Most lava flows don’t travel very far from the volcano that produced them. On rare occasions, fluid basaltic lava like the kind commonly seen in Hawaii can stretch 10 to 15 miles from an erupting vent. More silica-rich lava, however, behaves very differently. With a thick, sticky consistency similar to molasses, these viscous lava flows typically move slowly and stop much closer to their source.
But in Washington State’s recent geologic past, two lava flows from the Goat Rocks Wilderness broke that rule in a big way. Known as the Tieton Andesite Flows, these massive flows traveled extraordinary distances across the landscape. One of them stretched an incredible 46 miles, making it the longest known viscous lava flow on Earth.
Geologists believe the flows followed the path of the ancestral Tieton River valley, allowing gravity and topography to guide the lava over unusually long distances. As the lava cooled, it formed thick layers of columnar and blocky volcanic rock that can still be seen today along parts of the Tieton River canyon. These flows are considered one of the most unusual examples of long-distance viscous lava movement on Earth and continue to be studied as scientists try to understand how such thick lava was able to travel so far.
