Fredrick Winslow Taylor - "The Principles of Scientific Management"

GEORGE BERNARD SHAW - "MAJOR BARBARA"

John William Draper - "History of the Conflict Between Religion and Science"

Edna Ferber - "Roast Beef, Medium"

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Books: The Elements of Geology

W >> William Harmon Norton >> The Elements of Geology




The point of origin, or FOCUS, of the earthquake was inferred from
subsequent investigations to be a rent in the rocks about twelve
miles beneath the surface. From the center of greatest
disturbance, which lay above the focus, a few miles northwest of
the city, the surface shock traveled outward in every direction,
with decreasing effects, at the rate of nearly two hundred miles
per minute. It was felt from Boston to Cuba, and from eastern Iowa
to the Bermudas, over a circular area whose diameter was a
thousand miles.

An earthquake is transmitted from the focus through the elastic
rocks of the crust, as a wave, or series of waves, of compression
and rarefaction, much as a sound wave is transmitted through the
elastic medium of the air. Each earth particle vibrates with
exceeding swiftness, but over a very short path. The swing of a
particle in firm rock seldom exceeds one tenth of an inch in
ordinary earthquakes, and when it reaches one half an inch and an
inch, the movement becomes dangerous and destructive.

The velocity of earthquake waves, like that of all elastic waves,
varies with the temperature and elasticity of the medium. In the
deep, hot, elastic rocks they speed faster than in the cold and
broken rocks near the surface. The deeper the point of origin and
the more violent the initial shock, the faster and farther do the
vibrations run.

Great earthquakes, caused by some sudden displacement or some
violent rending of the rocks, shake the entire planet. Their waves
run through the body of the earth at the rate of about three
hundred and fifty miles a minute, and more slowly round its
circumference, registering their arrival at opposite sides of the
globe on the exceedingly delicate instruments of modern earthquake
observatories.

GEOLOGICAL EFFECTS. Even great earthquakes seldom produce
geological effects of much importance. Landslides may be shaken
down from the sides of mountains and hills, and cracks may be
opened in the surface deposits of plains; but the transient
shiver, which may overturn cities and destroy thousands of human
lives, runs through the crust and leaves it much the same as
before.

EARTHQUAKES ATTENDING GREAT DISPLACEMENTS. Great earthquakes
frequently attend the displacement of large masses of the rocks of
the crust. In 1822 the coast of Chile was suddenly raised three or
four feet, and the rise was five or six feet a mile inland. In
1835 the same region was again upheaved from two to ten feet. In
each instance a destructive earthquake was felt for one thousand
miles along the coast.

THE GREAT CALIFORNIA EARTHQUAKE OF 1906. A sudden dislocation
occurred in 1906 along an ancient fault plane which extends for
300 miles through western California. The vertical displacement
did not exceed four feet, while the horizontal shifting reached a
maximum of twenty feet. Fences, rows of trees, and roads which
crossed the fault were broken and offset. The latitude and
longitude of all points over thousands of square miles were
changed. On each side of the fault the earth blocks moved in
opposite directions, the block on the east moving southward and
that on the west moving northward and to twice the distance. East
and west of the fault the movements lessened with increasing
distance from it.

This sudden slip set up an earthquake lasting sixty-five seconds,
followed by minor shocks recurring for many days. In places the
jar shook down the waste on steep hillsides, snapped off or
uprooted trees, and rocked houses from their foundations or threw
down their walls or chimneys. The water mains of San Francisco
were broken, and the city was thus left defenseless against a
conflagration which destroyed $500,000,000 worth of property. The
destructive effects varied with the nature of the ground.
Buildings on firm rock suffered least, while those on deep
alluvium were severely shaken by the undulations, like water
waves, into which the loose material was thrown. Well-braced steel
structures, even of the largest size, were earthquake proof, and
buildings of other materials, when honestly built and
intelligently designed to withstand earthquake shocks, usually
suffered little injury. The length of the intervals between severe
earthquakes in western California shows that a great dislocation
so relieves the stresses of the adjacent earth blocks that scores
of years may elapse before the stresses again accumulate and cause
another dislocation.

Perhaps the most violent earthquake which ever visited the United
States attended the depression, in 1812, of a region seventy-five
miles long and thirty miles wide, near New Madrid, Mo. Much of the
area was converted into swamps and some into shallow lakes, while
a region twenty miles in diameter was bulged up athwart the
channel of the Mississippi. Slight quakes are still felt in this
region from time to time, showing that the strains to which the
dislocation was due have not yet been fully relieved.

EARTHQUAKES ORIGINATING BENEATH THE SEA. Many earthquakes
originate beneath the sea, and in a number of examples they seem
to have been accompanied, as soundings indicate, by local
subsidences of the ocean bottom. There have been instances where
the displacement has been sufficient to set the entire Pacific
Ocean pulsating for many hours. In mid ocean the wave thus
produced has a height of only a few feet, while it may be two
hundred miles in width. On shores near the point of origin
destructive waves two or three score feet in height roll in, and
on coasts thousands of miles distant the expiring undulations may
be still able to record themselves on tidal gauges.

DISTRIBUTION OF EARTHQUAKES. Every half hour some considerable
area of the earth's surface is sensibly shaken by an earthquake,
but earthquakes are by no means uniformly distributed over the
globe. As we might infer from what we know as to their causes,
earthquakes are most frequent in regions now undergoing
deformation. Such are young rising mountain ranges, fault lines
where readjustments recur from time to time, and the slopes of
suboceanic depressions whose steepness suggests that subsidence
may there be in progress.

Earthquakes, often of extreme severity, frequently visit the lofty
and young ranges of the Andes, while they are little known in the
subdued old mountains of Brazil. The Highlands of Scotland are
crossed by a deep and singularly straight depression called the
Great Glen, which has been excavated along a very ancient line of
dislocation. The earthquakes which occur from time to time in this
region, such as the Inverness earthquake in 1891, are referred to
slight slips along this fault plane.

In Japan, earthquakes are very frequent. More than a thousand are
recorded every year, and twenty-nine world-shaking earthquakes
occurred in the three years ending with 1901. They originate, for
the most part, well down on the eastern flank of the earth fold
whose summit is the mountainous crest of the islands, and which
plunges steeply beneath the sea to the abyss of the Tuscarora
Deep.

MINOR CAUSES OF EARTHQUAKES. Since any concussion within the crust
sets up an earth jar, there are several minor causes of
earthquakes, such as volcanic explosions and even the collapse of
the roofs of caves. The earthquakes which attend the eruption of
volcanoes are local, even in the case of the most violent volcanic
paroxysms known. When the top of a volcano has been blown to
fragments, the accompanying earth shock has sometimes not been
felt more than twenty-five miles away.

DEPTH OF FOCUS. The focus of the Charleston earthquake, estimated
at about twelve miles below the surface, was exceptionally deep.
Volcanic earthquakes are particularly shallow, and probably no
earthquakes known have started at a greater depth than fifteen or
twenty miles. This distance is so slight compared with the earth's
radius that we may say that earthquakes are but skin-deep.

Should you expect the velocity of an earthquake to be greater in a
peneplain or in a river delta?

After an earthquake, piles on which buildings rested were found
driven into the ground, and chimneys crushed at base. From what
direction did the shock come?

Chimneys standing on the south walls of houses toppled over on the
roof. Should you infer that the shock in this case came from the
north or south?

How should you expect a shock from the east to affect pictures
hanging on the east and the west walls of a room? how the pictures
hanging on the north and the south walls?

In parts of the country, as in southwestern Wisconsin, slender
erosion pillars, or "monuments," are common. What inference could
you draw as to the occurrence in such regions of severe
earthquakes in the recent past?





CHAPTER XI

VOLCANOES


Connected with movements of the earth's crust which take place so
slowly that they can be inferred only from their effects is one of
the most rapid and impressive of all geological processes,--the
extrusion of molten rock from beneath the surface of the earth,
giving rise to all the various phenomena of volcanoes.

In a volcano, molten rock from a region deep below, which we may
call its reservoir, ascends through a pipe or fissure to the
surface. The materials erupted may be spread over vast areas, or,
as is commonly the case, may accumulate about the opening, forming
a conical pile known as the volcanic cone. It is to this cone that
popular usage refers the word VOLCANO; but the cone is simply a
conspicuous part of the volcanic mechanism whose still more
important parts, the reservoir and the pipe, are hidden from view.

Volcanic eruptions are of two types,--EFFUSIVE eruptions, in which
molten rock wells up from below and flows forth in streams of LAVA
(a comprehensive term applied to all kinds of rock emitted from
volcanoes in a molten state), and EXPLOSIVE eruptions, in which
the rock is blown out in fragments great and small by the
expansive force of steam.

ERUPTIONS OF THE EFFUSIVE TYPE

THE HAWAIIAN VOLCANOES. The Hawaiian Islands are all volcanic in
origin, and have a linear arrangement characteristic of many
volcanic groups in all parts of the world. They are strung along a
northwest-southeast line, their volcanoes standing in two parallel
rows as if reared along two adjacent lines of fracture or folding.
In the northwestern islands the volcanoes have long been extinct
and are worn low by erosion. In the southeastern island. Hawaii,
three volcanoes are still active and in process of building. Of
these Mauna Loa, the monarch of volcanoes, with a girth of two
hundred miles and a height of nearly fourteen thousand feet above
sea level, is a lava dome the slope of whose sides does not
average more than five degrees. On the summit is an elliptical
basin ten miles in circumference and several hundred feet deep.
Concentric cracks surround the rim, and from time to time the
basin is enlarged as great slices are detached from the vertical
walls and engulfed.

Such a volcanic basin, formed by the insinking of the top of the
cone, is called a CALDERA.

On the flanks of Mauna Loa, four thousand feet above sea level,
lies the caldera of Kilauea, an independent volcano whose dome has
been joined to the larger mountain by the gradual growth of the
two. In each caldera the floor, which to the eye is a plain of
black lava, is the congealed surface of a column of molten rock.
At times of an eruption lakes of boiling lava appear which may be
compared to air holes in a frozen river. Great waves surge up,
lifting tons of the fiery liquid a score of feet in air, to fall
back with a mighty plunge and roar, and occasionally the lava
rises several hundred feet in fountains of dazzling brightness.
The lava lakes may flood the floor of the basin, but in historic
times have never been known to fill it and overflow the rim.
Instead, the heavy column of lava breaks way through the sides of
the mountain and discharges in streams which flow down the
mountain slopes for a distance sometimes of as much as thirty-five
miles. With the drawing off of the lava the column in the duct of
the volcano lowers, and the floor of the caldera wholly or in part
subsides. A black and steaming abyss marks the place of the lava
lakes. After a time the lava rises in the duct, the floor is
floated higher, and the boiling lakes reappear.

The eruptions of the Hawaiian volcanoes are thus of the effusive
type. The column of lava rises, breaks through the side of the
mountain, and discharges in lava streams. There are no explosions,
and usually no earthquakes, or very slight ones, accompany the
eruptions. The lava in the calderas boils because of escaping
steam, but the vapor emitted is comparatively little, and seldom
hangs above the summits in heavy clouds. We see here in its
simplest form the most impressive and important fact in all
volcanic action, molten rock has been driven upward to the surface
from some deep-lying source.

LAVA FLOWS. As lava issues from the side of a volcano or overflows
from the summit, it flows away in a glowing stream resembling
molten iron drawn white-hot from an iron furnace. The surface of
the stream soon cools and blackens, and the hard crust of
nonconducting rock may grow thick and firm enough to form a
tunnel, within which the fluid lava may flow far before it loses
its heat to any marked degree. Such tunnels may at last be left as
caves by the draining away of the lava, and are sometimes several
miles in length.

PAHOEHOE AND AA. When the crust of highly fluid lava remains
unbroken after its first freezing, it presents a smooth, hummocky,
and ropy surface known by the Hawaiian term PAHOEHOE. On the other
hand, the crust of a viscid flow may be broken and splintered as
it is dragged along by the slowly moving mass beneath. The stream
then appears as a field of stones clanking and grinding on, with
here and there from some chink a dull red glow or a wisp of steam.
It sets to a surface called AA, of broken, sharp-edged blocks,
which is often both difficult and dangerous to traverse.

FISSURE ERUPTIONS. Some of the largest and most important outflows
of lava have not been connected with volcanic cones, but have been
discharged from fissures, flooding the country far and wide with
molten rock. Sheet after sheet of molten rock has been
successively outpoured, and there have been built up, layer upon
layer, plateaus of lava thousands of feet in thickness and many
thousands of square miles in area.

ICELAND. This island plateau has been rent from time to time by
fissures from which floods of lava have outpoured. In some
instances the lava discharges along the whole length of the
fissure, but more often only at certain points upon it. The Laki
fissure, twenty miles long, was in eruption in 1783 for seven
months. The inundation of fluid rock which poured from it is the
largest of historic record, reaching a distance of forty-seven
miles and covering two hundred and twenty square miles to an
average depth of a hundred feet. At the present time the fissure
is traced by a line of several hundred insignificant mounds of
fragmental materials which mark where the lava issued.

The distance to which the fissure eruptions of Iceland flow on
slopes extremely gentle is noteworthy. One such stream is ninety
miles in length, and another seventy miles long has a slope of
little more than one half a degree.

Where lava is emitted at one point and flows to a less distance
there is gradually built up a dome of the shape of an inverted
saucer with an immense base but comparatively low. Many LAVA DOMES
have been discovered in Iceland, although from their exceedingly
gentle slopes, often but two or three degrees, they long escaped
the notice of explorers.

The entire plateau of Iceland, a region as large as Ohio, is
composed of volcanic products,--for the most part of successive
sheets of lava whose total thickness falls little short of two
miles. The lava sheets exposed to view were outpoured in open air
and not beneath the sea; for peat bogs and old forest grounds are
interbedded with them, and the fossil plants of these vegetable
deposits prove that the plateau has long been building and is very
ancient. On the steep sea cliffs of the island, where its
structure is exhibited, the sheets of lava are seen to be cut with
many DIKES,--fissures which have been filled by molten rock,--and
there is little doubt that it was through these fissures that the
lava outwelled in successive flows which spread far and wide over
the country and gradually reared the enormous pile of the plateau.

ERUPTIONS OF THE EXPLOSIVE TYPE

In the majority of volcanoes the lava which rises in the pipe is
at least in part blown into fragments with violent explosions and
shot into the air together with vast quantities of water vapor and
various gases. The finer particles into--which the lava is
exploded are called VOLCANIC DUST or VOLCANIC ASHES, and are often
carried long distances by the wind before they settle to the
earth. The coarser fragments fall about the vent and there
accumulate in a steep, conical, volcanic mountain. As successive
explosions keep open the throat of the pipe, there remains on the
summit a cup-shaped depression called the CRATER.

STROMBOLI. To study the nature of these explosions we may visit
Stromboli, a low volcano built chiefly of fragmental materials,
which rises from the sea off the north coast of Sicily and is in
constant though moderate action.

Over the summit hangs a cloud of vapor which strikingly resembles
the column of smoke puffed from the smokestack of a locomotive, in
that it consists of globular masses, each the product of a
distinct explosion. At night the cloud of vapor is lighted with a
red glow at intervals of a few minutes, like the glow on the trail
of smoke behind the locomotive when from time to time the fire bos
is opened. Because of this intermittent light flashing thousands
of feet above the sea, Stromboli has been given the name of the
Lighthouse of the Mediterranean.

Looking down into the crater of the volcano, one sees a viscid
lava slowly seething. The agitation gradually increases. A great
bubble forms. It bursts with an explosion which causes the walls
of the crater to quiver with a miniature earthquake, and an
outrush of steam carries the fragments of the bubble aloft for a
thousand feet to fall into the crater or on the mountain side
about it. With the explosion the cooled and darkened crust of the
lava is removed, and the light of the incandescent liquid beneath
is reflected from the cloud of vapor which overhangs the cone.

At Stromboli we learn the lesson that the explosive force in
volcanoes is that of steam. The lava in the pipe is permeated with
it much as is a thick boiling porridge. The steam in boiling
porridge is unable to escape freely and gathers into bubbles which
in breaking spurt out drops of the pasty substance; in the same
way the explosion of great bubbles of steam in the viscid lava
shoots clots and fragments of it into the air.

KRAKATOA. The most violent eruption of history, that of Krakatoa,
a small volcanic island in the strait between Sumatra and Java,
occurred in the last week of August, 1883. Continuous explosions
shot a column of steam and ashes. seventeen miles in air. A black
cloud, beneath which was midnight darkness and from which fell a
rain of ashes and stones, overspread the surrounding region to a
distance of one hundred and fifty miles. Launched on the currents
of the upper air, the dust was swiftly carried westward to long
distances. Three days after the eruption it fell on the deck of a
ship sixteen hundred miles away, and in thirteen days the finest
impalpable powder from the volcano had floated round the globe.
For many months the dust hung over Europe and America as a faint
lofty haze illuminated at sunrise and sunset with brilliant
crimson. In countries nearer the eruption, as in India and Africa,
the haze for some time was so thick that it colored sun and moon
with blue, green, and copper-red tints and encircled them with
coronas.

At a distance of even a thousand miles the detonations of the
eruption sounded like the booming of heavy guns a few miles away.
In one direction they were audible for a distance as great as that
from San Francisco to Cleveland. The entire atmosphere was thrown
into undulations under which all barometers rose and fell as the
air waves thrice encircled the earth. The shock of the explosions
raised sea waves which swept round the adjacent shores at a height
of more than fifty feet, and which were perceptible halfway around
the globe.

At the close of the eruption it was found that half the mountain
had been blown away, and that where the central part of the island
had been the sea was a thousand feet deep.

MARTINIQUE AND ST. VINCENT. In 1902 two dormant volcanoes of the
West Indies, Mt. Pelee in Martinique and Soufriere in St. Vincent,
broke into eruption simultaneously. No lava was emitted, but there
were blown into the air great quantities of ashes, which mantled
the adjacent parts of the islands with a pall as of gray snow. In
early stages of the eruption lakes which occupied old craters were
discharged and swept down the ash-covered mountain valleys in
torrents of boiling mud.

On several occasions there was shot from the crater of each
volcano a thick and heavy cloud of incandescent ashes and steam,
which rushed down the mountain side like an avalanche, red with
glowing stones and scintillating with lightning flashes. Forests
and buildings in its path were leveled as by a tornado, wood was
charred and set on fire by the incandescent fragments, all
vegetation was destroyed, and to breathe the steam and hot,
suffocating dust of the cloud was death to every living creature.
On the morning of the 8th of May, 1902, the first of these
peculiar avalanches from Mt. Pelee fell on the city of St. Pierre
and instantly destroyed the lives of its thirty thousand
inhabitants.

The eruptions of many volcanoes partake of both the effusive and
the explosive types: the molten rock in the pipe is in part blown
into the air with explosions of steam, and in part is discharged
in streams of lava over the lip of the crater and from fissures in
the sides of the cone. Such are the eruptions of Vesuvius, one of
which is illustrated in Figure 219.

SUBMARINE ERUPTIONS. The many volcanic islands of the ocean and
the coral islands resting on submerged volcanic peaks prove that
eruptions have often taken place upon the ocean floor and have
there built up enormous piles of volcanic fragments and lava. The
Hawaiian volcanoes rise from a depth of eighteen thousand feet of
water and lift their heads to about thirty thousand feet above the
ocean bed. Christmas Island (see p. 194), built wholly beneath the
ocean, is a coral-capped volcanic peak, whose total height, as
measured from the bottom of the sea, is more than fifteen thousand
feet. Deep-sea soundings have revealed the presence of numerous
peaks which fail to reach sea level and which no doubt are
submarine volcanoes. A number of volcanoes on the land were
submarine in their early stages, as, for example, the vast pile of
Etna, the celebrated Sicilian volcano, which rests on stratified
volcanic fragments containing marine shells now uplifted from the
sea.

Submarine outflows of lava and deposits of volcanic fragments
become covered with sediments during the long intervals between
eruptions. Such volcanic deposits are said to be CONTEMPORANEOUS,
because they are formed during the same period as the strata among
which they are imbedded. Contemporaneous lava sheets may be
expected to bake the surface of the stratum on which they rest,
while the sediments deposited upon them are unaltered by their
heat. They are among the most permanent records of volcanic
action, far outlasting the greatest volcanic mountains built in
open air.

From upraised submarine volcanoes, such as Christmas Island, it is
learned that lava flows which are poured out upon the bottom of
the sea do not differ materially either in composition or texture
from those of the land.

VOLCANIC PRODUCTS

Vast amounts of steam are, as we have seen, emitted from
volcanoes, and comparatively small quantities of other vapors,
such as various acid and sulphurous gases. The rocks erupted from
volcanoes differ widely in chemical composition and in texture.

ACIDIC AND BASIC LAVAS. Two classes of volcanic rocks may be
distinguished,--those containing a large proportion of silica
(silicic acid, SiO2) and therefore called ACIDIC, and those
containing less silica and a larger proportion of the bases (lime,
magnesia, soda, etc.) and therefore called BASIC. The acidic
lavas, of which RHYOLITE and THRACHYTE are examples, are
comparatively light in color and weight, and are difficult to
melt. The basic lavas, of which BASALT is a type, are dark and
heavy and melt at a lower temperature.

SCORIA AND PUMICE. The texture of volcanic rocks depends in part
on the degree to which they were distended by the steam which
permeated them when in a molten state. They harden into compact
rock where the steam cannot expand. Where the steam is released
from pressure, as on the surface of a lava stream, it forms
bubbles (steam blebs) of various sizes, which give the hardened
rock a cellular structure (Fig. 220), In this way are formed the
rough slags and clinkers called SCORIA, which are found on the
surface of flows and which are also thrown out as clots of lava in
explosive eruptions.