The sun. [volume] (New York [N.Y.]) 1833-1916, 1906-03-22

Mr.. William r. Bruce told a graphic story
of the sea wave that came ashore in January
last on the Pacific coast of Colombia. Sew
eral hundred persons in the little town OF
Tumaco were drowned in the overwhelming
flood, and the horror Of the earthquake
that had just destroyed many homes was
thus intensified.
The story of such waves following an
earthquake is old, and 80 is the mistake
that many writer's perpetrate by describing
them as tidal waves Tidal influences nave
nothing to do with their formation. They
are caused by the earthquakes themselves
and are the natural result Of earthquake
shocks originating under certain conditions
This earthquake originated under the
ocean instead Of beneath the land surface.
Its e%picentrum (or, in other words, the place
beneath which the snbterranean disturb
anoe that caused the earthquake was still
ated) lay on the sea floor. The earth wave
set in motion by the subterranean shock
spread along the sea bottom till they reached
the shore and overthrow or shattered build
ings far along the coast of Colombia; and
the two waves we're caused by the disturb
ance of the sea floor in the epicentral tract.
1t is likely that a vessel passing over the
epicentrum would scarcely have noticed
the disturbance, but the whole mass OF
superintendent water was lifted into a
mound and the water then fell as far below
its natural level as it had been raised above
1t. The sea wave thus formed, according
to Mr.. Bruce's description, piled up to a
height Of about thirty feet as it reached the
shallow water of shore, nj fell upon the
low lying land, its onrush and prodigious
Weight crushing or ~overturning everything
in its path.
The epicentrum was not very far OIL the
coast, for Mr.. Bruce says that while the
second and greater shock was still in prog
ress he saw the high wave coming; and the
first slighter shock had been followed i'm
mediately by a smaller wave, that simply
ran up into the streets for a short distance,
doing little damage. The disturbance be-
meath the earth's crust probably originated
not more than fifteen or twenty miles out
at sea.
Many South American earthquakes along
the Pacific coast originate under the sea
floor, and are invariably followed by these
waves Of greater or lees destructive power.
The great earth waves that desolated the
coast Of Peru in 1858 were followed by water
waves WnlCn uaSneu upon tne buoro az
heights Of fifty to sixty feet, adding enor-
mously to the damage done. Many other
earthquake sea waves had been observed
and recorded along this coast line, perhaps
most conspicuously in the Iquique earth
quake of 1877. The calamity that de-
stroyed the city Of Lisbon in 1855 originated
under the sea floor, and the waves that
dashed against the coast, greatly increas-
ing the destruction, were from fifty to sixty
feet in height.
Just as little waves are formed when a
pebble is dropped into a pool and move in a
circle away from the centre, 30 these earth
quake sea waves move with great rapidity
in all directions from the region Of the shock.
Undoubtedly the big a observed by
Mr.. Bruce crossed the Pacific, and though
it was not perceptible out at sea, it may
have been observed on the coasts Of the
Hawaiian Islands and Japan. The water
waves from the Peru earthquake Of 1855
reached Honolulu, $3.50 miles, in twelve
hours, and Japan, 10 900 miles, On the next
day.
OF course, these waves are recorded by
tidal gauges, but they have no relation to
tidal waves, and an impression
is given to many readers who see this name
applied to them.