Tsunamis - Extreme Events: A Physical Reconstruction and Risk Assessment - page 112

to initially recede from the shore followed minutes later by the first wave crest.
Wavestravelling west first impacted the coast of Sri Lanka, India and the Maldives
as a crest followed by the trough. There were at least six waves of substantial
size that impacted the coasts. In the state of Tamil Nadu in southeast India the
largest waves were between 4 and 6 m high as they crossed the shore. Similar
wave heights were experienced in Sri Lanka and parts of Thailand. Many who
died were from Europe and elsewhere around the globe as they were holidaying
in popular coastal tourist destinations through the south Asia region for their
Christmas holidays. The total death toll exceeded 200 000 throughout the region
including tens of thousands dying in Thailand, Sri Lanka and India.
Other famous teletsunamis have occurred, following greater than magni-
tude 9 earthquakes, in Chile in May 1960 and in Alaska in March 1964. The
1960 Chile tsunami radiated across the Pacific Ocean causing devastation in
Hawaii approximately 15 hours, and in Japan 22 hours, after the earthquake.
The March 1964 Alaskan earthquake measured 9.4 on the Richter scale and sent
large tsunamis into the Pacific Ocean that impacted the west coast of Alaska,
Canada, United States, South America, Hawaii and Japan (Dudley and Lee, 1998).
Submarine landslides also generate devastating tsunamis. Often these tsu-
namis are more localised with the largest waves focused onto a section of coast.
These tsunamis have also been known to be very large. The Aitape tsunami
in 1998 focused its largest waves onto a section of coast approximately 10 km
in length. At Sissano Lagoon, only three waves impacted the shore. The first
and second of these waves were between 10 and 15 m in height at the shore
(Fig. 5.2). The waves were still at least 5 m high 400 m inland after they had
traversed the beach, penetrated a stand of Coconut and Casuarina trees along
the seaward side of the barrier, and then crossed a grassy field (Kawata et al .
1999). Landslide-generated tsunamis have not been known to spread out across
ocean basins like some earthquake tsunamis.
While they are typically more localised, some of the largest tsunamis ever
known in historical times were generated by both submarine and subaerial land-
slides. The largest known tsunami occurred in Lituya Bay, Alaska in July 1958
following an earthquake that caused an avalanche to plunge into the waters of
the fiord. A wave 30--50 m high roared down the bay towards the open ocean
outpacing several boats attempting to flee, and also propelling one boat with
people on board over trees standing at least 30 m high. The wave also ran up
the opposite side of the bay to a height of 524 m stripping all of the vegeta-
tion from the slope to this elevation. Other localised landslide tsunamis have
occurred numerous times. The 1994 Skagway, Alaska tsunami was generated
when a railroad dock, heavily laden with soil and rock, and pile driving equip-
ment, collapsed when the sediment supporting the dock slid into deep water.