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Antarctica 2018

Re: Antarctica 2018

Unread postby rockdoc123 » Mon 05 Nov 2018, 15:57:47

What are these other factors? Well, I'll try to explain it to you. The temperature at the base of the glacier is controlled by interactions between a number of factors, including the initial temperature of the snow and the atmosphere above the glacier, heat energy released by internal friction as the glacier flows, heat translocated downward into the glacier by meltwater, and the geothermal gradient.


Thanks for the penetrating insight into the obvious. The point is that there are measured regions in Western Antartic with very, very high heat flow associated with mantle activity whether it be volcanoes or plumes and also from thinned crust as a consequence of rifting. Ice sheet models (part of many of the studies published) arrive at temperatures at the base of portions of the Antarctic ice sheet at the phase change boundary and the presence of liquid in these areas agrees well with the models.

Fisher, A. T. et al, 2015. High geothermal heat flux measured below the West Antarctic Ice Sheet. Sci Adv, 1, e1500093. DOI: 10.1126/sciadv.1500093

The heat flux at this site is 285 ± 80 mW/m2 , significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2 . The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.


Note that measured heat flux at Yellowstone is ~ 200 mW/m2 in the central African rift it is around 160 mW/m2.

Perhaps you had better write discussion papers for all of the papers I pointed to above (and there are many others) which have said that areas of high heat flow in Western Antarctica are causing melt at the ice sheet base and contributing to ice flow speed. Apparently, these scientists don't know what they are talking about, and I suppose all the scientists involved in peer review of the large volume of research in this area also got it wrong. I am sure they will appreciate you correcting them. :roll:

I'll just summarize the viewpoint of a very large group of scientists with a quote from a fairly recent paper:

Begeman, C.B. et al, 2017. Spatially variable geothermal heat flux in West Antarctica: evidence and implications. Geoph. Res Lett, V44, 19, pp 9823-9832

Geothermal heat flux (GHF) is a significant source of heat in polar subglacial environments. It affects the temperature at the base of ice sheets, impacting the ice sheet mass balance directly through basal melting or freezing. GHF can have a large indirect effect on ice sheet mass balance when it brings the basal temperature above the melting point because the presence of basal meltwater reduces basal resistance, facilitating fast sliding of ice. GHF is prescribed as part of the lower boundary conditions for ice sheet models, which calculate patterns of basal melting and freezing to determine the degree of ice sliding. Ice sheet models are sensitive to the magnitude and spatial variability of GHF, particularly when the GHF contribution shifts basal temperatures across the melting point
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Re: Antarctica 2018

Unread postby Plantagenet » Mon 05 Nov 2018, 16:54:55

The point is that there are measured regions in Western Antartic with very, very high heat flow


Of course. Its part of geologists call a "rift zone". That means there is lots of faulting and volcanic activity along with high heat flow in that area. Do you get it now?

Perhaps you had better write discussion papers for all of the papers I pointed to above (and there are many others) which have said that areas of high heat flow in Western Antarctica are causing melt at the ice sheet base and contributing to ice flow speed. Apparently, these scientists don't know what they are talking about, and I suppose all the scientists involved in peer review of the large volume of research in this area also got it wrong. I am sure they will appreciate you correcting them.


You are having a total fantasy, dude. I never claimed that heat flow didn't play a role in melting at the base of a glacier. I simply tried to explain to you that other factors are involved....something you apparently still don't understand.

Do you get it now?

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Re: Antarctica 2018

Unread postby Plantagenet » Mon 05 Nov 2018, 16:59:48

Subglacial bedrock hills create surface channels on ice shelves in Antarctica

channels-antarctic-ice-shelves

As the climate warms and more ice shelves become unstable, meltwater runoff will likely utilize these pre-existing channels created by subglacial geology.

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Re: Antarctica 2018

Unread postby rockdoc123 » Mon 05 Nov 2018, 17:28:28

Of course. Its part of geologists call a "rift zone". That means there is lots of faulting and volcanic activity along with high heat flow in that area. Do you get it now?


what precisely am I supposed to be "getting". I'm the one who pointed out the high heat flow areas in West Antarctica and their contribution to basal melt.

You are having a total fantasy, dude. I never claimed that heat flow didn't play a role in melting at the base of a glacier. I simply tried to explain to you that other factors are involved....something you apparently still don't understand.


Right, as if it is that difficult to go back a page and copy what it was you said...here is what you actually said:

It sounds reasonable but if you do the math the amount of basal melting under glaciers attributable to heat flow is close to negligible. 


But the amount of energy contributed to the base of glaciers by heat flow is so minimal, even in high heat flow areas, that it is usually ignored in studies of glacier mass balance, which are much more influenced by factors like changes in atmospheric temperature, precipitation, etc., i.e. factors related to the climate


Heat flow is sometimes included included in models of glacier flow, but it is still a very minor factor.


all statements which are complete BS according to a significant amount of published literature. The contribution is significant and although heat flow is included in ice sheet models (contrary to your claim) traditionally the value of heat flow has been much lower than what has been measured in various regions. Including the higher measured heat flow in these models significantly changes the ice flow dynamics in various areas. It is all there for anyone who wants to read it.
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Re: Antarctica 2018

Unread postby Plantagenet » Mon 05 Nov 2018, 19:15:20

all statements ... are complete BS


Once again you demonstrate (1) you don't understand the physics involved and (2) you have an unusually nasty personality.

heat flow is included in ice sheet models (contrary to your claim)


I never said heat flow isn't included in ice models. I said heat flow is one factor among many, and often has a negligible effect.

And then I repeated it when you still didn't get it.

And now your new post shows you still you don't get it.

So now I've repeated it for a third time.

Three times should be enough or you to get it. But I bet you still don't get it. You never seem to get things. Your reading comprehension really is dismal.

-------------------------------------------------

Enough is enough.

Lets do the math, shall we?

The very high heat flow found at one site in the rifting area of West Antarctica is equivalent to enough energy to melt about 2 cm of ice at the glacier base over the course of a year. That means the amount heat flow will melt each day is about .0055 cm.....thats a pretty small amount considering that ice sheets are 1000+ m thick. It means that only about .0000055% of the glacier can be melted each day by heat flow, even when it is very very high as it is in the WAIS rift zone area. In glaciers in areas with more typical heat flow values, the amount of melting is even more negligible so that only ca. 0.00000055% of the glacier melt would be due to heat flow.

So if extremely high heat flow can only produce such insignificant basal melting in a glacier, then what causes melting. Well...there are other heat sources to consider. The bottom line here is that in addition to heat added to the base of a glacier by heat flow, heat is also released friction between the glacier and the bed, and heat is released by internal deformation of the ice. Temperatures at the bottom of a glacier are also influenced by the original temperature of the snow that makes up the glacier, and by the movement of liquid water within the glacier, especially where meltwater generated at the surface of the glacier penetrates to the bed of the glacier. And, of course, most ablation is due to surface melting and sublimation, and especially in Antarctica, due to calving.

Get it now?

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Re: Antarctica 2018

Unread postby rockdoc123 » Tue 06 Nov 2018, 18:01:42

The very high heat flow found at one site in the rifting area of West Antarctica is equivalent to enough energy to melt about 2 cm of ice at the glacier base over the course of a year. That means the amount heat flow will melt each day is about .0055 cm.....thats a pretty small amount considering that ice sheets are 1000+ m thick. It means that only about .0000055% of the glacier can be melted each day by heat flow, even when it is very very high as it is in the WAIS rift zone area. In glaciers in areas with more typical heat flow values, the amount of melting is even more negligible so that only ca. 0.00000055% of the glacier melt would be due to heat flow


OK Mr Science, Enough is enough.

Lets understand the actual physics, shall we?

perhaps it would help to actually read the papers that are pointing out the contribution is not through total melt (as I said several posts above) but through creating fluid along the base of the ice sheet which can increase glacial speed, thus contributing to greater wastage at the toe and hence decreased mass balance. You are back once again to the total amount of melt...it is relatively unimportant in terms of basal sliding. Frictional effects also create melting and that is generally not voluminous either but it does create enough fluid which under increased pH20 enhances sliding. Once again this is pointed out in countless papers a number of which I pointed to here and you, having not read any of them, have decided they must all be wrong. :roll:

As to it being insignificant....perhaps check your math. The paper by Fisher et al, 2015 which measured the 285 m/Wm2 notes that by their calculation the heat flux measured is the equivalent of 1.8 cm/yr at that location alone. You instead have calculated 2 cm over what area and what time period? Perhaps you better show us the details of your calculation including the details. And at this location, the temperature probe arrived at a temperature of zero C at the base of the ice sheet (~800 m) which isn't surprising due to the presence of melt. So they have high heat flow which would predict melt at the base of the glacier and the temperature measured is at melting point which would be predicted. Hard to argue with that observation without special pleading.

And to once again post from one of the papers Begeman et al, 2017 that summarizes it well:

Geothermal heat flux (GHF) is a significant source of heat in polar subglacial environments. It affects the temperature at the base of ice sheets, impacting the ice sheet mass balance directly through basal melting or freezing. GHF can have a large indirect effect on ice sheet mass balance when it brings the basal temperature above the melting point because the presence of basal meltwater reduces basal resistance, facilitating fast sliding of ice. GHF is prescribed as part of the lower boundary conditions for ice sheet models, which calculate patterns of basal melting and freezing to determine the degree of ice sliding. Ice sheet models are sensitive to the magnitude and spatial variability of GHF, particularly when the GHF contribution shifts basal temperatures across the melting point


And I never argued there was not other means of creating basal melt....the point is if all of the models have used a low heat flux then they will replicate glacial speed for the wrong reasons through tweaking other parameters when in fact the increased speed could very well be completely due to the influence of high heat flow from nearby magma chambers, active sub-ice vulcanism etc. By assuming the heat flow is below a level at which rock freezes to the ice sheet base these models have taken it out of the equation for the wrong reasons. Regardless of how much melt is created it will impact basal flow and that is the point I made numerous posts ago.
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Re: Antarctica 2018

Unread postby Plantagenet » Wed 07 Nov 2018, 12:42:50

OK Mr Science, Enough is enough.


All of a sudden you don't like learning about science? :lol: :razz: :)

the total amount of melt...is relatively unimportant in terms of basal sliding.


Thats one of the most ignorant statements I've ever read here (and that is saying something).

Once again you show you don't know what you are talking about. You are AMAZINGLY ignorant on this subject.

In glaciers meltwater is the MAIN source of water in the glacier and the main source of water contributing to basal sliding. Where else do you imagine most of the water in glaciers comes from if not from melting the glacier? And the more meltwater....the faster glaciers tend to slide because meltwater (1) lubricates the base of the glacier and (2)meltwater creates hydrostatic pressure within the glacier, and the more meltwater the greater that hydrostatic pressure, and the greater the tendency for the glacier to slide.

In temperate glaciers most of the meltwater in the glacier comes from surface melting and surface runoff from surrounding mountains onto the glacier. Many studies have shown that glacier sliding velocity in temperate glaciers varies DIRECTLY with the amount of meltwater being produced at the surface of the glacier. You can measure the air temperature, measure the amount of meltwater being produced, measure changes in hydrostatic pressure in the glacier, and demonstrate the direct link between meltwater production and glacier sliding velocity.

In high latitude glaciers like those in West Antarctica there is only minimal surface meltwater, so the meltwater in the glacier mostly comes from several sources, including basal melting caused by the geothermal gradient, and melting associated with heat released by basal friction and internal deformation.

But global warming can change that. For instance, in Greenland huge lakes are now forming on the ice surface, and then draining down through the ice sheet to the bed of the glacier. Adding more meltwater is causing Greenland glaciers to speed up.

That isn't happening in Antarctica.........yet. But as global warming continues we are going to see more surface meltwater in Antarctica too......just like we are now seeing in Greenland.

Sheesh!

Get a clue, dude!

Get it now?

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Re: Antarctica 2018

Unread postby rockdoc123 » Wed 07 Nov 2018, 14:28:45

Thats one of the most ignorant statements I've ever read here (and that is saying something).


apparently you haven't read most of your own posts.

Once again you show you don't know what you are talking about. You are AMAZINGLY ignorant on this subject.


And yet I have tens of references related to basal ice sheet sliding in West Antarctica which I've read at my fingertips....and you have what?

In glaciers meltwater is the MAIN source of water in the glacier and the main source of water contributing to basal sliding. Where else do you imagine most of the water in glaciers comes from if not from melting the glacier? And the more meltwater....the faster glaciers tend to slide because meltwater (1) lubricates the base of the glacier and (2)meltwater creates hydrostatic pressure within the glacier, and the more meltwater the greater that hydrostatic pressure, and the greater the tendency for the glacier to slide. 


OK. First off with regards to a discussion on mechanisms you are simple paraphrasing what I have already said with the exception regarding speed. It is very clear you do not understand the physics very well. If there is ice frozen to rock it doesn’t flow. If instead there is fluid of any amount it has a two fold effect, firstly fluid lowers friction and it doesn’t matter if it is 20 feet of fluid or 2 mm of fluid secondly the pore pressure effect is what drives this …the weight of the ice on top of the fluid increases pore fluid pressure which lowers the effective confining pressure and allows for the ice to move more effectively. There are literally scads of papers written on this and many lab experiments to demonstrate it. A simple experiment you can do for yourself is to take a weighted ice cube put it on a elevated slab and wait for a very thin film of water to form..a bit of inclination and it will move. If 2 mm of melt causes an increase in pore fluid pressure and a reduction in basal friction the ice will move if there are no perturbations in it’s way, it doesn’t have to be very thick column of basal melt.
As to more water causing faster speed…that is not always the case as perturbations along the floor can completely halt the ice sheet as does inclination topography on the ice sheet etc. Glacial lake Vostok sits below an Ice sheet that is not moving very fast and this is a very large body of water.

Sheesh!

Get a clue, dude!

What exactly did you say in this long diatribe that contradicted what I was saying in my post? Please enlighten us. You are off on a long diatribe that is completely unrelated to my original point.

As I pointed out the models have generally assumed low basal heat flow which means other elements are tweaked in the models in order to replicate the observed ice flow. Using the higher heat flow alters the outcome such that those other elements become less important. The whole point here is very high heat flow has been identified, it is thought to be an important contributor to ice flow by most of the scientists working in the area and when it is included in models it contributes to ice flow.

If you disagree that high heat flow in Western Antarctica can contribute to faster ice flow then you need to give us your reason including references that show why that is impossible. I’ve pointed to a number of references (and have many more) that indicate that basal heat flow in West Antarctica is quite high, that it creates localized melt zones and has an impact on glacial dynamics that has previously been poorly handled in ice sheet models. You chose not to discuss any of those papers but instead went off on a discussion about other things that impact basal melt, none of which refutes any of these published references.
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Re: Antarctica 2018

Unread postby Plantagenet » Wed 07 Nov 2018, 18:51:19

If there is ice frozen to rock it doesn’t flow.....


NO NO NO!

Thats totally wrong.

You are being a moron again. Please stop. Its so ridiculous the way you put on airs, and then when you try to discuss something scientific you say bonehead things that show you don't understand the most basic things.

Your claim that glacier ice frozen to bedrock its doesn't flow is moronically idiotically stupidly wrong. Totally, completely and absolutely wrong. You are WRONG WRONG WRONG!!!!!!! Consider yourself flunked and sitting in the corner wearing a dunce hat, dudette.

Image

Glacier ice frozen to its bed DOES indeed flow. It flows by internal deformation of the ice.

What it doesn't do is SLIDE. A glacier can't SLIDE if it is frozen to the bed. But it can still flow by internal deformation of the ice crystals.

Do I have to explain to you the difference between flowing and sliding now?

SHEESH!
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Re: Antarctica 2018

Unread postby Newfie » Wed 07 Nov 2018, 18:57:23

Unless it breaks off the hunk of rock and scours our the sides of the valley.
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Re: Antarctica 2018

Unread postby rockdoc123 » Thu 08 Nov 2018, 11:28:21

Do I have to explain to you the difference between flowing and sliding now?


changing the discussion once more I see. I actually do understand how glaciers move and the constraints on that movement. As I said a number of times I taught introductory Geology courses which include Physical geology many years ago at a couple of universities. I have a background in rock mechanics which is intertwined with the deformation that glaciers undergo (creep, glide, fluid pressure etc). So please cram your rant up your backside...a discussion about flow versus slide versus other mechanisms of deformation is irrelevant to my comments above.

Lets revisit.

First you said that elevated heat flow from the mantle whether it be volcanic or due to other crustal/asthenosphere interactions was insignificant. You also said it was so insignificant it usually wasn't included in models. Both of these statements are incorrect as they apply to polar ice sheets. When confronted with the fact there are tens of papers published that point out the importance of basal melt from geologic heat flow to ice sheet dynamics your response was to divert and try to talk about all the other variables that are important to ice sheet movement. At no point did you try to discuss where the calculations or models in those publications were incorrect. Instead you continue to try to change the story. First it is all about you pontificating on how glaciers move (something that anyone could pick up from a first year geology text) then you suggest the basal melt layer has to be thick to create flow (when experimentally that has proven to be completely false something like twenty years ago) and now it is about focussing on my using the term "flow". What I find absolutely astounding about all of this is a couple of years ago your claim was the only thing that controlled ice sheet movement was calving and that was due mostly to tidal influence...you were quite adamant about it. I subsequently pointed out how ice sheets flow and now you are sending this back at me as if I don't understand that principle? :roll:

As I said if you can show how basal heat flow is unimportant to the dynamics of Antarctic ice sheets then please do so. You must have scores of publications to refute the claims made in the publications I pointed to or you are otherwise capable of tearing apart those papers as you seem adamant they can't be correct.
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Re: Antarctica 2018

Unread postby Plantagenet » Thu 08 Nov 2018, 15:21:53

I actually do understand how glaciers move


So you claim.

But then you post utter nonsense like your claim that glaciers that are frozen to their beds can't flow. :lol: :P :roll:

cram....backside


In contrast with your limited knowledge of glaciers, I don't question your in-depth knowledge of backsides.

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Re: Antarctica 2018

Unread postby dissident » Thu 08 Nov 2018, 17:45:09

To add to the thread:

1) Coastal ice shelves are heavily influenced by sea water heat. The global oceans are an enormous heat reservoir because water has a very large heat capacity and the fact that water a couple of meters below the surface is essentially adiabatic. That is, the only way that heat is lost to the atmosphere and then to space is via mixing near the surface. Below surface currents basically do not lose thermal energy via radiation as they traverse thousands of kilometers.

Antarctica is surrounded by a robust zonal current (thanks to the lack of land mass blocking). Thus current, like the stratospheric polar vortex acts as a containment vessel separating cold waters at higher southern latitudes from the warmer middle southern latitude waters. Global warming has been changing the properties of this containment by allowing more warm water to mix towards the Antarctic coast. Just because the surface is cold does not mean that below surface heating by inmixing and transport of warmer waters is not acting 24/7/365.

2) As has been posted here a billion times, coastal ice shelves act like buttresses reducing the flow of glaciers locate farther inland towards the coasts. Break down of coastal shelves due to warming of the ocean waters increases the ice loss from the glaciers covering most of Antarctica.

3) Volcanic activity is an irrelevant factor for the ice balance in the Antarctic. Over the last 37 million years, the massive Antarctic ice sheet has never receded from heat released by volcanoes. The primary control is the amount of atmospheric CO2, which fell below 400 ppmv about 40+ million years ago and triggered the growth of Antarctic ice. Due to hysteresis the current 400+ ppmv of CO2 in the atmosphere is not resulting in deglaciation. It will take a long time for the Antarctic ice sheet to disappear and it will require over 400+ ppmv CO2 levels to be persistent.
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Re: Antarctica 2018

Unread postby rockdoc123 » Thu 08 Nov 2018, 19:43:16

But then you post utter nonsense like your claim that glaciers that are frozen to their beds can't flow. :lol: :P :roll:


taken out of context. My discussion was about flow at the boundary between rock and ice as described in detail in the paragraph you extracted that comment from...it was not in the context of overall flow of the glacier.

But then how about regaling us with how all these papers pointing to the importance of high heat flow from magmatic or similar activity in the West Antarctic are completely wrong? They have to be for your claims to be correct. We are still waiting. :roll:

3) Volcanic activity is an irrelevant factor for the ice balance in the Antarctic. Over the last 37 million years, the massive Antarctic ice sheet has never receded from heat released by volcanoes. The primary control is the amount of atmospheric CO2, which fell below 400 ppmv about 40+ million years ago and triggered the growth of Antarctic ice. Due to hysteresis the current 400+ ppmv of CO2 in the atmosphere is not resulting in deglaciation. It will take a long time for the Antarctic ice sheet to disappear and it will require over 400+ ppmv CO2 levels to be persistent.


sorry that statement is just utter and complete horseshit. What is your proof? You certainly must have proof that
Over the last 37 million years, the massive Antarctic ice sheet has never receded from heat released by volcanoes
, please show us what it is. It certainly has never been published anywhere as far as I have seen, but maybe I missed it. We know that even a slight amount of melt created at the base of an ice sheet can contribute to speed by which that sheet moves and especially so if the pore pressure is elevated enough such that the effective stress is less than the confining stress. Numerous papers have been recently published indicating the importance of basal heat from magmatic activity and thinned crust in Western Antarctica. Yet you somehow "know" volcanoes have never had any impact on the ice sheet speed and hence wasting at the toe (i.e. mass balance). :roll: The internal dynamics of the Antarctic ice sheets (and certainly the deep deformation) are analyzed mainly through ice sheet models. As I (and more than one of the papers I pointed to) have indicated if you assume low geothermal heat flow (which they all do currently) you end up tweaking other variables to match the speed of overall flow (eg: bed deformation, vertical shear etc), essentially getting a right answer for the wrong reason.

As to CO2 being in control....again that is a supposition and not a fact as you portray it. There is no observation that can link the increased CO2 to Antarctic mass balance, in fact throughout the runup in CO2 over the past few decades the average satellite-based temperature has remained more or less the same if not slightly decreased (I posted this plot on a previous thread to this one). The ice cores from Antarctica show a several hundred year offsets between temperature and CO2. Surface atmospheric temperatures measured at automatic and manned weather stations across the continent are few and far between but what they show is only a few areas (mainly the peninsula) that have seen atmospheric warming whereas other areas have seen flat to falling temperatures. I have shown plots from these stations a couple of years ago on one of the predeceasors to this thread. So there is a fair amount of evidence suggesting there isn't a one to one relationship between CO2 and Antarctic mass balance. In fact, suggesting it is all to do with CO2 is a massive step back in the current scientific understanding of Antarctic ice sheets and mass balance by about twenty years. :roll:
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Re: Antarctica 2018

Unread postby Plantagenet » Fri 09 Nov 2018, 10:56:45

It will take a long time for the Antarctic ice sheet to disappear and it will require over 400+ ppmv CO2 levels to be persistent.


I hate to break it to you, but atmospheric CO2 is currently over 405 ppm and going higher. Looks like your criteria for the Antarctic ice sheet to disappear are being met.

volcanoes have never had any impact on the ice sheet speed and hence wasting at the toe


You are having another fantasy. Trust me---volcanoes actually do impact glacier behavior. There are many examples of this.

It is well known that sub-glacial volcanic activity in Iceland strongly influences the behavior of glaciers at Vatnajokull and other volcanoes. Some glaciers in Iceland have surged (i.e. greatly accelerated for brief period of time) after subglacial eruptions. Here in Alaska we see similar effects. For instance, the Katmai 1912 eruption buried glaciers under thick ash deposits near Mt. Katmai, and these glaciers have behaved anomoulsy every since the 1912 eruption.

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Re: Antarctica 2018

Unread postby Plantagenet » Fri 09 Nov 2018, 11:24:30

Missing lakes under East Antarctica

Satellite data had suggested the presence of numerous large lakes in East Antarctica under the Recovery Glacier, a huge ice stream dumping ice into the Filchner Ice Shelf and from thence into the ocean. But a recent study found far fewer lakes then originally were thought to be there.....

missing-lakes-east-antarctic-ice-sheet

Image
The discovery that the Recovery Glacier is streaming into the Filchner Ice Shelf without numerous lakes at its base raises questions about how it is flowing so efficiently. This is of global interest since there is concern the Filchner Ice Shelf will become unstable like multiple Ice Shelves in West Antarctic, debuttressing the Recovery Glacier and contributing to sea level rise.

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