Week 1

Question 1

Components of the Cryosphere (6)

Answer 1

Snow
Sea Ice
Ice Shelves
Ice Sheets
Ice Caps
Permafrost (discontinuous, continuous, isolated).

Question 2

Where are the majority of glaciers today?

Answer 2

Mostly in the Arctic north of 60 degrees (Svalbard, Greenland, Norway, N. Canada)

Question 3

Topographically unconstrained ice masses:

Answer 3

Ice sheet
Ice Cap
Ice Shelf
Ice Stream
Ice Tongue

Question 4

Topographically constrained ice masses:

Answer 4

Highland ice field
Valley Glacier
Piedmont Glacier
Cirque Glacier
Ice Apron/hanging glacier
Rejuvinated glacier

Question 5

Cirque Glacier

Answer 5

A Mountainout basin that has good yearly snow accumuation. Favourable at the highest peaks, with steep relief that means adjacent peaks have no glaciers.

Question 6

Valley Glacier

Answer 6

Climate allows ice to extend to lower elevations, (valleys) where flow is constrained and directed by topography.

Question 7

Ice Fields:

Answer 7

If climate cools or accumulation increases, glaciers can coalesce into an ice field with some peaks appearing through the field.

Question 8

Ice Caps

Answer 8

<50,000km sq, ice may subsume mountain peaks, and this starts to go beyond topographically directed ice flow.

Question 9

Ice Sheets

Answer 9

> 50,000 km sq consumes mountain ranges, flow may be entirely independent of topography. ‘organsed flow’ is common at margins as ice streams and outlet glaciers.

Question 10

Outlet Glaciers

Answer 10

Incision of fjords organises and directs ice flow.

Question 11

Ice Streams

Answer 11

Fast moving Ice that fractures perpendicular to flow.

Question 12

Ice Shelves and Tongues

Answer 12

Floating ice that extends offshore until calved away.

Question 13

Tropical glaciers

Answer 13

Found at extremely high elevation only within the tropics.

Question 14

Polar/Continental glacier

Answer 14

Climate dictates ice is below the freezing point year-round, except for a thin surface layer in summer.

Question 15

Temperate/Maritime glacier

Answer 15

Climate dictates that ice is above the freezing point throughout the year except for a thin surface layer in winter.

Question 16

Accumulation Area Features:

Answer 16

Ice domes, divides and dispersal centres (large ice masses), cirque basins and ice fields for smaller ice masses.

Question 17

Ablation area features

Answer 17

Ice streams, outlet glaciers, ice shelves, ice bergs, tongues, piedmont lobes, calving terminus.

Question 18

Evidence for Glacial Theory

Answer 18

Glacial features downstream of current glaciers, e.g. moraines.
Agassiz (1837) used evidence of striations, sediment deposition to suggest N. America had been glaciated over.

Question 19

Astronomical Theory of Ice Ages

Answer 19

• Eccentricity of Earth’s orbit, circular to ellipsoid over time, tilt and precession (wobble) also change with time, changing solar forcing on Earth, dictating climate.

Question 20

Recent Methodological Advances

Answer 20

Shells of marine organisms are a proxy for global temp (oxy-18 record).
ice cores are a proxy for temperature record from air bubbles.
Advancements in description and classification of sediments recently.
Satellite based remote sensing.

Question 21

Dating Methods

Answer 21

TCN - Terrestrial cosmogenic nucleide - dates boulders and bedrock surfaces, dating when the rock was exposed from ice.
OSL - Optically stimulated luminescence dating of grains of sand.

Question 22

Snowball Earth Theory

Answer 22

Evidence of widespread glaciation in Africa, we think there was a supercontinent in tropics, where various factors produces a low CO2 atmos, creating snowball earth.

Question 23

Glacier Formation

Answer 23

• Snow remains on ground for multiple years, gradually compressing and recrystallizing (firn) crystals grow, air pockets shrink and restricts to bubbles, Glacier ice is formed.
• Density increases with depth, profiles of this illustrate the rate at which snow turns to ice, which depends on accumulation rate and presence of meltwater.
• Once dense enough, ice absorbs red light leaving a bluish tint in the ice.

Question 24

What is Mass Balance?

Answer 24

The difference between mass gains and losses to a glacier or part of it.
Positive = net gain
Negative = net loss

Question 25

Melting Processes (Ablation)

Answer 25

- Surface melting most important for land-terminating glaciers. - Subaqueous melt at lake- and ocean-terminating glaciers. - Basal melt through friction heating, geothermal heating and rainfall runoff. - Meltwater that refreezes elsewhere doesn't count. - Highest melt rates where steep mass balance gradients enable glaciers to extent into relatively warm low altitudes.

Question 26

Sublimation

Answer 26

Transition from solid ice straight into water vapour, occurs in cold, dry climates.

Question 27

Solid Ice Discharge (Ablation)

Answer 27

- Either directly in a lake or ocean (iceberg calving) - Or motion of ice across grounding line (begins to float) - Can result in rapid loss of several km3 of ice (e.g. Helheim Glacier, Greenland) Important for Greenland (50%) and Antarctic (90%) Ice sheets as well as tidewater glaciers. - Calving from ice sheets dont count as its already floating.

Question 28

Accumulation Processes

Answer 28

- Snowfall - Deposition of other forms of ice (freezing rain, rime ice (frozen fog)) - Avalanches - Wind blown snow - Basal freeze on - Superimposed ice (freezing of water saturated snow).

Question 29

What produces the highest and lowest accumulation rates?

Answer 29

Highest: Mountainous regions with frequent onshore winds and much orographic precipitation e.g. West coast NZ and Patagonia) Lowest: Very dry and cold regions such as interior of the Antarctic.

Question 30

What is Surface Mass Balance?

Answer 30

Mass balance process occurring at the glacier surface. This is partly dependent on surface energy balance: the net energy produced by solar radiation, longwave radiation, sensible heat from atmosphere, latent heat related to phase changes. If energy balance is + after surface is at melting point, ablation processes will occur.

Question 31

Typical Temperature and Snowfall Lapse Rates

Answer 31

Temp decreases 6.5 celcius per km altitude under normal conditions. Snowfall normally increases with elevation : orographic precipitation and high proportion of snow vs rain at higher altitude. Reduces past a certain point as air cannot hold sufficient moisture.

Question 32

Mass Balance Gradient

Answer 32

This is the rate at which mass balance changes with elevation, related to temp and precipitation lapse rates. High gradient = high ablation and accumulation, e.g. Maritime glaciers such as NZ. Calculate as the average of the accumulation and ablation gradients.

Question 33

Typical Seasonal Mass Balance Pattern:

Answer 33

Most accumulation in winter, little in summer. | Most ablation in summer, little in winter.

Question 34

Quantifying Accumulation

Answer 34

Seasonal acc measured by reference to upper surfave of the previous season's firn. Multi-year acc measured by digging a snow pit, or extracting shallow ice core and identifying key seasonal variation in structure and density. Short term acc measured by ablation stakes.

Question 35

Quantifying Ablation

Answer 35

Direct field measurements of stakes drilled into the ice surface.

Question 36

Quantifying Net Mass Balance

Answer 36

Compare ablation with accumulation over the balance year.

Question 37

Quantifying Glacier Volume Change | GEODETIC METHODS

Answer 37

- Repeat topographic surveys or DEMS to compare contours. Terrestrial photogrammetry too. - Must convert volume change to mass change (need to know density of ablated/accumulated material.) - We can calibrate surface elevation changes with snow pits and cores, or use average densities for snow firn and ice.

Question 38

Quantifying Glacier Volume Change | HYDROLOGICAL METHOD

Answer 38

Used in valley catchment glaciers, use stream gauges to measure glacier catchment and runoff, R. Measure precipitation, P, on and off ice. Estimate or measure evaportation, E. Balance = P - R - E

Question 39

Quantifying Mass Balance | MASS FLUX METHOD for ice sheets

Answer 39

Compare the mass flux (depth averaged ice flow and thickness) through a downstream vertical cross section (often at grounding line) with upstream observed or modelled accumulation & melt.

Question 40

Weighing Ice Sheets?

Answer 40

Satellite gravimetry measures changes in Earths gravitational field every 30 days. Temporal changes in mass distribution of ice and underlying bedrock can be extracted after moving the effects of tides, changes in circulation and atmospheric loading.

Question 41

How does mass balance relate to climate?

Answer 41

Knowledge of mass balance of current glaciers and its relationshp with climate can be used to reconstruct past climates, and predict impacts of changing mass balance on water resources.

Question 42

Contemporary mass balance proxies

Answer 42

- Snow line mapping of glaciers as a proxy for mass balance. - ELA estimated by mappign end of the summer snow line. - Relative position of snow line and firn line can be use to assess longer-term trends in mass balance. - Snow line adjacent to bare ice = positive mass balance relative to last year. - Snow line separated from bare ice by firn = negative mass balance relative to last year.

Question 43

Palaeo Mass Balance Proxies

Answer 43

- Maximum altitue of lateral moraines delineate the ELA based on evacuation of debris by ice flow in ablation zone. - Accumulation area ratio (AAR) where we determine the relative size of palaeo glacier extent (ELA lies below ≈60% of former glacier area). - Area Altitude Balance Ratio (AABR) varies between glaciers based on hypsometry. Balance ratio improves AAR by accounting for shape and mass balance gradient (Rea, 2009).

Question 44

Glacier Response times

Answer 44

Time taken for glaciers geometry to adjust to a new steady state after a change in glacier mass balance. Depends on glacier volume and area and mass balance gradient.

Question 45

What controls the extent of mass balance change?

Answer 45

- speed of change depends on glacier's response time and rate of climate change. - size of change depends on elevation range and hypsometry of glacier (greater proportion of area close to ELA = bigger response to change in ELA)