Meltwater Pathways Exam

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 melt come from?

Answer 2

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 3

What are the pathways of water?

Answer 3

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

Question 4

What are moulins?

Answer 4

Large pothole that goes straight down to the bed.

Question 5

What are cut and closure channels?

Answer 5

Supraglacial streams cut downwards and creep closes the roof on them.

(Gulley et al, 2015)

Question 6

What are the subglacial water pathways?

Answer 6

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

Question 7

What are linked cavities?

Answer 7

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 8

What are canals?

Answer 8

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 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

What are the two types of flow systems?

Answer 11

Fast systems

Slow systems

Question 12

What are fast systems?

Answer 12

Channelized dendritic system (mostly R)

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

Question 13

What are slow systems?

Answer 13

Distributed system

High water pressure

Question 14

Seasonal evolution of the hydrological system

Answer 14

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 15

Spring Event

Answer 15

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 16

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 16

• 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 17

Storage and glacier motion

Answer 17

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 18

Eskers

Answer 18

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 19

What are R channels?

Answer 19

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

Question 20

What are N channels?

Answer 20

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

Question 21

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

Answer 21

Sun and rain

Basal friction

Question 22

Seasonal evolution of a hydrological system such as Arolla

Answer 22

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 23

Seasonal evolution simplified

Answer 23

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