Roadside Geology - Yakima River Canyon

funding for this series is made possible in part by the Dhananjay and Charles T coal Charitable Foundation and by the department of geological sciences at Central Washington University hi I'm Nick and I love Washington's geology I've been teaching it for 20 years now let's hit the highways visit places you all know and I can help you see Washington like you've never seen Washington before welcome to central rocks roadside geology just south of Ellensburg Washington the Yakima River Canyon is a wonderful place to study and enjoy the great outdoors Ellensburg main street flows directly south to Canyon Road the old two-lane highway winds its way from miles through the canyon finally emerging at the city of Yakima to explain the canyons formation the earliest residents of the Northwest the Chinook people created a myth involving a fight between a giant beaver and a giant coyote to cut the canyon for thousands of years local Native Americans made careful observations of the Yakima River and the ridges of Central Washington as the first geologists of the area the Chinook people had an explanation for these curious canyon cuttings across the landscape in the early days of the world wish push the giant beaver lived on Lake Cle Elum wish push always killed all of the animals that wanted to fish there by drowning them in the lake coyote the wisest and most cunning of the animals made up his mind to kill whoosh push one day coyote speared whoosh push with all of his might and the giant beaver plunged to the bottom of Lake clay elem dragging coyote with him coyote fought so desperately with wish push that the banks of the lake were torn out water surged through the break and they plunged through the mountains the water rushed madly into the broad Kittitas Valley and formed another lake the struggle between coyote and wish pushed continued and they destroyed the banks of that lake and they fought as the waters surged madly into the lower Yakima basin and a lake was formed at Toppenish this continued until the fighting animals made it all the way to the Pacific Ocean over the past century classically-trained field geologists have also pondered the canyons formation they also have noticed that the canyon is not straight and that meandering canyon cuts directly across a series of ridges today we tackle the question who formed first the ridges or the Yakima River to start we need to learn the basics of rivers and the rocks that they typically drop rivers deposit rocks that are rounded sorted by size and varied in rock type but things get interesting when we start finding river rocks in places that rivers are not ah spectacular with Craig's Hill in the middle of Ellensburg Washington right in town we have this glorious outcrop most people don't look at it very carefully but of course we do let's be real careful let's observe like we've done in other spots already today rocks let me pull them out uh-huh right let me collect a few I'll throw my hammer down every one of these guys has rounded corners most of these guys roughly the same size and if we look carefully we've got an incredible variety now you're a quick student you know what this means already don't you rounded rocks about the same size incredible variety say it with me river deposit River deposition but where's the river we're in the middle of town the Yakima River that we know and love is at least two miles to the west of us in other words this spot is 2 miles east of the present river great evidence that the Yakima River has not always been in its current spot and our business about channels migrating laterally and rivers change in their path this is the evidence we need we've even got something better than that in Craig Co up above us out of sight is a volcanic ash layer above us a volcanic ash layer that's in this hill 5 million years old so if this lay if these rocks are below that 5 million year old volcanic rock layer then we know that these rocks were deposited older than 5 million years ago when the area was flat ok so let's think about this for a second these two rocks have been sitting there to each other for at least 5 million years until right now we've got Sun hitting that spot for the first time at at least 5 million years that's power deposits like those at Craigs he'll help us understand that rivers don't always stay in place if the terrain is flat and if there is enough geologic time the channel of a river system will naturally begin shifting laterally why is this what causes the river to pick up and move next door a quick trip to a research lab helps us answer that question stream table modeling shows that as rivers age they go through different stages at birth rivers are youthful and straight but as they age their meanders become more exaggerated why is this a close look at one curve tells us that fast water on the outside of the curve erodes the land while on the inside of the curve slow-moving water deposits sediment the net result a continual shifting of the rivers channels well now we're on to something different stages of river development tells us about the region where the river is flowing if the land is flat the river is allowed to push through all five stages often going through those stages again and again Craig's Hill and other deposits like it in the Kittitas Valley build a strong case that the Yakima River went through many River stages when central Washington was flat so here we are I'm an Oshkosh Ridge just south of Ellensburg Washington and down below us by hundreds of feet is the Yakima River itself the river has cut a beautiful canyon by now you've seen many images of the canyon itself and you know the basic geometry the river is not rate therefore the canyon is not straight and in fact this meandering river canyon cuts directly across Menashe Tesh ridge and a series of other edges through Central Washington now that we know about the history of these rivers and how they develop stages I hope it's obvious to you by now that the rivers course had to be set in this meandering pattern before the ridges started to grow seems to me if you try to argue the opposite way that the ridges have always been here and the Yakima River decided to use this place to punch a hole through Menashe - Ridge okay fine maybe there was a fault zone or some weakness in the ridge but it would have to be a straight river right it would have to be a straight path a straight youthful burst instead of this very graceful old aged meandering talk to any geologist you want the river came first the ridges came second the ridges came second the ridges came second how is that possible the Chinook people assumed that the ridges had always been there but understanding of our globe's plate tectonics made clear just fifty years ago has now enlightened us tectonic uplift is often the driving force for intense erosion at the surface uplift intensifies erosion and then somebody flipped the switch a tectonic switch to start lifting all of this land against this river that's when the canyon started cutting when we started lifting against the river so we don't want to visualize the river eating its way down like I think many people visualize geologically we want to visualize the river holding its position and having the whole series of rock layers lifts against the river so who was here first who's who was here first the chicken or the egg in this case who was here first the river or the ridges we say the river was here first it couldn't develop those meanders unless this area was flat perfectly flat no Canyon no ridges and as soon as that flat landscape allowed that Yakima River system to develop those beautiful meanders then the uplift began then these ridges started growing and the canyon started cutting this poor River is trapped in stage four no chance to move on to stage five because all of its energy now is in a vertical sense not a horizontal sense everybody enjoys this canyon we enjoy it too geologically funding for this series is made possible in part by the Dhananjay and Charles T coal Charitable Foundation and by the department of geological sciences at Central Washington University

Channel: Central Washington University

Views: 18,832

Rating: 4.9764705 out of 5

Keywords: Earthquake, Documentary, History, Cascades, Education, Central Washington University Organization, Eastern Washington, Central Washingtion University, Ellensburg Citytownvillage, Flood, Ice Age Floods, Cwu, Ellensburg, Geology Field Of Study, Cwu Geological Sciences, Cwu Geology, Central Washington University, Cwu Science, Geology, Roadside Geology, Central Rocks

Id: 4J0nN9yWL5Y

Length: 11min 56sec (716 seconds)

Published: Fri Feb 22 2013