Mudflows began quickly. They
formed as snow and ice was melted by hot ash and rock released during the
eruption.
Mudflows began quickly. They
formed as snow and ice was melted by hot ash and rock released during the
eruption.
Rushing water combined with loose
rock and sediments. This formed a highly destructive, cement-like
slurry. It scoured and buried the areas it passed over. The mudflows
traveled as fast as 90 miles an hour on the steep upper slopes of the
volcano.
As the flows reached flatter and
wider areas, they slowed to about 30 miles an hour.
In some areas mudflows went up
valley walls as much as 360 feet. They went over hills as high as 250
feet.
Geologists estimated the depth of
the mudflows. At their peak, the larger mudflows averaged from 33 to 66
feet deep. However, the deposits left by the mudflow were often less
than 3 feet thick.
The boundaries of these erosive
flows are clearly marked. The undisturbed forest is visible along the
edge of the valleys. Notice the high-water mark left by the passing
mudflow.
Mudflows
Plants and Animals
Mount St. Helens
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