The Earth's Shifting Crust by Charles Hapgood - wire of information

NORTH AMERICA AT THE POLE 205
A special phase of the volcanism must now attract our at-
tention. Most volcanoes produce dust, sometimes in vast
quantities (87:271). This dust is rapidly distributed through
the atmosphere. The effects of volcanic dust on the climate
have been the subject of intensive studies (231, 375). We must
stop for a moment to summarize the essential results of these
studies.
The fundamental work on the relationship of volcanic
dust to climate is The Physics of the Air, by Humphreys,
which has been cited in earlier chapters. Humphreys shows
that volcanic dust can have a remarkable effect in lowering
temperature. He points out that the effect of the particles
depends upon whether they happen to be more efficient in
intercepting the sun's light and reflecting it back into space
than they are in preventing the radiation of the earth's heat
into outer space. What is important is the size and shape of
the dust particles as compared with the wave lengths of the
radiation. Particles of a given length will have great reflecting
and scattering power on sunlight, and none on the
radiation of heat from the earth (which, of course, is not
in the form of light). Humphreys concludes that it is neces-
sary to determine the approximate average size of the individual
grains of floating volcanic dust, as well as the wave
lengths of the radiation involved. He accomplishes this satisfactorily.
After mathematical treatment of the various factors
he concludes: ". . . the shell of volcanic dust, the particles
all being of the size given, is some thirty fold more effective
in shutting out solar radiation than it is in keeping terrestrial
radiation in. . . ." (231:580). He also points out:
. . . The total quantity of dust sufficient ... to cut down the
intensity of solar radiation by 20% ... is astonishingly small only
of a cubic mile. . . .
i74th part of a cubic kilometer, or the 727th part
(231:583).
This, of course, means that the sun's radiation is reduced
to this extent over the whole surface of the earth. It re-
quires only a few days for volcanic dust projected into the