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What began as a quiet morning suddenly took a violent turn. At 8:32 a.m. a
strong earthquake shook the Earth, triggering an avalanche and tearing the
volcano apart. The volcano's bulge and summit suddenly began to slide and
collapse, setting off powerful explosions. Rocks, ash, volcanic gas, and steam
were blasted outward. The blast flattened whole forests.
This lateral blast continued for two minutes and then stopped. Moments later
the volcano began to erupt upwards. An eruptive plume of ash rose more than
25 kilometers into the sky. Winds blew the ash eastward. Lightning, generated
by the swirling ash, set off forest fires. The Plinian eruption
continued until about 5 p.m. During that time, nearly 540 million tons of ash
fell over an area of over 57,000 square kilometers. The
total volume of uncompacted ash was about 1.25 cubic
kilometers—enough to fill a football field about 240 kilometers
high with fluffy ash.
Around noon, the volcano began giving off flows of pumice and ash, like a "pot
of oatmeal boiling over." These flows lasted for the next five hours. Mudflows
also started, sweeping down the volcano slopes, surging over hills, and causing
destruction to the areas below.
By early the next morning, most activity of this very large eruption ceased.
The sun rose to reveal a volcano that had changed in many ways—most
dramatically, it was 1,313 feet (400 meters) shorter than it had been the