The Savannah morning news. (Savannah, Ga.) 1900-current, 1902-05-25
NATURE OF ERUPTIONs.
Prof. 1. c. Russell of Michigan Uni
yersity Describes These Natural
Phenomena.

EfOt. L. u russell OF mlcn1E0n UNI
yersity Describes These Natural
Phenomena.
From the New York Tribune.
Israel c. Russell professor of geology
in the University of Michigan, has
written for the Tribune an article on
volcanoes, in which he says:
When reduced to it's simplest terms,
volcano may be defined as a tube, or
conduit, in the earth's crust, through
which molten rock is forced to the sur
face. The conduit penetrates the cool
and rigid rocks forming the superficial
portion of the earth, and reaches its
highly heated interior.
The length of volcanic conduits can
only be conjectured, but, judging, from
the approximately known rate of in
crease of heat with depth Con an aver
age l degree Fahrenheit for each so
feet and the temperature at which
volcanic rocks melt from 1900 to 200
degrees Fahrenheit, when not under
pressure), they must seemingly have a
depth of at least twenty miles. There
are other factors to be considered, but
in general terms. it is safe to assume
That lIle COllQultS VI NOlCdHOcS dI6 IL
regular openings, many miles in depth,
which furnish passageways for molten
rock Qava) from the highly heated
sub-crust portion of the earth to its
surface.
Volcanoes are frequently arranged in
we'll defined lines as in Central Ameri-
ca and the Lesser Antilles. These and
other evidences may be accepted as
proving that they are located on
breaks or cracks in the cool and rigid
rocks composing the outer portion of
the earth. The breaks referred to are
proba bly, not single clean cut gashes
but irregular and branching fractures
through rocks that for the most part
are under enormous pressure. Owing to
the irregularities of the assures the
molten rock pressed up from below
does not commonly rise through them
freely, but at the most favorable To-
calities, as where two or more frac-
lures intersect. There have been times
in the history of the earth when out
wellings of molten rock have occurred
throughout the extent of many long
assures, and vast foundations of lava
have resulted, as, for example, when
the lava plains crossed by the Column
bia river were formed. These plains,
some 200,0G0 square miles in area, are
underlain by sheets of once molten
rock, which have an average thickness
of something like 1000 feet. Between
outpourings of veritable floods of lava,
as in the instance cited, and the erup-
ton of the smallest volcano there is a
complete graduation, showing that all
volcanoes have essentially the same
mode of origin.
Local eruptions, or volcanoes, in dis
tinction from "fissure eruptions," pre-
sent two leading characteristics one
class the lava is poured out quietly.
frequently in vast quantity, but with
out explosions; and in the other class
the matter extruded is generally COM
paratively small in amount, but ac-
companied by explosions frequently of
great violence.
Erupfions of Quiet Type.
During eruptions OF the quiet type,
the lava comes to the surface in a
highly liquid condition--that Is. 1t is
thoroughly fused, and flows with all
most the freedom of water. It spreads
widely even on a nearly level plain. and
may form a comparatively thin sheet
several hundred square miles in area,
as has been observed in Iceland and
Hawaii On the Snake river plains. in
Southern Idaho, there are sheets Of
once molten rock which were poured
out in the manner just stated, some
four hundred square miles in area and
not over seventyfive feet in average
thickness. When an eruption Of highly
liquid lava occurs in a mountainous re-
gion. the molten rock may cascade
down steep slopes and flow through
narrow valleys for fifty miles or more
before becoming chilled sufficiently to
arrest It's progress. Instances are
abundant where quiet eruptions have