On Mon Jan 15 2001 - 09:55:46 EST,
bivalve (bivalve@mail.davidson.alumlink.com) 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.
The real problem is falsely extrapolating the rates
of snow accumulation from the coastal location where
the planes are found to the interior location where
the ice cores are taken. If a person compares local
rates of measured snow accumulation with the rates
of accumulation determined from the decompaction of
the ice cores, a person finds that they are very
similar.
A person can "decompact" according to depth, the
change in thickness and stretching of the ic, the
original thickness of snow a certain thickness of
ice represents reliably.
>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?
This is not a reason. However, in the area of the
planes the ice sheet is moving coastward. The ice
cores are located on stable divides. Below is a
post from talk.origins that explain this matter in
detail.
+++++ reposted text below this line ++++++++
Re: The lost squadron/Annual rings
Author: Andrew MacRae <macrae@agc.bio_NOSPAM_.ns.ca>
Date: 2000/08/11
Forum: talk.origins
Posted on: 2000/08/11
Message-ID: <8n1ppq$iq$1@darwin.ediacara.org>
In article <3991B0C1.11CF3C8A@research.bell-labs.com> Ken Cox
<kcc@lucent.com> writes:
|mefleharty@my-deja.com wrote:
|>
|> Dr. Hovind went to the Denver National Ice Core
|> Laboratory and saw several ice core samples that they
|> had drilled out of various places such as Antartica
|> and Greenland. He was told that these samples of ice
|> were proof that the earth was much older than 6000
|> years.
|>
|> The samples of ice contain rings which the Ice Core
|> Laboratory officials claimed were annual rings like
|> tree rings. Since there were at least 135,000 rings
|> they claimed that this was irrefutable evidence that
|> the earth is older than 6000 years.
|>
|> Dr. Hovind claims that these rings are not actually
|> annual rings, rather that they represent alternations
|> of warm/cold/warm/cold during the year.
|>
|> In 1990 Bob Cardin dug out a P-38 that had landed in
|> Greenland in 1942. The P-38 was burried under 263
|> feet of ice in 48 years.
I.e., according to these numbers, about 80m of
ice in 48 years, which corresponds to a rate of about
1.67 metres per year, and that is after some compaction of
it (see below), so it probably represents much more in
terms of the initial snowfall. Parts of Greenland get
10 metres of snow per year. Other parts get far less
than a metre per year.
|Airplanes are denser than ice. When you drop something
|denser than ice on top of ice, it will sink slowly into
|the ice. The depth at which the plane was found thus
|has more to do with how far it had sunk than how much
|ice had accumulated on top of it.
No. In this case, it is the latter -- it has to
do with how much ice (really snow and only partially
compacted snow, known as firn) had accumulated on top.
The planes were found (if I recall correctly) fairly
close to the (eastern?) coast of Greenland. Here, closer
to the ocean, snowfall rates are higher than far in the
interior of the icecap, where it is extraordinarily dry,
and the annual snow accumulations are considerably thinner
-- in the case of the location of the GISP cores, about
70-75cm/year (Mayewski et al., 1994). Basically, Hovind's
rationale depends upon the rate of snow accumulation at
the site of the planes to be the same as the area where
the ice cores have been drilled, so he should provide
this data. As it turns out, the rates are less at the
GISP cores, but, realistically, even comparing 0.7
metres/yr of uncompacted snow accumulation to an
interpreted, average rate of 1.67 metres/yr for the
firn (snow/ice in the early stages of compaction) at the
plane site is not accurate either. It is probably more
like a 10:1 ratio between them, I would bet.
Upon being compacted beneath many more metres
of overlying snow and ice, the annual layers thin and
stretch considerably, to the wafer-thin laminae that are
seen in the deep ice cores. Their thickness at depth
therefore does *not* correspond to the thickness of the
original snow when it was deposited on the surface, or
even within the top several tens of metres. This
compaction trend with depth is well documented, and
it means the 80 metres of recently-deposited snow and
firn on top of the planes can not be compared directly
to the deep ice in the cores, even if the local snow
deposition rates were the same, which they probably
aren't.
From the available data, if the planes had
landed where the ice cores were collected, they
probably wouldn't be buried nearly as deeply, and if they
were left there long enough (we are probably talking about
many centuries of accumulation), they would be squashed
increasingly flat by the weight of the ice. Then it might
finally be valid to start making thickness comparisons for
the intervening ice.
|> Is there other evidence that indicates that these
|> rings are actually annual rings? I realize that many
|> of the rings are correctly correlated with volcanic
|> erruptions however we don't have know the precice
|> dates of volcanic erruptions many thousands of years
|> ago.
|
|Actually, we do. We know that Thera (Santorini) went off
|within a few years of 1630 BCE, for example; we know of
|the Vesuvius eruption in 79 CE; we know of the Krakatau
|eruptions in 416 and in 1883. All of these show up in
|the cores, with the expected number of layers in between
|them.
|
|This means Hovind has to explain why there just happens
|to be 3630 ice layers above the Thera remnants, and 1921
|above the Vesuvius ones, and 117 above the later Krakatua
|ones, if those layers are not indeed annual.
That is easy. Up until a few thousand years ago,
they weren't annual, rather like the way that the speed
of light has reached its present value only recently
(reference: c-decay). I'm sure an appropriate exponential
curve could be formulated to meet Hovind's preconceptions
and still satisfy the data. :-)
References (this probably isn't the best for this sort of
data, but it was handy):
Mayewski, P.A.; Wumkes, M.; et al., 1994. Record drilling
depth struck in Greenland. EOS, Transactions of the American
Geophysical Union, v.75, no.10 (March 8, 1994), p.113, 119,
124.
-Andrew
macrae@agc.bio._NOSPAM_.ns.ca
+++++++++++ End of reposted text ++++++++++>
As noted above, Young Earth creationists, such as "Dr."
Hovind, seem to be unaware that dramatic differences in
the rates of snow accumulation exist between the locations
where the planes were found and where the ice cores were
taken. If a person was to move inland from where the planes
were found, the average measured annual snowfall decrease
dramatically to rates consistent with those calculated
from the ice cores. In the regions where the ice cores
come from, the rates of snow accumulation calculated from
the ice cores match those of the local snowfall. Using the
airplanes to calculate rates of burial for ice core sites
is like using the rainfall averages for the forests on
the east coast of Australia to estimate how long it would
take to fill dry lakes in the outback of Australia.
For the details, a person can go to:
Putnins, P. (1970) "The Climate of Greenland," in S.
Orvig, ed., Climates of the Polar Regions, Elsevier.
Benson, C. S. (1962) Stratigraphic Studies in the Snow
and Firn of the Greeland Ice Sheet (U.S. Army Snow,
Ice, and Permafrost Research Establishment Research
Report no.70 (July, 1962).
Yours
Keith Littleton
Littlejo@vnet.net
New Orleans, LA
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