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Lecture-18-F10 - EAS 111 General Announcements • Moving...

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Unformatted text preview: EAS 111 General Announcements 11/10/10 • Moving Water today = Ice sheets, ice caps, Rivers & Floods • Next week: – Water use and groundwater – Ground collapse and Slope stability • Lab NEXT Week = Happy Hollow Field Trip! – Be ready for any weather, be on time – Specifics in your lab section on gear, etc. – GO TO YOUR OWN LAB SECTION EAS 111: Happy Hollow Park EAS 111: Happy Hollow Park What to expect: • Transportation to the field and back to campus on a Purdue bus • Flat, easy, short hike along paved roads and easy packed dirt trails. Two tiny hills to climb • About 1.5 hours outside What to bring? • Comfortable, walkable shoes + appropriate gear for weather • Something to write on and with – can leave other gear in bus • Your immense powers of observation, reasoning and thought Earth and Atmospheric Sciences 111 Fall 2010 Landscape Features of Continental Ice Sheets a all ss on ssiion Rece ne Rece raiine Mo Mora Esker Esker Kettle Kettle Lakes Lakes Dru mli ns Glacial Outwash Glacial (Sediment) (Sediment) Te r Mo mina rai l ne 14.13.a na iinall Term ne Term iine Mora Mora Eskers Observe features left behind by continental glaciers Observe in the Great Lakes region Glacially smoothed troughs Glacially 14.13.a5 What are these long ridges? A.Eskers B.Drumlins C.Tectonic features related to faults D.Recessional or terminal moraines Rough, nonglaciated areas Landscape Features of Mountain Landscape Glaciers Glaciers Arêtes Moraines 14.12.a Cirque Hanging valley Observe the setting of glaciers, Observe ice sheets, and ice shelves near West Antarctica near 14.16.a Ice sheet Ice builds on land and moves toward sea toward Outer parts of ice Outer sheet float on the sea as ice shelves shelves What could happen to West Antarctica if global What temperature or sea levels rise? temperature Part of Part Larsen Ice Shelf collapsed in 2002 in Before Before collapse collapse 14.16.b After After collapse collapse One possible scenario: One rising sea level floats more ice sheet, detaching it from bedrock bedrock EAS 111: Earth Science News EAS van den Broeke, et al, Science 13 November 2009: 984-986 Greenland Ice Cap Melting Faster Than Ever -confirmed acceleration in the rate of melting since the 1990s -273 Gt per year (1 Gt is the mass of 1 cubic km of water) through 2006-08 -0.75 mm of global sea level rise per year. -if the whole Greenland ice cap melted, it would raise global sea level 7m -130,000 years ago -> -Recent maximum melt -Contributed about 4 m to sea level rise Consider the impact of a 6 Consider meter (~20 feet) rise in sea level on the East Coast level What areas are most What vulnerable and why? vulnerable Low lying areas next to a Low relatively gentle and flat coastline coastline 14.16.d1 Investigation: How Could an Episode of Global Warming Investigation: or a Glacial Period Affect North America? or 14.17.a1 The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. In this figure, the globally averaged warming corresponds to 3.0 °C (5.4 °F). http://en.wikipedia.org/wiki/Global_warming How Does Water Move? How The Hydrologic (Water) Cycle Observe how water moves between settings Precipitation (rain, snow, (rain, hail) hail) Infiltration: Infiltration: water seeps into ground ground Groundwater Groundwater flows flows Groundwater flows Groundwater onto surface onto Condensation Air currents Runoff Evaporation (oceans, lakes, (oceans, rivers,…) rivers,…) Most precipitation Transpiration Transpiration iinto ocean; some nto evaporates on way from plants from down down 17.01.b1 Lake Superior Superior Lake Lake Huron Huron Lake Lake Michigan Michigan Lake Lake Erie Erie Lake Lake Ontario Ontario Drainage Basins Drainage Observe the red and Observe blue areas and their boundary boundary Red area Red drained by one stream, and blue area by another: each is a drainage basin basin Boundary between basins is a drainage divide 16.01.b1 Tributaries and Drainage Networks Tributaries Smaller Smaller subsidiary channels are tributaries tributaries Types of Drainage Patterns Tributaries Tributaries spread out discharge over time over 16.01.c-d Dendritic Radial Structurally controlled North American Drainage Basins Drainage Observe these drainage Observe basins and find where runoff in your area ends up in 16.01.m1 Watershed vs. Drainage Basin • Watersheds are associated with individual river systems at a convenient political/management scale • Watersheds are the most common unit of analysis for land managers – Pollution control, water supply, etc. • Drainage basins are mapped to overall geography, raindrop to base level • Drainage basins are a better unit of analysis for understanding hydrology, flood hazards, total discharge, etc. River shape • Profile along length • Curves and bends • Cross section profile – Terraces – Levees River shape • Profile along length • Curves and bends • Cross section profile – Terraces – Levees How Do Rivers Change Downstream? How Observe this profile of a river. How would Observe you describe this pattern to someone? you Rivers tend to be steep Rivers near their origin, such as in hills and mountains in A river generally becomes less river steep (more gentle) down 16.04.a2 stream stream Base Level Base The lowest level to The which a river can erode: base level base High above base level: High much erosion much Closer to base level: less erosion less 16.04.b1 Landscape reflects Landscape decreasing gradient decreasing Sea level Sea is ultimate base level base River shape • Profile along length • Curves and bends • Cross section profile – Terraces – Levees Curves in Rivers and Streams and This This river is braided braided Observe these satellite images of rivers This river has This meanders meanders 16.05.a What Processes Operate on Meanders? What Small graphs show profiles across the river channel; observe the channel profiles for different parts of the river Straight channel: Straight symmetric, fastest fastest in center Outside bend: Outside deeper and faster; erosion of cutbank cutbank Inside bend: Inside shallow and slower; deposition of point bar point 16.05.b1 Erosion and deposition Erosion may be balanced may Faster side Faster erodes and deepens deepens How Do Meanders Form and Move? Form Deep side faster Deep and more water, so erosion so Inside slower Inside and less water, so deposition so Erosion or overflow Erosion erosion: cutoff cutoff meander and meander oxbow lake oxbow 16.05.c1-6 Erode outside Erode bend, increasing curvature; migration outward and outward downstream River shape • Profile along length • Curves and bends • Cross section profile –Terraces – Levees 16.10.b8 16.10.b9 Character of River Terraces Character Highest Highest terrace terrace Middle Middle terrace terrace Highest Highest terrace terrace Lowest terrace Modern Modern floodplain floodplain Active channel Many rivers flanked by relatively flat benches (terraces) 16.11.a2 16.11.a3 16.11.a4 CPS: What caused these terraces to form? A.Flow and erosion power of the stream increased B.The landscape was being driven upwards by tectonics C.Base level dropped D.Potentially any or more than one of these 16.11.a5 River shape • Profile along length • Curves and bends • Cross section profile – Terraces –Levees How Do Levees Form? How Levee: raised embankment Coarser sediment than Coarser floodplain floodplain 16.08.b Flood: water spills out Flood: and deposits sediment and River behavior • Discharge – What is it? – Time-related changes – Geometry-related changes • Floods – Flood mechanics – Flood frequency How Do We Measure the Volume of Water that Flows Through a Channel? that To calculate volume, To multiply width X height X 3rd dimension Amount of water flowing Amount through a channel over a given time is discharge discharge 16.14.a2 What is the volume here? 02.08.c4 Discharge calculated by Discharge multiplying channel width X depth X velocity of water: depth units are cubic meters/sec units or cubic feet/sec or Discharge During a Flood Discharge Increase discharge, peaking Increase after storm after Before storm Return to Return normal 16.14.a4 How Do Rivers Vary Over Time? How Rivers vary in discharge Rivers during the year during Suggest some factors Suggest that might explain such a pattern such Rivers have longterm trends in term discharge and sediment load, with some interruptions some 16.03.c Is the Wabash river likely to flood this weekend? A.Definitely- we’re already at flood stage B.Maybe, if there’s a big storm because the river is full. C.Unlikely, the river is nowhere close to flood stage http://www.crh.noaa.gov/ahps2/index.php?wfo=ind EAS 111: Assignment for Monday 11/15/10 • Exploring Geology • Water Resources and Groundwater – 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.8, 17.9 – for interest and more detail, I recommend also reading 17.7 and 17.10 on exploring for groundwater and cleaning up groundwater contamination ...
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