‘ VOLCANOES 343 
that for some reason, the power of the steam was not 
sufficient to keep the tube or fissure clear; and there- 
fore in this vent, the lava, which has cooled from liquid 
to consolidated rock, thus forms a plug in the tube. 
When this is accomplished, the voleano becomes dor- 
mant; but it may be gathering force for a terrible 
eruption. When the accumulated energy of the steam 
becomes great enough, either the plug is blown out, 
or the cone split and partly thrown into the air. 
These are the most terrible of eruptions, and the 
experience of Vesuvius warns us against believing any 
voleano to be actually extinct so long as the cone 
shape lasts. It need not surprise us at any time 
to hear of violent eruptions in some of the so-called 
extinct volcanoes of the Far West, which are possibly 
only dormant. Still in process of time, the supply of 
energy so far fails as to become inadequate to cause 
further eruption, and then the cone does become actu- 
ally and permanently extinct. 
Eruption of Krakatoa.— The most notable eruption that has 
been carefully studied, is that of Krakatoa in the Straits of 
Sunda. In the spring of 1883, after a long period of quiet, this 
cone began to show signs of activity, and from it proceeded 
numerous earthquakes. These evidences. of awakening energy 
culminated in the latter part of August, 1883, in an outbreak, 
which blew one-half of the island into the air (Fig. 208). A 
prodigious mass of ash and dust was hurled upward, apparently 
reaching elevations as great as fifteen miles above the level of 
