Geoscience Reference
In-Depth Information
the resonance condition, will change from
H
to
H
. As a result, the resonance
condition will be violated, and growth of the amplitude will stop. Further enhance-
ment of the amplitude is possible in certain cases, when the resonance conditions are
continuously corrected by variation of the velocity
V
or by realization of a certain
particular profile of depths along the route.
±
ξ
4.4 Cosmogenic Tsunamis
Recently, particular interest has been shown in the possibility of catastrophic
tsunami waves arising due to bodies falling into the ocean from outer space.
Such waves are conventionally termed cosmogenic tsunamis in modern scien-
tific literature. Geological structures, reminiscent in shape of craters and found
on all continents, have been understood to be traces of collisions of meteor bod-
ies with the Earth only during the past 30-40 years. Such ring structures called
astroblemes—star scars, contain rock that was produced under huge pressures (up
to a million atmospheric pressures) and exhibit signs of shock wave transformations
of the mineral components and are often related to diamond deposits. At present,
on Earth already 150 such objects have been found with characteristic dimensions
from 1.2 km (Arizona crater, USA) up to 100 km (Popigai astroblem, East Siberia,
Russia). The World Ocean occupies approximately two thirds of the surface of our
planet, therefore a great part of meteorites falls precisely into the ocean, the bot-
tom of which guards the traces of many such collisions, that in the past caused
catastrophes of a planetary scale [Kharif, Pelinovsky (2005)].
Since in this section we are entering into a field far from oceanology, we shall
define some concepts.
Meteorites
are the remains of
meteor bodies
that survived
transition through the atmosphere and that have fallen to the Earth's surface from
outer space. According to their composition, meteorites are divided into three main
classes: stony (93.3%), stony-iron (1.3%) and iron (5.4%). When a meteor body
enters the atmosphere, air resistance causes the body to heat up strongly and to
shine brightly (the
bolide
phenomenon). According to modern ideas, meteorites are
fragments of parent bodies—asteroids.
Asteroids
are considered small planets of
diameters approximately between 1 and 1,000 km.
The task of describing cosmogenic tsunamis can be divided into three stages.
First, it is necessary to determine the characteristics (dimensions, density and veloc-
ity) of meteorites, that can fall into the ocean, and to estimate the probability of such
an event. Second, the essentially non-linear process of interaction of a meteorite
with the water column must be described, and the relationship between parameters
of the initial perturbation of the water column and characteristics of the celestial
body must be revealed. At the third stage an analysis must be performed of the pe-
culiarities of cosmogenic tsunami propagation in open ocean and of waves running
up shores. All three stages are connected with numerous uncertainties that arise pri-
marily because no cosmogenic tsunami has been recorded yet.
