One of the greatest volcanic explosions ever recorded was that of the island of Krakatoa, between Sumatra and Java, in 1883. The greater part of the island was blown away and there was water 1,000 feet deep, where just before the island stood hundreds of feet high. About a cubic mile of rock material was sent into the air mostly in the form of fine dust--some of it for seventeen miles--and completely hid the sun, causing total darkness during the eruption. Dust fell over an area of several hundred thousand square miles. Several days after the explosion ships more than 1,000 miles away were dust covered. Such enormous quantities of a light porous lava called "pumice" fell and floated upon the sea that navigation was badly obstructed many miles from the volcano. Extremely fine dust gradually spread through the whole earth's atmosphere, causing the extraordinary red sunsets for several months. The sound of the explosion was heard for hundreds of miles. Great sea waves 50 to 100 feet high were stirred up and they swept inland for several miles over the low-lying coast lands of neighboring Java and Sumatra, overwhelming hundreds of villages and drowning tens of thousands of people. [Illustration: Fig. 17.--The great hole left after the top of Mt. Katmai in southern Alaska was blown off in 1912 by one of the most tremendous volcanic explosions in the annals of human history. The water in the lake is hot. (After Griggs, National Geographic Magazine.)] One of the greatest explosions on record was that of Katmai volcano, several thousand feet high, on the coast of Alaska, in June, 1912. Not only was the top of the mountain completely blown off, but also a great crater pit, three miles wide across the top and several thousand feet deep, was developed in the stump of the former mountain. Volcanic dust fell to a depth of several feet within twenty-five to fifty miles of the mountain. Dust accumulated to a depth of nearly a foot in the village of Kodiak, 100 miles east of the mountain, where total darkness prevailed for more than two days. A lake of very hot water now occupies the bottom of the great new crater. The noise of the explosion was heard for at least 750 miles. [Illustration: Fig. 18.--Diagrammatic vertical or structure section through a portion of the earth illustrating the common modes of occurrence of igneous rocks. P, deep-seated (plutonic) igneous rock; S, strata; D, dikes; M, mass of igneous rock forced between strata bending them upward; F, feeding channel of volcano; V, volcano; L, lava sheets. (By the author.)]