_Stereo Copyright, Underwood & U._ _London and New York_
In geysers the suggestion that the fountains of steam and hot water originate by the contact of water with hot rock is irresistible.]
In steep-walled mountain valleys earthquakes nearly always cause landslips, and these may completely block the course of a river. The lake formed in this manner during the great earthquake of January 25th, 1348, in Carinthia destroyed no fewer than seventeen villages, and to-day, nearly six centuries afterwards, the area is a great marsh. After the earthquake near Lake Baikal in Siberia, of which we have spoken and in which the ground sank, the sunken area was soon after invaded by the waters of the lake. Sometimes when the earthquake takes place near the mouth of a great river, the channels of the streams are changed. After the Californian earthquake of 1857 the current of the River Kern was turned upstream; and the San Gabriel River left its bed to follow a new course offered to it by an earthquake fissure. After the Japanese earthquake of 1891 a former lake was cut in half by one of the earthquake displacements, and one half of the lake was left high and dry. Near Flagstaff, Arizona, there is an old earthquake crack along which the waters of several rivers which intersect it all disappear down the crevice. The most remarkable revelation of the process of lake draining during earthquake shocks was furnished, however, according to Professor Hobbs, by the former Lake Eulalie near New Madrid. After the shocks of 1812 the lake completely disappeared. On the lake bottom thus exposed there was revealed a series of fissures down the funnel-shaped openings which the waters had disappeared.
It will be seen from many of the foregoing instances that whatever are the principal causes of earthquakes, they must have played a great part in the shaping of events in the geological past; and the only limitation which we can place in the importance of the part they played will depend on whether we regard the earthquake as having been caused by a movement of the underlying strata, or whether we believe that the same cause which produces earthquakes may produce alterations in the lie of the strata themselves. In the next chapter we shall describe some of the effects produced on land by earthquakes. But impressive as some of these effects are, it is by no means certain that the greatest earthquakes take place on land at all. They may take place at sea, deep underneath the ocean. Our opportunities for observing such quakes, however, are much smaller than are afforded by land earthquakes. The instruments which have been devised for observing earth tremors will measure the smallest of such disturbances, and will record earthquakes the centres of which are thousands of miles away. These delicate instruments often record distant earthquakes, the exact locality of which is never determined. No doubt, some of these distant tremors originate in the ocean bed; but the seaquake can only be localised when the water is put into a state of vibration sufficiently energetic to rock the ship and its loose objects and thus affect the senses. Vast waves are sometimes rolled in on the shores of continents, and are undoubtedly caused by some great disturbance beneath the ocean.