enough, though I have fallen into it I do not know what the surface temperature in McMurdo Sound is at the height of summer, but it is for at least 2 months, high enough to melt the sea-ice. Let us qualify that, it become warm enough not to freeze, the thinning of ice pack takes place mainly from the top on sunny days. Suppose we have a horrendous increase in summer temperatures, warm water flows under the Ross Ice Shelf and thins it from its present thickness to, say 500ft. It would then be less able to resist cracking by northerly swells and the face could retreat by say a hundred miles. What is the effect going to be on world sea-levels? Absolutely none, as a floating body displaces its own weight of water, as that Greek fellow (Archimedes) realised when he was taking a bath. Suppose we have a population that has increased to 10 billion all panting out heat and CO2 and we burn four billion tons of coal a year and world temperatures rise by 5ºC. The Ross, the Ronne, the Filschner, the Larsen and the Amery Ice shelves all retreat until they reach a point where the ice is aground, even if below sea level. However, being aground, the tide cannot flow under it, and melting is restricted to the ice front. It then becomes a matter of, does the rate of ice-flow seaward at 200-800m/yr match the rate of melting along the face? As we are now a long way further south it probably would in most cases. The Ross Ice shelf front is in actual fact, currently further north than it was in 1955. With open seawater much closer, the humidity and snowfall would increase greatly and the average mean temperature would still be around -40ºF, at which not a great deal melts if you will pardon the sarcasm. So our southern Ice Cap as well as the Greenland one are comparatively stable structures with a great deal of inbuilt inertia and resistance to change. A little thinning might take place around the continental margins, but possibly more than offset by increased snowfall, possibly a few toes of rock might show. Sea-level could rise by a few inches, with which our civil engineers could no doubt deal with, but on the other hand if snowfall is increased enough, the ice-caps could thicken and sea-level fall. Our knowledge of climate control is not good enough at this point to be positive, so many people are simply guessing. Sea levels can change locally with prevailing winds but the Chief Oceanographer in Hawaii assures me no definite sea-level change has been detected in the last fifty years. Other sources claim rises of 0.9 to 3mm/yr, which given the rate at which mountain glaciers are going in temperate regions could be true. (Though Sweden show the highest rate of change with sea-level declining.) Other data show sea-levels to vary from 0 to 123m below present over the last 250,000 yr, none being higher. Claims of the possible melting of the Greenland Ice Cap with sea-level rises of 15 – 18m are not really believable, as stable continents such as Australia do not show terraces etc indicative of sea-level ever being above present. The most unstable iceforms are probably not the ice-shelves, but the wall-sided glaciers that exist in the Dry Valleys which are very susceptible to average snow fall and mean annual temperature. I took a pic of one in 1955 (shown above) and have spent a fair amount of time trying to get permission to go back and take another pic from exactly the same point 48 years later which should reveal all. Permission has always been strongly denied, science is not rated very highly these days and politically correct opinion is all, and politically correct opinion says the ice-caps will all melt and we will all drown except for a handful of Tibetans so who am I to say different? Long Term Climatic Changes
The above diagram from Petite et al, 1999 shows the results of the 2623m ice core drilled above Lake Vostok by an international consortium. While not the first it is the most convincing demonstration of climatic changes in the last half million years. Some commentators claim that the greenhouse effect accentuates the temperature differences which are claimed to parallel the precessional orbital solar distances, others deny this. The CO2 atmospheric content has ranged from a minimum of 180 to a maximum of 290 ppm. Forest clearance and the burning of vast amounts of coal and oil, have put current CO2 levels up to 360 ppm, well above anything seen for half a million years but less that seen in the Ordovician before widespread carbonate rocks and the coal measures were laid down, when CO2 was at 4400 ppm levels and temperatures much as present day. We are looking for the precessional variation data; please pass it on it you know of any.
Above are the results of a core taken near the Australian Mawson base, showing the detail over a single cycle from 150,000 yr to present. No less than 10 minor variations occur in between, the maximum and minimum T and CO2 support the findings of Petit et al.
A long term diagram from cores going back to 2.5 million years. Before about 800,000 years, the glacial periods were of shorter duration. Near the centre of the West Antarctic ice has been cored ~ 10,000ft to bedrock by the EPICA at what is called Dome C, ( E. Brook et al, 2005, Science) and extends to 650,000 yrbp. Like Vostok and the 1992 Greenland Icecap cores, (Jouvel etal, Nature 429, 2004), the same 4 prominent iceages occurring at roughly 100,000 year intervals te seen but the 500, and 600,000 yr ones are less severe and have a longer interglacial. There are no sections missing, ie both Greenland and west and East Antarctica have been icecovered continuously for 650,000 years and possibly much longer and no melting has taken place. However, throughout this time the CO2 and methane levels have been lower than they are at present. Current Polar Climatic Trends Apparent glacial recession is most apparent in the Dr Valley Area. As we pointed out back in 1962 (Gunn & Warren, 1962 NZ.Geol.Surv.Bull.71) this is due to the failure of the main outlet glaciers of the region to wear down their thresholds which block the flow of Plateau ice. The Mawson to the north and the Mulock and the Barne (= Byrd) Glaciers to the south have much more deeply incised thresholds. Mt Feather also plays a part in deflecting wind-blown drift. The age of the ice maximum in the Dry Valleys now may be taken as being in the range 2.5 - 3 million years bp, based on duration of exposure of rock to radiation, to weathering, and on the presence of unglaciated volcanic rock of Late Pliocene age. Temperature variations of the last half million years have changed the extent of grounded ice, coastal ice levels, the extent of ice-shelves and has changed sea levels so that some valleys may have become fiords as the Skelton currently is. |___| << View of south side of the Taylor Valley showing very level lines which are not moraine lines and can only be beach lines during interglacials. In general there has been a painfully slow retreat of ice in the Dry Valleys, as plateau supply and wind-drift were cut off. Ancient ice still persists under ablation moraine so the process is not complete. There are no prominent stranded lateral moraines or sequence of terminal moraines as seen in temperate zones to indicate even minor re-advances. The greater mass of the East Antarctic Ice Sheet (the EAIS) seems to have remain substantially unchanged. No retreat is seen in much of NVL, in the Queen Maud Mts and the Horlick Mts. Plateau lowering and increase or reduction in ice capture may take place at any of the outlet Glaciers. Truncated spurs and underfit glaciers may occur but similar signs are not seen in neighbouring glaciers. High snow levels in NVL especially may mean the ice is locally thickening with climatic warming. Ice Axes There is only one rule regarding an ice-axe and that is: Never go a dozen yards on ice or snow without one. Even on rock with an ice-axe to act as a third leg, one will never slip and fall and you cannot afford to fall when 400 miles from home. On snow you must prod for crevasses, you must be able to ram the shaft home in the snow and take a turn of the rope round it to belay another man who has "gone down the mine" or looks as though he might. Your ice-axe will protect you against a leopard seal, or an attacking skua. It will help anchor the tent in a blizzard, with it you chop ice to melt to drink. You can use it (and nothing else will do) to kill a seal for the dogs, or to save yourself from starvation in the event your chopper has crashed and there is not another within 500 miles to save you (as happened to us once.) A really massive ice-axe is needed, it should reach your hip bone when the ferrule is on the ground, the right length for a walking stick. Antarctic ice is very hard, a light axe will shatter. I have seem people carry silly little things about 2 feet long as used as a pick on a steep ice climb, these are quite useless on the ice, one cannot even prod for crevasses with them. You may have to cut steps to cross a tide crack, or to get up an awkward bit on a mountain. I once had two men fall off on me when descending an icy couloir, a belay round the point of the pick in a tiny crack saved them, (and me). I have lost count of the times a good belay rammed into snow has stopped the fall of someone who has slipped, or had an ankle turn when on crampons. I have known the man in front go through a crevasse six times in an hour, the ice-axe saved the situation every time. I would rather be without my pants. If you left a clock or camera behind, too bad. No salt or sugar? Put up with it and learn a lesson. No ice axe or climbing rope? Go home! |
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