Sequence of events at 1991 eruption.
16th July 1990
Large earthquake 100 km northeast
of Mt Pinatubo.
3rd August 1990
Loud rumbling heard, a landslide
near the summit, and steaming ground. First volcanic activity in 500 years.
August 1990
Five earthquakes near Pinatubo.
15th March 1991
Rumbling and earth tremors.
2nd April 1991
Steam and ash exploded from a 1.5
km long fissure high on the northern slopes of Pinatubo. Smell of sulphur
and ash fell 10 km away.
3rd April 1991
200 small earthquakes registered
at the volcano.
23rd April 1991
US Geological Survey arrived with
monitoring equipment.
26th April 1991
Monitoring station set up at Clark
Air Base 25 km to the east of the volcano.
13th May 1991
30-180 earthquakes per day were being
recorded. Volcano releasing sulphur dioxide indicating molten magma was
rising beneath the volcano. Alert level 2 issued.
23rd May 1991
First hazard map completed.
28th May 1991
A tenfold increase in sulphur dioxide
emissions in previous 2 weeks.
1st June 1991
Earthquakes became centered 5 km
below the volcano.
5th June 1991
Sulphur dioxide emissions almost
stopped as the vents became blocked. Earthquakes continued and the mountain
started to bulge as magma moved towards the surface.
7th June 1991
1500 earthquakes under Pinatubo.
An ash eruption sent a cloud to 8 km high. Alert level 4 issued stating
an eruption coud happen within 24 hours. Danger zone extended to a 20 km
radius.
Lava reached the surface and formed
a small dome 1 km northwest of the main crater.
9th June 1991
Sulphur dioxide began escaping again
from the volcano. The first nuee ardentes rolled down the volcano. A large
eruption of ash. People evacuated from a 20 km radius.
10th June 1991
Evacuations begun at Clark Air Base.
(14,400 people)
12th June 1991
Ash eruptions to 20 km above the
volcano on Philippine Independence Day.
13th June 1991
Ash eruption to 25 km high followed
by 28 hours without an explosion. Earthquakes continued.
14th June 1991
Violent explosion at 1:09 pm. Eruption
column to 21 km in 15 minutes. Nuee ardentes devastated the main valleys
radiating from Mt Pinatubo.
15th June
1991
The Main
Eruption
Typhoon Yunya passes 100 km northeast
of Pinatubo. Mudflows raged down the mountain at 30 km/hr.
At 3:39 pm the main eruption began.
In 9 hours 90 percent of the total material for the eruption was expelled
from the volcano.
Cauliflower columns of ash, gas and
steam rose 34 km high and travelled 400 km. At 4:30 pm the summit of Pinatubo
began to sink. The evacuation area was increased to 40 km radius.
The eruption stopped at 10:340 pm.
Effects of the Eruption
740 people killed.
A huge caldera was formed 2.5 km
across.
260 m was lost off the summit of
the volcano.
The ash entered the stratosphere
and covered the whole earth within 12 months.
Global temperatures were reduced
by 0.5 degree C the year after the eruption.
Forests buried under 50-200 m deep
ash and pumice.
During the last five months of 1991
200 mudflows raced down the valleys of Pinatubo.
Damage amounted to $450 million dollars.
8,000 houses were destroyed and 75,000
houses damaged.
2 million people were affected by
the eruption.
The biggest volcanic disaster of
the 20th century was avoided due to good planning and monitoring. |
