Geoscience Reference
In-Depth Information
reefs, and its smell was brought by the wind from the sea. Although the weather was
good, there was a heavy swell on the sea all day.
63.
1923, November 4, 10 h 20 min.
Several strong earthquakes occurred on the northern coast of New Britain.
...The water surface was in a very agitated state.
64.
1930, December 24, 7 h 30 min.
A strong earthquake shook Mal Island and the surrounding islands. Immediately
after the earthquake there were two tidal waves.
From the side of the south-eastern end of the island a loud sputtering was heard,
that was similar to the noise of escaping vapour; two large dense clouds of smoke
or vapour hung over the sea.
In the middle part of Lau Island all foliage was destroyed, as if the trees had ex-
perienced a strong drought, and they became covered with a thin coating of yellow-
white sandy loam.
A similar picture, but even to a larger extent, was observed on Pihun island,
the inhabitants of which left the island and went to Amot Island. People said that
they could not return to their island owing to the terrible stink of dead fish.
65.
1959, August 18, 08 h 05 min.
A seismic sea wave was excited, most likely, somewhere in the region of the west
coast of Ranongga Island.
An eyewitness said that in the morning on the east coast of Velia Island there had
been a 'tidal whirl'. From Simbo Island it was also said that in the morning there
was a strong and chaotic agitation on the sea.
7.1.2 Analysis of Historical Testimonies and the Physical
Mechanisms of Vertical Exchange
The phenomena, described in Sect. 7.1.1, testify in favour of the possibility of signif-
icant enhancement of the vertical exchange in the ocean in the case of an underwater
earthquake. We shall present possible mechanisms (scenarios) leading to enhance-
ment of the vertical exchange in the water column in the case of seismic movements
of the bottom. In reality, the mechanisms may combine arbitrarily.
1st scenario. Direct generation of turbulence by a tsunami wave (when it passes
over shallow water, in case of wave breaking and run up on the shore). The mech-
anism is efficient only in the case of shallow water, since at large depths the ve-
locity of motion of water particles in the wave is small. It can be assumed that,
with the exception of cases of smooth inundation of the shore or of waves of
small amplitude, the mechanism considered is always manifested. The existence
of such a mechanism gives rise to no doubt that sea sand has been repeatedly
seen to be carried up onto the shore. Modern studies of paleotsunamis are based
on the analysis of intact ('conserved' among layers of soil, peat and volcanic
ash) sediments of sea sand brought up the coast by waves [Pinegina et al.(1997);
Pinegina, Bourgeois (2001)].
