Sensitivity of glacially-fed rivers to rapid climate change: Ladakh,

NW Himalaya

Daniel HobleySupervisors: Hugh Sinclair,

Patience Cowie, Tibor DunaiGrant Institute

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“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

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0 2000 4000 6000 8000 10000 12000

Distance downstream / m

Ele

vati

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/ m

Unglaciated catchment

Typical fluvial profile

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0 5000 10000 15000 20000 25000

Distance downstream / m

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vati

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/ 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?