Poolkappen, IJsbergen en Gletsjers #2

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'Megadam kan Noordpoolijs beschermen'

AMSTERDAM - Een Nederlands onderzoeker heeft een plan gelanceerd om het ijs op de Noordpool te beschermen met een gigantische dam.

Klimaatdeskundige Rolf Schuttenhelm pleit voor de aanleg van een ruim 300 kilometer lange dam in de Beringzee. Zo'n bouwwerk kan de omstandigheden voor ijsvorming op de Noordpool volgens hem aanzienlijk verbeteren.

Zijn plan is gepubliceerd op de website www.cleverclimate.org, een nieuw internationaal platform waarop wetenschappers grootschalige en vernieuwende plannen tegen de opwarming van de aarde kunnen lanceren.

Alaska

De dam van Schuttenhelm zou gebouwd moeten worden tussen St. Lawrence Island en het vasteland van Alaska en Siberië. Er zou dan in verhouding meer zoet water vanuit de rivier de Yukon naar de Noordpool kunnen stromen. En hoe minder zout zeewater is, hoe makkelijker het bevriest en hoe trager het smelt.

Het plan zou ijsvorming ook bevorderen, omdat de stroming in het Noordpoolwater lokaal afneemt door de plaatsing van een dam. Verder zou de temperatuur van het water dalen, omdat er minder relatief warm water wordt aangevoerd vanuit de Stille Oceaan. Andere klimaatonderzoekers nemen het plan voor de zogenaamde St. Lawrence Dam serieus.

Interessant idee

"Dit is een interessant idee", zo reageerde de Amerikaanse wetenschapper Walt Meier van het National Snow and Ice Data Centre (NSIDC), dat toezicht houdt op de Beringzee.

"Dit plan kan zeker de genoemde impact hebben op het klimaat. Al zijn er mogelijk ook onvoorziene consequenties. Een dramatische verandering van de stroming in de Noordpool zou ook invloed kunnen hebben op de Stille Oceaan en de omliggende landen. Verder is het een behoorlijke financiële en technologische uitdaging. De Beringstraat is misschien smal, maar deze dam is nog steeds een stuk groter dan de gemiddelde dam."

Schuttenhelm vindt het vooral belangrijk dat de discussie over klimaatplannen wordt aangewakkerd. "Het is waar dat er nu nog te veel onzekerheden in het plan zitten. Maar we moeten wel over deze schaal van oplossingen durven nadenken. Als we niets doen, zijn de gevolgen enorm. Met dit plan wil ik vooral een open debat onder geschoolde klimaatonderzoekers uitlokken. En ik blijf natuurlijk een Nederlander. Ik heb vertrouwen in de mogelijkheden van dijken en dammen."

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NASA: 2 Trillion Tons of Ice Have Melted Since 2003

WASHINGTON — More than 2 trillion tons of land ice in Greenland, Antarctica and Alaska have melted since 2003, according to new NASA satellite data that show the latest signs of what scientists say is global warming.

More than half of the loss of landlocked ice in the past five years has occurred in Greenland, based on measurements of ice weight by NASA's GRACE satellite, said NASA geophysicist Scott Luthcke. The water melting from Greenland in the past five years would fill up about 11 Chesapeake Bays, he said, and the Greenland melt seems to be accelerating.



NASA scientists planned to present their findings Thursday at the American Geophysical Union conference in San Francisco. Luthcke said Greenland figures for the summer of 2008 aren't complete yet, but this year's ice loss, while still significant, won't be as severe as 2007.

The news was better for Alaska. After a precipitous drop in 2005, land ice increased slightly in 2008 because of large winter snowfalls, Luthcke said. Since 2003, when the NASA satellite started taking measurements, Alaska has lost 400 billion tons of land ice.

In assessing climate change, scientists generally look at several years to determine the overall trend.

Melting of land ice, unlike sea ice, increases sea levels very slightly. In the 1990s, Greenland didn't add to world sea level rise; now that island is adding about half a millimeter of sea level rise a year, NASA ice scientist Jay Zwally said in a telephone interview from the conference.

Between Greenland, Antarctica and Alaska, melting land ice has raised global sea levels about one-fifth of an inch in the past five years, Luthcke said. Sea levels also rise from water expanding as it warms.

Other research, being presented this week at the geophysical meeting point to more melting concerns from global warming, especially with sea ice.

"It's not getting better; it's continuing to show strong signs of warming and amplification," Zwally said. "There's no reversal taking place."

Scientists studying sea ice will announce that parts of the Arctic north of Alaska were 9 to 10 degrees warmer this past fall, a strong early indication of what researchers call the Arctic amplification effect. That's when the Arctic warms faster than predicted, and warming there is accelerating faster than elsewhere on the globe.

As sea ice melts, the Arctic waters absorb more heat in the summer, having lost the reflective powers of vast packs of white ice. That absorbed heat is released into the air in the fall. That has led to autumn temperatures in the last several years that are six to 10 degrees warmer than they were in the 1980s, said research scientist Julienne Stroeve at the National Snow and Ice Data Center in Boulder, Colo.

That's a strong and early impact of global warming, she said.

"The pace of change is starting to outstrip our ability to keep up with it, in terms of our understanding of it," said Mark Serreze, senior scientist at the National Snow and Ice Data Center in Boulder, Colo., a co-author of the Arctic amplification study.

Two other studies coming out at the conference assess how Arctic thawing is releasing methane — the second most potent greenhouse gas. One study shows that the loss of sea ice warms the water, which warms the permafrost on nearby land in Alaska, thus producing methane, Stroeve says.

A second study suggests even larger amounts of frozen methane are trapped in lakebeds and sea bottoms around Siberia and they are starting to bubble to the surface in some spots in alarming amounts, said Igor Semiletov, a professor at the University of Alaska in Fairbanks. In late summer, Semiletov found methane bubbling up from parts of the East Siberian Sea and Laptev Sea at levels that were 10 times higher than they were in the mid-1990s, he said based on a study this summer.

The amounts of methane in the region could dramatically increase global warming if they get released, he said.

That, Semiletov said, "should alarm people."

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'Opwarming Antarctica begonnen'

UTRECHT - Sinds de jaren 50 is de temperatuur rond de Zuidpool, waar 90 procent van 's werelds ijs ligt, met 0,5 graden gestegen, blijkt uit verzamelde gegevens van satellieten en weerstations.

Twee dagen na het bericht over het desintegreren van een grote ijsplaat op het Antarctisch schiereiland komt een groep Amerikaanse wetenschappers met een overzicht van alle beschikbare meetgegevens van het zuidelijke continent.

In tegenstelling tot het door klimaatsceptici frequent geproclameerde kouder worden en aangroeien van Antarctica, laat de wetenschappelijke realiteit geen enkele ruimte meer voor ontkenning: Klimaatverandering heeft de Zuidpool bereikt. En zoals overal: sneller dan we verwachtten, stellen de onderzoekers.

Eric Steig

"Wat je continu hoort is dat Antarctica kouder wordt en dat is simpelweg niet het geval", zegt Eric Steig van de Universiteit van Washington in Seattle, hoofdauteur van de studie die vandaag in Nature wordt gepubliceerd.

De gemiddelde temperatuurstijging is sterk vergelijkbaar met het mondiale gemiddelde, vertelt Steig. Klimaatsceptici stelden in het verleden dat Antarctica kouder zou worden als bewijs dat de mondiale opwarming een mythe zou zijn.

De Amerikaanse onderzoeksgroep schrijft dat de gemeten Antarctische opwarming moeilijk te verklaren is zonder deze te koppelen aan de sterk toegenomen antropogene uitstoot van broeikasgassen, voornamelijk door grootschalig gebruik van fossiele brandstoffen.

West-Antarctische ijskap

Op het Britse onderzoeksstation Rothere, op het Antarctisch schiereiland, was het gisteren 2,6 graden boven nul. "Maar het gebied waar we de opwarming meten is veel groter dan alleen het schiereiland. Ook de gehele West-Antarctische ijskap warmt op", zeggen de Amerikanen. "En de gemiddelde oppervlaktetemperatuur van het hele continent neemt toe", meldt de studie.

"West-Antarctica zal uiteindelijk smelten als deze opwarming zo doorzet", zegt Drew Shindell, een medeauteur van het NASA Goddard Institute for Space Studies.

Groenlandse ijskap

Daarvoor zou volgens hem een gemiddelde temperatuurstijging van 3 graden voor nodig zijn. Ook de Groenlandse ijskap zou bij een dergelijke temperatuurstijging niet overleven.

Tezamen bevatten zij genoeg ijs voor een gemiddelde zeespiegelstijging van 14 meter. De ijsmassa op Oost-Antarctica bevat zelfs voldoende water om de zeespiegel wereldwijd met nog eens 50 meter te laten stijgen. Deze ijskap is echter minder kwetsbaar voor de huidige opwarming.

"Maar zelfs wanneer slechts een fractie van Groenland en West-Antarctica smelt kunnen we deze eeuw nog meters zeespiegelstijging zien, met desastreuze gevolgen" target="_blank", zegt Barry Brook, directeur van het onderzoeksprogramma naar klimaatverandering van de Universiteit van Adelaide.

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Antarctica is warming up
The continent of Antarctica is warming up in step with the rest of the world, according to a new analysis.

Scientists say data from satellites and weather stations indicate a warming of about 0.6C over the last 50 years.

Writing in the journal Nature, they say the trend is "difficult to explain" without the effect of rising greenhouse gas levels in the atmosphere.

Meanwhile, scientists in Antarctica say a major ice shelf is about to break away from the continent.

The Wilkins Ice Shelf is said to be "hanging by a thread" from the Antarctic Peninsula, the strip of land pointing from the white continent towards the southern tip of South America.

In isolation

Most of Antarctica's scientific stations are located along the peninsula, and scientists have known for many years that this portion of the continent is getting warmer
But trends across the bulk of the continent have been much harder to discern, mainly because data from land stations is scarce.

It is somewhat insulated from the rest of the world's weather systems by winds and ocean currents that circulate around the perimeter.

In the new analysis, a team of US scientists combined data from land stations with satellite readings

"We have at least 25 years of data from satellites, and satellites have the huge advantage that they can see the whole continent," said Eric Steig from the University of Washington in Seattle.

"But the [land] stations have the advantage that they go back much further in time.

"So we combined the two; and what we found, in a nutshell, is that there is warming across the whole continent, it's stronger in winter and spring but it is there in all seasons."

They conclude that the eastern region of the continent, which is larger and colder than the western portion, is warming at 0.1C per decade, and the west at 0.17C per decade - faster than the global average.

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Kolossale ijsplaat Zuidpool verdwijnt in zee

UTRECHT - De Wilkinsplaat, een reusachtige Antarctische ijsplaat, staat op het punt te desintegreren en in zee te stromen, zeggen Britse en Nederlandse onderzoekers.

De ijsplaat heeft een oppervlak van duizenden vierkante kilometers en steekt als een platte berg 20 meter boven zeeniveau uit. Op satellietbeelden is te zien dat de plaat inmiddels vol grote scheuren zit en enkel nog wordt bijeengehouden door een steeds smallere strook zee-ijs.

Deze 40 kilometer lange ijsdam, die 'als een kurk op een fles' de rest van de gebarsten ijsplaat fixeert, was in 1950 nog 100 kilometer breed. Inmiddels rest volgens de British Antarctic Survey (BAS) niet meer dan een ‘splinter’ stabiel ijs, slechts 500 meter breed. Zodra deze doorbroken wordt, zal ook de achterliggende massa in zee stromen, verwachten de onderzoekers.

Nederlands onderzoek
“Het kan nu elk moment gebeuren” zegt David Vaughan, een glacioloog van BAS. “We zijn hier getuige van de laatste momenten van de Wilkins-ijsplaat.” Om de bewegingen van het ijs te registreren heeft Vaughan een GPS-meter op de plaat gestationeerd. Deze verzamelt gegevens voor onderzoek van IMAO, het Instituut voor Atmosferisch en Marien Onderzoek van de Universiteit Utrecht.

“Deze ijsplaten zijn een soort gletsjers, die op hun plek worden gehouden door bijvoorbeeld eilandjes'', vertelt Michiel van den Broeke, van IMAO. “Het is zeer zorgwekkend dat ze nu zo snel verdwijnen.” Het afbreken van de beschermende ijsplaten kan er volgens Van den Broeke voor zorgen dat ook de achterliggende gletsjers sneller naar zee gaan stromen. Dit kan de zeespiegelstijging versterken.

Grote delen van de ijsplaat werden in maart vorig jaar, aan het einde van de Antarctische zomer, instabiel. In voorgaande jaren verdwenen al de 'Prince Gustav Channel', 'Larsen Inlet', 'Larsen A', 'Wordie', 'Muller' en de Jones-ijsplaat in zee. Het meest geruchtmakend was het instorten van ‘Larsen B’ in 2002. Deze omvangrijke ijsplaat verdween in 30 dagen volledig van de kaart. Uit sedimentonderzoek is gebleken dat de ijsplaten in elk geval meer dan 10.000 jaar oud waren.

Massaverlies
"Het verdwijnen van deze ijsplaat en de negen andere is een direct gevolg van klimaatverandering", zegt Vaughan. Het Antarctisch schiereiland is daar relatief gevoelig voor, omdat het ijs daar vrij ver in de omringende oceaan steekt. De gemiddelde temperatuur is er sinds 1950 al met drie graden gestegen. Maar ook de West-Antarctische ijskap verliest de laatste jaren massa, blijkt uit satellietmetingen. En in tegenstelling tot de populaire theorie dat hogere temperaturen het ijs op Antarctica zouden versterken met extra sneeuwval, blijkt ook de nog immer zeer koude Oost-Antarctische ijskap niet te groeien.

Vanwege de vele onzekerheden is in de officiële voorspellingen voor zeespiegelstijging van het IPCC tot nog toe echter geen rekening gehouden met een mogelijk versneld bewegen van gletsjers op Antarctica en Groenland. Het laatste grote klimaatrapport, uit 2007, gaat nog uit van een stijging van 18 tot 59 centimeter.

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Gletsjers Pyreneeën smelten snel
AMSTERDAM - De Pyreneeën hebben in de laatste eeuw bijna negentig procent van hun gletsjerijs verloren en het resterende ijs kan door de opwarming van de aarde binnen enkele decennia verdwenen zijn.

Dat zegt het Spaanse ministerie van milieu.

Het ministerie liet onderzoek doen naar de gevolgen van de opwarming van de aarde voor de Pyreneeën
3300 hectare

De onderzoekers constateerden dat van de 3300 hectare ijs die in het begin van de twintigste eeuw het gebergte bedekte nog maar 390 hectare over is. Het restant is ongeveer gelijk verdeeld tussen Frankrijk en Spanje.

Daarbij komt dat het overgebleven ijs steeds sneller smelt. Tussen 2002 en 2008 verloren de Spaanse Pyreneeën ongeveer een kwart van hun gletsjerijs, aldus het vorige week vrijgegeven onderzoeksrapport.

Broeikaseffect

De onderzoekers leggen een rechtstreeks verband tussen het smelten van de gletsjers in de Pyreneeën en andere gebergten, de opwarming van de aarde en veranderingen in neerslagpatronen.

De Spaanse voorzitter van de organisatie voor behoud van gletsjers in de Pyreneeën, Fernando Lampre, zegt in een interview in de krant El Pais te vrezen dat de meeste gletsjers over 25 tot dertig jaar zijn verdwenen.

"En tegen het midden van de eeuw zijn ze allemaal weg", aldus Lampre.

VN

Volgens het Milieuprogramma van de Verenigde Naties worden gletsjers in de hele wereld bedreigd. De website van de VN-organisatie zegt te hopen dat de Klimaatconferentie van eind 2009 in Kopenhagen voor een doorbraak zal zorgen. Zo niet, dan 'is het mogelijk dat gletsjers in de 21ste eeuw volledig uit veel bergketens verdwijnen'.

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Melting glaciers may redraw borders
ROME, Italy (CNN) -- Melting glaciers in the Alps may prompt Italy and Switzerland to redraw their borders near the Matterhorn, according to parliamentary draft legislation being readied in Rome

Franco Narducci of Italy's opposition Democratic Party is preparing a bill to redefine the frontier with neighboring Switzerland, his office said Wednesday.

Narducci is a member of the foreign affairs panel in Italy's lower Chamber of Deputies. Foreign Minister Franco Frattini has authorized the bill.

Switzerland also has cooperated with Italy on the matter.

The Italian Military Geographic Institute says climate change is responsible for the Alpine glaciers melting.

"This draft law is born out the necessity to revise and verify the frontiers given the changes in climate and atmosphere," Narducci said. "The 1941 convention between Italy and Switzerland established as criteria [for border revisions] the ridge [crest] of the glaciers. Following the withdrawal of the glaciers in the Alps, a new criterion has been proposed so that the new border coincides with the rock."

The border change only affects uninhabited mountaintop terrain. The deputy excludes the possibility of any family having to change citizenship.

The border between Italy and Switzerland was fixed 1861, when Italy became a nation, but it has been occasionally modified, the Military Geographic Institute said. The border was last modified in the 1970s when the Switzerland-Italy highway was built at the Brogeda crossing.

The bill is expected to become law by the end of April, Narducci said.

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Antarctic sea ice increasing: study

In recent years all the headlines have been about ice melting in some of the globe's chilliest places. But it seems that global warming may actually be leading to an increase in sea ice in parts of the Antarctic.

Scientists in the United Kingdom have produced a study which shows ice has grown by 100,000 square kilometres each decade in the past 30 years.

The increase is being put down to the hole in the ozone layer.

The British Antarctic Survey combined with NASA to look at the levels of ice in the region over the long term.

What was clear was that climate change produces complex results. Instead of a widening hole in the ozone layer, produced by human activity, warming temperatures as they have in the Arctic, in Antarctica it was having the opposite effect.

Scientists such as Julienne Stroeve from the National Snow and Ice Data Centre in the United States say they are not that surprised by the news of the study and its findings.

"There's been a change in atmospheric circulation around Antarctica related to the stratospheric ozone depletion and this actually causes stronger winds, which then pushes the ice away from the coast in some regions of Antarctica, which actually then causes more new ice formation and increases the overall sea ice in that region," she said.

"In other parts of Antarctica the temperatures have been decreasing and this is again sort of what we've expected to see, at least according to what the climate models tell us should be happening.

"But if you look at the Antarctic Peninsula for example, that's where you've had really strong warming and you've had a warming of about 3 degrees Celsius in the last 50 years.

"And if you look at changes in sea ice in that region they all show very strong negative trends.

"The paper shows an overall positive trend if you look at all of Antarctica, but there's regional differences that are quite different from different regions.

"We have to deal with what we know about warming in certain regions and changes in circulation and wind patterns in other regions."

Dr Stroeve argues that the rate of ice expansion, even as it translates to hundreds of thousands of square kilometres, is relatively insignificant.

"This recent paper shows you know a change in the annual mean ice extent of Antarctica of only 0.97 per cent per decade which is really close to zero," she added.

"In contrast if you look at the Arctic, you see statistically significantly trends of about 4 per cent per decade in the opposite direction right now if you look at the annual mean. Certainly it's a very small change for the Antarctic.

"The Antarctic is very different than the Arctic and what we're noticing is that you'll see negative trends in some areas of the Antarctic and positive trends elsewhere.

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The Wilkins Ice Shelf, on the western side of the Antarctic Peninsula, experienced multiple disintegration events in 2008. A rapid retreat started in February, near the end of the Antarctic summer. Another breakup began in May, during the Antarctic winter. And fresh cracks appeared on the shelf in late November 2008. By the beginning of 2009, a narrow ice bridge was all that remained to connect the ice shelf to ice fragments fringing nearby Charcot Island. That bridge gave way in early April 2009.
Days after the ice bridge rupture, on April 12, 2009, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured this image of the southern base of the ice bridge, where it connected with the remnant ice shelf. This image shows ice fragments of varying sizes mixed with ice mélange. A crack in the east reveals dark ocean water below. Although the ice bridge between the shelf and Charcot Island had played a role in stabilizing the ice fragments in the region, its rupture didn’t guarantee an immediate ice exodus. The Wilkins Ice Shelf experienced a breakup event in 1998, yet the ice blocks from that breakup froze in place for a decade.
In this image, the low angle of the Sun accentuates shadows, and highlights an interesting feature. The large slab of ice in the lower left corner of this image displays a slight linear bulge along its northeastern edge. This area of raised ice is consistent with ice shelf modeling in numerous studies.
An ice shelf is a thick slab of ice that is attached to a coastline. The seaward extension of the shelf floats on the water like sea ice. Unlike sea ice, however, ice shelves can have thicknesses in excess of 100 meters, with part of the ice front above water and part of it below. After part of an ice shelf breaks away, the remaining ice shelf, despite its thickness, doesn’t remain impervious to the change. In both ice and water, pressure increases with depth, but the pressure gradient is steeper in water. This means that ocean water tends to deform the ice, pushing inward on the ice slab’s front. On its top surface, the ice slab bulges, and its top edge rotates outward and downward. The raised area along the front of the ice slab in this image suggests that ocean water has deformed this ice slab as predicted.

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New warning over Arctic ice-cap

The Arctic ice-cap, a permanent feature for at least 100,000 years, could vanish in summertime far sooner than predicted, a leading scientist says.

Professor Peter Wadhams, from the University of Cambridge, told BBC News he has brought forward his estimates of the ice-cap's demise.

He believes the ice is now so thin that almost all of it will disappear in about a decade.

He says it will become seasonal, forming only during the winter.

He told the BBC: "By 2013 we will see a much smaller area in summertime than now, and certainly by about 2020, I can imagine that only one area will remain in summer."

His assessment is based on analysis of nearly 40 years of sonar data gathered on Royal Navy submarines patrolling beneath the ice - the first, HMS Dreadnought, was in 1971.

Until recently, most climate forecasts suggested that the Arctic Ocean would have ice-free summers only towards the end of the century.

The most extreme scenario was for the ice to retreat as soon as 2013, but that was dismissed by many as far too soon.

Now Professor Wadhams, who has studied the Arctic for the past 40 years, says that there is "almost a breakdown" in the ice-cover.

Over most of the Arctic, there has been a massive decline in the amount of so-called multi-year ice - ice that is tough enough to withstand the summer warmth.

Much of what is left of this ice accumulates in an area north of Greenland and Ellesmere Island in Canada, and may form what he calls "a last holdout, a kind of Alamo".

Professor Wadhams said: "The change is happening so fast. It's the result of this steady thinning over four decades that has brought it to a state where its summer melt is causing it to disappear.

"It's like the Arctic is covered with an egg shell and the egg shell has been thinning to the point where it is now just cracking completely."

The rest of the story continues here...

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Origin of Antarctic ice revealed

Incredible peaks and valleys, buried beneath ice for 14 million years, have revealed evidence of how the East Antarctic ice sheet first formed.

Scientists used radar to map an area of the Gamburtsev mountains - believed to be the point of origin of the ice.

The region would have been cold enough for the first glacier to form.

Writing in the journal Nature, the researchers say their findings provide important clues about how the ice sheet will behave as our climate changes.

"This is the largest reservoir of ice on Earth, and the most poorly understood place on our planet," said the British Antarctic Survey's Fausto Ferraccioli, a scientist involved in a separate international project to study the region.

He explained that the elevation and location of the Gamburtsev Mountains - in the centre of the ice sheet - made them an "ideal place" for the formation of the very first ice.

Icy unknown

Sun Bo from the Polar Research Institute of China, who led this study, has now provided further insight into the evolution of the ice sheet.

He and his colleagues travelled 1,235km (767 miles) by tractor train from a research station at the edge of East Antarctica, to the summit of Dome A of the Gamburtsev range, near the centre.

Dr Sun's team then attached radar equipment to the tractor and drove around, meticulously surveying a 30km by 30km square of the glacial region.

Their radar revealed a landscape that, 14 million years ago, looked similar to the European Alps.

"This is true scientific exploration," said Martin Siegert, head of the school of geosciences at Edinburgh University, who was also involved in the study.

"There's nothing to guide you really. Peering down at the ice sheet beneath your feet, you just don't know what's under there."

And for this type of exploration, the use of radio waves is very powerful.

When the waves reach the interface between ice and rock they bounce back, because of the difference in electrical properties between the two.

....Rest of story...

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Argentine Glacier Advances Despite Global Warming

BUENOS AIRES, Argentina — Argentina's Perito Moreno glacier is one of only a few ice fields worldwide that have withstood rising global temperatures.

Nourished by Andean snowmelt, the glacier constantly grows even as it spawns icebergs the size of apartment buildings into a frigid lake, maintaining a nearly perfect equilibrium since measurements began more than a century ago.

"We're not sure why this happens," said Andres Rivera, a glacialist with the Center for Scientific Studies in Valdivia, Chile. "But not all glaciers respond equally to climate change."

Viewed at a safe distance on cruise boats or the wooden observation deck just beyond the glacier's leading edge, Perito Moreno's jagged surface radiates a brilliant white in the strong Patagonian sun. Submerged sections glow deep blue.

And when the wind blows in a cloud cover, the 3-mile-wide glacier seems to glow from within as the surrounding mountains and water turn a meditative gray.

Every few years, Perito Moreno expands enough to touch a point of land across Lake Argentina, cutting the nation's largest freshwater lake in half and forming an ice dam as it presses against the shore.

The water on one side of the dam surges against the glacier, up to 200 feet above lake level, until it breaks the ice wall with a thunderous crash, drowning the applause of hundreds of tourists.

"It's like a massive building falling all of the sudden," said park ranger Javier D'Angelo, who experienced the rupture in 2008 and 1998.

The rupture is a reminder that while Perito Moreno appears to be a vast, 19-mile-long frozen river, it's a dynamic icescape that moves and cracks unexpectedly.

"The glacier has a lot of life," said Luli Gavina, who leads mini-treks across the glacier's snow fields.