Before the lava dome began to
grow, the crater of Mount St. Helens was relatively flat. A small hole
about 150 feet across marked the volcano's eruptive vent.
Before the lava dome began to
grow, the crater of Mount St. Helens was relatively flat. A small hole
about 150 feet across marked the volcano's eruptive vent.
The vent connects the surface of
the volcano to an underground network of molten rock.
The first dome of crusty,
volcanic lava was observed after a steam and ash eruption on June 12,
1980.
This dome was destroyed by an
explosive eruption on July 22.
A second dome, observed on
August 8, was destroyed by the October 16 eruption. A third was observed
forming on October 18, when molten rock, or magma, pushed up through the
vent and formed a small, circular lava flow....
...Glowing cracks in the lava were
at least 1,700 degrees Fahrenheit.
The lava flow grew for 2 days. It
formed a dome-shaped pile of lava 900 feet across and 110 feet tall.
Geologists affectionately called this early dome "Muffie", because it
looked like a giant muffin.
Two months later, another batch
of magma pushed up through the vent and into the dome. Most of the
magma oozed out onto the dome's surface, increasing its height by about
150 feet.
Three months later, another lava
flow oozed onto the surface of the dome. It continued down the side of
the dome at about 20 feet per hour.
These lava flows overlap each
other like a giant stack of thick, lava pancakes. Each one added to the
dome's height and width.
The dome-building eruptions
usually last less than 3 days. However, one eruption in 1983 lasted for
12 months.
During this eruption, magma rose
into the dome slowly. It did not leak onto the surface. Instead, it
caused the east side of the dome to grow outward.
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Lava Domes
After the Eruption
Mount St. Helens
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