The “Lost squadron” is a group of 8 aircraft (6 P38 Lightings and 2 B17 Flying Fortresses) that force-landed on the Greenland icecap in WWII. on July 15 1942. The aircraft were only
variably damaged and resting horizontally on the snow surface. In 1992 a P38 (nicknamed “Glacier Girl”) was recovered from under snow and ice a depth of 82 m
(http://www.lost.dk/gb.html).
The expedition report says that although there is 5 m of snowfall each year, net accumulation is only 2 m a year (http://www.lost.dk/gb.html). The rest is lost. Dry snow has a density
of 0.01, where 1 = water (Colbeck 1980). Data summarised in Sudgen and John (1976 p18-19) shows that this compacts to firn (density 0.4) over a year. This occurs within the top two
m. The same authors show data from Greenland that show that firn compacts to glacier ice (density 0.8) at a depth of about 60 m. At a depth of about 100 m it is fully compacted with
a density of 0.91. Thus dry snow compacting to dense glacier ice forms a layer only 0.011 its original thickness. This means a year’s net snow accumulation of 2 m forms 2.2 cm of
dense glacier ice.
The Greenland ice sheet is typically 3000 m thick. At this rate of accumulation, the icesheet accumulated in 136 Ky, which, given the uncertainties, accords well with the calibrated
Camp Century core which goes back 80 Ky with a depth of 1,390 m (Sugden and Johns 1976 p21 & 132). The Camp Century core had an average annual accumulation rate of 1.73 cm/year.
Given the dangers of extrapolation from modern rates this is an excellent agreement. So there is no justification for YEC claims (http://www.answersingenesis.org/docs/233.aspthat) the
accumulation rates at this site invalidate the age the Greenland ice cap determined from ice core studies.
However, this does not mean that all is clear about the glaciology of the site. With the described accumulation on site and the compaction rate from the Camp Century ice core, the
aircraft should be buried to a depth of about 5 m. Clearly the aircraft are much deeper than they should be. I don’t know why this is the case. They would not have sunk to that
depth, as some suggest. The aircraft had run out of fuel, and so would be light. They might have sunk a little, but the ice would soon have a density similar to that of the aircraft,
preventing further sinking Nor did they melt their way down as others have suggested, as there was no fire. Possibly snowdrifts accumulating round the aircraft were a factor. As you
suggest, most likely some glaciological/meterological process is the answer. it could involve flow, lower compaction ratios, or higher than average accumulation. What it might be I
have no idea.
Jon
References
Colbeck, S. C. 1980. Dynamics of snow and ice masses. Academic press NY.
Sugden, D. E. and Johns, B. S. 1976. Glaciers and landscape. Edward Arnold, London.
bivalve wrote:
> The invalidity of extrapolating from the top 200 feet to the bottom should be emphasized, as glacial ice is greatly compacted relative to the surficial layers.
>
> Another factor that must be considered is the configuraiton of the plane relative to local ice flow patterns. Was the overlying ice entiraly the result of subsequent accumulation?
>
> Dr. David Campbell
> "Old Seashells"
> Biology Department
> Saint Mary's College of Maryland
> 18952 E. Fisher Road
> St. Mary's City, MD 20686-3001 USA
> dcampbell@osprey.smcm.edu, 301 862-0372 Fax: 301 862-0996
> "Mollusks murmured 'Morning!'. And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!
>
> ---------- Original Message ----------------------------------
> From: David_Bowman@georgetowncollege.edu
> Date: Mon, 15 Jan 2001 09:41:17 -0500
>
> >Regarding:
> >>>> The WW II airplane was found beneath, I think, more than two hundred feet
> >>>> of ice. I would think the large surface area of the plane's wings would
> >>>> have prevented it from exerting enough pressure on the ice to melt its
> >>>> way down through the ice. Assuming that's true, then the ice accumulated
> >>>> over the plane since it went down.
> >>> ...
> >> If the possibility of the plane melting its way through the ice or snow
> > is
> >>at issue, what would be important would not be just relative densities (as if t
> >he
> >>issue were simply buoyancy) but whether or not the plane would exert sufficient
> >>pressure to depress the freezing point enough to liquify the ice.
> >>That would depend on the plane's mass distribution & the surrounding
> >>temperatures. But doing the calculation is perhaps overkill since, as you note
> >,
> >>this YEC argument is one of desperation.
> >
> >One thing one might want to keep in mind here is the order of magnitude of
> >the freezing point depression of water--which happens to be about only
> >0.0075 deg C/atm. This means that a local pressure in excess of 130 atm is
> >necessary to depress the freezing point by only 1 deg C. An even lower
> >freezing point requires a correspondingly proportionate pressure increase.
> >Even with the realization that snow is mostly air pockets rather than
> >solid ice, and even with the realization that various sharp parts on the
> >underside of the plane would initially locally exert much greater
> >pressures than other parts, I suspect that any significant melting that
> >would occur because of the introduction of the airplane into the
> >environment would be nearly completely a result of the released energy
> >upon impact from the energy of the crash itself, and and maybe from any
> >burning fuel. It seems to me that the *crash* of the airplane would be
> >sufficiently energetic for at least parts of the plane to be relatively
> >deeply burrowed into a preexistent field of snow.
> >
> >Another thing to keep in mind is that it takes a lot of initial surface
> >snow to eventually wind up much later as a thin deep pack ice layer.
> >
> >Another thing to bear in mind is that the ice accumulation proccess
> >that would happen around an inhomogeneous obstruction like an airplane
> >would be expected to be modified to a large degree by the plane's
> >presence compared to the accumulation process out in more open spaces.
> >
> >Any calculation of the depth of burial relative to the time since the
> >plane crash would need to at least account for some of these other
> >processes that would be expected to swamp any static pressure-induced
> >freezing point depression effect. In any event, I agree with George's
> >assessment that "doing the calculation is perhaps overkill since, ...
> >this YEC argument is one of desperation".
> >
> >David Bowman
> >David_Bowman@georgetowncollege.edu
> >
> >
This archive was generated by hypermail 2b29 : Mon Jan 15 2001 - 19:39:42 EST