Physical Geography by Alan Arbogast Chapter 17

1. Physical Geographyby Alan ArbogastChapter 17 Glacial Geomorphology: Processes & Landforms Lawrence McGlinn Department of Geography State University of New York - New Paltz

2. History of Glaciation • As early as 2.3 B years ago, ice covered much of Earth, and off and on since then • Most important Ice Age was Pleistocene Epoch, 1.8 M years ago till 10K years ago • Glacial – period when glaciers expand from poles – cooler temps, lower sea level, • Interglacial – period when glaciers recede: warmer temps, higher sea level

3. Pleistocene Glaciations • Named for southern extent of ice sheet in North America • Nebraskan – 1 million yrs ago • Kansan – 625 K yrs ago • Illinoisan – 300 K yrs ago • Wisconsin – 35 K to 10 K yrs ago • Laurentide Ice Sheet – eastern North America • Cordilleran Ice Sheet – western North America

4. Maximum Extent of Pleistocene Glaciation 30% of earth’s surface covered by ice sheets (Only 11% coverage today)

5. Oxygen Isotopes

6. Evidence of More Glaciations? • Ice core samples suggest more than the known 4 glaciations – show more cool, glacial periods • Oxygen isotopes O-16 & O-18 both in water, but O-18 evaporates more in warmer climate, so ratio of O-16 to O-18 in ice cores can indicate relative warmth of climates over 1 million yrs ago!

8. Causes of Glaciation • Summer temp (melting) is key to glaciation • Possible Factors:1. Variations in solar radiation (dust, sunspots…) 2. Reduced carbon dioxide (escaping heat) 3. Increased volcanic activity (reflective dust) 4. Variations in Earth-Sun geometry (axial tilt, shape of orbit, rotation)

9. Milankovitch Theory • Dominant theory of causes of glaciation, based on Earth-Sun geometry: • Orbital eccentricity – strongly elliptical orbit puts Earth farthest from Sun in summer, cooling it • Tilt obliquity – Earth’s tilt varies from 22.1º to 24.5º - less tilt means lower angle Sun and less insolation at poles, thus cooler summers • Orbital precession – wobbles of Earth’s axis - North Pole may point toward Sun at farthest point of orbit, creating a cool summer

10. Milankovitch Theory Orbital Eccentricity Axial Tilt Orbital Precession When three factors coincide, high probability of glaciation Glacial Geomorphology: Processes and Landforms

11. Climate Change and Glaciers • Since mid-1800s glaciers have been receding, both alpine and continental • Alps, Parts of Andes, Mt. Kilimanjaro melting • Thousands of sq miles of Antarctica & Greenland ice sheet lost over last 30 years due to warming • Melting area of Greenland has increased rapidly since early 1990s

12. Climate Change and Glaciers

13. Climate Change and Glaciers

14. Periglacial Processes and Landscapes • In near-glacial environments – constant freeze/thaw cycle effects on landscape • Permafrost – ground that is permanently frozen • Continuous – poleward of -7ºC mean annual isotherm – all surfaces frozen exp under water – avg 400 m thick, up to 1000 m thick • Discontinuous – poleward of -1ºC mean annual isotherm – thinner than continuous, esp. on south facing slopes

15. Extent of Permafrost

16. Permafrost Processes • Active Layer – soil that melts & refreezes daily or seasonally – as thin as 10 cm in continuous permafrost, up to 2 m thick in discontinous • Dramatic warming in arctic is making active layer much thicker & releasing tons of CO2 • Talik – body of unfrozen ground within permafrost, e.g. under a lake, important for movement of groundwater

17. Periglacial Landscape(Cross Section)

18. Ground Ice • Ground Ice – distinct zones of frozen water within the ground – variable amts of water • As these areas freeze & thaw, expand & contract, they cause physical weathering • Ice Wedge – water enters crack in active layer • Pingo – surface bulges because of ice under pressure below • Patterned Ground – land broken into polygons as frost pushes coarser material to surface

19. Ground Ice Landforms Ice Wedge Pingo Patterned Ground