Large crater(s) in Siberia

  1. Astronuc

    Staff: Mentor

  2. jcsd
    Earth sciences news on Phys.org
  3. Greg Bernhardt

    Staff: Admin

    Here is the video from the link



    Likely a cave system that collapsed?
     
    Last edited: Jan 6, 2015
  4. davenn

    davenn 3,570
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    One comment had been that as this is ~ 40 km from a large oil and gas field,
    its quite possible that the crater is the result of an underground gas explosion.

    Its not just a collapse as the video and other pics I have seen clearly show ejecta

    cheers
    Dave
     
    Last edited: Jul 19, 2014
  5. jim hardy

    jim hardy 4,655
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    My first thought was a lava dome because it looks so black down there. Judging by the streaks on the side of the shaft water has seeped in for some time, ...

    Is the local geology there limestone , as around Patomskiy crater?

    [​IMG]
     
  6. I built a numerical model of what is now happening that predicts the surface air temperature of 54F from only the reported 9.6% CH4 concentration measured at the bottom (~200 feet deep). Here is my model, and a few comments:

    "Molecular weight" of air is 98.97 and of CH4 it is 16. Thus the molecular weight of a 9.6% CH4 + 90.4% air mix is: 0.096x16 + 0.904x 28.97 = 27.725 so if down in the hole the temperature is 273K (both ice and water are there) and at the surface the temperature is T, then also assuming the ideal gas law, for there to be net lift in the mix, 27.725 / 28.97 = 0.9570, the lighter molecular density lift must not by more than offset by the temperature contraction increase of the density, which is by the factor 273 / T.

    I. e. for 9.6% methane concentration to rise up out of the hole, 0.957 < 273 /T is required. Or T < 273/ 0.957 = 285.266K, which in more familiar units is 12.266C or ~54F. I.e. there should be methane laden air flowing up out of the hole, probably mainly in the center with 54F or colder air descending in an annulus around the column of methane enriched air. On the warmest Siberian days there will also be CH4 enriched air flowing up too, but the CH4 concentration will be higher then than the 9.6% then.

    This inflow of CH4 free air would of course reduce the concentration of CH4 in the hole so long as it continues, but a dynamic equilibrium would be reached with the CH4 inflow from the saturated thawing permafrost. The time scale for this dynamic "steady state" to be establish is certainly less than an hour. I.e. the observed 9.6% CH4 concentration was the steady state one when the temperature was about 54F.

    Thus by my analysis, I tell you that at the time the 9.6% CH4 was measured, the surface air temperature was ~54F which I think quite reasonable for Siberia at that latitude, in June or July when they measured the 9.6% CH4 concentration. Further more in winter the concentration will be much lower. I.e. the CH4 will be streaming up about as fast as it is being released by the permafrost.

    What do you think of my model? What first opened the hole, I don't know, but note this transport of surface air heat down is a mechanism for "fast release of CH4" from the deep methane hydrates - some orders of magnitude faster than thermal conduction down thru ~200 feet of ice and snow.
     
    Last edited: Jan 1, 2015
  7. Chestermiller

    Staff: Mentor

    Hi BillyT,

    I'm trying to get an understanding of your model. To test my understanding, I'm going to try to articulate what you are saying, and then I have some questions. So, here goes.

    CH4 is being released at the base of the crater. It has a lower density than air, so you are expecting a natural convection cell to be set up within the crater, with CH4 and CH4-laden air rising up the center, while surface air is drawn in around the rim, and flows downward along the sides. The air mixes with the CH4 toward the bottom. Even though the surface air is hotter than the methane below, the methane molecular weight is lower, so the effect of CH4 density wins out. For this to happen, according to your rough calculations, the surrounding air temperature cannot be lower 54F. This value seems to be consistent with the air temperature around the crater in summer.

    You noted that all this has nothing to do with how the crater was first established. It is just what is occurring now. You also noted that the convection cell that you are proposing has a significant effect on the rate of heat transfer, and can act as a feedback mechanism for more rapid release of CH4. Somehow, this enhances the rate of growth of the crater?

    I have some modeling questions after getting confirmation on my understanding.

    Chet
     
    berkeman likes this.
  8. jim hardy

    jim hardy 4,655
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    slip of the finger? 28.97 is what you used and 29 is what i've used since stone age....
    at first i thought somebody had made new units (again)..... :nb)

    old jim
     
  9. Yes "sharp eyed" old Jim. Thanks. I am a little dyslexic and did not note that, but fortunately, I got it correct where it mattered:

    In this equation: the molecular weight of a 9.6% CH4 + 90.4% air mix is: 0.096x16 + 0.904x 28.97 = 27.725
    You got it right, but I inserted a few clarifying words in green text in your sentence, to make sure that all understand that sentence is not true in general.

    What now exists in Siberia, is the world's largest thermometer ! I. e. in the stead state, the bottom CH4 concentration tells the surface air temperature. If for example a warm front rapidly moved over the crater, quickly raising the surface temperature to 60F, that warmer air would be lighter than the 9.6% CH4 concentration mix and the vertical flow would stop, until the CH4 concentration at the bottom rose higher and made the bottom atmosphere, once again have slightly lower density than 60F air. Then a new dynamic equilibrium flow would be established.
    Thus in addition to being a thermometer, it is also a large natural vertical pump for CH4.

    The way this flow "enhances the rate of growth of the crater" is that convection heat transfer is much more rapid than conduction transfer.

    If you do still have more questions ask away, Chet
     
    Last edited: Jan 5, 2015
  10. I want to note, that the concentric but reversed flow need not be of a gas. It could be cold 4C bottom water with lots tiny bubbles in it rising up in the center of an annulus of warmer "bubble free" water being pulled down. There are many claims in the literature that the even if the Siberian Arctic shelf did release CH4, perhaps because a "finger" of the much salter and warmer Gulf Stream is now entering and flowing along the shallow bottom, that would not make any contribution to atmospheric CH4 concentrations as the tiny bubbles have a very small "terminal rise velocity" and would all dissolve before reaching the surface.

    This "solid theory" is now being refuted by circular columns of water, up to 1Km in diameter, filled with CH4 bubbles so dense that sub sonars can't be used in them. I.e. these methane hydrates are now decomposing and releasing Siberian coastal shelf CH4 into the air in greater volume each year.

    Why am I now reminded of reading long ago a few theoretical discussions that the bumble bee's wings were so small and beat so fast that the turbulence would destroy any significant (in comparison to his body weight) lift? Can you guess?

    Only problem seems to be, than no one has told the tiny CH4 bubbles or the bumble bee that theory prooves neither can rise up into the air.
     
    Last edited: Jan 5, 2015
  11. Chestermiller

    Staff: Mentor

    Hi BillyT,

    You mention that the convection heat transfer rate is much more rapid as a result of the circulation driven by the rising CH4, and this flow enhances the rate of growth of the crater. I'm a little confused about this. I thought that the growth of the crater involved actual removal of porous rock from inside the crater. I'm not an expert in geophysics, so maybe that picture is incorrect. Can you give more details on the relationship between the enhanced heat transfer and crater growth?

    My understanding is that the current version of the model consists mainly of the rough calculations of buoyancy you described in your first post. If that's the case, I think that it is only suggestive of what might be happening, but without any convincing quantification. Do you plan to do any detailed numerical modeling, say involving computational fluid dynamics to predict the magnitude of the flow velocities involved and the heat transfer rate? You could introduce a methane flux at the base of the crater, and then allow the model to also determine the mixing and the concentration distribution of methane within the crater at steady state. Certainly results of this type would be very valuable in supporting your case.

    Chet
     
  12. Bystander

    Bystander 3,441
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    One of the links discusses debris/rubble 120 m from edge of crater. Guessing at rim height from pictures, shadow lengths, it doesn't take a long run-out slide to move material that far. Pingo still doesn't look all that unlikely.
     
  13. Chestermiller

    Staff: Mentor

    By the way, have they determined the mass of the ejecta and compared it with the mass of displacement material from the crater?

    Chet
     
  14. There is clear evidence of water erosion down the sides of the crater. This water also delivers heat to the bottom and helps decompose the CH4 hydrates, that most likely are there and a source of most, if not all, the CH4. I.e. the "porous rocks" may be in large part CH4 ice (CH4 hydrates) that turn to gas and water. It seems clear to me that the volume of the crater hole is much larger than the volume of rim around the top is above the surrounding area. No trucks hauled any dirt / "porous rocks" away.
     
  15. Chestermiller

    Staff: Mentor

    So are you saying that the rock filling the crater is close to being unconsolidated, and has a very high porosity?

    Chet
     
  16. An aerial view, showing undisturbed tree less than crater radius away. Some in foreground at right at the crater rim. Thus the volume of "rim dirt and "porous rocks" is small compared to hole, ` 200 feet deep & 200 foot diameter.
    [​IMG]
    Below is photo from ground level clearly showing water erosion of soft material - possibly dried mud and some of your "porous rocks."
    [​IMG] Note in the foreground left many "drying cracks" typical of drying mud. Note in the inter walls especially at the top left clear stratification levels - Probably accumulated show turned to ice? Here is link to this and some comments there:
     
  17. Chestermiller

    Staff: Mentor

    So you are saying that the original contents of the crater was high porosity rock filled with ice in its pores, and that, once the ice melted the, particles accumulated in the bottom of the crater? Otherwise, where did all the solid rock go?:confused:

    Chet
     
  18. it http://en.wikipedia.org/wiki/Methane_clathrate]]:

    No. Perhaps you don't know what CH4 ice hydrates are: here (I Hope it posts. If it does not see it at wiki link below of quote, which should be: http://en.wikipedia.org/wiki/Methane_clathrate ) is photo of some of that ice burning including the H20 "Cage" The CH4 is trapped in. Cold temperatures and a minim pressure are required for it to be stable, but so much is that the amount of carbon stored in the CH4 ice is greater than all that in all the coal that ever existed ! (Water has a permanent polarization as the two Hs are only 105 degrees apart and with net + charge, while the O has a negative charge. At lower temperatures water is not one H2O but nH2O atoms in a 3D structure. (many besides the one illustrated as a CH4 cage.) Below 4C these large n atomic structures become so common and general have internal voids, so that is why 3C is lighter than 4c and why ice floats.
    [​IMG] [​IMG] http://en.wikipedia.org/wiki/Methane_clathrate Having trouble posting photo of burning ice. If you know how to, please do it for me. edit time soon to go I'll try t find another.
    I. e. there need not be much in the way of "porous rocks" to hold tons of of CH4 where that big hole is now.


    In answer to your last question, the photos indicate there were very little, if any, "solid rocks" - it would not be uncommon for ice from the last ice to be more that 200 feet thick. Even to day in central half of Greenland has an ice cover that is a mile thick. - why if it all melts many coastal cities will be under water if not protected by tall dikes, and they may not work as there are too many drains to the sea that would all need to be sealed.
    [/URL][/URL]
     
    Last edited: Jan 7, 2015
  19. Chestermiller

    Staff: Mentor

    Thanks very much.

    Chet
     
  20. Just a couple of pieces of data from a chemist: when flammable gases mix with air they may or may not form an explosive mixture. Too much gas (above the Upper Explosive Limit) and the ignited gases starve for oxygen to support combustion. Too little gas (below the Lower Explosive Limit) and the flame cannot propagate to the other fuel molecules. For methane in air the LEL is 5.0% methane, and the UEL is 15.0% methane. The 9.6% reported was definitely a prime candidate for a fuel-air explosion: http://en.wikipedia.org/wiki/Thermobaric_weapon

    Solid methane hydrate (as it is called in the pipeline industry) forms readily when methane and water are in contact with each other at a temperature below 55° F. When warmed above this temperature it slowly 'sublimes' (evaporates directly from the solid), possibly leaving a small puddle of water (depending on the humnidity). Pipeline operators may add methanol to their pipelines to prevent the water from forming clathrates with methane.

    Ethane, propane, and argon also form clathrates with water because the molecules are small enough to fit inside the cages that water can form.
     
  21. upload_2015-1-9_12-39-55.png
    Thanks. I agree, 9.6% CH4 in air is very explosive. Here, if it posts, are the stability curves for methane in cold deep ocean and in tundra.[​IMG][/URL] I have had trouble posting graphs so try several ways and remove worst if more than one works, by edit. If none do: See them here http://large.stanford.edu/courses/2010/ph240/harrison1/: Looks like one did and two tries did not. Why it is at top of this post and small, I don't know.
    [​IMG][/URL]
     
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