The Colfax chronicle. [volume] (Colfax, Grant Parish, La.) 1877-1981, 1885-09-05
EARTHQUAKES.
Distinguished Scientists Opinion Of thu
Cause of Subterranean Activities.


earthquakes were not followed by those
subterranean disturbances, and alex
planning electricity has been called upon
| TO explain how earth-throes might have
caused atmospheric disturbances. /
know of no way in which such conse-
quences could have followed from a dis
placement of the earths crust. To me
it seems far more natural to conclude
that the hurricanes and earthquakes
were alike produced (the hurricanes
chiefly, the earthquakes partially by,
the atmospheric compression which pre-
ceded the subterranean disturbances.
This compression indicated a heaping of
air over the disturbed region; the earth's
crust yielded under this increase of
pressure, combined with the action of
other forces, and earthquakes followed;
the compressed air swept away to re-
gions of less pressure, and the rarefac-
ton following led in the usual way to
the indraught which precedes cyclonic
disturbance in the air.
But while the action of atmospheric
pressure in helping to excite subterran-
| can activities must not be overlooked,
the varying pressure exerted by seas and
oceans is more potent disturbing fac
tor. Atmospheric pressure is distribu-l
ted in such a way that though the weight
of air on any given area is continually
changing. there are no sharply defined
lines, at any time, which separate re-
gions of less pressure from regions of
greater pressure. 1t is otherwise with
the sea along shore line. Here we
have the sea acting with constantly
varying intensity. as its level changes,
on the seward side of the shore line,
while on the landward side there are no
such variations of pressure. Let us con-
slider what this means. Take a tolera-
bly, straight shore line 500 miles in
length, and suppose that along this
shore line region of ocean 100 miles
broad rises through height of three
feet under the combined action of sun
and moon raising tidal wave. and
favoring strong winds urging the water
shoreward. Then we have 1000 square
miles of sea-water, three feet deep. ad-
ded as so much lightweight to that part
| of the earth's crust which underlies
the seas along that shore. Each
sqnare mile contains in round num-
bers 100000 square yards, or H.
100000 square feet. The addition
al weight corresponds. then Gas the
added-layer is three feet deep.) to 5O.-
| 900 times 1000, 900 cubic feet of water,
each weighing 64a pounds. or to 49,
| 600, 900, 900 tons. 1t is clear that the
| addition of so enormous weight as
this to the submerged part of the earth s
| crust, outside the shore line, may well
| produce strains too great to be resisted.
| 1t must be remembered that the very
existence of precipitous shore line Gas
| distinguished from one where the land
above water and the parts submerged
form one great slope) indicates the COM
| parative weakness of the crust along
that coast. 1t has yielded on one side
to pressure thrusting it upward above
the sea-level, and on the other side to
the pressure of the water forcing it
down. 1t is true, the actual line of
| yielding may not coincide with the
| existent shore line. For the action of
the sea waves may (and generally must)
| have altered the position of the coast
| from that which it occupied when first
formed. But it may be taken for granted
that not far from every precipitous
shore line lies line of weakness, where
the crust has given way in the past, and
may give way again. In this considera-
ton undoubtedly we find part of the
explanation of the observed fact that
almost all the great regions of subter-
ranean activity on the earth lie near the
| sea-shore.
But while the changes of atmospheric
and oceanic pressure are potent factors
in the production of earthquakes. and
are probably in the great number of
cases their direct occasion. it is, OF
course, to the subterranean regions
| themselves that we must look for the
forces at work in upheaving the crust
of the earth. The forces acting from
the outside are as the pull on the
| trigger; the imprisoned gases and
vapors generated by internal heat are as
the. powder by whose explosion the
missile is elected.
Yet even in considering the earth S
subterranean activities we still have to
look outside for part at least of the
causes of disturbance. The ar perhaps
may in this respect be neglected, but
the water is all-important. 1t has been
said. indeed, and probably with nearer
| approach to truth than usual in the
case of concentrations of the sort.
| without water there can be no vol
cano," and similar rule (not quite so
generaD applies to earthquakes. Few
probably occur, possibly none, save
through the action of water in some
way or other All active volcanoes ex-
cept one Tin mid-Asia) are by the sea
shore. Nearly all the great earthquakes
recorded by history have taken place,
and have apparently had their center Of
disturbance, near the sea.
There can be very little doubt, in
decd, that the direct cause of every
great subterranean disturbance is water
in the form of steam-steam SUPER
heated. under great pressure, and there
fore possessing much greater expansive
| power than steam at. ordinary tempera-