The Atlanta constitution., 1902-07-07
Volcanic
Activity.

New York Tribune: The calamity
which has just overtaken two islands of
the Windward group in the Antilles will
unquestionably lead to a fresh discussion
of the causes of volcanic disturbance
All of the phenomena involved therein
are not yet fully understood. and con
corning some of them there are per
ceptible differences of opinion among ex-
perts. On at least one point however
there is general agreement. At a depth
of about 30 miles the internal heat OF the
earth Is probably great enough to melt
! every known substance. Confinement,
may keep In rigid condition the ma
| terial which lies beneath the solid crust,
but II any avenue OF escape Is once
| opered the stuff would soften and ooze
upward. There is a growing tendency,
| moreover, to recognize the Importance
of gravitaton in producing eruptions.
| The weight of several miles of rock IS
almost inconceivable, and IL certainl;
| ought to compel potentially plastic
| matter to rise through any crevice that
might be newly formed Russell, Gilbert
and some other authorities regard this
as the chief mechanical agent in an erup-
ton. at least when there is a considerable
| outpouring of lava.
| Leakage from Sea-
! As to the extent to which water ope7-
| ates there is some lack of harmony among
vulcanists. Shaler. Milne and others hold
| that substance largely. If not entirely,
| responsible for the trouble. They point TO
| the fact that many volcanoes are situat-
| ed near the coast of continents or on
| islands where leakage from the ocean
| may possibly occur. Russell on the other
| hand, regards water not as the initial
| factor but as an occasional. though inn
portant. reinforcement. He suspects that
when the molten rock has risen to con
| siderable distance IL encounters mat
| fluid perhaps in a succession OF pockets
and that steam is then suddenly general
| ed. The explosive effects whlch ehSue
are of two kinds.
| BY the expansion of the moisture which
| some Of the lava contains the latter Is re-
duced to state of powder, and thus
| originate the enormous clouds of fine
| dust which are elected. Shocks OF greater
| or less violence are also produced. Ihe
| lass severe ones no doubt sound like the
| discharge OF artillery and give rise 10
| tremors in the immediate vicinity. In eX-
| treme cases enough force is developed 70
| rend the walls of the volcano itself.
! Russell attributes the blowing up of
| Krakatoa 10 steam. The eliminating
! episode of the Pelee eruption last week.
though not resulting so disastrously TO the
mountain. would seem 20 be due to the
/ same immediate cause. To this particular
explosion. too. IT seems safe to assign
| the upheaval which excited tidal wave.
Cracks in Earth's Crust.
| Tho nre.ise manner in which the plastic
| material inside of the terrestrial shell gets
! access ia the surface is not entirely clear.
| Nevertheless. it is possible to get some
/ light on the matter. IT is well known that
| in many places there are deep cracks. or
! faults" in the earths crust Some OF
them in the remote past have been VIDE
! and deep enough to admit molten material
! from below. The palisades of the Hudson
! are believed to have been formed by sach
an intrusion, the adjacent rock on the
eastern face having since been worn away
by the weather or other agents. II has,
| been observed that many volcanoes are
/ distributed along similar faults.
/ The existence OF chain of volcanic Is
/ lands in the West Indies suggests the
probability that 1t follows a crack Of
! great antiquity, thoush the issue of lava
and ashes for several centuries may nave
been limited to a few isolated points. Just
how these vents have been reopened is
| one Of the most difficult questions still
left for investigation. Given a line of
! weakness IN the rocks. though. and A suS
| ceptibilty to fresh fracture is afforded.
/ Professor McGee suggests that the over
/ loading of the ocean bed by silt from the
| Mississippi river or other sources may
have been the Immediately exciting cause
Of the recent outbreaks. Other biologists
have found a similar explanation accept
able In the ease of eruptions elsewhere.
The theory has much TO commend IT 10
favor.
Theory as to Volcanoes.
A dispatch to The New York World
from Cambridge. Mass. says: y. s.
Shaler. professor of geology in Harvard
| university, and one of the most eminent
geologists In the country. In mis- lectures
to his class, gave the following as his
theory of volcanoes:
Volcanic outbreaks are merely the ex-
plosion of steam under high pressure:
steam which is bound in rocks buried un-
derneath The surface of the earth and
there subjected to such tremendous heat
that when the conditions are right its
pent-up energy breaks forth. and II shat
ters its stone prison walls into dust.
''The process by which the water be-
comes buried in this manner is a long
one. Some contend that 1t leaks down
from the surface of the earth through
fssures IN the outer crust, but this theory
Is not generally accepted.
THE common belief Is that water en-
ters the rocks during the crystallization
period. and that these rocks. through the
natural action of rivers and streams
become deposited in the bottom of the
ocean. Here they lay for many ages be-
coming buried deeper and deeper under
the masses of like sediment which are
constantly being washed down upon them
from above This process is called the
blanketing process.
What "Blanketing" Means.
Each additional layer of sediment,
while not raising the level of the sea bot
tom, buries the first layers Just so much
deeper and adds to their temperature.
just as does the laying of extra blankets
on a bed.
when the first layer has reached a
depth of few thousand feet the rocks
which contain the water of crystallizaton
are subjected to a terrific heat. This
heat generates steam, which is held in Il
state of frightful tension in its rocky
prison.
at is at these moments that volcanic
| eruptions occur, because of wrinklings In
the outer crust of the earth surfaC..,
wrinklings caused by the constant
shrinking of the earth itself and by the
contraction of the outer surface as 1t
settles on the plastic center underneath.
"Fissures are caused by these foldings.
1 and as these assures reach down into the
earth the pressure Is removed from the
! rooLs and tho cOmpreSSed steam in them