some time afterwards, the whole body of the sea retires from the coast,
and then returns in waves of overwhelming force. The first movement
seems to be an immediate consequence of the earthquake affecting
differently a fluid and a solid, so that their respective levels are
slightly deranged: but the second case is a far more important
phenomenon. During most earthquakes, and especially during those on
the west coast of America, it is certain that the first great movement
of the waters has been a retirement. Some authors have attempted to
explain this, by supposing that the water retains its level, whilst the
land oscillates upwards; but surely the water close to the land, even
on a rather steep coast, would partake of the motion of the bottom:
moreover, as urged by Mr. Lyell, similar movements of the sea have
occurred at islands far distant from the chief line of disturbance, as
was the case with Juan Fernandez during this earthquake, and with
Madeira during the famous Lisbon shock. I suspect (but the subject is
a very obscure one) that a wave, however produced, first draws the
water from the shore, on which it is advancing to break: 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
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