The distal lahar deposits
The lower reaches of the Toutle and Cowlitz Rivers as well as a section of the Columbia River were filled with lahar deposits after the 1980 eruption. It was imperative that these be dredged quickly to restore navigation. (A dozen ocean-going vessels a day would come up the Columbia to Portland before the eruption). The products of this dredging are still visible in spoil piles bordering I-5 along the Cowlitz. Although the silt and clay was largely washed farther downstream, the sand and gravel fractions of the lahars are well-represented in these piles.
Photo by James Maynard © 2011 - free use with attribution [full-size jpeg]
Glacially polished and faceted cobble from the dredge spoil. Note the diagnostic 5-sided shape. There is a continuum of material from glacial deposits to debris flows to stream deposits in the Cascades, one system feeding into the next.
Photo by James Maynard © 2011 - free use with attribution [full-size jpeg]