Introduction - Tsunami - page 15

1.6 Meteorological Phenomena, Freak

Waves and Storm Surges

anomalous tides up to 0.4 m from Portugal to the Straits of
Dover (Tappin et al. 2013 ). By far the most dramatic event
occurred during a storm on November 23, 1829 in the
English Channel. One or more large waves with tsunami
characteristics overwashed Chesil Beach flooding the large
backing lagoon to a depth of 9 m and racing inland to a
height of 13 m above sea-level. Meteo-tsunami events in
the UK relate to the passage of squall lines over the sea; far-
travelled, long-period waves generated by mid-North
Atlantic, atmospheric, low-pressure systems; or with storms
that may have induced large-amplitude standing waves.
They have resulted in damage and loss of life.
Meteorological tsunami can consist of single or multiple
waves. For example, a meteorological tsunami was probably
the cause of the single wave that swept Daytona Beach,
Florida, late at night on 3 July 1992 (Churchill et al. 1995 ).
The wave swamped hundreds of parked cars and injured 75
people. More recently, a series of large waves came ashore in
Boothbay Harbor, Maine around 3 PM on October 28, 2008
(Woolhouse 2008 ). Reports state that a giant wave rushed
into the harbor and water levels rose 3.66 m within 15 min.
The sea then receded, but a further two waves occurred, each
time damaging docks and pilings. However, isolated occur-
rences and single waves are rare. Meteorological tsunami
often affect a particular inlet or bay along a coast because
they are also the product of resonance due to the geometry
and topography of a specific section of coastline (Wiegel
1964 ). Resonance explains why meteorological tsunami
recur at specific locations, have constant periodicities, occur
as a wave train, and have high localized amplitudes. Harbors
and bays are particularly vulnerable to resonant excitation of
waves even where no wave is noticeable along the adjacent
open coast. Friction and non-linear processes weaken the
formation or propagation of meteorological tsunami so that
they disappear in narrow or shallow inlets.
One of the most unusual phenomena to explain is the
occurrence of freak waves arriving at a coastline on fine days
(Wiegel 1964 ). These waves are probably solitary waves that
have a peak rising above mean water level, but no associated
trough (von Baeyer 1999 ). Solitary waves may only have a
height of several centimeters in deep water, but when they
enter shallow water, their height can increase dramatically.
For example, very fast boats such as catamaran ferries can
produce a wake that behaves as a solitary wave (Hamer
1999 ). In shallow water, the wakes have reached heights of
5 m, overturning fishing boats, and swamping beaches under
placid seas. Isolated freak waves can also be caused by the
occurrence of a small, localized, submarine landslide—in
some cases without an attendant earthquake. Such freak
waves are usually treated as a novelty and consequently have
not received much attention in the scientific literature. Unlike
meteorological tsunami that occur repetitively at some spots,

Meteorological or meteo-tsunami have the same periods,
spatial scales, physical properties and destructive impact as
seismically generated tsunami (Rabinovich and Monserrat
1996 ; Monserrat, et al. 2006 ) Meteorological tsunami are
associated with the passage of typhoons, fronts, atmospheric
pressure jumps, or atmospheric gravity waves; however, not
all of the latter produce meteorological tsunami even at
favorable locations. Other forcing mechanisms may be
involved. For example, tidally generated internal waves
play an essential role in the formation of seiches in the
Philippines and Puerto Rico, while wind waves can generate
seiching in many harbors. Meteorological tsunami occur
when the atmospheric phenomenon generating any surface
wave moves at the same speed as the wave. Hence storm
surges can be classified as meteorological tsunami if the
forward speed of the storm matches that of the surge
(Bryant 2005 ). For example, during the Long Island Hur-
ricane of 1938, people described the storm surge as a 13 m
high wall of water approaching the coast at breakneck
speed. This description is similar to some that have been
made for 10-15 m high tsunami approaching coastlines.
Meteorological tsunami take on various local names:
rissaga in the Balearic Islands in the eastern Mediterranean,
abiki or yota in bays in Japan, marubbio along the coast of
Sicily, stigazzi in the Gulf of Fiume, and Seebär in the
Baltic Sea (Monserrat et al. 2006 ). They also occur in the
Adriatic Sea, the South Kuril Islands, Korea, China, the
Great Lakes of North America, and numerous other lakes
that can come under the influence of atmospheric activity.
Meteorological tsunami can be significant recurrent phe-
nomena. For example, the south end of Lake Michigan near
Chicago has experienced many atmospheric events, with
one of the largest generating a 3 m wave in 1954 (Wiegel
1964 ). In Nagasaki Bay, Japan, eighteen abiki events have
occurred between 1961 and 1979 (Monserrat et al. 2006 ).
The event of March 31, 1979 produced 35-min oscillations
having amplitudes of 2.8-4.8 m. It was triggered by a
pressure change in the East China Sea of only 3 mb. In
Longkou Harbor China, thirteen seiches have occurred
between 1957 and 1980 with a maximum amplitude of
2.9 m (Monserrat et al. 2006 ). In the Mediterranean Sea,
meteorological tsunami with heights up to 3 m have been
recorded at numerous locations (Rabinovich and Monserrat
1996 ). Meteorological tsunamis, or meteo-tsunamis, have
occurred on the coast of southern Britain, in the English and
Bristol Channels, and in the Severn Estuary (Haslett and
Bryant 2009 ; Haslett et al. 2009 ). Events on clear days are
known as ghost storms. The most recent event occurred on
June 27, 2011 near Plymouth synchronously with