Skip to main content
U.S. flag

An official website of the United States government

Geologist describes the formation of lava tubes and tree molds from...

Detailed Description

Research geologist Carl Thornber leads a group of Mount St. Helens National Volcanic Monument interpretive rangers and volunteers along the boardwalk at the Trail of Two Forests, explaining the formation of lava tubes and tree molds from the 1900-year-old Cave Basalt Flow on the south side of Mount St. Helens.