Heavy rain at Mount St. Helens washes sediment downstream to the Kalama River

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The eroded sediments are volcanic deposits on the south-southwest side of the volcano.

On October 10, intense rain at Mount St. Helens eroded volcanic deposits on the southwest flank of the volcano above Butte Camp dome. Field observations revealed unmistakable tracks of recent debris flows that started in two separate channels some distance above the Loowit 216 trail, and continued as a debris flow at least as far as the Toutle 238 trail crossing. By the time runout reached and merged with the clear-running Kalama Springs discharge, it was all fine material that was easily suspended in the flow and transported far downstream into the Kalama River. Similar debris flow run-outs may have entered the Kalama through another tributary channel. Because the source material for this debris flow consisted of creamy white volcanic deposits, it imparted an unusually light color to the river. With time, the river color will change as the sediment settles out of the water. Additional analysis is underway to better define source material.

Read more about Hydrologic Monitoring at Mount St. Helens on our webpage.