Snoqualmie Falls - Volcano

Volcano

Geologists recently discovered that the Falls flow over a 20 million year old extinct volcano. A team led by Washington’s DNR geologists recently found that the volcanic rock in the Snoqualmie Valley was more local and younger than previously thought. Until recently, geologists had attributed the Valley’s volcanic rock to Mount Persis, an extinct volcanic area to the north in Gold Bar. A closer examination showed the Valley’s volcanic rock are about 20 million years younger than the 40-50 million year old rock of Mount Persis.

A few key observations helped geologists come to their conclusions. When volcanoes spew lava, gas, and earth, the heavier material can’t travel as far as the lighter matter. The heavier content – called volcanic bombs when larger than 2.5 inches in diameter but can be much larger – acquires a round shape during flight and the subsequent landing. Geologists found hundreds if not thousands of volcanic bombs near the falls, suggesting the center of the volcano was nearby. Also, the entire Falls area is dominated by lava flows and the flows usually don’t move very far from the volcano, according to geologists.

While recent glacial and seismic activity make it hard to pinpoint, geologists are confident the center of the volcano lies very near the Falls. Visitors can see evidence of the volcano by walking down to the wooden platform across from the base of the falls. A careful eye will spot volcanic bombs across the Snoqualmie River.