Ape Cave is a lava tube. It
was formed when Mount St. Helens erupted about 1900 years ago.
Ape Cave is a lava tube. It
was formed when Mount St. Helens erupted about 1900 years ago.
A
lava flow, like this
one in
Hawaii, came down from high on the slopes. It traveled eight miles south
to the Lewis River.
This type of smooth-flowing lava
is called "pahoehoe" basalt.
Over several weeks, the lava
flow began to cool and crust over on the surface. The lava beneath the
surface continued to flow.
At the end of the eruption, the
lava flowed out of the tube. It left behind Ape Cave as we see it
today.
Ape Cave is 12,810 feet long--
that's almost 2-1/2 miles long! It is the longest intact lava tube in the
United States, and the second longest in the world.
No lava tubes were formed during
the 1980 eruptions of Mount St. Helens. The volcanic material that came
out was a different type of lava.
There are active volcanoes in
Hawaii that are much less
explosive than Mount St. Helens. We can study the formation of lava
tubes there.
Geologists must carefully
approach a skylight, or opening
in a lava tube to photograph lava moving through an active tube.
Skylights form when small
parts of lava tubes do not form, or when the tube collapses.
Ape cave was named in honor of a
local youth group called the St. Helens Apes. They hiked and explored on
Mount St. Helens.
Return to:
Mount St. Helens & Other
Volcanoes
Ape Cave
Before the Eruption
Mount St. Helens
VolcanoWorld