EPOW - Ecology Picture of the Week

Toutle River mudflow outwash plain, southwest Washington USA

Explanation:  On May 18, 1980, Mount St. Helens blasted some 400 meters (1300 feet) off its summit and flattened 570 square kilometers (220 square miles) of timberland ... initially caused by an earthquake that triggered a massive debris avalanche.  

The avalanche ran down the Toutle River valley some 23 kilometers (14 miles), changed the morphology of the river, and buried the valley with mud and rock to a depth of 18-183 meters (60-600 feet).  This was followed by volcanic mudflows that ran the length of the Toutle River all the way to the Columbia River, 97 kilometers (60 miles) away.  

Eventually, the Army Corps of Engineers dredged some 85 million cubic meters (110 million cubit yards) of sediment from the Toutle River and built a $65 million sediment retention structure on the North Fork.  

Some 28 years later, the river is still recovering, although some parts of its pre-eruption ecology such as the aquatic insect populations rebounded quickly.  

The river has reformed wide meanders and braided floodplains -- shown in these photos -- that are once again inviting riparian shrubs and wildlife.  

In the upper Toutle River Valley now reside more than 500 Roosevelt elk.  The river is home to several fish species including coho salmon, fall chinook, and winter steelhead, although the latter two are listed under the Endangered Species Act and are considered depressed stocks.