Geoscience Reference
In-Depth Information
The danger carried by tsunami waves is primarily related to the following three
factors: the sudden inundation of part of the land, the impact of waves upon build-
ings and erosion. Strong flows of water, reaching velocities of tens of meters per
second, are capable of breaking up houses and of displacing them, washing out
substructures of buildings, destroying bridges and buildings in ports. The flows
of water often carry pieces broken off buildings and other structures, trees, small
and large vessels, which leaves people, picked up by the fast-moving water, no
chance of survival. The damage caused by tsunamis may, also, be due to fires, pol-
lution of the environment and epidemics resulting from devastation of the coastal
infrastructure.
Depending on the scale of the area, in which the destructive force of tsunamis
is manifested, one conventionally distinguishes local, regional and remote (telet-
sunami) events. The latter are sometimes termed transoceanic tsunamis. Local
tsunamis include events, the destructive effect of which is concentrated within dis-
tances not exceeding 100 km from the source. If destruction occurs at distances up to
1,000 km from the source, then such an event is classified as regional; when above
1,000 km, as a teletsunami. Most catastrophic events pertain precisely to local or
regional tsunamis. At least 18 such events were recorded in the Pacific during the pe-
riod between 1975 and 1998. The occurrence of transoceanic tsunamis is much less
frequent, but they are, naturally, much more dangerous. After having caused signif-
icant destruction in the immediate vicinity of the source, these waves are capable of
travelling many thousands of kilometers from the source and to continue carrying
with them death and devastation. In the past 200 years at least 17 such events took
place in the Pacific Ocean.
1.2 Manifestations of Tsunami Waves on Coasts
There exist numerous descriptions of the effect of tsunamis on a coast that are due to
eyewitnesses or scientists investigating the consequences of these events. Detailed
information on tsunami manifestations can be found in tsunami catalogues and his-
torical databases, e.g. [Soloviev et al. (1974), (1975), (1997)], http://tsun.sscc.ru/,
http://www.ngdc.noaa.gov/.
We shall present brief descriptions of some of the outstanding events.
The 1868 tsunami near the city of Arica (Chile) was caused by an underwater
earthquake of magnitude
M
= 8
.
8. In the evening, after it became dark, an enormous
'wall' of phosphorescent foamy water mixed up with sand arrived from the ocean
with a thunderous noise. The height of the waves amounted to 15-18 m. Upon hit-
ting the coast with an enormous force, the wave then carried the large US warship
'Wateree' from the harbour 2 miles inland and gently put it down at the rocky foot
of the Andes. This event permitted Gabriel Garcia Marquez to depict the fantastic
scene of an encounter with a three-mast sailboat amongst trees in the remote jungles
(selva) of South America.
