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Rabaul Caldera, Papua New Guinea
This was probably the most important eruption
of 1994. Certainly the eruption did more damage than any in nearly a
decade. Large portions of the town of Rabaul were destroyed by ash from
the eruption. Just what happened at Rabaul?
Rabaul, the town, is inside Rabaul,
an 8 x 14 km (~5 x 9 mile) wide caldera that is mostly filled by Blanche
Bay, an arm of the ocean. Its pretty dangerous to have a town inside
of a volcano, but there have been no eruptions there for 51 years.
- On the morning of September 19, 1994,
two volcanic cones - Vulcan and Tavurvur - began erupting on the opposite
side of the harbour from the town. By 10:30 AM an airplane pilot reported
that the ash cloud was 15-18 km (9-11 miles) above Rabaul. Other estimates
placed the top of the cloud as high as 30 km (~18 miles). This was a
powerful eruption!
- Ash fell all over the town and satellite
photographs showed an ash cloud carrying volcanic dust westward over
much of New Guinea. The ash that fell over the town was first reported
to be 20-25 cm (8-10 inches) deep, and it later was as much as 75 cm
deep (about two feet). Heavy rains turned the ash into mud that fianlly
dried to be nearly as hard as cement. The roofs of many buildings collapsed
from the weight of the ash.
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- A small lava flow came from a vent near
Tavurvur and flowed slowly for about 25 days. Also, some of the clouds
of ash eruptions collapsed back on themselves and a mixture of ash and
gases flowed rapidly down the side of the volcanoes and out into the
bay. Such ash and gas mixtures are called pyroclastic flows. Pyro is
a Greek work for fire, and clastic is Greek for broken pieces of rock.
Some of the ash and pyroclastic flows made floating rafts of pumice.
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- The eruptions declined in strength, and
by Oct. 2, Vulcan was no longer erupting; Tavurvur continued throughout
October and November.
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- Despite the great danger of this eruption,
only five people died; four from collapses of roofs, and one person
was struck by lightning. The reason so few people were hurt is that
volcanologists at Rabaul had been expecting an eruption someday. They
had educated the people of Rabaul to the dangers of volcanic eruptions
and even practiced eruption drills - sort of like fire drills in a school.
When intense earthquakes started the night before the eruption, the
volcanologists and government officials evacuated nearly all of the
town people before the eruption started. This was a tremendous success
for science, for that night and the next few days, nearly 50,000 people
were removed from a place of great danger to safety. Rabaul did not
become a great tragedy, but was a great triumph!
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