Tower Bridge
Because lahars move as a viscous flow, they do not have the degree of internal turbulence of a stream. In fact the flow more closely resembles a lava flow or glacier. One consequence is that lahars, like glaciers, can carry very large objects. Another is that they can carry quite delicate objects, items that would be quickly broken up in stream transport. The location shown below is at Tower Bridge over the Toutle River just below the confluence of the South and North Forks. Here the river valley narrows, and flow rates for the lahars was faster. The highway bridge is a replacement for one that was completely swept away.
Photo by James Maynard © 2010 - free use with attribution
View upstream. Note these photos the large size of the clasts and their heavy erosion since being deposited on this point bar.
Photo by Demet Yildrim © 2010 - all rights reserved
