When they stopped, the mud and debris solidified in place. At Arlington, more than 60 miles downstream from Glacier Peak, lahars from these eruptions deposited more than 7 feet of sediment. Between 6,300 and 5,900 years ago, lahars extended at least to Minkler Lake, near Sedro Woolley in the Skagit River, and probably made it to the Skagit Delta. Smaller lahars have occurred during at least three episodes since 5,900 years ago. The largest of those made it only to the mouth of the White Chuck River.
Volcanoes also produce huge landslides that can transform into lahars.
At Mount St. Helens in 1980, a giant landslide decapitated the volcano and triggered the largest lahar of the eruption. At Mount Rainier, an even larger landslide about 5,700 years ago disaggregated into a lahar that filled in stream valleys as far as Puget Sound. Smaller landslides also produce lahars. Landslide-caused lahars are typically made of clay and weathered lava from the volcano's edifice. In contrast, lahars caused by eruptions are made of fresh pumice and ash.