Geography Reference
In-Depth Information
as social relations, economic trends and geological
phenomena.
sucked into jet engines, which increases the
operating pressure ratio of turbine compressors
and may cause the engines to stall or flame out.
Eruptions of Redoubt Volcano in Alaska and
Galunggung in Indonesia led to in-flight
emergencies and severe damage to aircraft,
although fortunately not to casualties. Hence steps
have been taken to utilise real-time vulcanological
information in flight control (Casadevall 1991). Of
particular use are AVHRR images from, for
example, the NOAA 10 and 11 satellites, which
can help to map the height, distribution,
temperature and concentration of plumes and
indicate their paths of movement.
About one-tenth of the world's 450-500 active
volcanoes may erupt in any single year. Although
relatively few are intensively monitored, fifteen are
considered to offer such a high risk of disaster that
they are the subject of a special monitoring
initiative under the auspices of the International
Decade for Natural Disaster Reduction (Figure
5.1), and all potentially active sites of vulcanism
have been catalogued (Bullard 1984).
Vulcanologists were among the first to make
intensive use of the Internet for the exchange of
data and information, and the Global Volcanism
Network is now one of the most active and
extensive of such operations. Vulcanologists make
considerable use of electronic communications
and satellite monitoring, with special emphasis on
Total Ozone Mapping Spectrometry and
Advanced Very High Resolution Radiometry for
the height and composition of atmospheric
plumes derived from eruptions, infrared data from
the Thematic Mapper for the volume and
temperature of emitted radiation, and radar and
global positioning system (GPS) data for
monitoring the deformation of a volcano's surface.
One aspect of volcanoes that has consistently
been studied by a small number of physical
geographers is their geomorphology. They have
concentrated on the alternation of constructive and
destructive land-forming processes, in which
magma is extruded at the Earth's surface and its
products are remodelled by blast effects and erosion
(Ollier 1988). The implications for applied
geomorphology are considerable and are developed
PHYSICAL GEOGRAPHY
The physical geography of earthquakes and
volcanoes has been studied in a multiplicity of
ways. For example, improvements in the collection
of atmospheric data and their analysis as time-
series have enabled the climatic impact of volcanic
eruptions to be assessed accurately (Handler 1989).
At the same time, improvements in remote sensing
have led to more comprehensive and accurate
assessments of the extent and composition of
volcanic aerosols. Erupting and passively degassing
volcanoes are estimated to emit the following
quantities of gases into the atmosphere each year:
100-200 million tonnes (Mt) of carbon dioxide,
18.7 Mt of sulphur dioxide, 0.4-11 Mt of
hydrochloric acid and 0.06-6 Mt of hydrogen
fluoride. For the most part, tropospheric gases are
easily swept out by precipitation, and CO2
emissions are dwarfed by those from
anthropogenic sources. Hence the main effect of
eruptions is to inject large amounts of SO2 into
the stratosphere (e.g. 17 Mt by Mount Pinatubo
in 1991), and these may oxidise photochemically
to sulphuric acid aerosols, which both add to the
acidity of precipitation and reduce global
temperatures by up to 0.5°C for a few years by
reflecting some insolation back into space.
Quantities of hydrogen fluoride (HF) are also
significant and may gradually help to change the
composition of the Earth's atmosphere.
There has been increasing interest in the
hazards to aviation associated with suspended
particulates and gas plumes from volcanic
eruptions. Acidic aerosols can etch the exterior
surfaces of aircraft, especially cockpit wind-screens.
Thus in the early 1980s the Mexican volcano El
Chichón injected 0.5-0.6 km
3
of sulphur-rich
products into the stratosphere and one airline
found that it had to replace up to forty-two
aircraft cockpit windows in a single month at a
total cost of US$6.8 million (Bernard and Rose
1990). Moreover, glass pyroclasts can remelt when
