1GY 301: GeomorphologyGY 301: GeomorphologyLecture 24: Continental Glaciations UNIVERSITY OF SOUTH ALABAMAhttp://www.kgs.ku.edu/Publications/PIC/28figures/fig4.jpgLast TimeGlacial Geomorphology (Continental variety)• Continental glaciers today and in the past• Erosive features• Depositional featuresContinental Glaciers• Thick ice masses actually depress the lithosphere below sea levelhttp://opa.yale.edu/images/articles/6449-E-Oice.jpg• Polished and striated bedrock• Roche moutoneeContinental Glaciation and Erosionhttp://upload.wikimedia.org/wikipedia/commonshttp://libwiki.mcmaster.ca/clip/uploads/Main/rocheformation.jpgContinental Glaciation and Deposition• Landforms are produced by the motion of a thick ice sheet Moraines Drumlins Eskers Erratics Outwash Kettle Lakes/Kames Varves Loesshttp://geopanorama.rncan.gc.ca/calgary/geotour/6_e.phphttp://z.about.com/d/geology/1/0/E/L/esker.jpgBedshiel eskerContinental Glaciation and Deposition•Outwashplains are large areas of deposition produced during by meltwater.http://www.soils.umn.eduhttp://geoimages.berkeley.edu2Continental Glaciation and Deposition• Varves are laminated silt layers deposited in glacial lakes. http://www.backyardnature.net/loess/vertbluf.jpghttp://brianmillerphoto.comhttp://www.geologyrocks.co.uk/system/files/u2/varves.jpgContinental Glaciation and Deposition•Loessis wind blown silt deposited on alluvial plains a long way from the glacier.http://www.backyardnature.net/loess/vertbluf.jpghttp://landcovertrends.usgs.govA) Cenozoic temperature shifts (GY 112)B) Causes of Plio-Pleistocene GlaciationsC) Consequences of Plio-Pleistocene GlaciationsToday’s LectureThe Ice Age• 18,000 years ago, the last glacial maximum covered all of Canada and a good chunk of Europe in a continental glacier… WHY?Plio-PleistoceneIs most notable for rapid, short duration shifts in temperature and ice volume.Plio-PleistoceneBut major world-wide cooling first began in the early Eocene.3Plio-Pleistocene• Intense glaciations started around 5 million years ago. • Isthmus of Panama – Emplaced 3.5–3 M years ago– Started modern circulation• Gulf stream carries salty Atlantic north• Cools, sinks– Oceanic conveyor belt• High latitudes coolMilankovitch CyclesThree major changes in Earth’s orbit are linked to glacial oscillations•Eccentricity•Obliquity•PrecessionChalk BoardMilankovitch CyclesWhen taken together, the 3 cycles are capable of dropping temperatures globallyMilankovitch CyclesWhen taken together, the 3 cycles are capable of dropping temperatures globally. These cycles have been confirmed via stable isotope analysis of deep sea foraminifera (ice volume).Paleoclimate Phases1) Greenhouse EarthGreenhouse Earth(no continental glaciers present)2) Icehouse EarthIcehouse Earth(continental glaciers present)a) Glacial stage (18 KA)b) Interglacial stage (Today)We now recognize two major Earth climatic phaseshttp://www.snowballearth.org/end.htmlGlacial/Interglacial Stages> 500 KANebraskanglacial435 – 500 KAAftonianinterglacial300 – 435 KAKansanglacial265 – 300 KAYarmouthinterglacial125 – 265 KAIllinoisanglacial75 – 125 KASangamoninterglacial10 – 75 KAWisconsinianglacial0 - 10 KAHoloceneinterglacialTime frameName of stageGlacial/interglacial stage4Defining Glacial MaximaGlacial Maximum: the maximum coverage of continental glaciation on a continentSeveral lines of evidence•1) Erratic bouldershttp://gsc.nrcan.gc.ca/landscapes/photos/slave_natmap/img0036.jpg• 2) Distribution of moraines and basins associated with glaciationDefining Glacial Maxima• 3) Depression/rebound of the land (e.g., Hudson Bay)http://www.unavco.org/research_science/science_highlights/glacial_rebound/glacial_rebound.htmlhttp://www.geology110.com/files/lecture13/html/images/objects/obj29-2.jpgDefining Glacial Maxima• Lowering of sea level– Exposed continental shelvesConsequences of Continental Glaciations• Migration of species– Mammals crossed Bering Strait on land corridors– Vegetation changed in response to global changesConsequences of Continental Glaciations• Ocean circulation changed during glaciation– Glacier in NJ– Tundra in Washington, D.C.Consequences of Continental Glaciations5• Great lakes– Last glacial maximum• 35,000-10,000 years ago•Wisconsin Stage– Remained when ice sheets melted backConsequences of Continental Glaciations• The Great Flood (catastrophic emptying of Lake Missoula)Consequences of Continental Glaciationshttp://hugefloods.com/Lake_Missoula_Map.gif• The Great Flood (catastrophic emptying of Lake Missoula)Consequences of Continental Glaciationshttp://formontana.net/shores.jpgWave cut terraces marking the former shoreline of Lake Missoula• The Great Flood (catastrophic emptying of Lake Missoula)Consequences of Continental Glaciationshttp://www.nps.gov/iceagefloods/J-ext1.JPG• The Scablands: the area affected by the flooding Consequences of Continental Glaciationshttp://www.nps.gov/iceagefloods/J-ext1.JPG• Climate impacts were felt globally– Steepened temperature gradients– Increased aridity– Exception: Great Basin•Lakes• Great Salt Lake Consequences of Continental Glaciations6• Climate impacts were felt globally– Sahara expanded– Rain forests restricted• Isolated gorilla speciesConsequences of Continental GlaciationsEnd of the Ice Age• Glaciers began to retreat around 15,000 years ago– Waters drained to lakes– Sea level rose– Tundra shifted northward– Deciduous trees migrated northwardUpcoming StuffHomeworkAlpine Glaciation Lab(due Friday)Next Lecture: Deserts and Wind ProcessesFriday’s Lab: Map interpretation (continental