UO GEOL 308 - Chapter 10: Columbia River Plateau

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Exam 3 Study GuideChapter 10: Columbia River PlateauTerms: Coulee: a long trench-like valley from ice age floods Eastern WashingtonDiatoms: a major group of algae - unicellular, have glass like cell wallsLava Flow Colonnade: lower portion of a lava flow with well-formed parallel shrinkage columns (think upright regular columns)Lava Flow Entablature: upper portion of a lava flow that displays irregular, thin shrinkage columns often at sharp angles to the colonnadeNumerous sedimentary basins (low areas in which sediment collected) were formed in the area of the Columbia River Plateau during the Miocene.- How did they form?- When the Columbia River basalts disrupted drainage patterns of streams and water backed up as ponds and lakes.- Water reached the top of the lava surface  spilled across  create vast reservoirs in shallow depressions and they collected sediments. - Name and briefly describe one of these basins from OR & one from WAMcKay Basin (OR)- Famous for Late Miocene vertebrate fossils recovered from the McKay formation.- Extensive plant and animal remains reflect an assortment of paleo environments that included pond banks, woodlands, and grasslands.Pasco Basin (WA)- Largely deprived of sediments, and standing water & swampy.- Conditions were widespread. Pasco basin of SE = ‘sediment straved’. What kinds of animals and plants lived in the area of the Columbia River Plateau during the Miocene Epoch? What microscopic fossils are abundant in this area? What was the climate like?- Animals: aquatic rhinoceros, giant turtle, beaver, large cat and dog like predators, antelope, deer, bear, catfish.- Plants: bald cypress, oak, fir, maple, beech. - Microscopic fossils: diatoms, compressed leaves, several species of rare beetle- Climate: rainy, warm, temperate, short mild winters, humid summers. Name any two of the formations (large, widespread rock units) that comprise the Columbia River basalts. Although the tectonic forces that allowed the basaltic magma to move up to the Earth's surface are not completely understood, what is the best current tectonic explanation for the origin of the Columbia River basalts, according to the textbook authors?- Same tensional forces that produced fault block topography of Basin and Range mighthave caused this.- Back arc spreading where stretching east of the Cascade volcanic archipelago thinned the crust, induced wide spread faulting that released volcanic material upward along fissures and cracks.- In the Columbia River Basalt Group, how many formations are there?- 6 Formationsa) Imnahab) Grande (Same time: Picture Gorge & Prineville)c) Wanapum d) Saddle Mountains- Which is oldest?- Imnaha basalts - Which is youngest?- Saddle Mountains- Which one contains more than 859percent of the total volume of the Columbia River basalts?- Grande RondeUsing an epoch term from the geologic time scale, how old are the lava flows making up the Columbia River basalts?- Miocene, 17.5 million years- What was the climate like at that time, and how can we tell?- Rainy, warm and temperate with short mild winters & humid summers- From fossils, mostly plant- How are these lava flows related to the dike swarms occurring in northeastern Oregon and southeastern Washington?- Same lava flows- When the flows ceased magma inside fissures hardened, it formed vertical tabletop shaped igneous intrusions called dikes. - Fissures occurred in clusters = resulting dikes in clusters = dike swarms.What impact did Columbia River Basalt lava flows have on contemporaneous (simultaneously) streams, including the Columbia River?- Disrupted drainage patterns of streams when waters were pushed from their channels, they cut new channels or retrenched original valley.- Streams that couldn’t cut through lava packed up as ponds or lakes.- Columbia River was repeatedly blocked by stiffening cooling basalt lava flowsWhere, how, and when (state how many thousands of years ago) did the Missoula floodsoriginate?- Idaho and mostly Montana- Canada ice sheets travelling south began to melt – it crossed the path of the dam and the ice just melted creating the lake  ice froze again  melted which eventually caused floods- Ice damns ruptured on great glacial lakes along the Clark Fork River, a branch of the Columbia- 15000 and 12500 years ago- How many floods were there, and how do we know?- 40 cataclysmic (disastrous) floods- Touchet layers exposed in walls of a deep arroyo - Describe the approximate route that the floodwaters traveled.- Spreads out through Eastern Washington and funnels slightly into ORTwo main paths:1. Idaho Panhandle E to the Spokane River Valley2. From the Panhandle to S- List and describe the major erosional and depositional effects along the path of this flood.- Channeled scabland of WA gouged (extracted) into Miocene basalts- Thick sequences of wind-deposited Palouse dust or loess were stripped away beforelayers of basalts were removed.- Bounders and gravel carried in chunks of ice and tumbled along in stream along Moses Lake.- Elongated basins and buttes that parallel flow of water. - Coulees: Long Trench-like Valleys- What was Lake Allison?- Lake created by flood of Lake Condon of water that reached southward in Eugene inWillamette valley of Oregon. - What was Lake Condon?- Lake formed by blocks of ice, boulders, sand and gravel jammed into the narrows near the Dalles, OR. How do the ground surfaces of the Palouse Hills and the channeled scablands differ in appearance and origin?- Palouse Hills are smooth dust deposits - Channeled scablands are pock-marked channels of gravel barsWhat is loess?- Fine silt is produced by the grinding action of glaciers, then transported beyond the margin of the ice by running water and deposited. - Later – fine silt is picked up by strong winds and deposited as loess. - Where are the main deposits of loess on the Columbia River Plateau?- Palouse Hills in southeast WA and northern ID- What is the source of this loess?- Originally as Aeolian or wind blown.- Fine dust originated as rock flour ground up by glaciers.- Dumped on the outwash plain of melting ice sheets, the loose material was collected by strong winds and carried away. What is the Olympic-Wallowa lineament? Did it form during crustal compression or during crustal extension?- A large-scale prominent line on the surface of the earth that reflects major structural features such as faults.- Formed during crustal extension - Extends from the Straight of Juan de Fuca

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