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.

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

Valley Glacier Anatomy: Ablation and Accumulation Regions

Classification – Sea Ice vs. Ice Bergs

Glaciology

Classification – Valley Glaciers

Classification – Ice Caps

Classification – Ice Sheets

Classification – Tidewater or Tidal Glaciers

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

Glaciology – Mass Balance Profiles

The ELA: Equilibrium Line Altitude

Glaciology

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

Glaciology – Total Mass Balance

Mass Balance Schematic

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

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

Implications of Ice Discharge Profile 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 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.

Lateral Moraines as Paleo-ELA Indicators

Ice Motion – Block of ice on an inclined surface 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 z

Velocity Profiles: Newtonian vs. Nonlinear Fluirds

Glenn’s Flow Law

Borehole Deformation

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

Phase Diagram for Water

Regelation

Bumps on Bed

Evidence for Regelation from Carbonate Glacial Valleys Blackfoot Glacier, Montana

Down valley ice speeds

The Laurentide Ice Sheet

Ice Sheet Profiles

Glacier Surging – the Variegated Glacier, Alaska

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