132
The Last Resource
high carried out a sudden onslaught on Honolulu, smashing
hundreds of buildings and tearing up roads and railway tracks.
173 people were killed and about £10,400,000 (some 25 million
dollars) of damage was done. The energy for these monster waves
had been generated by an earthquake in the Aleutian Trench and the
seismic sea waves, or tsunami as these waves are generally called,
had taken a mere 4 hours and 34 minutes to cover over 2,000 miles
of intervening ocean. The report on the tsunami published by F. P.
Shepard of the Scripps Institution of Oceanography was to lead to
more detailed investigations of this freakish phenomenon. Shepard
himself had been forced to take refuge in a tree while the tsunami
tore into his house.
Three kinds of geological event are now known to cause tsunamis :
‘
earthquakes where the sea bed suddenly slumps or rises; submarine
landslides; and nally submarine volcanic eruptions. And of these,
earthquakes appear to be the most important. It is no accident,
therefore, that tsunamis occur most frequently in the Pacic Ocean
since the Pacic is practically encircled by zones of earthquake
activity, many of them centred in submarine trenches which gash
the deep ocean oor. Tsunamis also occur in the Indian Ocean and
to a lesser extent in the Mediterranean. They are practically unknown
in the Atlantic Ocean although a large tsunami followed the great
Lisbon earthquake of 1755, adding further to the destruction.
The type of disturbance in the ocean oor which creates the
tsunami also dictates the nal form of the waves; if created by a
slumping of the oor, the tsunami starts with a trough whereas a
volcanic eruption creates a crest. At rst it consists of a few simple
waves, but as the tsunami progresses over the ocean its energy is
spread over a ‘train’ of long shallow waves with the highest waves
bringing up the rear. When it moves into shallower waters, the
reverse process occurs with energy being pushed into a successively
smaller volume of water. By the time it reaches the shoreline the
waves extend down to the sea bottom and they can raise themselVes
to a height of 120 feet or more. The fact that the onslaught may start
with a temporary retreat as a trough arrives and that successive
waves may well increase in height only adds further to the terror.
Some of the danger can be removed from the situation by ade—
quate warning of a tsunami’s approach. When seismic events likely
to generate such waves are detected, providing the centre of the
disturbance is known, the likely arrival of the resulting tsunami can
The Last Resource
high carried out a sudden onslaught on Honolulu, smashing
hundreds of buildings and tearing up roads and railway tracks.
173 people were killed and about £10,400,000 (some 25 million
dollars) of damage was done. The energy for these monster waves
had been generated by an earthquake in the Aleutian Trench and the
seismic sea waves, or tsunami as these waves are generally called,
had taken a mere 4 hours and 34 minutes to cover over 2,000 miles
of intervening ocean. The report on the tsunami published by F. P.
Shepard of the Scripps Institution of Oceanography was to lead to
more detailed investigations of this freakish phenomenon. Shepard
himself had been forced to take refuge in a tree while the tsunami
tore into his house.
Three kinds of geological event are now known to cause tsunamis :
‘
earthquakes where the sea bed suddenly slumps or rises; submarine
landslides; and nally submarine volcanic eruptions. And of these,
earthquakes appear to be the most important. It is no accident,
therefore, that tsunamis occur most frequently in the Pacic Ocean
since the Pacic is practically encircled by zones of earthquake
activity, many of them centred in submarine trenches which gash
the deep ocean oor. Tsunamis also occur in the Indian Ocean and
to a lesser extent in the Mediterranean. They are practically unknown
in the Atlantic Ocean although a large tsunami followed the great
Lisbon earthquake of 1755, adding further to the destruction.
The type of disturbance in the ocean oor which creates the
tsunami also dictates the nal form of the waves; if created by a
slumping of the oor, the tsunami starts with a trough whereas a
volcanic eruption creates a crest. At rst it consists of a few simple
waves, but as the tsunami progresses over the ocean its energy is
spread over a ‘train’ of long shallow waves with the highest waves
bringing up the rear. When it moves into shallower waters, the
reverse process occurs with energy being pushed into a successively
smaller volume of water. By the time it reaches the shoreline the
waves extend down to the sea bottom and they can raise themselVes
to a height of 120 feet or more. The fact that the onslaught may start
with a temporary retreat as a trough arrives and that successive
waves may well increase in height only adds further to the terror.
Some of the danger can be removed from the situation by ade—
quate warning of a tsunami’s approach. When seismic events likely
to generate such waves are detected, providing the centre of the
disturbance is known, the likely arrival of the resulting tsunami can