Lake Vostok


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  • #951

    Sciencetech
    Keymaster

    For a long time now people have been thinking about Lake Vostok and other Antarctic sub-glacial lakes — and I have too, but not exactly in the same way. Most of the discussion has been about the possibility of life in the lakes. I have convinced myself (isn’t that the most important part?) that some, if not all of the inland lakes may be under extreme pressure.

    When I first posed this question to a researcher during an MCM science lecture back in 2000, he was dismissive — even rude. No, no, it couldn’t be. Since then there has been some discussion about the possibility that bacteria could be off-gassing (probably C02 from aerobic processes) and therefor the lakes might be “carbonated”, and under a small amount of pressure. This is not really a concern because the amount of gas pressure in the water would almost certainly be a lot less than the weight of the water in the column formed by the drill hole — in short, it couldn’t come spouting out because the hole is too deep.

    Keep in mind we’re talking about lakes that are (and I’m guessing here, but I think I’m pretty close) maybe 2 kilometers below the ice or deeper, so it would take quite the drill hole to tap into them. These holes, like the one at Vostok that stops just short of penetration, are typically filled with fluid to keep the hole open. In the case of Vostok, it’s diesel. The counter-weight of 2 km of fluid in the hole is enough to prevent any lake pressure from bubbling up to the top.

    Okay, got the picture? Over the years I’ve approach a few scientists and said, wait a minute… You’ve got 2 kilometers of ice on top of that water. Water that’s, say, a few 100 meters deep (does anyone know how deep the lakes are?). That’s a tremendous amount of weight. The off-the-cuff response is usually, “It’s floating, so your concerns are misplaced.” This only indicates to me that they haven’t thought it through.

    The ice is not floating.

    For buoyancy, i.e. to float, something has to be displacing liquid. The ice is not displacing the liquid; in fact, it’s just sitting on top of it pressing down like a big piston. If you tap into it and relieve that pressure, the water is going to come geysering up the hole until the ice is sitting flat on bedrock. The only way to achieve buoyancy is to displace an equivalent volume water to equal the mass of the ice above it.

    I have yet to hear an valid argument against this, although recently I did get one group to concede that they really don’t know what will happen when they drill in to one of these lakes.
    :mrgreen:

    #8765

    Baghdad Jim
    Member

    Soooo….those aliens that you guys have been hiding all this time, they can’t help?

    I know what I’m talking about…I’ve seen the Thing and X-Files, ya know.

    😉

    #8766

    Anonymous
    Member

    Interesting subject.

    Let me start off by saying that I know very little about drilling, and even less about these sub-glacial lakes. So these questions are not meant to be rhetorical, or snide, but questions.

    I agree that the Ice above the lakes is not floating, unless those lakes are huge. Are they Huge? But are we sure the water is supporting the ice? Could it be more like an ice cave situation? Are we even sure the ice is next to the lake, or could their be a gaseous pocket between the two (I’m guessing that one is known, but maybe not)? If I understand it right, for all practical purposes the ice is acting like a hard soil, there are tons of pockets under soil all over the place ( I have a well under my house, so this is something I’m very aware of), some are pressurised, some are not, so I could see this going either way?

    I remember as a kid a grade school teacher describing how the ice age glaciers generate so much friction as they moved that they actually melted the most bottom layer, and they then rode on this layer of melted ice and gas. Now I may not be remembering this right, and it was many moons ago, but is this what is causing/caused these lakes? or is it something else?

    Anyway I do find this subject interesting, and I’d be curious to hear what you find out.

    John

    #8767

    Sciencetech
    Keymaster

    Hi John,

    The lakes range from small to huge. That said, the only confirmed “lake” is Lake Vostok. There are many other place where lakes are suspected, but nobody has proof yet.

    This is all new stuff to me too, so I don’t claim to be an expert.

    The usual theory about why there is water under the ice is that heat from the earth (caused by natural nuclear decay) is trapped there. Under enough heat and pressure, the ice turns to water and the heat is retained because the ice above it is an excellent insulator. For this to work there has to be enough ice, maybe a minimum of 2-3 kilometers. So, ironically, there are more [suspected] subglacial lakes in the middle of the continent, where it’s much colder, than around the fringes — because the ice is thicker in the middle.

    I think it’s very unlikely that there are any air pockets or caves at that depth. Glaciers are very plastic, and will compress and fill any cavity. And consider the mass of the ice: For instance, at about 1km deep there is so much pressure that any small air bubbles in the ice are compressed to near nothingness, making the ice extraordinarily clear. The same would hold true for larger air pockets as well. Voids can only exist where there is not much pressure (i.e., shallow like in your back yard) or in a material that is extremely rigid (hard rock).

    As far as floating, my hunch is that the water has no place to go. So instead of displacing the water, the ice is sitting on top of it the same way a heavy object sits on the floor — it wants to go down, but there’s no way for it to do so. My theory is that if you give the water an escape route, it will take it. Forcefully.

    And in answer to Jim’s question, yep, that’s exactly where the UFOs are hidden. Shhh, don’t tell anybody!

    g

    #8768

    Sciencetech
    Keymaster

    Okay, I’m going to back-pedal a bit.

    Water is denser than ice (1.0kg/l versus 0.92kg/l for ice without air bubbles), so assuming the drill hole was filled with water the pressure at the bottom end of the hole (exerted on the surface of the lake) would be approximately 1.1 times the pressure exerted by the ice, preventing the lake water from reaching the surface. If the hole was filled with air, the lake water would come up the hole, but either way the water level would settle about 9/10ths of the way to the surface — assuming there are no other factors such as dissolved gasses, extra pressure from surrounding glacial formations, geothermal sources, etc. No geyser.

    HOWEVER… The hole is not filled with water or air. My understanding is that it’s filled with diesel. I’m assuming they used JP-8 (kerosene), although considering that the average temperature of the ice is probably around -55C (and the melting point of JP-8, depending on the mix, is around -50C) it would be wiser to use AN-8, which is similar to JP-8 but with some extra additives to lower the melting point — additives that would probably also lower the density.

    The density of JP-8 at 20C (or thereabouts, again depending on the mix) is between .75-.82kg/l. I’m going to assume the high-end density, call it .85kg/l, because it will be cold and under pressure. I haven’t been able to find good numbers for the density of diesel at -50C but there has to be somebody around here — of all places! — that would know it. The fluid’s compressibility is another factor, but I have no numbers at all for that.

    Anyway, the point here is this: if the diesel has a significantly lower density than the lake water, what’s going to happen is that the lake water will rise up in the hole and force some of the diesel out. So while the reasoning is different, for now I stand by my assertion that when they penatrate the lake you don’t want to be anywhere near the drill hole. Only in this case it’s going to be a fountain of diesel spewing up.

    I’ll see if I can find a good density number for cold diesel or AN-8….
    😉

    g

    #8769

    Been There
    Member

    Glenn,

    Just to add to the problem, during the drilling at Vostok the density of the drill fluid was adjusted to compensate for depth to prevent the hole from closing. And you really don’t want to even know what was used as a densifier, dry cleaning fluid.

    Been There

    #8770

    Anonymous
    Member

    Here’s another dumb question. If holes filled with JP-8 or dry cleaning fluid penetrate the ice ceiling that covers the lake, will the suspected pressure of the water force the chemical back out to the surface? Because if not, it would pollute the lake.

    The former must be true, because everybody has been so careful about trashing resources in Antarctica.

    Sorry to ask it, but I love stuff like this! 🙂

    Angie in Texas, US

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