Glacial hydrological Processes

Question 1

What is always operating together in a glacier?

Answer 1

Water in it’s frozen and liquid state within a glacier is always operating together.

Question 2

Where does the majority of water come from in glacial hydrology?

Answer 2

Surface melt

Question 3

Where does melt come from?

Answer 3

Surface melt

As the glacier moves, it generates internal heat which causes internal deformation.

As the glacier moves over the bed basal friction occurs.

Geothermal heating

Question 4

What are the pathways of water?

Answer 4

Surface- supra glacial
Inside- englacial
At the bed- subglacial

Question 5

What are moulins?

Answer 5

Large pothole that goes straight down to the bed.

Question 6

What is englacial flow?

Answer 6

Either flows through…

veins (gaps between ice crystals)
tunnels (conduits) or
crevasses.

Question 7

Conduits can be…

Answer 7

Englacial or subglacial

Question 8

What are cut and closure channels?

Answer 8

Supraglacial streams cut downwards and creep closes the roof on them (Gulley et al, 2015).

Question 9

What are the subglacial water pathways?

Answer 9

• Channels/Conduits
– R-channels (Rothlisberger, 1972)
– N–channels (Nye, 1953) (cut into bed rock)
– Canals (Clark and Walder, 1994)
– Braided system

Question 10

What are linked cavities?

Answer 10

Glacier will move away from the bumps on the leeside and leave an air filled gap (cavities)
Eventually water will be able to flow through the wall (linked cavities).

Question 11

What are canals?

Answer 11

Broad flat channels where you have a glacier resting on a deforming bed, instead of having dentritric R channels you get canals.

Braided drainage network.

Question 12

What is the concept of water film in subglacial water pathways?

Answer 12

Weertman (1972) suggested that all warm-based glaciers floats on a 1mm thin water layer.

Question 13

What is the concept of water sheet in subglacial water pathways?

Answer 13

Creyts and Schoof (2008) suggest you could have a thicker layer, where the glacier rests on class (macroporous).

Question 14

What are the two types of flow systems?

Answer 14

Fast systems

Slow systems

Question 15

What are fast systems?

Answer 15

Channelized dendritic system (mostly R)

Low water pressure- water is collecting in channels and flowing through

Question 16

What are slow systems?

Answer 16

Distributed system

High water pressure

Question 17

Seasonal evolution of the hydrological system

Answer 17

In Arolla, early in the season, flow is in linked cavities, but later in the season flows in conduits

In mid-may, sun starts to shine on glacier… linked cavities start filling up

As seasons go on, more ice is melted, goes into glacier, goes through system, at first fills up- linked, eventually they flow in conduits.
Nienow et al (1998)

Question 18

Spring Event

Answer 18

Links winter and summer- glacier suddenly speeds and rise up on a day that marks the spring.

Typical of warm based alpine galciersl

During the spring, meltwater builds up in the cavities, then suddenly the water passes a threshold, and the cavities are linked

So much water the glacier will lift off the bed- bed separation occurs

Glacier is uplifted and velocity increases

Question 19

Water stored in winter,early spring, released in summer (Stenborg, 1970; Willis et al, 1993)

In winter passages are constricted so any ablation goes into storage, which is later released
Where…?

Answer 19

• Fountain et al(1998) suggest that cavities too small, so water must be stored englacially
• Murray et al (2000) found from Falljökull, water was stored in veins and lenses smaller than 10cm
• At Black Rapids and Fels glacier (Raymond et al., 1995). 80-90% of the water carried in ‘slow systems’ the rest in ‘fast’ systems.

Question 20

Storage and glacier motion

Answer 20

Different system at Skálafellsjökull
Spring and autumn – subglacial fast system
Summer – 50% water goes into storage
Winter–water comes out of storage to produce the largest annual discharges

Question 21

Eskers

Answer 21

Sedimentary effects of water in a glacier
Eskers form from conduit sedimentation
Long sinuous ridges composed of sand and gravel
1-20m wide, 1-30m high, >100 m length

Question 22

What are R channels?

Answer 22

These are semi-circular channels cut upward into the ice.

Question 23

What are N channels?

Answer 23

Those incised into bedrock, perhaps suggesting long-term channel stability under some glaciers.

Question 24

In a typical alpine day where does the majority of…
The supraglacial component come from?
The subglacial component come from?

Answer 24

Sun and rain

Basal friction

Question 25

Seasonal evolution of a hydrological system such as Arolla

Answer 25

In winter, early in the season, flow is in linked cavities- DISTRIBUTED SYSTEM.

Later in the season (mid may) sun starts to shine, snow melts off.

Starts to fill up linked cavities to then flow in conduits- CHANNELISED SYSTEM.

Question 26

Seasonal evolution simplified

Answer 26

Winter (distributed system) -> Spring event -> Summer (channelized system)