THE VOLCANIC ISLAND OF ICELAND
The island of Iceland consists of a number of volcanic mountains some
of which are still active. As can be seen from the map, shown in
Fig. 11, Iceland lies in the North Atlantic Ocean, immediately below
the Arctic Circle, about 250 miles east of Greenland, and 600 miles
west of Norway. Its length from east to west is about 300 miles, and
its breadth about 200 miles, its total area, including the adjacent
islands, being more than 40,000 square miles.
Were all the water removed from the North Atlantic Ocean, it would be
seen that Iceland rests on the bed of the Atlantic, on a submarine
plateau or highland; for, in this part of the ocean the water is only
from 1,500 to 3,000 feet deep. This submarine plateau extends as far
as Norway on the east, Greenland on the north, and the island of Jan
Mayen on the northeast. Immediately north of the plateau the ocean
suddenly drops to a depth of 12,000 to 15,000 feet.
[Illustration: FIG. 11. ICELAND]
Toward the south the plateau extends with but few interruptions
through the middle of the ocean to a shoal known as the _Dolphin
Shoal_, as far as lat. 25° N. This part of the ocean, which can only
relatively be called a shoal, is not generally deeper than 9,600 feet,
although in some places the water is more than 12,000 feet deep. On
each side of the Dolphin Shoal the water is much deeper, being in
places 15,000 feet on the east, while on the west there are depths
as great as from 17,000 to 21,000 feet.
This sunken plateau, possibly including the shallower plateau on the
north, is believed by some to be the remains of the fabled continent
of _Atlantis_, to which we shall refer in another part of this book.
The coast line of Iceland is unbroken on the southeast, but the
remainder of the coast is deeply indented with bays or fiords in which
are many excellent harbors.
Iceland is liable to frequent earthquake shocks and volcanic
eruptions. From careful records that have been preserved in the
history of the island, we learn that since the beginning of the
twelfth century there have practically never been intervals longer
than forty years, and more generally not longer than twenty years,
in which there has not been a great earthquake or a great volcanic
eruption. These volcanic eruptions are often very protracted. For
example, one eruption of the volcano Hecla continued for six years
without ceasing. Sir Charles Lyell, the great English geologist,
writes as follows about Iceland:
"Earthquakes have often shaken the whole island at once,
causing great changes in the interior, such as the sinking
down of hills, the rending of mountains, the desertion of
rivers by their channels, and the appearance of new lakes.
New islands have often been thrown up near the coast, some
of which still exist, while others have disappeared, either
by subsidences or the action of the waves.
"In the interval between eruptions innumerable hot springs
afford vent to the subterranean heat, and solfataras
discharge copious streams of inflammable matter. The
volcanoes in different parts of the island are observed,
like those of the Phlegræan Fields, Italy, to be in
activity by turns, one vent often serving for a time as a
safety valve for the rest. Many cones are often thrown
up in one eruption and in this case they take a linear
direction, running generally from southeast to northwest."
The volcanic eruptions of Iceland belong for the greater part to the
fissure type. During a volcanic eruption in Iceland the ground is
split in fissures or cracks, generally parallel to each other, and
varying in width from a few inches to several yards. These fissures
extend for great distances across the country. The lava quietly wells
out along the fissures not unlike the way quiet spring waters flow
from their reservoirs.
According to Dr. Th. Thoroddsen, the Icelandic geologist, there are
two systems of fissures extending through Iceland, from southwest to
northeast in the southern part of the island, and from north to south
in the northern part. Where two lines of fissures cross each other the
points of intersection may be especially active.
Dr. Th. Thoroddsen arranges the volcanoes of Iceland under three
heads, i. e., _cone-shaped volcanoes_; _lava cones_; and _chains of
craters_, the last being the commonest. Out of 107 volcanoes examined
by him in Iceland, eight were of the Vesuvian type, or were built up
of layers of lava and volcanic ashes; sixteen were of the lava-cone
type, similar to Mt. Loa, of the Hawaiian Islands, and the remaining
eighty-three were of the type of crater chains.
The volcano of Snaefell Jökul, 4,710 feet above the level of the
ocean, is built up of alternate layers of lava and hardened volcanic
mud. It is not, however, a true cone-shaped mountain.
The largest volcano in Iceland, the Dyngjufköll, with its immense
crater of Askja, has an area of some twenty-five square miles. In its
form it resembles Snaefell.
Volcanoes of the lava-cone type have been built up entirely of lava
and have a slight angle of inclination. These volcanoes range in size
from small hillocks to the largest mountains on the island. Their
cones generally stand on a base of wide circumference and frequently
rise to great heights, the top being occupied by a caldera, or pit
crater like that on Mt. Loa or Kilauea.
Volcanoes of the type of chain-craters follow the natural fissures in
the crust. These craters are generally low, seldom being more than 350
feet high.
There are also seen in Iceland caldron-shaped depressions that have
been formed by explosive eruptions. One of the best instances of such
craters is Viti, on the side of Mt. Krafla. This crater was formed by
the sudden eruption of May 17th, 1724.
The lava sometimes quietly runs out of the entire length of the
fissure without forming any cone. This was the case of a great fissure
known as the Eldgja Chasm. Here three lava streams covered an area of
270 square miles.
As the lava comes out of the fissures, it generally produces long
ramparts of slags, and blocks of lava that are piled up on either side
of the fissure. Sometimes a line of low cones is built up. These cones
consist of heaps of slag, cinders, and blocks of lava. Their craters
are not rounded as in the case of volcanoes of the Vesuvian type, but
are oblong, or have their greatest diameter extending in a direction
of the fissure.
Icelandic lava as it escapes from the fissures is peculiar in that
it is very viscid or plastic and can be readily drawn out into long
threads that can be spun into ropes. When such lava runs down the
sides of a steep slope, it often splits on cooling into separate
blocks. Where it runs over flat, level ground, however, it spreads
uniformly on all sides, producing vast level lava deserts that are as
flat as the surface of a well built floor.
There are many rivers in the north and the west of Iceland. Now, as
the lava streams flow out of the fissures they enter the channels of
the rivers so that the streams of water must find new paths to the
sea, and this operation may be repeated again and again. Often the
time between eruptions is long enough to give the rivers opportunity
to cut deep channels or gorges in their new channels; but on the next
escape of the lava these gorges and valleys are again filled with the
molten rock, and the rivers must begin their channel cutting all over.
You will note the frequent use of the word Jökul, as Snaefell Jökul,
Skaptar Jökul, Orefa Jökul, etc. The name Jökul means a large mass of
ice, or a mountain that is continually covered with snow, for example,
Snaefell Jökul, is a beautifully shaped, snow-covered mountain
situated on a point of land on the western coast of the island,
extending out nearly fifty miles into the sea, between the Faxa Fiord
and the Briela Fiord. It is a very conspicuous object, being visible
to passing ships at considerable distances from the island. Orefa
Jökul is the highest mountain in Iceland. Skaptar Jökul is one of the
active volcanoes of Iceland.
There can be no doubt that Iceland has been formed entirely by lava
thrown up from the bottom of a submarine plateau, until it extended
above the surface of the waters. To make an island entirely of lava
with an area of 40,000 square miles, must, of course, have required
many cones or craters that continued to pour forth lava for periods of
time much longer than those during which man has lived on the earth.
The surface of Iceland is far from attractive. The interior is
practically a vast lava desert, covered with snow-clad mountains or
Jökuls. There is no plant life except in marshy lands near the coasts,
and even here scarcely enough grass is raised to feed the few cattle
and horses owned by the inhabitants. There is no agriculture, owing
to the very short summers, so that all grain is brought from Europe.
Every now and then the grass crop is destroyed by accumulation of
Polar ice on the northern and western coasts. Such failures are always
attended by great famines, when many of the people die.
Should you ever visit Iceland you would probably be surprised to hear
the people speaking about their forests. You might go over all the
coasts of the island without seeing anything larger than a birch bush,
not much higher than six feet. These are what the Icelanders like to
speak of as their forest trees, and I suppose there is no harm done,
if one only understands just what they mean by "trees."
While, however, Iceland has practically no trees, yet it has no
difficulty in obtaining a plentiful supply of timber, since in the
deep fiords or bays on the western and southern coasts there can
always be found much drift timber brought there by the ocean currents
from the forests of America.
The principal town or settlement in Iceland is Reykjavik, the capital
of the island, on the southwestern coast; this is the chief trading
place on the island. Thingvalla is also an important town.
The lavas that form the entire mass of Iceland were thrown out both
before and since the glacial age. It is the opinion of Geikie that
these outflows have continued uninterruptedly since that age to the
present time. It is known that the lavas of Iceland were thrown out
both before and after the glacial age, because during the glacial age,
deep cuttings or groovings were made on the surface of the earth by
the glaciers as they slowly moved over it. Now lava beds containing
the glacial scratches have been found and resting on them are other
lava streams. The scratched lavas must, therefore, have been thrown
out before the glacial age, and the second lavas after that age.
Let us now examine some of the more active volcanoes of Iceland and
their eruptions. We will begin with the well-known volcano of Skaptar
Jökul.
The following description of this volcano has been taken from a book
on Iceland by E. Henderson, published in Boston, 1831. Skaptar Jökul
lies in the south central part of Iceland about forty odd miles from
the coast. It takes its name from the Skaptar River, down whose
channel the lava flowed its entire distance of forty miles from the
ocean. Skaptar Jökul consists of about twenty conical hills lying
along one of the fissures that extends from northeast to southwest.
It appears from Henderson's account that people living in the
neighborhood of Skaptar Jökul were greatly alarmed by repeated
earthquakes that were felt at different times from the first to the
eighth of June, 1783. These earthquake shocks increased in number and
violence, so that the people left their homes and awaited in terror
the coming catastrophe. On the morning of the eighth a prodigious
cloud of dense smoke darkened the air, and the surrounding land soon
became covered with ashes, pumice, and brimstone. As is common with
eruptions in Iceland, that have been preceded by long periods of rest,
the heat produced by the escaping lava and the sulphurous gases,
melted such quantities of ice that great floods were produced in the
rivers.
On the 10th of June vast torrents of lava that had been escaping
from the craters entered the valley of the Skaptar River, and
commenced flowing through its channel. Immense quantities of steam
were produced, and, in less than twenty-four hours, the river was
completely dried up, for the lava had collected in the channel,
which in many places flows between high rocks from 400 to 600 feet
in height and nearly 200 feet in breadth, and had not only filled
the river to its brink, but had overflowed the adjacent fields to a
considerable extent, and flowing along the cultivated banks of the
river destroyed all the farms in its path.
On gaining the outlet, where the channel of the Skaptar emerged
into the plain, it might have been supposed that the burning flood
would have at once spread over the low fields, which lay immediately
before it, but, contrary to all expectations, this flow was for a
time stopped by an immense unfathomed abyss in the river's bed, into
which it emptied itself with great noise. When this chasm was at
last filled, the lava increased by fresh flows, rose to a prodigious
height, and breaking over the cooled mass, proceeded south towards the
plain.
In the meantime the thunder and lightning, together with subterranean
roars, continued with little or no intermission.
On the 18th of June, 1783, another dreadful eruption of red hot lava
came from the volcano. This flowed with great velocity and force over
the surface of the cooling stream that had been thrown out principally
on the tenth of the month. Floating islands consisting of masses of
flaming rock were seen on the surface of the lava stream, and the
water that had been banked up on both sides of the stream was thrown
into violent boiling.
In the meantime people living along the Hverfisfloit, the next largest
river to the east of the Skaptar, had not yet been visited by the
lava streams. It is true that their vegetation had been destroyed by
showers of red hot stone and ashes, and that both atmosphere and water
were filled with poisonous substances. The land had also been plunged
in utter darkness, so that it was scarcely possible at noonday to
distinguish a sheet of white paper held up at the window from the
blackness of the wall on either side. But the molten lava streams had
not yet reached the people of this valley and they hoped that the
eruption would soon be over, and that the lava flow would continue to
follow the Skaptar. On the 3d of August, however, they were alarmed by
seeing steam escaping from the River Hverfisfloit, and soon all its
water was dried up, and a fresh lava flow poured down upon them. As in
the case of the Skaptar, the melted rock completely filled the empty
channel to the brink, and then overflowing, covered the low grounds on
both sides, so that by the ninth of August it had reached the open and
level country near its mouth and in the course of a few hours spread
itself for a distance of nearly six miles across the plain. This flow
continued after the end of August, and, indeed, even as late as the
month of February, 1784, when a new eruption took place in this part
of the country.
Hecla, another well-known volcano in Iceland, situated about thirty
miles from the southern coast, consists of three peaks, the central of
which is the highest. Its craters form vast hollows on the sides of
these peaks, and at the time of the eruption in 1766 were covered with
snow. Hecla is believed to have been an active volcano long before
Iceland was inhabited. No less than twenty-three eruptions have been
recorded between A. D. 1004 and the great eruption of 1766-68.
Volcanic history frequently repeats itself. There had been no great
eruption of Hecla for a period of about twelve years, and the people
living in the neighborhood were congratulating themselves on the
belief that the mountain was becoming actually extinct, and that
therefore they need not trouble themselves about eruptions. Others,
however, more farseeing, pointed out the fact that the lakes and
rivers in the vicinity did not freeze, and that the amount of water
they contained was greatly decreased.
The following description of the great eruption of Hecla that was
remarkable both for its violence, as well as for the time during which
it continued, is taken from Symington's "Sketches of Faroe Islands and
Iceland":
"On the 4th of April, 1766, there were some slight shocks
of an earthquake, and early next morning a pillar of sand,
mingled with fire and red hot stones, burst with a loud
thundering noise from its summit. Masses of pumice, six
feet in circumference, were thrown to the distance of ten
or fifteen miles, together with heavy magnetic stones,
one of which, eight pounds weight, fell fourteen miles
off, and sank into ground still hardened by the frost. The
sand was carried towards the northwest, covering the land,
150 miles round, four inches deep, impeding the fishing
boats along the coast, and darkening the air, so that at
Thingore, 140 miles distant, it was impossible to know
whether a sheet of paper was white or black. At Holum, 155
miles to the north, some persons thought they saw the stars
shining through the sand-cloud. About mid-day, the wind
veering round to the southeast, conveyed the dust into the
central desert, and prevented it from totally destroying
the pastures. On the 9th of April, the lava first appeared,
spreading about five miles towards the southwest, and on
the 23d of May, a column of water was seen shooting up in
the midst of the sand. The last violent eruption was on the
5th of July, the mountains, in the interval, often ceasing
to eject any matter; and the large stones thrown into the
air were compared to a swarm of bees clustering around the
mountain-top; the noise was heard like loud thunder forty
miles distant, and the accompanying earthquakes were more
severe at Krisuvik, eighty miles westward, than at half the
distance on the opposite side. The eruptions are said to
be in general more violent during a north or west wind than
when it blows from the south or east, and on this occasion
more matter was thrown out in mild than in stormy weather.
Where the ashes were not too thick, it was observed that
they increased the fertility of the grass fields, and
some of them were carried even to the Orkney Islands, the
inhabitants of which were at first terrified by what they
considered showers of black snow."
The largest volcano in Iceland is Dyngjufjoll. This has on its summit
the gigantic crater of Askja, some twenty-five square miles in area.
This crater is of the intermediate form; the most general form of
volcanoes on the island consisting of a number of craters that closely
follow fissures.
Professor Johnstrup, in a report to the Danish Government, on this
volcano, states that the valley of Askja has been gradually filled
by repeated flows of lava from enormous craters on the edge of the
mountain. In many places the surface of the earth is covered with
bright red pumice stone that was thrown out during an eruption March
29th, 1875. Some of these craters are filled with steam that escapes
with an almost deafening roar. The surprising feature of this eruption
was the immense quantity of pumice stone that escaped.
The volcanoes in the Nyvatus Oraefi are entirely different. This
barren plain is thirty-five miles in length and thirteen miles in
breadth. Suddenly on the 18th of February, 1875, a volcano appeared in
the centre, and four other craters were formed at subsequent dates.
The mass of lava that was thrown out of these openings has been
estimated at 10,000,000,000,000 cubic feet, or eighteen times the
estimated mass of lava that has been emitted from Vesuvius between
1794 and 1855. This lava is basalt.