Lecture 7 - Subglacial Hydrology

Flashcards reviewing key concepts from a lecture on sub glacial hydrology.

What is the primary factor affecting super glacial hydrology after energy fluxes?

Melt on the surface and water forming.

What determines the vertical penetration of water through a wet snowpack?

Equations related to the saturated snow.

What must be satisfied first in a dry snowpack before water flows?

The irreducible water content.

In a saturated snowpack, how does water move?

Downslope, following the ice surface profile.

What is an aquifer in the context of a glacier?

Water storage in the fern.

How do open streams on a glacier act during the melt season?

Just as they would in a terrestrial environment.

What determines the thermal regime of a glacier?

The temperature profile.

In which area of a glacier is there typically net freezing at the bed?

The upper area, or accumulation area.

What warms the ice towards the bed of a glacier?

Friction and pressure.

Where on a glacier is ice and snow transported the smallest distance?

Around the equilibrium line.

What happens when heat is added to cold ice?

The ice becomes slightly less cold but remains below the pressure melting point.

What must be present for liquid water to exist in a temperate glacier?

Ice at the pressure melting point.

How is water transferred between ice crystals in a temperate glacier?

Slowly, acting as either storage or transfer.

What characteristics do polythermal glaciers exhibit?

Attributes of both warm and cold ice.

What is the term for water movement around ice crystals and in veins?

Primary permeability.

How are larger tunnels or conduits formed within a glacier?

By meltwater melting back to increase channel size.

What is hydrofracture?

Water gathering and opening fractures due to hydrostatic pressure.

What two factors determine where water flows within a glacier body?

Change in elevation and change in pressure (ice thickness).

Why do anglacial channels need to be full of water to remain open?

To keep water pressure equal to or greater than ice overburden pressure.

What is the primary control on sub glacier drainage?

The type of bed (hard bedrock or sediment).

How does water flow through soft, deformable sediment beneath a glacier?

In a number of ways including saturation, pore spaces, or capillaries.

What are linked cavities and braided canals?

Small, high-pressure systems that cannot efficiently evacuate meltwater.

Describe film flow under a glacier.

Thin layers of meltwater between the ice and the bedrock.

What are the two most common types of sub glacial drainage networks?

Linked cavities/canals switching to channels.

What characterizes R-channels?

Channels melting upwards into the ice.

What characterizes Nye channels?

Channels incising downwards into the bedrock.

What processes counteract ice overburden pressure in sub glacier channels?

Sufficient meltwater flow.

Where do link cavity systems typically occur?

In hard bedrock with undulations where gaps from between the ice and the bedrock.

What typically joins cavities in a link cavity system?

Small orifices or channels/canals.

What is the result of soft saturatable sediment beneath a glacier?

Saturation and bulk movement.

What is Darcyan flow?

Water moving between the sediment grains while the sediment remains stationary.

What is till dilation?

Individual sediment grain movement due to high stress, which changes pore space.

What terms are used to describe sub glacier drainage according to how they occur over the glacier bed?

Discrete and distributed.

Which type of sub glacier drainage system typically exists over winter?

A link cavity system.

What happens to the link cavity system at the start of the melt season?

The link cavity system becomes overwhelmed and collapses into channelized drainage.

What is the key indicator of the progressive switch to channelized drainage up glacier?

Location to the snowpack line.

What is the water pressure/water flux relationship in linked cavities?

Positive relationship: increased water flux increases water pressure.

What is the water pressure/water flux relationship in sub glacial conduits?

Negative: As discharge increases, the melting action leads to decreased water pressure.

What is the arborescent drainage network structure?

High pressure branches in up-glacier areas that combine into a low pressure system.

What does Shreves Law state?

Hydraulic Potential is dependent on the density of water, gravity, and elevation but is also affected by the ice overburden pressure.