The Island of Hawaii, the principal island of the group, we may safely say contains the most enormous volcano of the earth. Indeed, the whole island, which is 4000 square miles in extent, may be regarded as of volcanic origin. It contains four volcanic mountains—Kohola, Hualalia, Mauna Kea and Mauna Loa. The two last named are the chief, the former being 13,800 feet, the latter 13,600 feet, above the sea-level. Although their height is so vast, the ascent to their summits is so gradual that their circumference at the base is enormous. The bulk of each of them is reckoned to be equal to two and a half times that of Etna. Some of the streams of lava which have emanated from them are twenty-six miles in length by two miles in breadth.
On the adjoining island of Maui is a still larger volcano, the mighty Haleakala, long since extinct, but memorable as possessing the most stupendous crater on the face of the earth. The mountain itself is over 10,000 feet high, and forms a great dome-like mass of 90 miles circumference at base. The crater on its summit has a length of 7 1/2 and a width of 2 1/4 miles, with a total area of about sixteen square miles. The only approach in dimensions to this enormous opening exists in the still living crater of Kilauea, on the flank of Mauna Loa.
The peaks named are the most apparent remnants of a world-rending volcanic activity in the remote past, by whose force this whole Hawaiian island group was lifted up from the depths of the ocean, here descending some three and a half miles below the surface level. The coral reefs which abound around the islands are of comparatively recent formation, and rest upon a substratum of lava probably ages older, which forms the base of the archipelago. The islands are volcanic peaks and ridges that have been pushed up above the surrounding seas by the profound action of the interior forces of the earth.
It must not be supposed that this action was a violent perpendicular thrust upward over a very limited locality, for the mountains continue to slope at about the same angle under the sea and for great distances on every side, so that the islands are really the crests of an extensive elevation, estimated to cover an area of about 2000 miles in one direction by 150 or 200 miles in the other. The process was probably a gradual one of up-building, by means of which the sea receded as the land steadily rose. Some idea of the mighty forces that have been at work beneath the sea and above it can be gained by considering the enormous mass of material now above the sea-level. Thus, the bulk of the island of Hawaii, the largest of the group, has been estimated by the Hawaiian Surveyor General as containing 3,600 cubic miles of lava rock above sea-level. Taking the area of England at 50,000 square miles, this mass of volcanic matter would cover that entire country to a depth of 274 feet. We must remember, however, that what is above sea-level is only a small fraction of the total amount, since it sweeps down below the waves hundreds of miles on every side.