Please enable JavaScript.
Coggle requires JavaScript to display documents.
Haut Glacier d'Arolla (As melt season progressed (Dye return curve…
Haut Glacier d'Arolla
Nienow 1998 Method
Over 500 tracer tests carried out
Spanning 3 full summer melt seasons (1990, 1991, 1992)
From > 30 moulins
To infer drainage system nature
As melt season progressed
Dye return curve shows
1. Decreasing diffusivity
2. Decreasing travel time
(routing through drainage)
3. Earlier peak concentration
--> As subglacial drainage efficiency increased
Nienow Findings
Increasing efficiency subglacial drainage system
--> as melt season progressed
Seasonal travel t vs water flow v
Dye travel time
Remains the same once channelised
Decreases with time
Convert to velocity
Assume straight line flow distance
N.B. velocity is minimum estimate since sinuous flow = faster)
Velocity Finding:
Earlier in season = Slower
indicative of
distributed, inefficient drainage
Later in season = Faster
suggest
channelised efficient drainage
Water velocity increases
as season progresses
Spatial variability flow efficiency
Subglacial drainage efficiency
increases moving upglacier
Water velocity increases as season progresses
Early season - snowpack
Later season - exposed ice / conduits
Seasonal Drainage Efficiency Evo
Seasonal increase drainage efficiency
mimics snowline retreat
Early in season -
snowpack present
∴ only
small melt input
into subglacial system
Late melt season -
snowpack removed
Greater melt input
Higher flow velocities
as system = channelised
Seasonal evo glacier drainage
Start season
Snowpack
covers
glacier
Throughout melt season
Snowline retreats upglacier
--> Exposing moulins at surface
With increasing melt input
Hydraulically efficient channels develop
However, not whole glacier channelised
Inefficient drainage
upglacier accumulation area(abovesnowline)
between moulin
Moulin
∴ Drained by efficient channels