DISTRIBUTION OF THE EARTH'S VOLCANOES
Having now considered at some length the principal volcanoes of the
earth, and endeavored to obtain some idea of the many wonders they
exhibit, especially as regards the vast quantities of material they
bring from the inside of the earth, as well as the great force with
which they sometimes throw these materials out of their craters, it
will be well to point out where such volcanoes are to be found.
It may have seemed to you, when you have carefully followed what has
been said about the earth's volcanoes, that they are to be found
pretty nearly everywhere, at least so far as latitude is concerned;
and in this supposition you are correct; for there are volcanoes in
the Arctic Ocean, as in the volcanic island of Jan Mayen between
Iceland and Spitzbergen, there are Mt. Erebus and Mt. Terror in the
Antarctic Ocean, besides very numerous volcanoes in the Atlantic,
Pacific, and Indian Oceans, and their shores in both the temperate and
the torrid zones.
There is, however, one thing that you have probably especially
noticed and that is that volcanoes are seldom found at very great
distances from the ocean, except on some of its arms or seas, such
as the Mediterranean Sea. I do not mean by this that all the earth's
volcanoes are either situated directly on the coast of the continents
or on islands, since, in such a large body as the earth, a distance of
a few hundred miles from the ocean is hardly to be regarded as being
very far from it. But it is true that all the earth's volcanoes are
either situated on the coasts of the continents, or on islands, and,
moreover, they are situated to a greater or less extent along lines,
which, as we have already pointed out, are believed to mark weak
portions of the earth's crust that have been fissured or fractured.
In order that you may have some idea of this distribution, I think it
will be well to give you a number of interesting facts that have been
pointed out by Dana. According to this authority, there are something
in the neighborhood of 300 active volcanoes on the earth. Of these,
no less than five-sixths, or 250, lie either on the borders of the
Pacific Ocean, or on some of its many islands. Thirty-nine either
lie within or on the borders of the Atlantic, of which thirteen are
in Iceland, or near the Arctic Circle, three in the Canaries, seven
in the Mediterranean Sea, six in the Lesser Antilles, and ten in
the Atlantic Oceanic Islands. The Indian Ocean contains only a few
active volcanoes. There are, however, a much greater number of extinct
volcanoes, which may at any time again become active.
The following is the distribution of the earth's volcanoes as given
by Dana. As you will see, from an inspection of Fig. 24, all of the
regions of volcanoes lie either on the borders of the continents, or
on islands in the oceans. The districts are as follows:
1. _Scattered Over the Pacific Ocean._--This district includes the
following active volcanoes; i. e., the Hawaiian Islands, nearly in
mid-ocean, almost directly below the Tropic of Cancer; in the west
central parts of the South Pacific; in the New Hebrides; in the
Friendly Islands, the Tongan or New Zealand Islands, in the Santa Cruz
Islands, and in the Ladrones.
[Illustration: FIG. 24. MAP OF THE WORLD, SHOWING LOCATION OF
ACTIVE AND RECENTLY EXTINCT VOLCANOES]
2. _On the Borders of the Pacific._--This district includes the
volcanoes that extend from the southern part of South America
at intervals along the Andes Mountain range. Of these there are
thirty-two in Chile, seven or eight in Bolivia and Southern Peru;
about twenty in the neighborhood of Quito. Further north there are
thirty-nine in Central America, and seven in Mexico. Proceeding
northwards through the United States, there are a number of volcanic
mountains, generally extinct, in portions of the Sierra Nevadas
and Cascade Ranges. Probably a number of volcanic mountains exist
in portions of Canada lying between the northern boundaries of the
United States and Alaska, and a number in Alaska; some twenty-one
volcanic mountains in the Aleutian Islands; some fifteen or twenty
in Kamtschatka; thirteen in the Kuriles; some twenty-five or thirty
in Japan and the neighboring islands; some fifteen or twenty in the
Philippines; several along the northern coasts of New Guinea; a number
in New Zealand and south of Cape Horn; the volcanoes of the Deception
Island with its hot springs, and also in the South Shetlands 62° 30' S.
3. _In the Indian Ocean._--On the western border of the Indian Ocean
there are a few volcanoes in Madagascar; in the Island of Bourbon;
Mauritius; the Comoro Islands; and in Kerguelen Land on the south.
There are also volcanoes on the western border of the Indian Ocean
where the lofty peak of Kilima Ndjro, 18,000 feet, is volcanic.
4. _Over the Seas that Separate the Northern and the Southern
Continents and in their Vicinity._--This is an especially active
region of volcanoes. For the sake of convenience the continents of the
world are sometimes divided into three pairs or double continents;
namely, North and South America, connected by the Isthmus of Panama;
Europe and Africa, connected by the Isthmus of Suez; and Australia and
Asia, completely separated by a sunken isthmus, the summits of which
form the Sunda Island chain. In the first of these regions we have the
very active group of the West Indies, where there are ten volcanic
islands. In the second pair of double continents we have the volcanoes
of the Mediterranean and Red Seas, and their borders, such as Sicily,
Vesuvius, and other parts of Italy, Spain, Germany, the Grecian
Archipelago, Asia Minor, and extending eastward through the Caspian,
Mt. Ararat, Demavend, on the south shores of the Caspian, Mt. Ararat,
and some few others along the borders of the Red Sea.
In the East Indies we find the most intense centre of volcanic
activity in the world. Here there are some 200 volcanoes of which
there are nearly fifty in Java alone, more than half of which are
still active. There are nearly as many volcanoes in Sumatra, and many
in the small islands near Borneo, the Philippines, etc.
5. _On the Borders of the Atlantic and Elsewhere._--It is an
interesting fact that there are no volcanoes on the eastern borders
of the Atlantic north of the West Indies Island chain. In the South
Atlantic the only volcano on the borders is one of the Cameroons
Mountains. In the Atlantic Ocean we have Iceland, the Azores, the
Canaries, Cape Verde, Ascension, St. Helena, and Tristan d'Acunha.
This curious distribution of the volcanoes of the world near the
oceanic waters appears to be dependent rather on the very early shapes
of the continents and the ocean beds than on their present shapes.