CHAPTER XVI

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.

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.