Geoscience Reference
In-Depth Information
4.1 Tsunami Generation by Landslides
After tsunamis of seismotectonic origin, most often encountered are so-called
land-
slide tsunamis
. This term stands for gravitational surface waves caused by under-
water landslides and mud flows, fragments of steep coasts, rock and icebergs, and
sometimes, even buildings in harbours, collapsing into the water. At present, only in
the Pacific region over 80 tsunamis are known to have been caused by the mecha-
nisms indicated. As a rule, landslide tsunamis are considered local events. But stud-
ies, performed in recent years, reveal that landslides can give essential additional
contributions to tsunamis generated by strong earthquakes [Gusiakov (2001)].
As compared to the horizontal dimensions of seismic sources (10
4
-10
5
m),
coastal and underwater landslides usually exhibit smaller scales (10
2
-10
3
m).
The largest known in geological history Storegga landslide took place in the late
quaterny period in the region of the steep continental slope off the coast of Norway
[Jansen et al. (1987); Harbitz (1992)]. Its horizontal extension is estimated to have
amounted to tens of kilometers.
In spite of their local character, the destructive force of landslide tsunamis is
no less than that of waves of seismotectonic origin. Such tsunamis are particularly
dangerous in narrow straits, fjords and closed gulfs and bays [Murty (1977); Jiang,
LeBlond (1992)]. Among the best known events one must mention the catastrophic
tsunamis in Lituya Bay (Lituya Bay, South-East Alaska, 1958) and in Vaiont Valley
(Vaiont Valley, Northern Italy, 1963). The tsunami in Lituya Bay was caused by
the fall of rock matter at the bay apex into the water, which led to the formation of
a huge wave, the run-up height of which amounted to 524 m [Miller (1960); Murty
(1977); Lander (1996)]. The catastrophe in Vaiont Valley resulted in the destruction
of an entire city, and about 2,000 people died [Wiegel et al. (1970); Murty (1977)].
Landslide tsunamis are characterized by a high repetition rate at certain parts of
the coast. For example, in situ studies at Lituya Bay, carried out after the catas-
trophic event of 1958, revealed that gigantic waves, caused by landslides, had also
occurred there previously—in 1853-1854 (120 m), in 1874 (24 m), in 1899 (60 m)
and in 1936 (150 m) [Miller (1960)]. Even the Laperouse expedition suffered from
a tsunami in this bay—a two-mast schooner of the squadron with a crew of 21 men
was shattered by an 'unusual wave' against the cliffs of the island in 1787.
It is interesting that landslide tsunamis can occur not only in oceans and seas,
but also in large rivers. The description of one such event, which took place in river
Volga in 1597, is presented in [Didenkulova et al. (2007)]. We have succeeded in
finding reference to another river tsunami, which took place in river Irtysh in 1885.
Here, we quote the topic of travel notes by K. M. Stanyukovich, the well-known
Russian writer on the Sea, 'To far lands' (Collection of works in 10 volumes, Vol. 1 -
Moscow: Pravda, 1977):
The right sandy bank of the Irtysh, being constantly washed out, once in while
caves in, and, then, as the Siberians say, the 'landslides', that fall from the height into
the water with a crash and noise, happen to cause accidents and misfortunes. Such
a misfortune occurred just three weeks before we passed there. About two hundred
