Introduction - Tsunami - page 14

In Australia, 48 confirmed tsunami events have been
recorded, beginning with the 1868 Arica, Chilean event
(Bryant and Nott 2001 ; National Geophysical Data Center
2013 ). The closest sources for earthquake-generated tsu-
nami lie along the Tonga-New Hebrides trench, the Alpine
Fault on the west coast of the South Island of New Zealand,
and the Sunda Arc south of the Indonesian islands. The
Alpine Fault is an unproven source because it last fractured
around 1455, before European settlement. It has the
potential to produce an earthquake with a surface wave
magnitude, M s , of at least 8.0, with any resulting tsunami
reaching Sydney within 2 h. Additionally, the east coast lies
exposed to tsunami generated by earthquakes on seamounts
in the Tasman Sea. Active volcanoes lie in the Tonga-
Kermadec Trench region north of New Zealand. In 1452,
the eruption of Kuwae volcano in Vanuatu created a crater
18 km long, 6.5 km wide, and 0.8 km deep (Monzier et al.
1994 ). The eruption, which was 3-4 times bigger than
Krakatau, produced a tsunami wave 30 m high. Finally,
local slides off the Australian continental shelf also cannot
be ignored, especially along the coast centered on Sydney
(Jenkins and Keene 1992 ; Clarke et al. 2012 ).
The largest tsunami to be recorded on the Sydney tide
gauge was 1.07 m following the Arica, Chile, earthquake of
May 10, 1877. However, the Chilean Tsunami of May 22,
1960 produced a run-up of 4.5 m above sea level. In Sydney
and Newcastle harbors, this tsunami tore boats from their
moorings and took several days to dissipate. The northwest
coast is more vulnerable to tsunami because of the preva-
lence of large earthquakes along the Sunda Arc, south of
Indonesia. The largest run-up measured in Australia is 6 m,
recorded at Cape Leveque, Western Australia, on August 19,
1977 following an Indonesian earthquake. Waves of 1.5 and
2.5 m height were measured on tide gauges at Port Hedland
and Dampier respectively. Another tsunami on June 3, 1994
produced a run-up of 4 m at the same location. The Krakatau
eruption of 1883 generated a tsunami run-up in Geraldton,
1,500 km away that obtained a height of 2.5 m. This tsunami
moved boulders 2 m in diameter 100 m inland and more
than 4 m above sea level opposite gaps in the Ningaloo Reef
protecting the Northwest Cape (Nott 2004 ). South of the
Northwest Cape, tsunami heights decrease rapidly because
the coastline bends away to the east.

A wall of water swept 524 m above sea level on the
opposite shore, and a 30-50 m high tsunami propagated
down the bay, killing two people. Steep-sided fjords in both
Alaska and Norway are also subject to similar slides. In
Norway, seven tsunamigenic events have killed 210 people
(Miller 1960 ). The heights of these tsunami ranged between
5 and 15 m, with run-ups surging up to 70 m above sea
level.
Inland seas are also prone to tsunami. There have been
20 observations of tsunami in the Black Sea in historical
records (Ranguelov and Gospodinov 1995 ). In Bulgaria,
maximum probable run-up heights of 10 m are possible.
One of the earliest occurred in the 1st century BC at Kar-
varna. In AD 853, a tsunami at Varna swept 6.5 km inland
over flat coastal plain and travelled 30 km up a river. On
March 31, 1901, a 3 m high tsunami swept into the port of
Balchik. Bulgarian tsunami originate from earthquakes on
the Crimean Peninsula or from the eastern shore in Turkey.
Submarine landslides are also likely sources because the
Black Sea is over 2,000 m deep with steep slopes along its
eastern and southern sides. The Anatolian Fault Zone that
runs through northern Turkey and Greece has produced
many tsunami in the Black Sea and the Sea of Marmara to
the west. At least 90 tsunami have been recorded around the
coast of Turkey since 1300 BC (Kuran and Yalçiner 1993 ).
A tsunami flooded Istanbul on September 14, 1509, over-
topping seawalls up to 6 m high. At least 12 major tsunami
have occurred historically in the Sea of Marmara, mainly in
Izmit Bay. The most recent occurred on August 17, 1999
(Altinok et al. 1999 ). This tsunami appears to have been
caused by submarine subsidence during an earthquake.
Maximum run-up was 2.5 m along the northern coast of the
bay and 1.0-2.0 m along the southern shore. Ten tsunami
generated by earthquakes or landslides have been recorded
in the Caspian Sea (Zaitsev et al. 2004 ). Seven of these
occurred on the west coast and three on the east coast.
However, the risk is small, as run-ups for the 1:100 event do
not exceed 1 m.
Finally, tsunami can be generated even in small lakes.
The Krakatau eruption of August 27, 1883 sent out a sub-
stantial atmospheric shock wave that induced a 0.5 m high,
20-min oscillation in Lake Taupo situated in the middle of
the North Island of New Zealand (Choi et al. 2003 ). Burdur
Lake in Turkey has had numerous reports of tsunami
although the lake is only 15 km long (Kuran and Yalçiner
1993 ). On January 1, 1837 an earthquake-generated tsunami
swept its shores and killed many people. Tsunami have
washed up to 300 m inland around this lake. A rare case of
a tsunami-like wave appeared on April 1939 in Avacha Bay,
Kamchatka. The bay was frozen over at the time (Gusiakov
2008 ). A 3.5-4.0 m wave appeared on the frozen surface.
The supposed mechanism was an underwater slide or a
slump on the bottom of the bay.

1.5.5 Bays, Fjords, Inland Seas, and Lakes

Tsunami are not restricted to the open ocean. They can
occur in bays, fjords, inland seas, and lakes. The greatest
tsunami run-up yet identified occurred at Lituya Bay,
Alaska, on July 9, 1958 (Miller 1960 ). The steep slope on
one side of the bay failed following an earthquake, sending
0.3 km 3 of material cascading into a narrow arm of the bay.