Via press release from Eurekalert: Glaciers Help High-Latitude Mountains Grow Taller
A UA-led team of geologists reports that glaciers can help actively growing mountains become taller – contrary to the conventional view that the only role for glaciers in mountain formation is shrinking them through erosion.
Glaciers can help actively growing mountains become higher by protecting them from erosion, according to a University of Arizona-led research team.
The finding is contrary to the conventional view of glaciers as powerful agents of erosion that carve deep fjords and move massive amounts of sediment down mountains. Mountains grow when movements of the Earth’s crust push the rocks up.
The research is the first to show that the erosion effect of glaciers – what has been dubbed the “glacial buzzsaw” – reverses on mountains in colder climates.
The researchers were surprised, said first author Stuart N. Thomson, a research scientist in the UA department of geosciences. “We were expecting to see the buzzsaw.”
The team discovered the protective effects of glaciers by studying the Andes Mountains in the southernmost region of South America, known as Patagonia.
UA co-author Peter W. Reiners said, “It’s been thought that glaciers limit the height of mountain ranges worldwide.”
The key is climate. Glaciers atop mountains in temperate latitudes flow downhill, scouring away the surface of the mountain. Over millennia, such erosion can reduce the height and width of a mountain range by miles.
However in very cold climates such as the Patagonian Andes, rather than scraping away the surface of the mountain, the team found that glaciers protect the mountain top and sides from erosion.
The team dubs the action of the cold-climate glaciers “glacial armoring.”
“Climate, especially through glaciers, has a really big impact on how big mountains get,” said Reiners, a UA professor of geosciences.
“What we’re seeing is that below certain latitudes, glacial buzzsaws clearly and efficiently operate, but south of about 45 degrees, it not only doesn’t work – it has the opposite effect,” he said. “The glaciers actually protect the surface and allow themountains to grow higher.”
He and his colleagues anticipate that glacial armoring also occurs on cold-climate mountains very far north, such as those in Alaska.
The team’s paper, “Glaciation as a destructive and constructive control on mountain building,” is in the Sept. 16 issue of the journal Nature and featured on the journal’s cover. Additional co-authors are Mark T. Brandon and Nathaniel J. Wilson of Yale University in New Haven, Conn.; Jonathan H. Tomkin of the University of Illinois at Urbana-Champaign; and Cristián Vásquez of the Universidad de Chile in Santiago. The National Science Foundation and the Chilean Fondecyt funded the work.
The Andes are the textbook example of actively growing mountains that are limited in height and size by glaciers, Thomson said. The Andes are actively being pushed higher by movements of the Earth’s crust. However, if the glacial buzzsaw is active, the mountains also are ground down.
“We’re trying to understand how mountains are built and destroyed,” Thomson said. “Why are mountains high?”
In actively growing mountains, hot rocks from deep in the Earth are being thrust up. At the same time, erosion sands away the tops and sides of the mountains, bringing those once-hot rocks closer to surface. The speed at which the rocks cool indicates how rapidly the surface material above the rocks was removed by erosion.
To figure out how fast the glaciers had scoured the Andes, Thomson and his colleagues needed to analyze rocks now exposed on the mountains. The scientists sailed up glacially-cut fjords to the foot of remote glaciers and collected soccer ball-sized rocks.
The team collected rocks from latitude 38 degrees south to 56 degrees south, for a total of 146 samples.
The researchers analyzed the rocks in laboratories at the UA and at Yale University to determine what geologists call the “cooling age” of the rocks. The cooling age tells how fast the rock was exposed by erosion.
The researchers used two independent dating methods, apatite uranium-thorium-helium and fission-track dating, to determine cooling ages. Both methods showed the same result – that the rocks cooled faster in the north and slower in the south. The slower the cooling, the more slowly the mountains are eroding.
Reiners said, “What corroborates this is that the mountains are higher in the south than in the north. Uplift is winning in the south, and the glacial buzzsaw is winning in the north.”
The importance of climate in the formation of mountains is currently a matter of scientific debate, Thomson said. The new finding indicates that climate plays a key role.
Said Thomson: “Climate determines the size of a mountain range – whether there is a glacial buzzsaw or glacial armoring.”
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Since the earth’s crust is like a float on a sea of lava, if you remove material from one place, the effect is to lighten the crust and then allow it to rise. So, the obvious effect of glaciers which scour away the valleys, is to cause the peaks to rise as material is removed causing the land to up-swell!!
Of course, the ice itself also has weight, and it is well known that the ice depresses the height of the land simply by its weight. That is why the North of Britain is still rising after the last ice-age. And this redistribution of land mass is also the reason the South of Britain is still sinking (which has nothing to do with rising sea level — even if sea levels were rising!)
If high lattitude glaciers help build mountains, increased melting will help weather them. Rock weathering removes CO2 from the atmosphere resulting in a negative feedback to the warming.
What a crock and is a perfect example of “cum hoc ergo propter hoc” or “Correlation does not imply causation”. A high mountain is high because a glacier protects it…. and lower latitude mountains erode faster from a melting glacier.
First, my theory is “All brontosauruses are thin at one end, much thicker in the middle and then thin again at the far end. … ”
Second, is this a joke post?
*palm to forehead…
ALL mountains started as lower hills and went through the same processes. THE SAME EROSION.
So that would mean NO glaciers let the mountains grow when they are formed the same way.
Glaciers formed when the mountains got higher in altitude. Causing a build up of snow, melting, freezing. The higher altitude, the more ice built up and growth of a glacier. The explanation of our earths crest allowed the mantel to push up as a mountain through separation or thinning of the crust letting the mantel push up. And even some become …….here’s a new idea… Volcanoes.
Glaciers don’t dictate or control the height of a mountain, the earths core and mantal does. The higher altitudes, glaciers don’t melt as quick as lower ones and ergo less run off for erosion…at the top. Younger glaciers at lower altitude are forming on a newer exposed strata, ice developing and caving with more fluctuation of run off, BUT, Atmospheric moist and the line of freezing/melting altitude will be the same. Meaning run off should be the same when calculating a comparison of area and altitude over a year , give or take a sun cycling and seasonal fluctuation.
It would be funny if the Pleistocene glaciations reduced rock weathering, causing a rise in CO2, which warmed the planet, causing the interglacials…
If the warming lagged behind the CO2, such a model might work.
OT
How to spin a short arctic ice melt season.
http://www.bbc.co.uk/news/science-environment-11322310
Lava flows/intrusions also work to protect land from erosion.
Glaciers help build mountains
This should read instead: Glaciers help shape surface of mountains.
Sometmes I find it depressing how everyone is so keen to pile on with their own uninformed opinion – not you, Phil Fluck – when the article doesn’t merit it. There’s an important word being ignored: “can” – as in ” glaciers can help actively growing mountains become taller – contrary to the conventional view that the only role for glaciers in mountain formation is shrinking them through erosion.”
‘Can’ is not the same as ‘always’. Really, it’s a pretty common-sense point in many respects: glaciers that don’t move – in other words, a skin of ice-armour for a mountain – will protect against various kinds of erosion caused by weather.
From the article:
“What we’re seeing is that below certain latitudes, glacial buzzsaws clearly and efficiently operate, but south of about 45 degrees, it not only doesn’t work – it has the opposite effect,” he said. “The glaciers actually protect the surface and allow themountains to grow higher.”
Honestly! And we’re summarily expected to believe that horse pucky?
So let’s see: Jokenhaggen didn’t go over well, carbon credits and trading hit the skids, and now the EPA wants to regulate —and tax— breathing.
Just anything to rescue the scam, right?
So now science works differently in South America.
But only in South America
Yeah, sure, ya betcha! (chuckle, snort! guffaw!)
Like most things to do with water, glaciers are both a positive and negative effect.
Should I take the title of the article literally, then I should be able to pile up some glacial ice on a flat portion of the earth somewhere and expect mountains to start forming–sorta like watering part of my field in the dry season and getting a luxurious crop of weeds.
Folks, there’s no way “Glaciers help build mountains”. First, the term “grow” means to make bigger. If the exercise is one in which it is shown that certain glaciers slow down the erosion effects, that’s fine, but you cannot and should not call that “growth” (similar to the way politicians try to make political points with their constituents by reducing the increase in spending and telling you they’re cutting back when all they’ve cut back somewhat is the amount of INCREASE–it’s all propaganda).
Semantics is what this article is about–glaciers don’t cause mountains to “grow” (i.e., form, increase, get taller, bigger, etc.) any more than scattering glacial ice around would produce a crop of mountains (or even hills, for that matter). You’d actually have a depression in the earth’s surface from the weight of the ice.
That relatively thin, cold ice deposits can sometimes armour the upper portions of mountains against erosion is fairly obvious. However, the article does seem to be drawing some over-strong conclusions.
First, even at the equator high mountains are sufficiently cold that their upper slopes can be armoured this way, so I am dubious about the suggested latitude dependence. My doubts are strengthened when I observe that the world’s highest mountains are actually at rather low latitudes (the Himalayas).
Second, even near the poles, glaciers on the lower slopes flow downhill, causing substantial erosion, so it is unlikely that any mountains will be protected from erosion throughout.
Third, tectonic and volcanic mountain building is usually much faster than erosion; the final maximum height is more or less an equilibrium height based on things like the buoyancy of the mountain root (ie, determined by sub-terranean geology). The only significant effect of ice here would be to load the mountain with extra weight and so reduce its net height.
What this ice armouring could do is help mountains last longer before getting worn down. This would mean that, at any given time, most of the affected mountains would be higher than they otherwise would have been (and that the number of high mountains would be greater than it would otherwise have been). So I think it would be more accurate to say that some glaciers can help preserve mountains (not build them).
This is all BS. I tried this at home by putting a homegrown glacier in my pants to see my “mountain peak” grow to enormous proportions. I said, hon look!
At what dear? o_O
After the glacier had melted though . . . is when you truly understand the importance of emergency services having an easy to dial number.
Headline “Climate Change Destroys Mountains”
In a resent study, scientists have found that glaciers prevent mountains from eroding. It has been speculated that with the disappearance of glaciers do to Climate Change, our most beautiful scenery may someday disappear.
In general this kind of studies would diminish in number if not to disappear at all if the condition to achieve a PHD would change to an examen instead of silly research. Funding in such a case should go to schools instead of individuals.
The Nature cover seems misleading. Am I getting this wrong? I see, to paraphrase the low resolution, Glaciers build mountains.
If so, I could understand ‘help build’ them, if the geology was raising some mountains under them. It’d be a narrow interpretation though wouldn’t it? Something like saying, ‘light breezes help build mountains grow faster by reducing erosion during their growth’… and then having Nature reduce it to ‘wind builds mountains’?
Layperson here just wondering if I am getting this right, so feel free to set me straight.
Correction on last comment: The example i gave, ‘light breezes help build mountains grow…’ should not contain the word ‘build’
Might be that I’d never phrase it like that in the first place. I’d tend towards ‘net growth over time is higher with the absence of erosion.’ That way it couldn’t be regurgitated as, erosion causes growth to the eroded portion, just less with increased erosion. Echoes of what Lance of BC said maybe? An inverting of cause and effect purely through syntax?
Isostatic rebound ideas:
Suppose a glacier weighing a zillion pounds grinds down a valley for 50,000 years. Suppose the glacier never weighs more, and never weighs less.
Then suppose, during that 50,000 years, the same glacier removes a zillion pounds of rock from the valley’s bottom.
The continent beneath does not know or care whether it is ice or rock that has vanished. It rebounds, and isostatic uplift occurs.
In some cases the valley bottom is ground away about as fast as it is uplifted. However the mountains on either side of the valley are not ground away by the ice, and just rise higher and higher and higher. This is what creates the majestic fiords in Norway.
It also tends to surround an ice-field with enclosing ranges of mountains, as occurs in Greenland. The ice field actually builds the very mountains that hold it in. (It seems to have occured during the last ice age in Scandinavia, which is flatter in the middle (Sweden) with mountains around the edge (Norway; Finland.))
Scandinavian geologists are pretty good on this stuff.
Large file, but good reading: http://folk.uio.no/yuripo/papers/medvedev_geology_2008.pdf
@ur momisuglyMike Haseler says:
September 16, 2010 at 12:14 am
“Since the earth’s crust is like a float on a sea of lava”
The earth is solid all the way to the outer core. The earth’s crust “floats” on the solid mantle.
@ur momisugly Lance of BC says:
September 16, 2010 at 2:33 am
Lance, you really have no idea what you are talking about I am sorry to say. For example, I would LOVE to hear you tell me how the earth’s core controls the height of mountains.
Folks, here is the skinny. The materiel that makes up the thickened continental crust (aka mountains) has a certain density. The density of the crust is different then the density of the underlying mantle. Let’s use average values for fun, eh? So the average density of the cont. crust is 3.0 g/cm^3 and the mantle, is 3.3 g/cm^3.
Okay, so the name of the game is isostasy. That’s what is important here. If I have 50 km thick section of continental crust, how much of that crust would be above and below the “equilibrium line” (think of it was the water line of a boat floating in water. If a fat person get’s in the boat, that is, the density of the boat increase, the water line moves up)?
3.0/3.3 * 100 to make it a percent, means ~91% of a mountain range is under the “water line”. So in that 50km block example, that would mean that 45.5 km are below, with 4.5 km above.
Okay, so if I erode a large valley via glacial action, that lowers the density and the, the block of continental crust rises. It’s like the fat man above got out of the boat. I am not adding mass, I am not “growing mountain materiel” but I am effectively growing mountains by removing mass.
This idea is nothing new.
http://earth.geology.yale.edu/~brandon/Eprints/Pinter&Brandon1997.pdf
Good link Caleb, thanks for tossing it out there. Very understandable too.
If you really want to protect mountains, then very dry and very cold climate is the way to go. In the Dry Valleys of the Transantarctic mountains where there has never been any glacial ice, where temperature almost never rises above freezing and what little snow falls simply sublimates away, there is almost no erosion whatsoever. The landscape preserves river valley where rivers probably stopped flowing 20 million years ago, and soft and friable volcanic ash that fell 15 million years ago is still there, completely unweathered.
” “We’re trying to understand how mountains are built and destroyed,” Thomson said. “Why are mountains high?” ”
Everybody has to make a living.
I like your explanation Benjamin, the ice/water equilibrium analogy helps a lot. I think I probably assumed that the plates themselves were more rigid (where you’d expect a change in the piece of floating ice to result in a tip, not a bend or slumping) , and that the mass of the spread materials and the distance carried would be too small in comparison with the mass and depth of the area of plate beneath to make so much of a difference.
Would it be safe to guess that this effect varies with the location and other local tectonic factors or is it equally apparent in mountain building in, for instance, the Himalayas where plates are colliding, compared to say Iceland where plates are being seperated (I guess I mean their centerpoints since those edges keep growing and never actually open up) )?
Seems like just another example of academicians drawing premature conclusions from overly simplified scientific studies of specific sites and then projecting their ‘new findings’ to everywhere else in the world! Where have we seen that before?
Otherwise, this discussion has reminded me of some semantic trivia which will serve to further confuse the discussion…..
A mineral is defined as a naturally occuring inorganic compound having an orderly internal structure and chacterisitic chemical composition, crystal form, and physical properties. Frozen water fits all the definitional requiremnets, meaning ice is a mineral. And, since a rock is an assemblage of one or more minerals, that means that glacial ice is a monomineralic rock!
But, how do we classify this rock? Is it a sedimentary rock (resulting from the consolidation of sediment)? Is it an igneous rock (solidified from a melt)? Or, is it a metamorphic rock (solid state changes resulting from changes in pressure, temperature and shearing stresses)? Glacier ice is a combination of all of the above! Snow is the sediment, liquid water is the melt, and plastic deformation processes change the firn to ice and then to flow ice.
With these definitions in mind, my proposed layman’s summary for the paper is:
Adding more rocks to the top of a mountain will make it get bigger faster!
Philip Finck says:
September 16, 2010 at 4:45 am (Edit)
……
It has long been known that glaciers are both wet based and cold based. Cold based glaciers are typically thin, and this does not allow for pressure melting at the base or built up heat from crustal sources. Thus these glaciers flow by means of internal shearing. The base of the glacier is effectively frozen to the bedrock and little or only sporadic erosion occurs. In contracts, in wet based glaciers, pressure melting creates water. Thus the ice slides over the bedrock as a flow mechanism, also internal shear in places, etc.
—…—…
If so, then how does one determine if a given glacier is wet-based or dry-based?
What keeps the wet-based glacier water “trapped” under the glacier ice so it can allow flow – given the tremendous number of large (1-3 meter) changes and inflections in the sub-glacier valley bottom? A turbine bearing only 24 inches in diameter is machined to a 1/1000 of an inch tolerance to maintain the bearing surface suspended at 3600 rpm (3000 rpm in Europe): even so, the oil surface suspending the bearing is less than 9 inches long. A glacier is moving at 1 km a year over a surface with huge differences and changes in valley height, no dams, no “ponds” and a constant slope on average to the valley tip. No water can be trapped underneath.