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10 ROY H. GABRIELSEN
that poses a threat to human life;
disasters
that characterise the (severe) effect of a
natural hazard event to society, usually during a limited time span and within a
restricted geographical area, whereas
catastrophes
are massive disasters (Keller &
Blodgett 2006). In other words, there would be no natural disasters if it were not for
humans; without humans these would be only natural events (Nelson 2014).
Risk Analysis
Risk can be seen as an expression for the relationship between humans and
geologically induced processes (Nelson 2014). Natural hazards can be monitored,
mapped, and sometimes predicted based upon good understanding of natural
processes of the Earth supplied with historical data from past events and patterns of
events. Such information must be quantified in space, time and with respect to the
level of energy involved in the processes. Natural hazards are accordingly amenable
to analysis by the use of common methods of risk assessment. The risk analysis of
natural hazards describes the likelihood of the occurrence of disastrous effects of
natural processes that affect humans, and what the consequences would be.
Natural hazards are phenomena that occur regularly only in restricted time
frames and space. The natural risk hazard was significantly different in earlier
periods in the brief history of humanity as compared to what they are today, and even
more so when geological time spans of millions of years are taken into account.
Disastrous geological events tend to cluster in time due to changing natural (and also
anthropogenic-related) fluctuations.
For example in Norway and on its continental shelf rock-falls and submarine
slides were much more frequent in the first millennia in the aftermath of the last ice
age compared to that of the Present (e.g. Ramberg et al. 2008).
Volcanic activity is also commonly cyclic. Vesuvius, the biggest and most
dangerous volcano in Europe, experienced periods of particularly high activity in the
periods 79-203 (the effects of the major event from 79 AD well documented from
Pompeii) and 1661-1794, so that concern for future activity is heavily debated among
volcanologists. An eruption of the magnitude well known from repeated events in
the near past would of course be disastrous today, taken into account the pattern of
habitation in Campania which includes a number of villages, but where a major
eruption is also likely severely to affect the major city in the vicinity of Vesuvius,
namely Naples (e.g. Scarth 2009).
An illustrative example of the effects of densified habitation are the effects of
two separate eruptive events (mud flows) associated with eruptions of the volcano
Nevado del Cruise, Columbia in 1845 and 1985, that caused 1,000 and 21,000
casualties respectively, although the first event was the more severe of the two. The
disparity was due to the growth in population and settlement structures over a time
span of 140 years (Keller & Blodgett 2006).
Some natural scientists even claim that earthquake “storms” have not only
influenced, but literally controlled historical events like the termination of some of
the ancient Mediterranean cultures approximately 1200 years BC (Nur 2007). The