Glaciers and Glacial Deposits

1. Glaciers and Glacial Deposits

2. Glaciers • Climate indicators • Growth is episodic (advance and retreat) • Long term changes (Miller et al.) in Cenozoic (and earlier) • Shorter term changes associated with insolation (100 ky and 23 ky cycles- Milankovitch Cycles) • High resolution changes (< 1000 years) • Mini- ice ages (Washington crossed frozen Delaware) • Use physical characteristics of glacial processes to infer climate • e.g., Pangaea was covered with glaciers • So America, Africa, India, Australia

3. Types of Glaciers • Alpine- elevation dependent • valley glaciers • confined to within mountain walls • piedmont glaciers • form at base of mountain and are coalesced valley glaciers • Continental- high latitude • 3 scales • ice sheets • only in Antarctica and Greenland; over 50,000 km2 • includes ice caps (Smaller ice sheets) • ice shelves (extend over sea; floats on water).

5. http://visibleearth.nasa.gov/

6. Growth • Function of water budget and mass balance • add snow, keep it through summer • above snow line! or cold summer temps like poles • begin to build glacier as snow becomes more dense (Snow->Firn ->then glacial ice) • CAN’T GROW W/O SNOW! • Add snow; lose snow • Balanced if acc. = ablation • Growth if accumulation > ablation

7. Growth • Balance between amount of ppt (growth) and amount of melt (ablation) • add ppt, more glacier/ advance/ Wax • ablation- water melts down snout of glacier, thinning and retreating • ablate, less glacier / retreat/ Wane

8. Growth/ Motion • Glacial motion • 1x10 cm/s to 2x10 cm/s (max ~ 1 m/day) • flows as high-viscosity fluid; • SQUEEZED • fastest flow on top; lower towards base and walls • entrains sediments

9. Environments • 4 environments to describe glacier itself • basal (subglacial) zone • in contact with bed • supraglacial zone • upper surface of the glacier • ice- contact zone • around margin of glacier • englacial zone • within glacial interior

10. Surrounding environments • Proglacial • area around glacier but not in contact • influenced by melting ice • Outwash plain • glaciolacustrine, glaciofluvial, glaciomarine • Periglacial • non-glacial phenomena that function in cold climates • permafrost

11. http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988757http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988757

12. Life History • Glacier builds, begins to move • Glacier erodes and entrains sediments • Glaciers rework its own sediment as glacier advances and retreats • Most sediment is incorporated as glacier moves along • Sediments are usually compositionally and texturally immature • Traverses hills, previously deposited moraines • Rocks at base are scoured • scratches bedrock; striations // to flow

13. Life History • Death! • melts back (rarely completely) • glacier actually always has a forward motion • mass of ice squeezes it forward even in retreat • melts completely when nose thins to ~ 50 m thickness • leaves sedimentary depositTill • Previously incorporated sediment which melts out • Poorly sorted • Outwash • tunnels often run beneath ice, flushing out sediments • or breaks off in to seaeventually breaks off into the ocean

15. http://earthobservatory.nasa.gov/

16. http://earthobservatory.nasa.gov/

17. Erosion Processes • Glaciers affect land surface by eroding it and/or leaving landforms behind • Erosion • scrapes up sediment • erodes rock • cirque- deep erosional recess • arete- as cirques grow headward • horn- pointed, 3-sided • col- knifes edge boundary between adjacent cirques • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

18. horn • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

19. cirque • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

20. arete • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

21. col • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

22. Hanging valley • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

23. U-shaped valley • http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms

25. Grooves

26. Glacial Deposits -Till • Till • material deposited as glacier retreats • gravel, pebbles, sand, mud • rocks are ground as glacier moves

29. Glacial Deposits- Moraines • End moraine • when glacier stalls (low accumulation relative to ablation), glacier continues to move debris to melting snout; this is the accumulation • Lateral • Marginal • debris is concentrated along edges of glacier • bound by wall • Medial • where lateral moraines join, can form in middle • Ground • sheet of debris developed during retreat • Recessional • like end, but occurs during retreat

30. End

31. http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandformshttp://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/glossary.html#erosionallandforms Medial, Lateral This photo shows two medial moraines (blue arrows) as seen from the air. The black arrows point to lateral moraines that have formed along the sides of the valley wall. Where the two main glaciers shown in the photo flow together, their lateral moraines join to form a medial moraine. The medial moraine on the right formed in the same way, however we can't see where the glaciers flow together to form the moraine.

32. Ground

33. Rivers and Lakes • Rivers • Generally braided streams, especially near glacial front • lots of coarse but fines also present too

34. http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490

35. Rivers and Lakes • Lakes • forms from damming (ice or moraine damming as glaciers drain water • most sediments (and water) released in summer • Laminated sediments accumulate finer sediments (glacial flour) • 1 varve = 2 layers (couplet) of light (summer) and dark (winter • delta may form at river mouth • coarse sediments closest to river; sediments thin away from delta • generally better sorted than river; no clays • distal • should find dropstones • turbidites from sediment overload ; density driven lobes of sediments

37. http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490

38. http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988490

39. Eolian • Winds attack deposits on outwash plains • lead to loess deposits • most effective after glacial melt and before re-vegetation • cap the facies by reworking glacial sediments

41. Glacial- marine • little reworking • when glacier meets sea it dumps load • sediments can fall out of melting glaciers (IRD) • IRD- Ice Rafted Debris • silty freshwater plume rides over denser, saline water • sediments settle out of suspension • turbidity current

43. http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988757http://www.glacier.rice.edu/land/5_depositionalproglacial.html#anchor988757

45. Other glacial features • Kettles- small lakes • small piece of ice breaks off and is covered by sediments, then melts • Eskers- • water flow thru tunnels stops and deposits seds; tunnel eventually collapses; leaves snakey deposits which remain after ice has melted; coarse seds accumulate under tunnels; often well- sorted (fluvial- like) • Drumlin • tear-drop shaped mounds; glacier deposits material and then rides over it; // to flow • Glacial erratics • boulders and other rocks which don’t match regional lithology (carried in)

47. esker

48. http://www.canadiangeographic.ca/Landforms/eskers.htm

49. drumlin