Thus, in the Charleston earthquake of 1883, the
surface over an area of many hundred square miles was pitted with
small craters, formed by the uprush of water impelled by its contained
gases. These little water volcanoes--for such we may call
them--sometimes occur to the number of a dozen or more on each acre of
ground in the violently shaken district. They indicate one result of
the physical and chemical alterations which earthquake shocks bring
about. As earthquakes increase in violence their effect upon the soil
becomes continually greater, until in the most violent shocks all the
loose materials on the surface of the earth may be so shaken about as
to destroy even the boundaries of fields. After the famous earthquake
of Riobamba, which occurred on the west coast of South America in
1797, the people of the district in which the town of that name was
situated were forced to redivide their land, the original boundaries
having disappeared. Fortunately, shocks of this description are
exceedingly rare. They occur in only a few parts of the world.

Certain effects of earthquakes where the shock emerges beneath the sea
have been stated in the account of volcanic eruptions (see page 299).
We may therefore note here only certain of the more general facts.
While passing through the deep seas, this wave may have a height of
not more than two or three feet and a width of some score miles. As it
rolls in upon the shore the front of the undulation is retarded by the
friction of the bottom in such a measure that its speed is diminished,
while the following part of the waves, being less checked, crowds up
toward this forward part. The result is, that the surge mounts ever
higher and higher as it draws near the shore, upon which it may roll
as a vast wave having the height of fifty feet or more and a width
quite unparalleled by any wave produced from wind action. Waves of
this description are most common in the Pacific Ocean. Although but
occasional, the damage which they may inflict is very great. As the
movement approaches the shore, vessels, however well anchored, are
dragged away to seaward by the great back lash of the wave, a
phenomenon which may be perceived even in the case of the ordinary
surf. Thus forced to seaward, the crews of the ships may find their
vessels drawn out for the distance of some miles, until they come near
the face of the advancing billow. This, as it approaches the shore,
straightens up to the wall-fronte