Geoscience Reference
In-Depth Information
Grand Rivière
Macouba
Basse Pointe
Le Prêcheur
Rivière Blanche
St Pierre
Nueés ardentes
May 8
After
May 8
Fort de France
0
10
20 km
Location map of Mt Pelée.
Fig. 11.10
out, sending a large mudflow down the Rivière
Blanche to the coast. The lahar killed 25 people. When
the 35 m high wall of mud hit the ocean, it generated a
tsunami that crashed into the lower part of St Pierre,
killing 100 people there. On 6 May, Mt Pelée issued
tephra that was so voluminous that it crushed roofs and
clogged streets. All the rivers around the mountain
then flooded for the next two days as the mountain
began roaring and blowing out pumice. Hot gases
rose to the surface, expelling groundwater from the
watertable. On 7 May, Mt Soufrière on the adjacent
island of St Vincent erupted and reports soon
circulated that this eruption had released the pressures
building up under Mt Pelée. Then Mt Pelée quietened,
supporting this rumor.
During these events, the government, headed by
Governor Mouttet, struggled to make sense of the
eruptions. Scientific advice was sought, but there was
no expert living on the island. Rumors were dispelled
by press releases stating that there was no threat.
Comparisons were made with Krakatau, which had
erupted nineteen years earlier. Because Mt Pelée was
not near the ocean, the risk of tsunami was dismissed.
Earthquakes were viewed as the main hazard. No one
realized that the nuées ardentes that had begun on
7 May heralded an unfamiliar phenomenon that posed
far more of a threat. Without any adequate knowledge
of what to expect next, Mouttet - in what must be rated
as one of the most foolhardy acts in history - took his
wife and most of the senior members of his adminis-
tration to St Pierre on the evening of 7 May to
allay fears of impending doom amongst the citizens.
Troops were ordered to begin patrolling the streets the
following morning to prevent panic. Those citizens
who wanted to leave St Pierre had already done so.
At 8:00 am on 8 May, a series of four violent explo-
sions shot dust to heights of 15 km. A second cloud was
blasted as a basal surge, horizontally to the south-west.
This cloud immediately flowed down the Rivière
Blanche. When it came to the bend in the river valley,
it overrode the bank, and part of the flow, traveling
at velocities in excess of 160 km hr
-1
, swept through
the city of St Pierre at 8:02 am. Eyewitness accounts,
from the few people who had fled the city early that
morning, describe the pyroclastic flow as a hurricane of
flame. Temperatures within the gas cloud were as high
as 1075°C. Walls of buildings were blown down, a
three-ton statue of the Virgin Mary was tossed 12 m, 18
of the 20 ships in the harbor were sunk, and most of
the standing city set ablaze. The hot blast exploded a
rum distillery and ignited rum, which then flowed
through the streets completing the incineration of the
city (Figure 11.11). The dust cover averaged only
30 cm in thickness throughout the city, but it engulfed
the area in complete darkness. Towards the mouth of
the Rivière Blanche, pyroclastic deposits thickened to
4 m. Up to 30 000 people, including Governor
Mouttet, died within two minutes. Many had clothing
