sensitivity of glacially-fed rivers to rapid climate change: ladakh, nw himalaya daniel hobley...
TRANSCRIPT
Sensitivity of glacially-fed rivers to rapid climate change: Ladakh,
NW Himalaya
Daniel HobleySupervisors: Hugh Sinclair,
Patience Cowie, Tibor DunaiGrant Institute
?
“Late Cenozoic uplift of mountain ranges and global climate change: chicken or egg?”
(Molnar & England, 1990)
• Disequilibrium alters process rates
• Timescales?
• Erosive mechanisms?
• Relative importance?
Glacial rivers vs normal rivers• Enhanced erosion
• Enhanced discharge
• Reduced variability
• Temperature controlled
• Altered sediments
•…but with Jokulhlaups
• Signals transmitted
…we need to quantify these effects.
Study area: Ladakh, NW Himalaya
• Restricted glacial area, variable down batholith
• Simple chronology
• Dry (Arctic desert)
• Constant forcings
• Limited human alteration
• Many comparable catchments
100km
Approach1. GIS study
3200
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3600
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4000
4200
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4800
5000
0 2000 4000 6000 8000 10000 12000
Distance downstream / m
Ele
vati
on
/ m
Unglaciated catchment
Typical fluvial profile
3000
3500
4000
4500
5000
5500
0 5000 10000 15000 20000 25000
Distance downstream / m
Ele
vati
on
/ m
Glaciated catchment
Fluvial section
Major knickpoint
Increased concavity(elevated erosion
rates)
Slope plot
Max modern glacial extent
Approx extent of significant glacial alteration
DEMs used to obtain channel form, drainage area, slope data
2. Fieldwork • Groundtruthing
• Measuring critical field parameters…
•…and how they vary downstream
• Cosmogenic samples
• Compare glaciated and unglaciated catchments
Sediment supplied
Channel morphometry
Sediment caliber
Channel width
Modern glacial behaviour
Nature of knickpoint & gorging
(Crave & Davy 2001)
3. Modelling
• Can we mechanistically understand the response to the imposed disequilibrium?
• Shape vs hydrology
• Analytical models?
• Or numerical? (e.g., EROS)
• Non-“steady state” analysis required…
Outstanding questions
Glaciers seem to increase downstream erosion, but…
• Fluvial (shape) vs glacial (hydrological) response?
• Distribution of erosion in time?• Lifetimes of various aspects of disequilibrium?• Can we scale up? (e.g., to Indus)• Understanding of transient responses of
systems?