Geography Reference
In-Depth Information
are water-saturated, as they often are near shorelines because of high water tables,
the bonds between the composite grains break, leading the sediments to liquefy and
lose strength, ensuring that buildings become unsupported, topple and sink. Another
example of increased risk comes from the use of different
construction materials
which increase the scale of devastation from some natural hazards. Zebrowski's
(
1997
) penetrating review of the disasters produced by natural events provided a
salutary example of this point in his comparison of the differences in death tolls be-
tween the 1906 San Francisco earthquake, which recorded 8.3 on the Richter scale,
with that of Messina in Southern Italy in 1908 which had a rather lower intensity of
7.5. Although lower in destructive size, an estimated 83,000 people were killed in
the Sicilian city, with only a 45 % survival rate, whereas 99 % of people survived in
the Californian centre. The difference was in large part due to the greater density of
development in Messina and its more rigid buildings—which used heavy masonry
construction, granite walls and brick-tile roofs—compared to the many wooden
and one-storey buildings of San Francisco, which proved more flexible and less
likely to collapse, even though they were damaged. Indeed, San Francisco suffered
more damage from the fires that came from the ruptured gas lines than the actual
earthquake, another example of greater collateral damage from a natural disaster.
Perhaps the example illustrates the old aphorism that 'it is buildings that kill more
people', rather than the direct effect of the natural disaster. This problem of the
greater impact of natural hazards on certain types of construction can also be il-
lustrated by the vulnerability of shanty towns or informal settlements, which often
account for between 20-40 % of dwellings in the cities of developing countries.
These houses are flimsy constructions made out of bits and pieces of unwanted
materials that are barely cobbled together. Not only are these easily destroyed by
storms but they are often on precarious sites—usually previously unwanted land,
not developed by formal plans—such as the steep slopes of Rio de Janeiro's hillside
favelas, or the wetlands now occupied by slums in Lagos.
Another set of problems stemming from human activity come from
variations
in the quality of services and regulatory standards
in settlements. In the developed
world the industrial nineteenth century cities had unsanitary conditions, densely
packed housing and limited safety and medical facilities which led to high death
rates. As described in Chap. 13 (Healthy Cities) it led municipalities—usually with
national government laws—to create systems that provided safe drinking water
from new reservoirs and treatment plants, combined with new sewage systems and
better regulation of housing construction and plans. Zoning or development control
measures were also implemented to prevent incompatible land uses being built in
close proximity, which meant factories with noxious products were banned from
residential areas. So the release of toxic substances either from human error or from
buildings destroyed by natural hazards was drastically reduced.
There have been many cases where natural hazards have exposed the
inadequa-
cies of traditional defences against environmental problems
. For example, the em-
bankment of rivers in many cities may have reduced the seasonal risk of regular
flooding, but they are rarely capable of coping with the water flows from extreme
events, as seen in New Orleans during the Hurricane Katrina storm of 2005. The
