Scientists Date Mount Rainier's Electron Mudflow to Summer 1507

A team of scientists has precisely dated the Electron Mudflow, a lahar from Mount Rainier, to the late summer of 1507 using tree-ring analysis. The study, published in the February issue of Geology, was led by Bryan Black of the University of Arizona and included geologist Patrick Pringle of Centralia College. The lahar, which buried forests near Orting, Washington, was named by the late geologist Rocky Crandell. By analyzing Douglas fir samples from Vancouver Island and buried trees in the Puyallup River valley, researchers created a master chronology that allowed them to match growth-ring patterns. The date suggests the lahar was not caused by a rainstorm or volcanic eruption, but likely by melting ice saturating clay-rich volcanic rock. This finding helps scientists understand lahar frequency and improve hazard communication. The Electron Mudflow is one of about 11 large lahars from Mount Rainier in the past 6,000 years. The new chronology also aids in dating other low-elevation geologic events, such as the Bonneville Landslide. The study highlights the ongoing threat of lahars to communities like Orting, which conducted a large evacuation drill in April 2026.