63
Explosion of Krakatoa (Rakata)—also found
in Indonesia—with VEI value of 6 (1883) caused
the death of 36,000 people. The cause of the high
number of casualties was the devastation of a tsunami developed as a result of the volcanic explosion. In contrast, the explosion of Mount St.
Helens (1980) that was smaller by only 1 value
caused only 57 casualties. This cannot be
explained by smaller population density much
more by the development of science.
Volcanologists studied the mountain in detail and
based on several signs they concluded that the
volcano will erupt (Brantley and Myers 2000).
Locals were alerted months before the actual
eruption and authorities demarcated a security
zone within which people were prohibited.
Casualties were caused by that some people
entered the security zone and also by that the
security zone was not large enough (Box 3.1).
Data related to the eruption of Mt. Pelée
(1902) on Martinique are also informative. The
explosion with a much smaller energy than
Mount St. Helens with a VEI value of 4 destroyed
the town of Saint-Pierre at the foot of the mountain within minutes causing the death of 30,000
people. The above data support the importance of
forecasting explosive volcanic eruptions. Gentle,
lava producing volcanoes with relatively welltraceable lava flows along their sides practically
cause no casualties but may cause damage to
property. Hawaii and Stromboli in Europe are
typical examples of such volcanoes.
Volcanic eruptions could cause different damage as well to the society. Air transport could be
made dangerous by volcanic ash clouds. A numBox 3.1 Explosion of Mount St. Helens
The volcano is part of the Cascade Range
in the North American Cordillera,
Washington, United States. It was one of
the most complete volcanic cone with its
height of 2551 m before the famous eruption and thus was referred to as the Fuji of
North America (Fig. 3.3).
After 130 years of dormant state scientists detected several signs of eruption in
1980: increasing number of small earthquakes occurred around the mountain from
March and then the northern slope of the
volcano appeared to bulge at a surprising
rate (1.5 m a day). This phenomenon made
it clear that the volcano will erupt in the
near future. Volcanologists demarcated a
security zone entrance into which was prohibited to prevent people highly risking
their lives. The eruption started at 8:32 am
on 18 May 1980 following a magnitude 5.1
earthquake in a specific way: a major landslide occurred on the northern slopes thus
the explosion threw material sideways.
Magma and the crushed rocks of the mountain rose to a height of 24 km while the
majority of the exploded hot material was
flowing down the slopes at a speed of
500 km/h smashing everything in its way
on the mountain slopes (Figs. 3.4 and 3.5).
David A. Johnston, colleague of USGS
received permission to enter the security
zone in order to observe the surface changes
of the volcano. He was one of the 57 victims who died despite many precaution
measures due to the destruction of the
speeding and hot ash cloud. The debris
flow of 2.5 km
3
destroyed an area of almost
30 km
2
. Wind transported the material
towards east and ash fall was recorded
afternoon on that day in a distance of
1000 km. The sad fact is that most victims
were found outside the security zone. Still
scientist cannot be blamed for the false
demarcation of the “red zone” because
such special explosion has not been
detected yet and there was no experience
regarding the truly secure distance from the
volcano in the case of the above explosion.
They have to be thanked instead since without their warning and the efforts of the
authorities destruction and casualties
would have been much more extensive.
3.2 Effects of Material Flows in the Mantle and the Lithosphere on the Society
Explosion of Krakatoa (Rakata)—also found
in Indonesia—with VEI value of 6 (1883) caused
the death of 36,000 people. The cause of the high
number of casualties was the devastation of a tsunami developed as a result of the volcanic explosion. In contrast, the explosion of Mount St.
Helens (1980) that was smaller by only 1 value
caused only 57 casualties. This cannot be
explained by smaller population density much
more by the development of science.
Volcanologists studied the mountain in detail and
based on several signs they concluded that the
volcano will erupt (Brantley and Myers 2000).
Locals were alerted months before the actual
eruption and authorities demarcated a security
zone within which people were prohibited.
Casualties were caused by that some people
entered the security zone and also by that the
security zone was not large enough (Box 3.1).
Data related to the eruption of Mt. Pelée
(1902) on Martinique are also informative. The
explosion with a much smaller energy than
Mount St. Helens with a VEI value of 4 destroyed
the town of Saint-Pierre at the foot of the mountain within minutes causing the death of 30,000
people. The above data support the importance of
forecasting explosive volcanic eruptions. Gentle,
lava producing volcanoes with relatively welltraceable lava flows along their sides practically
cause no casualties but may cause damage to
property. Hawaii and Stromboli in Europe are
typical examples of such volcanoes.
Volcanic eruptions could cause different damage as well to the society. Air transport could be
made dangerous by volcanic ash clouds. A numBox 3.1 Explosion of Mount St. Helens
The volcano is part of the Cascade Range
in the North American Cordillera,
Washington, United States. It was one of
the most complete volcanic cone with its
height of 2551 m before the famous eruption and thus was referred to as the Fuji of
North America (Fig. 3.3).
After 130 years of dormant state scientists detected several signs of eruption in
1980: increasing number of small earthquakes occurred around the mountain from
March and then the northern slope of the
volcano appeared to bulge at a surprising
rate (1.5 m a day). This phenomenon made
it clear that the volcano will erupt in the
near future. Volcanologists demarcated a
security zone entrance into which was prohibited to prevent people highly risking
their lives. The eruption started at 8:32 am
on 18 May 1980 following a magnitude 5.1
earthquake in a specific way: a major landslide occurred on the northern slopes thus
the explosion threw material sideways.
Magma and the crushed rocks of the mountain rose to a height of 24 km while the
majority of the exploded hot material was
flowing down the slopes at a speed of
500 km/h smashing everything in its way
on the mountain slopes (Figs. 3.4 and 3.5).
David A. Johnston, colleague of USGS
received permission to enter the security
zone in order to observe the surface changes
of the volcano. He was one of the 57 victims who died despite many precaution
measures due to the destruction of the
speeding and hot ash cloud. The debris
flow of 2.5 km
3
destroyed an area of almost
30 km
2
. Wind transported the material
towards east and ash fall was recorded
afternoon on that day in a distance of
1000 km. The sad fact is that most victims
were found outside the security zone. Still
scientist cannot be blamed for the false
demarcation of the “red zone” because
such special explosion has not been
detected yet and there was no experience
regarding the truly secure distance from the
volcano in the case of the above explosion.
They have to be thanked instead since without their warning and the efforts of the
authorities destruction and casualties
would have been much more extensive.
3.2 Effects of Material Flows in the Mantle and the Lithosphere on the Society