Discussion: Plate Tectonics of the Pacific Northwest

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aubreyreynolds9@gmai	Plate Tectonics of the Pacific Northwest Oct 3 2009, 11:01 AM EDT I thought I would start a thread on the geology of the Pacific Northwest. It is a fascinating region with a variety of rock structures from igneous, metamorphic. to sedimentary. It was ether this or what is your favorite beer. Bill Post reply 2 out of 2 found this valuable. Do you find this valuable? Do you? Keyword tags: None
jakesrocks	1. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 11:16 AM EDT Since I don't drink, I'll vote for root beer. The new thread sounds like interesting reading. I'll be watching for your posts. Don Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
WilliOfTheValley	2. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 12:17 PM EDT I agree with Don on this new thread. It's sad that I've lived over here all my life and I don't know that much about the Pacific Northwest. Now I'll be able to learn something. Thank you so much Bill. Willi Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	3. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 12:35 PM EDT Thank you. I am looking forward to learning a lot. With Bob Jackson, Zeke, Aaron, Paul, Andy, Jake, Don and other North westerners we will have a great pool of knowledge. Bill Post reply 1 out of 1 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	4. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 1:21 PM EDT \| Post edited: Oct 3 2009, 1:25 PM EDT In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. The notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world. The West coast of the United States is at the boundary of massive plates that are in collision. In geologic terms, a plate is a large, rigid slab of solid rock. The theory of plate tectonics states that the Earth's outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. The idea has been around for a while before it was considered scientifically. I remember my eighth grade geography teacher pointing out how neatly South America and Africa fit together like a puzzle. In fact the two contents were part of one continent. A geologist can find the exact same geology in The western mountains of Africa as in the Eastern cliffs of South American. Incredible forces are moving the North American Continent west. Which means you folks are on the front lines of the collision. The continent is rising up over the Pacific plate as it plunges into the Earths mantel of molten rock. There is a Ring of Fire surrounding the Pacific that bears witness to the forces moving the land masses. The Ring of Fire is the most seismically and volcanically active zone in the world which is responsible for some of the most distinctive features of the Northwest. Mt Rainier, Mt Hood, Mt Saint Helen are part of this Ring of Fire. If we are pulling apart from Africa and Europe then there ought to be new land forming in the Atlantic Ocean. Indeed there is a volcanic ridge of mountains know as the Mid-Atlantic Ridge. This submerged mountain range, which extends from the Arctic Ocean to beyond the southern tip of Africa, is but one segment of the global mid-ocean ridge system that encircles the Earth. Post reply 6 out of 6 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	5. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 1:35 PM EDT \| Post edited: Oct 3 2009, 1:44 PM EDT The rate of spreading along the Mid-Atlantic Ridge averages about 1 inch per year. This might be a good place to discuss the most prominent feature of Washington and that is Mount Rainier. The mountain is a volcano born of fire and built up above the surrounding country by repeated eruptions and successive flows of lava. It is a relatively young volcano, only about one million years old. By contrast the mountains of the Cascade Range that Mount Rainier looks down upon are at least 12 million years old, created by the folding, buckling, and uplifting of the Earth's surface. Mount Rainier, highest point (14,410 feet) and third-most voluminous volcano in the Cascades after Mounts Shasta and Adams, dominates the Seattle-Tacoma area, where more than 3 million live . The Mountain is, however, the most dangerous volcano in the range, owing to the large population of the area. Most of Mount Rainier's cone was built by hundreds of thin lava flows inter bedded with breccia and minor tephra. About 20 small earthquakes occur yearly at Mount Rainier, more than at other composite cones in the Cascades except Mount St. Helens. I am going to take time out to hear from you'll, drink a root beer and burp. Post reply 6 out of 6 found this valuable. Do you find this valuable? Do you?
rockcandyguy	6. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 10:36 PM EDT \| Post edited: Oct 4 2009, 12:00 AM EDT Much of the danger posed by the Cascade volcanoes is via mud flows. When Mt. St. Helens erupted in 1980, mudflows reached the Columbia River. Because the volcanoes are capped by glaciers, an eruption melts immense quantities of ice/snow, adding liquid to a fast-moving flow of ash, which becomes mud. The Kent valley south of Seattle is a mud flow from Mt. Rainier. Today, the cities of Kent, Federal Way, Tukwila, Renton, and Auburn are all built on top of this mudflow. If Rainier were to produce another flow of this magnitude, and there is every reason to believe that it will again, this valley, now with a population of over 300,000; and a major manufacturing center, would be wiped out in a few hours. Several small towns closer to The Mountain (as we locals call Rainier) have mudflow warning systems in place, and marked evacuation routes to higher ground. I can only imagine the traffic jam when the warning system goes off. The other dangers posed by west coast shifting plates are earthquakes and tsunamis. The Seattle Fault appears to be capable of generating quakes as large as those on the San Andreas in California. Many other faults crisscross the NW. Eastern Washington has many centers of earthquake activity as well. A recent swarm of quakes centered near Richland have seismologists puzzled. A website which follows what's shaking in the NW, http://www.ess.washington.edu/recenteqs/latest.htm Post reply 6 out of 6 found this valuable. Do you find this valuable? Do you?
aubreyreynolds9@gmai	7. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 10:40 PM EDT \| Post edited: Oct 3 2009, 10:48 PM EDT Bob are you in the line of the mud flows if and when Rainier erupts? I understand the Mountain erupted in 1894. It must have been minor? Bill Post reply Do you find this valuable?
pvjjh	8. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 10:57 PM EDT \| Post edited: Oct 3 2009, 11:05 PM EDT "I thought I would start a thread on the geology of the Pacific Northwest. It is a fascinating region with a variety of rock structures from igneous, metamorphic. to sedimentary. It was ether this or what is your favorite beer. Bill " I myself really like Bob's home brew stout. Ours is a close second though. Can't we talk about beer instead??? Us PNW types don't like to think about all this plate tectonics stuff and volcanoes, lava flows and such, that is why we drink beers. ;-) Just a good way to forget that we are all living on borrowed time be it a ticking time bomb with the eruptions or the lahars (mudflows) and ash that would take us out as well. There are lenses of ash 10' deep around here from past Glacier Peak eruptions and who knows when the next great basin basalt flows may occur again. Heck our newest event could be a major shift in the Cascadia fault just off shore of WA state which could cause major tsunamis which could chance the coast line plus the quake damage itself destroying major populated areas. Again this is going to happen, but no one can put a good finger on the exact time it will occur. This is a very diverse geological region, still growing and experiencing those growing pains. Yup we live on borrowed time around here. It is just a matter of time when something else will start the newest change in the PNW. And anyway stout tastes good! Yeahhhhh..... :-) Paul Post reply Do you find this valuable?
aubreyreynolds9@gmai	9. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 11:09 PM EDT But it is also what makes Washington State one of the nation's most spectacular and the geology interesting enough to start a thread about. As for Bob's home brew I will have to wait on it. Post reply Do you find this valuable?
pvjjh	10. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 11:10 PM EDT "Bob are you in the line of the mud flows if and when Rainier erupts? I understand the Mountain erupted in 1894. It must have been minor? Bill" There have been minor changes in the mtns around the state. Mostly warming trends which has a tendency to create more localized mudflows. I think Mt Baker event poofed some steam. But most of the volcanic mtns have had some warming then they cool back off over the years. Many even a little bulge here and there, Bob wold know much better than I do about all this I am sure. Paul Post reply Do you find this valuable?
aubreyreynolds9@gmai	11. RE: Plate Tectonics of the Pacific Northwest Oct 3 2009, 11:35 PM EDT \| Post edited: Oct 3 2009, 11:37 PM EDT "There have been minor changes in the mtns around the state. Mostly warming trends which has a tendency to create more localized mudflows. I think Mt Baker event poofed some steam. But most of the volcanic mtns have had some warming then they cool back off over the years. Many even a little bulge here and there, Bob wold know much better than I do about all this I am sure. Paul" The main rock type that makes up the geologic history of Mount Rainier is andesite. There are many varieties of andesite that are found. Other lithologies that can be found there include diorites, granodiorites, breccias, quartz monzonite porphyries, basalts, rhyodacites, minor rhyolites, and others. Also, many different lava flows, ash deposits and pumices can be found indicating the eruptive history of the volcano. Andesite is the most common volcanic rock after basalt. It is porphyritic, that is, consists of coarse crystals (phenocrysts) embedded in a granular or glassy matrix (groundmass). Having a silica content of 57%, it is in the intermediate category (52–66% silica) of the silicic–mafic scale. Bill Post reply 6 out of 6 found this valuable. Do you find this valuable? Do you?
rockcandyguy	12. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 12:24 AM EDT \| Post edited: Oct 4 2009, 1:01 PM EDT "Bob are you in the line of the mud flows if and when Rainier erupts? I understand the Mountain erupted in 1894. It must have been minor? Bill" We are. Here's a map: http://vulcan.wr.usgs.gov/Imgs/Gif/Rainier/OFR95-642/rainier_mudflows.gif We live a bit north of Enumclaw, at 800 ft. The mudflow buried everything below 750 ft. The next one will bury the last one, and so on. When the radio tells us that a mudflow is coming, we can walk up the 2000 ft. hill behind our house, and watch it go by. With any luck, I'll have a keg of stout to take along, as it would likely be weeks before the surface of the flow would be safe to walk on. The 1894 eruption did not cause any damage outside the immediate vicinity of the cone. The last major eruption was about 500 years ago. For a period between 2,000 to 3,500 years ago, there was a major eruption about every 200 years. Whether the current lull will continue or return to the 200 year cycle is anybody's guess. There was another volcano located about where Rainier is today, which blew itself away in a cataclysmic eruption about 5 million years ago. An eruption like that would likely be the largest natural disaster in modern history. Imagine Krakatoa going off in an urban area! There would likely be a long period of harmonic earthquakes to warn of such a pressure build up. We learned a lot about eruption predicting from St. Helens 1980 eruptions. On the plus side for living here, the NW never has hurricanes and very few tornados, and few poisonous critters & plants. On the plus side for rockhounds, plate boundaries are great places for exotic geological elements to accumulate! Spruce would not exist were we not in a subduction zone. Bob Post reply 5 out of 5 found this valuable. Do you find this valuable? Do you?
gamaliel114	13. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 2:38 AM EDT \| Post edited: Oct 4 2009, 2:38 AM EDT There is a creek running off of Mt. Baker that is an obvious lahar flow channel. Boulder Creek. I'll take some pictures next week (its near Grandy). ~Zeke Post reply Do you find this valuable?
retiredoldfogee	14. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 12:44 PM EDT "Bob are you in the line of the mud flows if and when Rainier erupts? I understand the Mountain erupted in 1894. It must have been minor? Bill" Its ironic in Renton until a few years ago was mostly a manufacturing area with a few houses sprinkled here and there, in the last 6 years since Boeing start closing its huge facility there, huge Condominiums have been popping up around Lake Washington which is basically where the flow will land at the Cedar River basin. I often wonder if they built any sort of safety into these 8+ story condominiums for the possibility of mud flows. I noticed in a newer one across from Lowes and North of Frys has a huge couple story cement foundation wall facing towards Rainer, and the first 2 stories are parking. I assume the City of Renton being as hard as they are on permits and safety junk would of taken that into consideration when building the Condominiums. I used to live in Renton and they definitely discussed that area in the local newspaper as a danger zone oonce Rainer erupts again. Thanks, Aaron Post reply Do you find this valuable?
rockcandyguy	15. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 12:46 PM EDT "There is a creek running off of Mt. Baker that is an obvious lahar flow channel. Boulder Creek. I'll take some pictures next week (its near Grandy). ~Zeke" I found some nice jasperized wood fragments in Boulder Creek, when I was running around writing the Rockhound's Guide series. Not enough to list it as a locality, but a good tease. A similar occurrence on Weyerhauser land south of Cougar has wonderful jasperized leaf impressions. Have you seen any evidence of fossils in the Baker area? Bob Post reply Do you find this valuable?
rockcandyguy	16. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 12:59 PM EDT "Its ironic in Renton until a few years ago was mostly a manufacturing area with a few houses sprinkled here and there, in the last 6 years since Boeing start closing its huge facility there, huge Condominiums have been popping up around Lake Washington which is basically where the flow will land at the Cedar River basin. I often wonder if they built any sort of safety into these 8+ story condominiums for the possibility of mud flows. I noticed in a newer one across from Lowes and North of Frys has a huge couple story cement foundation wall facing towards Rainer, and the first 2 stories are parking. I assume the City of Renton being as hard as they are on permits and safety junk would of taken that into consideration when building the Condominiums. I used to live in Renton and they definitely discussed that area in the local newspaper as a danger zone oonce Rainer erupts again. Thanks, Aaron" Despite Renton's well-deserved reputation for complex permitting (used to live there also, and developed a property up the hill off Sunset, where we could watch the flow go by), I doubt anyone has come up with a mudflow-resistant construction design. Would be a great study for an irresistable force meeting an immovable object! Bob Post reply Do you find this valuable?
gamaliel114	17. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 1:43 PM EDT \| Post edited: Oct 4 2009, 1:43 PM EDT "I found some nice jasperized wood fragments in Boulder Creek, when I was running around writing the Rockhound's Guide series. Not enough to list it as a locality, but a good tease. A similar occurrence on Weyerhauser land south of Cougar has wonderful jasperized leaf impressions. Have you seen any evidence of fossils in the Baker area? Bob" No, but I've been too busy looking for the jade. I haven't looked too hard on Boulder creek either. I actually think there might be some where i'm heading this week though. I seem to recall something mentioned on a map...i'll look into it. I'd imagine it would be part of the "Chuckanut formation". ~Zeke Post reply Do you find this valuable?
retiredoldfogee	18. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 1:57 PM EDT \| Post edited: Oct 4 2009, 1:57 PM EDT Bob, Have you ever heard of any Jade producing areas up between I-90 and Snoqualmie? How about Serpentine zones? Thanks, Aaron Post reply Do you find this valuable?
rockcandyguy	19. RE: Plate Tectonics of the Pacific Northwest Oct 4 2009, 2:43 PM EDT \| Post edited: Oct 4 2009, 2:43 PM EDT "Bob, Have you ever heard of any Jade producing areas up between I-90 and Snoqualmie? How about Serpentine zones? Thanks, Aaron" I've seen the green garnetoid rocks of Denny Creek and surrounds mis-identified as jade, but have not encountered any jade or serpentinite in King County. An old state pub listed nephrite as occurring near the headwaters of the Snoqualmie North Fork, but since that is within the Snoqualmie Batholith, I'd guess the source was either glacial or from over the divide which drains the Wenatchee metamorphic belt. Bob Post reply Do you find this valuable?

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