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Hazard Maps of Ol Doinyo Lengai
(These are not
official hazard maps. They are my interpretation
of hazards posed by Ol Doinyo Lengai and were done
for a class project)
Ol Doinyo Lengai experiences
frequent activity, and thus its eruptions are relatively
small. A majority of eruptions receive only a 1 on the
Volcanic Explosivity Index, or VEI.
These minor eruptions pose very little hazards to the
local populace. The major hazards are from lava flows,
lapilli ash cone collapses, lahars, and pyroclasts. The
danger from lapilli ash cone collapses is limited to the
crater, the location of most of these cones. The lava
flows, while low in viscosity and very swift moving, are
generally confined to the crater during mild eruptions.
Lahars are also a small danger, as there are several
rivers along the north and east flanks of Ol Doinyo
Lengai. The chance of deadly lahars increases during
the rains that occur between March and May.
Finally, pyroclastic debris and ballistics are very
dangerous and may travel down the length of the flanks,
a distance of 4km.
Large
eruptions tend to occur at Ol Doinyo Lengai every few
decades. These eruptions tend to be rated a 3 on the
VEI scale.
According to the eruptive history of Ol Doinyo Lengai,
the hazards of ballistics and lava flows are similar to
the risks during more minor eruptions. The lahars,
however, can be more extensive, threatening people in
river channels that extend down the northern and eastern
flanks of the volcano. These lahars have been known to
travel up to 10 km down the flanks of the volcano.
One very major hazard in the event of an explosive
eruption is the potential for a large debris avalanche.
An ancient eruption of Ol Doinyo Lengai caused the
collapse of the north flank, prompting a massive debris
avalanche that traveled up to 25 km to the north,
reaching Lake Natron.
Finally, a major eruption could produce large quantities
of ash. Carried by prevailing winds to the west, ash
from Ol Doinyo Lengai can reach as far as 130 km to the
west and 70 km to the north.
A large eruption of Ol Doinyo Lengai can be quite
hazardous to citizens and property tens of kilometers
from the vent.
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