I Have Observed That This Happens With The Little
Waves From The Paddles Of A Steam-Boat.
It is remarkable
that whilst Talcahuano and Callao (near Lima), both situated
at the head of large shallow bays, have suffered during
every severe earthquake from great waves, Valparaiso,
seated close to the edge of profoundly deep water, has never
been overwhelmed, though so often shaken by the severest
shocks.
From the great wave not immediately following the
earthquake, but sometimes after the interval of even half an
hour, and from distant islands being affected similarly with
the coasts near the focus of the disturbance, it appears that
the wave first rises in the offing; and as this is of general
occurrence, the cause must be general: I suspect we must
look to the line, where the less disturbed waters of the deep
ocean join the water nearer the coast, which has partaken
of the movements of the land, as the place where the great
wave is first generated; it would also appear that the wave
is larger or smaller, according to the extent of shoal water
which has been agitated together with the bottom on which it
rested.
The most remarkable effect of this earthquake was the permanent
elevation of the land, it would probably be far more
correct to speak of it as the cause. There can be no doubt
that the land round the Bay of Concepcion was upraised
two or three feet; but it deserves notice, that owing to the
wave having obliterated the old lines of tidal action on the
sloping sandy shores, I could discover no evidence of this
fact, except in the united testimony of the inhabitants, that
one little rocky shoal, now exposed, was formerly covered
with water.
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