In My Opinion, We Have Scarcely Beheld,
Since Leaving England, Any Sight So Deeply Interesting.
In almost every severe earthquake, the neighbouring waters
of the sea are said to have been greatly agitated.
The
disturbance seems generally, as in the case of Concepcion, to
have been of two kinds: first, at the instant of the shock,
the water swells high up on the beach with a gentle motion,
and then as quietly retreats; secondly, 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:
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