Lecture 6 - Thermodynamics and Englacial Hydrology

Flashcards about englacial hydrology, thermal regimes of glaciers, water flow within glaciers, and related terminology.

What is the pressure melting point?

The temperature at which ice melts under pressure, which is colder than 0°C.

What is cold ice?

Ice that is below the pressure melting point, making it impermeable to water.

What is temperate or warm ice?

Ice that is at the pressure melting point, allowing for water movement and englacial hydrology.

What are temperate glaciers?

Glaciers where the entire ice body is at the pressure melting point.

What are cold glaciers?

Glaciers where the entire ice body is beneath the pressure melting point.

What are polythermal glaciers?

Glaciers that have both cold and temperate ice within them.

What are some basal heat sources that contribute to the temperature of glacier ice?

Friction, geothermal heat, and latent heat of freezing.

What are surface heat sources that affect the temperature of glacier ice?

Solar radiation, latent heat, and heat exchanges through conduction.

What is advection in the context of glacier ice movement?

The process where ice starts high in the accumulation zone, plunges to the deepest depths, and returns to the surface near the terminus.

What is primary permeability in englacial hydrology?

Movement between ice crystals at a granular scale, allowing for water flow and storage.

What is secondary permeability in englacial hydrology?

Larger-scale hydrological features such as meltback channels, tubes, capillaries, moulins, and crevasses within the ice.

What are capillaries in the context of englacial hydrology?

Voids and interconnected air parcels between ice crystals through which meltwater can move.

How do fractures form within glacier ice?

When the pressure from meltwater exceeds the strength of the ice, causing it to push apart and form small-scale channels.

What is cut enclosure?

The process by which a surface stream downcuts into the ice, eventually forming a lid over the channel.

In terrestrial environments, how does water flow?

Water flows downhill.

What two determinants affect water flow within a glacier?

Elevation and pressure.

Under what conditions will glacier channels be squeezed shut?

When the ice overburden pressure is greater than the water pressure.

Where does englacial hydrology occur?

Where the ice is at the pressure melting point.

What are moulins?

Vertical channels in glaciers that allow surface water to drain to the base.

What are crevasses?

Cracks in the surface of a glacier where surface streams can run off.

What is ice overburden pressure?

The weight and thickness of the ice above a certain point.

What is the englacial network?

Water moving through interconnected air spaces and capillaries.

What are fracture networks?

A network filled with water where the pressure from the water pushes back against the ice.

What is hydraulic potential?

The measure of potential energy of water in a glacier, considering elevation and pressure.

When ice overburden pressure is equal to water pressure, what happens to channels?

Channels remain open.

When water pressure is greater than ice overburden pressure, what happens to channels?

Channels will be growing and getting larger.

On what scale should we think about water storage in the englacial environment?

Hours to months towards a year.

What is the melting point beneath a kilometer of ice?

Minus 0.7 degrees.

What will one likely find on the surface of cold glaciers?

Streams rooted straight off the surface.

What kinds of polythermal glaciers are there?

Cold ice on the surface and warm ice at the bed, vice versa, or a mixture of the two.

What do we know to be true down in the ablation area?

We have surface melting.

What happens if we have a glacier flowing over obstacles and localized increases in pressure and melting and then freezing?

Latent heat exchanges.

If we are thinking about the equilibrium line somewhere in the center of the glacier, what will happen?

Highest ice, the surface ice, is going to be located quite close to that point.

What is the name of the glacier up in Svalbard?

Midrill Loughenbren.

What is the process of compressing snow over time to form fern and then ice?

Squeezing out of air particles

What has to happen to voids of capillaries to continue movement?

Have to be absolutely full of water.

What usually happen with glacier dynamic and movement on the bed when water drains?

We end up with short periods of rapid ice motion as the ice is carried along with that large amount of water that's drained.

What is hydralic potential dependent on?

Dependent on the density of water, gravity, and the elevation potential of water.

What is ice overburden pressure?

Has a strong determinant on whether water flows, and whether that is down slope as we might expect, or whether actually water can flow over, say, bumps in the bedrock beneath the ice or within the ice, not follow the most downslope direction.

What happens with larger channels when we get more meltwater through a melt season?

Larger channels are going to actively try and find larger channels. We're going to get lots of tributaries of smaller channels joining into larger ones.