Chickenheads and Knobs on Snow Creek Wall

[G-spotter]

There is liquid water even under polar glaciers - Lake Vostok ring a bell?

[Recycled]

At last we're getting somewhere.

 

Xenu's MY bitch, baby.

[ClimbingPanther]

My only question anymore is, Dru, where did you learn about glacial eroding? I've posted sites from believeable sources that support the theory that abrasion is done by the glacier scraping rocks across rocks, and silty water flowing is more of a side note than a primary erosion method. Could you please enlighten us as to where you got this theory from so we can be enlightened as well? If it's true, I want to read about it.

[G-spotter]

This is from a lecture in 2003:

 

PRODUCTION- AND TRANSPORT-LIMITED EROSION BENEATH ICE SHEETS: A COUPLED MODEL OF SUBGLACIAL EROSION AND SEDIMENT TRANSPORT

TULACZYK, Slawek1, VOGEL, Stefan1, BOUGAMONT, Marion1, JOUGHIN, Ian2, and HOWAT, Ian M.1, (1) Earth Sciences, UCSC, Santa Cruz, CA 95064, tulaczyk@es.ucsc.edu, (2) Jet Propulsion Lab, MS 300-235, 4800 Oak Grove Drive, Pasadena, CA 91109

 

Many of the highly populated regions of the Northern Hemisphere were shaped by sub-ice sheet erosion and sedimentation. In addition, glacial landforms and sediments give insights into past physical conditions beneath ice sheets. Yet, subglacial geomorphic and sedimentary systems are much less understood than their fluvial and eolian counterparts. Most existing models of subglacial erosion are based on observational studies performed on mountain glaciers. These models typically assume that glacial erosion rates are (nearly)linearly proportional to ice velocity or to work done by flowing water and ice. The ‘classical' models of subglacial erosion assume that subglacial sediment production is independent of sediment transport and make no provision for negative erosion rates (i.e. deposition).

 

Here we present a mathematical model, which couples subglacial erosion, transport, and deposition. The model is an outgrowth of our laboratory simulations of rock erosion by water flow and shearing till. Results of these laboratory experiments indicate that glacial erosion rates should decrease by up to several orders of magnitude when subglacial till builds up beneath an ice base. The classical, production-limited model of subglacial erosion is valid when debris removal rates are greater or equal to the rate of debris production. This should be the case where ice overrides resistant bedrock and/or subglacial water drainage abrades and removes debris very efficiently. The other end-member situation is the ‘transport-limited’ erosion, which should predominate where ice overrides highly erodible bedrock or sediments and debris is stored in a subglacial till layer. Then, subglacial erosion rates are dictated by the horizontal divergence of till flux.

 

We conjecture that widespread subglacial till layers should occur in these parts of an ice sheet where ‘transport-limited’ erosion predominates. We use ice velocity data from West Antarctica to illustrate that there the transport-limited parametrization of subglacial erosion is more successful at explaining the regional topography than the classical, production-limited parametrization.

 

Our main conclusion is that realistic models of subglacial geomorphic and sedimentary processes should incorporate the close coupling between subglacial erosion and sediment transport.

[ClimbingPanther]

So it seems that they are saying erosion isn't necessarily a function of ice movement, but rather it is dependent on the amount of till beneath the glacier. Since sub-glacial streams remove debris [and erodes a little too ], the glacier erodes the rock freely. When no effective method of debris removal exists, it builds up, slowing the erosion down dramatically by creating a buffer between the glacier and the ground below.

 

I do agree now that glaciers with running water beneath them erode far more than glaciers without running water, but I still don't think the running water itself is actually doing the lion's share of erosion.

 

Feel free to correct me if I missed something important (not that you need my permission ).

Edited September 21, 2006 by ClimbingPanther

[MarkMcJizzy]

So it seems that they are saying erosion isn't necessarily a function of ice movement, but rather it is dependent on the amount of till beneath the glacier. Since sub-glacial streams remove debris [and erodes a little too ], the glacier erodes the rock freely. When no effective method of debris removal exists, it builds up, slowing the erosion down dramatically by creating a buffer between the glacier and the ground below.

 

I do agree now that glaciers with running water beneath them erode far more than glaciers without running water, but I still don't think the running water itself is actually doing the lion's share of erosion.

You got it absolutely right, and Dru can't read worth a shit. This has been known for a long time. Glaciers do not "push" well, the shear strength of ice is low. Because of this, it is often easier for a glacier to over run it's sediments, than to transport them.

 

Dru is not undestanding the basic tennants of his arguements, and is mis-understanding what he reads. In other words: Dru is one dumb SOB.

[G-spotter]

No, what it's saying is that ice without water can't erode.

 

Just look at Murrin Park. some of the most polished rock at Squamish. Why? Because Indian Canyon channeled subglacial water. Browning Lake is itself a giant kettlehole eroded subglacially.

[MarkMcJizzy]

No, what it's saying is that ice without water can't erode.

 

Just look at Murrin Park. some of the most polished rock at Squamish. Why? Because Indian Canyon channeled subglacial water. Browning Lake is itself a giant kettlehole eroded subglacially.

 

You're talking yourself in circles. Now you are saying that ice erodes, and water is the primary transport vehicle. For a temperate glacier, I would agree. But when this argument started, your hole thrust was that sub-glacial waters were the primary erosive force in a glacial system. But your own scientific sources, and your own arguments repudiate this. For a glacial system to effectively and continuously erode a basement, the eroded waste must be removed. Sub-glacial fluvial action is very effective at this. In the absence of this fluvial action, the glacier will over-run it's lodgment, and effective erosion will cease.

 

By the way, Mr. Geomorphologist, a kettle is a depositional feature, and associated with stagnant and recessional ice. Although I am not familiar with this lake, it sounds like an eroded pool below a moulin

Edited September 22, 2006 by Markmckillop

[G-spotter]

crazyjz,

 

first of all you must be asleep at the wheel to not know that kettleholes can lso be formed in bedrock. you can see them today in any bedrock river reach. the normal explanation is that trapped stones eddy and grind out deep circular holes. with sediment-laden subglacial water and trapped boulders, Browning Lake is just a scaled-up example of the same thing.

 

secondly, you are wilfully misunderstanding the sources cited. Somehow you fail to understand that there is no transport without erosion. In the "cjz" model subglacial water can transport sediment but magically can not erode? How odd.

 

In the absence of subglacial water, as you note, deposition dominates and till builds up. Deposition is in fact the opposite of erosion so this is not a very convincing mechanism for your claim that subglacial erosion is a significant process in the absence of water. I realize that you don't deal with this much in petrology, so your confusion is understandable.

[G-spotter]

Also, how come there are no oil wells in Antarctica? Hmmm?

[Alpine_Tom]

Glaciers do not "push" well, the shear strength of ice is low.

Compared specifically with the shear strength of water?

 

I don't know, as a US-educated history major, it seems intuitive that rocks embedded in a moving slab of ice are going to abrade the rock beneath it. And the water, if anything, might serve to carry more rock down underneath the ice where it could become jammed and add to the 'grinding surface.'

 

I just can't buy the image of a river running underneath a glacier, moving back and forth methodically across the bed of the glacier, grinding down the rock below so that the glacier can settle down into it.

 

But geez, guys, it's is spelled with an apostrophe when it's a contraction, not a possessive. They even teach that in Canadian schools, apparently, in the time they save not saluting the flag.