Greinar (Vísindafélag Íslendinga) - 01.01.1977, Blaðsíða 60

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but it seems more to the point now to quote a recent paper
(46) in which a worldwide and very marked rise in explosive
volcanism is shown to have taken place with the Pleistocene
time. The method used is only capable of registering the ex-
plosive volcanism, but there is no obvious reason why the in-
crease in explosive volcanism should not have been accompani-
ed by increase in effusive volcanism. (The old theory of Ice
Ages, that they are due to volcanic dust in the air, can natur-
ally not alter the result that there is time connection between
Ice Age climate and explosive volcanism).
We can therefore now have no doubts that there is a genetic
connection between severity of climate and volcanic activity.
The connecting link is most naturally to be sought in wind
stress.
Who would have guessed that wind stress at the surface of
the earth is capable of causing such endogeneous processes,
per definitionem, as volcanism and strong seismic activity?
How can wind stress, of the order of dynes/cm2, break a crust,
the strength of which is of the order of 10-100 kg/cm2, as
derived from strain release in earthquakes? The answer is
quite simple if we use geoscientific evidence, and see its signi-
fiance.
To approach the solution, let us consider a well-known pheno-
menon in the floating Arctic winter ice, which already Nansen
observed and studied on Fram’s drift across the Arctic ocean.
I refer to the formation of pressure ridges in winter storms,
as explained in Fig 8. Let the wind of constant speed start
at zero on the x-axis. The wind stress is shear, x dynes/cm2,
along the surface of the ice, but at the distance x this stress
has been summarized into an essentially compressive stress,
whose average is T ‘ x/d, where d is the thickness of the ice.
If we put x~10 dynes/cm2, d=3m, and take 5 kg/cm2 as the
yielding strength of sea ice — which is much more plastic than
clearwater ice — we would get x^ = 1500 km. But we should
take into account that the pressure would not be so equally
distributed as we have assumed, nor entirely compressive, and
last but not least, the yielding strength of the plastic ice is