Tree Cast

September 20, 2002

Treecastcrawl copy

Provided by: Tim Martin, Greensboro Day School
Summary authors & editors: Tim Martin

The area around Mt. St. Helens documents the mountains eruptive history prior to the famous 1980 eruptions. This image of a horizontal tree mold was taken on “A Trail of Two Forests” located south of Mt. St. Helens.

“A Trail of Two Forests” is a short walk through an area that had been devastated by an earlier basaltic eruption 1900 years ago. Unlike the more recent explosive dacite lava eruption, basaltic eruptions tend to be of a much lower viscosity. As the fluid lava flowed down the mountain, it flooded a forest encasing both standing and fallen trees. The lava then cooled leaving molds of the trees that presumably burned away.

Numerous tree molds are visible along a short .25-mile trail. For the adventurous a ladder provides access to a 10+ meter crawl through the mold of a fallen tree. The inset detail shows a view of the wall of the tree mold. Detailed impressions of the tree bark remain in the nearly 2000 year old lava.

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