Red River Formation

Transcription

Hello Young People. Entrenched Meander. This is the Yakima River just south of Ellensburg, Washington. Meanders are a feature of old age. These sweeping curves of the river. As rivers age they develop more and more exaggerated meanders. We know this by flying over the Mississippi River system. And we see all stages of meander development back there. Eventually, the meander become so exaggerated that that curve is abandoned and an oxbow lake is formed. And the channel becomes straight again. We can only develop these curves when an area is flat like back east at the Mississippi. And here we've got these exaggerated curves as well which means central Washington used to be flat. But there's a twist. This place isn't flat anymore. This is a deep canyon system. So to understand that twist, how 'bout we get up on that rim and get a big picture view of the Yakima River Canyon. Let's go up there. High up above the Yakima River on the rim of the canyon looking down. There's one of our meanders. We know about meanders. The meanders got established when the area was flat. A subtle curve becoming a more exaggerated curve. But then we froze the position of this meander, and we entrenched it. Entrenched meanders tell us that the land is lifting against the river. The river wasn't up here and was cut down. We're sure that the river has been down there for millions of years and the land has been lifting against the meander - against the river. The river's been cutting, matching an uplift rate of the bedrock. Basalt layer after basalt layer exposing themselves on the way up. The future of this meander is not more exaggerated meander. Development of an oxbow lake. Instead, the future of this curve is more cutting. Because the uplift continues here in central Washington. Entrenched Meanders. Just south of Ellensburg, Washington.