The Yakima River meanders through the Yakima Fold Belt
between Ellensburg and Yakima
River flow is from lower right towards upper left
The Yakima river drains a large area of the east side of the Cascade Range with headwaters extending up to the crest of the range. The river supplies water for irrigated farms throughout its length and water rights and lack of water rights has been an ongoing struggle along the river for many years.
I had a nice view of the Yakima River between Ellensburg and Selah on a recent trip. The Yakima River's passage through the ridges of the Yakima Fold belt is a classic antecedent river. That is the river was there before the ridges formed. The meandering nature of the ancestral river is preserved where the river is entrenched and deeply incised through the ridge areas. The Yakima Canyon in the above picture is a classic example of entrenched meanders of an antecedent river.
An interesting feature of the river is that outside the meander loops stretches in the entrenched valley the river is more typically a braided stream with multiple rapidly shifting channels. The river alternates between these styles of flow as it passes through broad alluvial valleys and ridges.
Broad nearly circular loop forming a goose neck just south of the Kittitas Valley near Ellensburg
The exact cause of why the Yakima River, and for that matter a number of other rivers in the Columbia River system) became so entrenched has not entirely certain. The entrenching of the Yakima began approximately 3.4 million years ago with large volumes of previously deposited sediments in the valleys between the ridges and within the Columbia Basin removed (Reidel and others, 1994). I like the idea that the gradient of the river system changed once the Columbia became established in its current route through the Cascade Range. Prior to the down cutting there was a period of wide spread lake deposition within the Columbia Basin suggesting that Cascade volcanism had created a blockage of the Columbia system.
1 comment:
I canoed the Yakima from Ellensburg to the Columbia River last May. It was fascinating to go through so many different zones in just 150 miles. The braided area from Yakima to Granger was fairly dangerous with logjams and strainers. Then to Prosser, slow water in deep cut earth banks, and no trees. After the Prosser portage, it was channeled scablands with a river bottom of large boulders.
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