Global Volcanism Program | Image GVP-02840
A tree-ring core shows a pronounced narrowing of tree rings dated about 1480 CE resulting from reduced growth rates following an eruption that occurred sometime between the end of August 1479 and the end of May 1480. This eruption was the second largest Holocene eruption of Mount St. Helens, producing the "Wn" tephra layer. Another major eruption two years later that produced the "We" tephra layer, which also affected this tree.
Photo by David Yamaguchi (University of Washington).
This image is made available as a Public Domain Work, but proper attribution is appreciated.