The Mount Aso, or Aso-San, is a living volcano in the heart of the island Kiushiu, Japan, whose peaks rise to a height of several thousand feet out of a gigantic bowl. This bowl, which is many miles across, is an ancient crater surpassing in size all other known craters nearer than the moon. Some 5,000 people, grouped in half a hundred villages on the old floor, are living today, tilling the volcanic soil and trading in this vast crater, round about the base of the new and ever-active cone that has risen in it.

Kiushiu is the most southern of the four main islands in the Japanese archipelago. It is about 17,000 square miles in extent and is therefore larger than Vancouver Island, or almost equal in area to Massachusetts and New Hampshire combined. It is built up of very ancient rocks, both sedimentary and igneous, belonging to the paleozoic and mesozoic eras, as well as of younger rocks, and upon these as a foundation has been erected in more recent times, partly during the age of man, a superstructure of volcanic materials which now covers many thousand square miles, or about one half the area of the island. It contains twenty volcanoes, counting two that are just off the coast to the south, of which eight are now active. Among them Aso-san is on far the largest scale, though now it is in a decadent stage and is surpassed in activity by two or more of the others. Japan through all past ages has been a land of extraordinary geological activity, possessed of a vital energy which, continuing in force up to modern times, has been emphasized by the changes in level of its coasts and heralded by its ever-vigorous volcanoes.