VOLCANOES 411 



ally a movement of sufficient force occurs to produce serious 

 tremblings or quakes at the surface. This is the dreaded earth- 

 quake. The serious San Francisco earthquake of 1906 was 

 caused by a considerable movement of the deep underground 

 rocks in that region. The rocks for miles moved as much as 

 5 to 15 feet horizontally. Such internal changes inevitably 

 caused movement at the earth's surface and led to serious dis- 

 aster. Buildings were overthrown, bridges and railroads were 

 wrecked, crops were devastated, many lives were lost, and 

 thousands of people were made homeless (Fig. 277). A severe 

 earthquake occurred in Chili in 1822; after the earthquake it 

 was found that the land had been raised about 3 feet. Earth- 

 quakes are more numerous in some regions than in others. 

 Italy has suffered greatly from them. The United States is 

 fortunate in having had few violent earthquakes in the past. 

 Next to the San Francisco disaster, the most serious earth- 

 quake in this country was that which occurred at Charleston, 

 S. C, in 1886. 



Sometimes earthquakes take place at the bottom of the sea. 

 These earthquakes cause such violent disturbances of the 

 water that vast waves surge out from the area, and overwhelm 

 ships, and traveling shoreward engulf towns and villages. Italy, 

 Portugal, and Alaska have 

 experienced such disasters. 



Volcanoes. Volcanoes are 

 among the most striking 

 phenomena of nature. They 

 are usually cone-shaped (Fig. 



2 7 8), and from an opening - Diagram of a volcano. 



called a crater they pour forth at irregular intervals molten 

 rock, solid rock fragments, hot gases, and vapors. Some- 

 times the molten rock, or lava, streams out quietly; some- 

 times there is a violent eruption and large pieces of rock, 



