GY 301: Geomorphology Last Time Continental Glaciers Continental Glaciation and Erosion
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UNIVERSITY OF SOUTH ALABAMA Last Time Glacial Geomorphology (Continental variety) GY 301: Geomorphology • Continental glaciers today and in the past • Erosive features • Depositional features Lecture 24: Continental Glaciations http://www.kgs.ku.edu/Publications/PIC/28figures/fig4.jpg Continental Glaciers • Thick ice masses actually depress the lithosphere below sea level Continental Glaciation and Erosion • Polished and striated bedrock • Roche moutonee http://upload.wikimedia.org/wikipedia/commons http://libwiki.mcmaster.ca/clip/uploads/Main/rocheformation.jpg http://opa.yale.edu/images/articles/6449-E-Oice.jpg Continental Glaciation and Deposition • Landforms are produced by the motion of a thick ice sheet Moraines Drumlins Eskers Erratics Outwash Kettle Lakes/Kames Varves Loess Continental Glaciation and Deposition • Outwash plains are large areas of deposition produced during by meltwater. http://geopanorama.rncan.gc.ca/calgary/geotour/6_e.php Bedshiel esker http://geoimages.berkeley.edu http://www.soils.umn.edu http://z.about.com/d/geology/1/0/E/L/esker.jpg 1 Continental Glaciation and Deposition • Varves are laminated silt layers deposited in glacial lakes. Continental Glaciation and Deposition • Loess is wind blown silt deposited on alluvial plains a long way from the glacier. http://www.backyardnature.net/loess/vertbluf.jpg http://www.geologyrocks.co.uk/system/files/u2/varves.jpg http://brianmillerphoto.com Today’s Lecture http://www.backyardnature.net/loess/vertbluf.jpg http://landcovertrends.usgs.gov The Ice Age • A) Cenozoic temperature shifts (GY 112) B) Causes of Plio-Pleistocene Glaciations C) Consequences of Plio-Pleistocene Glaciations Plio-Pleistocene Is most notable for rapid, short duration shifts in temperature and ice volume. 18,000 years ago, the last glacial maximum covered all of Canada and a good chunk of Europe in a continental glacier… WHY? Plio-Pleistocene But major world-wide cooling first began in the early Eocene. 2 Plio-Pleistocene Milankovitch Cycles • Intense glaciations started around 5 million years ago. • Isthmus of Panama Three major changes in Earth’s orbit are linked to glacial oscillations – Emplaced 3.5–3 M years ago – Started modern circulation •Eccentricity •Obliquity •Precession • Gulf stream carries salty Atlantic north • Cools, sinks – Oceanic conveyor belt • High latitudes cool Chalk Board Milankovitch Cycles When taken together, the 3 cycles are capable of dropping temperatures globally Paleoclimate Phases Milankovitch Cycles When 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). Glacial/Interglacial Stages We now recognize two major Earth climatic phases 1) Greenhouse Earth (no continental glaciers present) 2) Icehouse Earth (continental glaciers present) a) Glacial stage (18 KA) b) Interglacial stage (Today) Glacial/ interglacial stage Name of stage interglacial Holocene Time frame 0 - 10 KA glacial Wisconsinian 10 – 75 KA interglacial Sangamon 75 – 125 KA glacial Illinoisan 125 – 265 KA interglacial Yarmouth 265 – 300 KA glacial Kansan 300 – 435 KA interglacial Aftonian 435 – 500 KA glacial Nebraskan > 500 KA http://www.snowballearth.org/end.html 3 Defining Glacial Maxima Glacial Maximum: the maximum coverage of continental glaciation on a continent Defining Glacial Maxima • 2) Distribution of moraines and basins associated with glaciation Several lines of evidence •1) Erratic boulders http://gsc.nrcan.gc.ca/landscapes/photos/slave_natmap/img0036.jpg Defining Glacial Maxima • 3) Depression/rebound of the land (e.g., Hudson Bay) Consequences of Continental Glaciations • Lowering of sea level – Exposed continental shelves http://www.geology110.com/files/lecture13/html/images/objects/obj29-2.jpg http://www.unavco.org/research_science/science_highlights/glacial_rebound/glacial_rebound.html Consequences of Continental Glaciations • Migration of species – Mammals crossed Bering Strait on land corridors – Vegetation changed in response to global changes Consequences of Continental Glaciations • Ocean circulation changed during glaciation – Glacier in NJ – Tundra in Washington, D.C. 4 Consequences of Continental Glaciations • Great lakes – Last glacial maximum Consequences of Continental Glaciations • The Great Flood (catastrophic emptying of Lake Missoula) • 35,000-10,000 years ago • Wisconsin Stage – Remained when ice sheets melted back http://hugefloods.com/Lake_Missoula_Map.gif Consequences of Continental Glaciations • The Great Flood (catastrophic emptying of Lake Missoula) Consequences of Continental Glaciations • The Great Flood (catastrophic emptying of Lake Missoula) Wave cut terraces marking the former shoreline of Lake Missoula http://formontana.net/shores.jpg Consequences of Continental Glaciations • The Scablands: the area affected by the flooding http://www.nps.gov/iceagefloods/J-ext1.JPG http://www.nps.gov/iceagefloods/J-ext1.JPG Consequences of Continental Glaciations • Climate impacts were felt globally – Steepened temperature gradients – Increased aridity – Exception: Great Basin • Lakes • Great Salt Lake 5 Consequences of Continental Glaciations • Climate impacts were felt globally – Sahara expanded – Rain forests restricted • Isolated gorilla species End 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 northward Upcoming Stuff Homework Alpine Glaciation Lab (due Friday) Next Lecture: Deserts and Wind Processes Friday’s Lab: Map interpretation (continental glaciers) 6
