Glacial hydrological Processes Flashcards
What is always operating together in a glacier?
Water in it’s frozen and liquid state within a glacier is always operating together.
Where does the majority of water come from in glacial hydrology?
Surface melt
Where does melt come from?
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
What are the pathways of water?
Surface- supra glacial
Inside- englacial
At the bed- subglacial
What are moulins?
Large pothole that goes straight down to the bed.
What is englacial flow?
Either flows through…
veins (gaps between ice crystals)
tunnels (conduits) or
crevasses.
Conduits can be…
Englacial or subglacial
What are cut and closure channels?
Supraglacial streams cut downwards and creep closes the roof on them (Gulley et al, 2015).
What are the subglacial water pathways?
• Channels/Conduits – R-channels (Rothlisberger, 1972) – N–channels (Nye, 1953) (cut into bed rock) – Canals (Clark and Walder, 1994) – Braided system
What are linked cavities?
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).
What are canals?
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.
What is the concept of water film in subglacial water pathways?
Weertman (1972) suggested that all warm-based glaciers floats on a 1mm thin water layer.
What is the concept of water sheet in subglacial water pathways?
Creyts and Schoof (2008) suggest you could have a thicker layer, where the glacier rests on class (macroporous).
What are the two types of flow systems?
Fast systems
Slow systems
What are fast systems?
Channelized dendritic system (mostly R)
Low water pressure- water is collecting in channels and flowing through
What are slow systems?
Distributed system
High water pressure
Seasonal evolution of the hydrological system
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)
Spring Event
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
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…?
- 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.
Storage and glacier motion
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
Eskers
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
What are R channels?
These are semi-circular channels cut upward into the ice.
What are N channels?
Those incised into bedrock, perhaps suggesting long-term channel stability under some glaciers.
In a typical alpine day where does the majority of…
The supraglacial component come from?
The subglacial component come from?
Sun and rain
Basal friction
Seasonal evolution of a hydrological system such as Arolla
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.
Seasonal evolution simplified
Winter (distributed system) -> Spring event -> Summer (channelized system)
