Glaciology: Why important? What are glaciers? How do they work?

1. Glaciology:Why important? What are glaciers? How do they work? Glaciers are important in their role in creating glacial landscapes (erosional and depositional features). Glacial extent over the globe is tightly linked to eustatic sea level, so the waxing and waning of global ice volume is strongly tied to the evolution of coastal landscapes. Glacial ice contains high resolution records of climate history. Ice has a planetary science interest - Martian ice caps and icy satellites of distant planets in our solar system. Glacial control of hydrology; Outburst floods.

2. Working definition: A natural accumulation of ice in motion due to its own weight and surface slope. Glaciology – Glacier Definition and Density Profile

3. Valley Glacier Anatomy: Ablation and Accumulation Regions

4. Classification – Sea Ice vs. Ice Bergs

5. Glaciology

6. Classification – Valley Glaciers

7. Classification – Ice Caps

8. Classification – Ice Sheets

9. Classification – Tidewater or Tidal Glaciers

10. Glaciology – Conservation of Mass – The Local Mass Balance: b(z)

11. Glaciology – Mass Balance Profiles

12. The ELA: Equilibrium Line Altitude

13. Glaciology

14. Glaciology – Conservation of Mass – The Total Mass Balance: B

15. Glaciology – Total Mass Balance

16. Mass Balance Schematic

17. Model of Ice Thickness Evolution Imposed mass balance profile held steady throughout simulation; Glacier achieves steady state after ~600 years of simulation.

18. Steady-State, Uniform-Width, Down Valley Discharge Profile

19. 1. Ice discharge increases down valley to accommodate new snow within accumulation area. 2. Negative local mass balance within ablation area implies that ice discharge must be decreasing down valley below the ELA. 3. So vertical component of ice parcel trajectories is downward in accumulation area and upward in ablation area. 4. Likewise, ice-embedded debris is moved toward the bed in the accumulation area and toward the surface in the ablation area. Implications of Ice Discharge Profile

20. 5. Topographic contours will bend up-valley above the ELA and down valley below the ELA – providing a handy way to estimate ELA position/elevation. 6. Debris moves away from valley walls in accumulation zone and toward valley walls in ablation zone, which accounts for the presence of lateral moraines only below the ELA. 7. Lateral moraines can, therefore, be used as landscape indicators of paleo-ELA position and, hence, paleo-position of the 0oC isotherm – a useful paleoclimate proxy. Implications of Ice Discharge Profile

21. Lateral Moraines as Paleo-ELA Indicators

22. Step 1. Expression for shear stress within the ice: Decompose the weight (product of density and volume) into two components: Normal Force – perpendicular to the incline surface Shear Force – parallel to the incline surface Stress (pressure) is a force per unit area. Step 2. Expression for ice rheology: Our rheology of interest relates the stress to the spatial (vertical) gradient in velocity. Start with a Newtonian fluid – stress is linearly proportional to the velocity gradient through the dynamic viscosity. Step 3. Combine to relate strain rate to position in ice. Step 4. Integrate to obtain velocity profile. H-z Ice Motion – Block of ice on an inclined surface z

23. Velocity Profiles:Newtonian vs. Nonlinear Fluirds

24. Glenn’s Flow Law

25. Borehole Deformation

26. Relative contributions of internal deformation and basal sliding How does the glacier accomplish the “sliding”?

27. Phase Diagram for Water

28. Regelation

29. Bumps on Bed

30. Evidence for Regelation from Carbonate Glacial Valleys Blackfoot Glacier, Montana

31. Down valley ice speeds

32. The Laurentide Ice Sheet

34. Ice Sheet Profiles

35. Glacier Surging – the Variegated Glacier, Alaska

36. Glacier Surging Time Lapse /Users/pna/Work/Teaching/Animations/variegated_cd.mov