Fig. 1. The Sunda Islands
A volcano is a mountain or hill, generally conical in shape, having at the top a nearly central opening, called a crater, from which at times melted rock and lava, vapor and gases escape. The lava either flows down the side of the mountain in a liquid condition, or is thrown upwards into the air. If the distance the lava is thrown upwards is sufficiently great the melted matter solidifies before it falls to the earth. In such cases the largest fragments form what are called volcanic cinders, the smaller pieces, volcanic ashes, and the extremely small particles, volcanic dust. If, however, the lava is thrown to a comparatively small height, it is still melted when it falls, and is then known as volcanic drops or driblets.
Fig. 2. Krakatoa Before the Eruption
It is not surprising that Krakatoa is a volcanic island, since it lies in one of the most active belts of volcanic islands in the world, and near the coasts of the most active of these islands; i. e., Java. This belt, as shown in the map, includes, besides the Sunda Island chain, parts of Gilolo, Celebes, Mindanao and the Philippine Islands. These islands lie between Asia on the northwest and Australia on the southeast.
Fig. 3. Krakatoa After the Eruption
There is no other part of the world with, perhaps, the single exception of Japan, where so many active volcanoes are crowded in so small a space. The island of Java, small as it is, has nearly fifty volcanoes, of which at least twenty-eight are active. They are situated in a lofty range running from east to west, some of the peaks of which are more than 10,000 feet above the level of the sea. Volcanic eruptions are so frequent that the island is seldom free from them.