Geoscience Reference
In-Depth Information
Epilogue
CHAPTER 14
CHANGING HAZARD
REGIMES
(Houghton et al., 1995, 1996; Bryant, 2001; Nott, 2003)
Throughout this topic the commonness of natural
hazards has been continually emphasized. For example,
the eruption of Krakatau in 1883 was not an unusual
event. It was matched by earlier eruptions of similar
magnitude and will be witnessed again. This argument
smacks of uniformitarianism, but it is not meant to
support this concept. Rather, it acknowledges that our
existing realms of natural hazards fit a magnitude-
frequency distribution that can be described, and from
which the probability of occurrence of future extremes
can be predicted. This is not necessarily how natural
hazards behave over time. Existing hazard regimes are
not immutable. They can change. My present research
into mega-tsunami illustrates this point. In the historic
record, tsunami in Australia have not exceeded 1.07 m
on tide gauges, did not have run-ups of 4 m above sea
level nor penetrate more than 1 km inland. Over the
past fifteen years, evidence has been found along
Australia's New South Wales coastline for large
tsunami that have gone inland up to 10 km, transported
boulders the size of boxcars up 30 m high cliffs (Figure
14.1) and swept over headlands 130 m high. Nor is the
evidence restricted to the New South Wales coastline.
In north-western Australia, one event penetrated 35 km
inland in the Great Sandy Desert. These mega-tsunami
Fig. 14.1
Imbricated boulders stacked against a 30 m high cliff face
on the south side of Gumgetters Inlet, New South Wales,
Australia. Some of these boulders are the size of a boxcar.
Note the person circled for scale.
have occurred at periodic intervals over the last
8000 years. They were generated by comet or meteorite
impacts with the surrounding oceans - because no
known earthquake or volcanic eruption has produced
similar magnitude evidence. Astronomers believe that a
large comet entered the inner solar system about
15 000 years ago. It broke up, and the Earth periodically
sweeps through its debris trail in late June or mid-
November each year. This is the Taurids meteorite
