The rockslide and pumice deposited in the region of the headwaters of the river have been eroded to a depth of more than 100 feet forming a new dendritic drainage pattern. The canyon on the right is shown in detail in Figure 6. Significant canyon erosion by mudflow which established the dendritic drainage pattern occurred on March 19, 1982. Detailed view of deep canyon on the right side of Figure 5. Photograph taken in August 1983.
Man provides scale.
The gorge is believed to have been breached between steam explosion pits by the mudflow of March 19, 1982. Mass wasting of the sides and water erosion of the channel have kept the gorge open, forming part of the new drainage network on the pumice plain at the headwaters of the North Fork of the Toutle River. It has allowed geologists to document local rates of erosion. An entire landscape has been subjected to various agents of sculpture including wave erosion, jetting steam, mass wasting, rill and gully erosion, sheet flooding, and mudflow erosion. The erosional features at Mount St. Helens are not unique, but are similar to those observed elsewhere.