Volcanic Eruptions - Tsunami - page 161

Chap. 3 by their greater thickness, lack of laminations, and
undifferentiated particle size. Homogenites differ from
debris flows by the absence of large clasts or rock pieces
derived from continental sediments.
Four types of homogenites can be differentiated (Cita
et al. 1996 ). In the western Mediterranean, on the Ionian
Abyssal Plain, a 10 to 20 m thick deposit, with an estimated
volume of 11 km 3 , was laid down on the seabed over an
area of 1,100 km 2 . It appears that the tsunami wave slam-
med into the continental shelf of north Africa and either
directly or indirectly triggered a mega-turbidity current.
This current carried terrigenous and shelf sediment into the
deep Mediterranean Sea, eroding flanks of undersea ridges
and depositing homogenites with an erosional base on
upslopes. In one location, this turbidity current rode up a
ridge 223 m above the abyssal plain and deposited sedi-
ment. In the eastern part of the Mediterranean, bottom
velocities and the related powerful pressure pulse liquefied
sand into depressions, forming uniform deposits several
meters thick with a sandy base overlying an erosional
contact. These deposits form in cobblestone-shaped basins
with a vertical relief of 200 m. Finally, in the Bannock
Basin, the passage of the wave destabilized evaporites. The
resulting deposits are 12 m thick and consist of 3 m of sand
overlain by 9 m of graded mud deposited from suspension
in high-density brines trapped at the bottom of 100 m deep
depressions in the seabed. All of the homogenites found in
the Mediterranean are derived from a single event and date
around the time of the Santorini eruption. Homogenites are
not found in the eastern Mediterranean Sea, where tsunami
wave heights were insufficient to cause resuspension or
liquefaction of bottom sediment.
Since the Santorini eruption around 1470 BC, there have
been many others (Pichler and Friedrich 1980 ; Druitt et al.
1999 ). Since 197 BC at least 9 eruptions have formed the
two islands that presently exist in the center of the caldera.
Eruptions in 1650, 1866, and 1956 have given rise to tsu-
nami with damaging consequences. An earthquake pre-
ceded the 1650 eruption and generated a 50 m high tsunami
that swept 4 km inland in places. The 1866 event generated
two tsunami that had run-up heights of 8 m along nearby
coasts. Earthquakes associated with the latest eruption on 9
July 1956 produced a tsunami that had a run-up height of
24 m and killed 53 people. The Santorini volcano remains
one of the most dangerous in terms of tsunami in the world
today.
The last three chapters have summarized how geophys-
ical processes originating from the Earth generate tsunami.
When reviewed, the magnitudes of tsunami associated with
these processes are indeed impressive. Tsunami have dis-
persed across the Pacific after numerous historical earth-
quakes. Five events since 1600 have produced run-up
heights of 51-115 m in elevation. The Indian Ocean event

of 2004 and the Lisbon event of 1755 indicate that cata-
strophic tsunami can occur in any ocean. Volcanic erup-
tions, while rarer in terms of tsunami, have generated
similar magnitude run-ups, but these have been localized.
The Santorini eruption of around 1470 BC may hold the
record for the biggest volcano-induced tsunami with an
initial wave height of 90 m. Tsunami generated by sub-
marine landslides may be bigger yet. The Lituya Bay
landslide of July 9, 1958 generated a wave that achieved a
run-up height of 524 m above sea level. Whether or not this
wave consisted of a mixture of water and air is a moot point.
In terms of area affected, the Storegga slide of
7950 ± 190 years ago may have been the biggest—con-
sidering that some suspicion hangs over some of the evi-
dence attributed to the Lanai slide in Hawaii. Many of the
tsunami induced by these processes produced some of the
signatures of tsunami outlined in Chaps. 3 and 4 . However,
only the Storegga event can be linked to the full range of
signatures that includes bedrock-sculpturing features. A
dichotomy thus exists in that observable tsunami have not
commonly been linked to bedrock-sculpturing features that
exist so widely along rocky coasts, especially those in
Australia. One mechanism, comet/asteroid impact with the
ocean, is capable of generating tsunami equivalent to or
bigger than the largest tsunami produced by other mecha-
nisms. The nature of cosmogenically induced tsunami will
be discussed in the next chapter.

References

R.J. Blong, Volcanic hazards: a sourcebook on the effects of eruptions
(Academic Press, Sydney, 1984)
H.J. Bruins, J.A. MacGillivray, C.E. Synolakis, C. Benjamini, J.
Keller, H.J. Kisch, A. Klügel, J. van der Plicht, Geoarchaeological
tsunami deposits at Palaikastro (Crete) and the late Minoan IA
eruption of Santorini. J. Archaeol. Sci. 35, 191-212 (2008)
E. Bryant, Natural Hazards, 2nd edn. (Cambridge University Press,
Cambridge, 2005)
E. Bryant, J. Nott, Geological indicators of large tsunami in Australia.
Nat. Hazards 24, 231-249 (2001)
B.H. Choi, E. Pelinovsky, K.O. Kim, J.S. Lee, Simulation of the trans-
oceanic tsunami propagation due to the 1883 Krakatau volcanic
eruption. Nat. Hazards Earth Syst. Sci. 3, 321-332 (2003)
B.H. Choi, S.J. Hong, E. Pelinovsky, Distribution of runup heights of
the December 26, 2004 tsunami in the Indian Ocean. Geophys.
Res. Lett. 33, L13601 (2006). doi: 10.1029/2006GL025867
M.B. Cita, A. Camerlenghi, B. Rimoldi, Deep-sea tsunami deposits in
the eastern Mediterranean: new evidence and depositional models.
Sed. Geol. 104, 155-173 (1996)
T.H. Druitt, L. Edwards, R.M. Mellors, D.M. Pyle, R.S.J. Sparks, M.
Lanphere, M. Davies, B. Barreiro, Santorini volcano. Geol. Soc.
London Mem. 19, 165 (1999)
Intergovernmental Oceanographic Commission (1999), Historical
tsunami database for the Pacific, 47 BC-1998 AD. Tsunami
Laboratory, Institute of Computational Mathematics and Mathe-
matical

Geophysics, Siberian Division Russian Academy of

Sciences, Novosibirsk, Russia, http://tsun.sscc.ru/HTDBPac1/