An Uncommon Eruption The formation of Ape Cave marks an unusual period in Mount St. Helens’ eruptive
history in that it is the only known basaltic eruption of the volcano.
Eruptions of fluid basaltic lava, much like those in Hawaii, are rare
occurrences in the Cascade Mountain Range. The Cascades usually erupt
lava of a thicker consistency. When this type of magma is coupled with
suspended gases, explosive eruptions tend to occur. The eruption of
Mount St. Helens on May 18, 1980, exemplifies this tendency. About 2,000 years ago, fluid basaltic lava poured down the southern
flank of the volcano. As the lava flowed, chunks of the lava’s
surface cooled, crashed and fused together creating a hardened crust.
In turn, the crust insulated the molten lava beneath, allowing it to
remain fluid and travel down to the Lewis River Valley. The hot flowing lava began melting into the pre-existing rock and
soil. This thermal erosion deepened and widened the channel of the
flow. The level of lava in the tube rose and fell as the eruption surged
and slowed, contributing to the unique contours of the walls. During this eruptive period, hot fluid lava pulsed through the tube
for months, possibly up to a year, until the eruption subsided. As
a result of this rare eruption, a spectacular 13,042 foot (3976m) long
lava tube, the third longest in North America, was created. What’s in a Name? Ape Cave was discovered in 1947 by a logger named Lawrence Johnson.
However, the cave was not explored until the early 1950’s when
a scout troop, led by Harry Reese, lowered a team of scouts down
a 17-foot overhang to the cave floor. Leaving footprints where no
one ever had, these explorers were able to travel through a pristine
lava tube full of fragile formations. Ape Cave was named by the Scout
Troop in honor of their sponsor, the St. Helens Apes. This local
group was made up primarily of foresters. The sponsor’s name,
St. Helens Apes, may have come from an old term used for foresters
in the area, “brush apes,” or from the legend of Bigfoot. |