Geoscience Reference
In-Depth Information
versts
1
from the estuary of Irtysh we saw a schooner lying helplessly on its side in
the sands. It had been passing one verst from the right bank, precisely when the bank
caved in. Such a mass of earth falling together with century-old trees caused the wa-
ter to shrink back from the bank, thus giving rise to agitation so strong that it cap-
sized the flat-bottomed schooner, which most likely had no appropriate ballast, and
threw it toward the left bank. The barge, towed by the schooner, withstood the wave
and remained unharmed. Of the crew and passengers of the schooner several peo-
ples died in the river, several were crippled. A day after the catastrophe, cries for
help were heard on the 'Reytern', that was passing by. The steamboat stopped and
took the people, asking help, on board
.
Studies of landslide tsunamis have a long history; however, until recently publi-
cations devoted to investigation of this phenomenon were quite rare. One of the first
attempts at detailed investigation of tsunami waves, caused by underwater land-
slides, was made by N. L. Leonidova [Leonidova (1972)]. This investigation was
based on earlier works of B. Gutenberg [Gutenberg (1939)] and R. Mitchell [Mitchel
(1954)], however, precisely this work laid the foundation for modern ideas concern-
ing the problem of landslide tsunamis. One must also mention the experimental
study, well known to specialists, carried out by R. Wigel [Wiegel (1955)], which
was devoted to investigating wave generation in a channel, when hard bodies of
different shape were made to slide along the channel bottom.
The recent enhancement of interest in studies of landslide tsunamis was initiated
by the catastrophic events in Papua New Guinea and Indonesia. The wave that de-
molished the coast of Papua New Guinea on July 17, 1998 was 15 m high. It was
due to a relatively moderate earthquake of
M
w
= 7
.
1, accompanied by a local under-
water landslide [Tappin et al. (1998); Heinrich et al. (2000); Imamura et al. (2001)].
The earthquake that took place on December 12, 1992, with magnitude
M
w
= 7
.
7on
island Flores (Indonesia) also gave rise to an underwater landslide and subsequent
tsunamis of heights up to 26 m.
The landslide process is usually the result of a prolonged accumulation of
sedimentary material during tens and hundreds of years. With time the sedimen-
tary masses on slopes lose stability. Numerous factors can provocate a landslide
[Ren et al. (1996); Kulikov et al. (1998)]:
•
Sudden surge of river silt during a freshet
•
Erosion of sedimentary layer on a steep underwater slope
•
Coastal construction projects
•
Prolonged rain, resulting in saturation of coastal land
•
Uncovering of coast during pronounced low tide
Recently, the role of gas hydrates in provocating underwater landslides is also dis-
cussed [Parlaktuna (2003)]. Earthquakes, naturally, serve as most important causes
of landslides and collapses. Volcanic eruptions, also, happen not to play the last part
in initiating landslide processes and collapses.
Sedimentary masses, deposited on underwater slopes during many decades, accu-
mulate huge potential energy. As they lose stability, they are capable of moving over
1
1 verst = 1.067 km.
