GLACIER MODELING Glacial Runoff and Hydrology Modeling

Irina Overeem

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OutlineOBJECTIVE• Learn How to Run GC2D in the CMT• Discuss science & technology challenges

associated with new process code and coupling.

THEORY & EXAMPLE : GC2D • ELA, Mass balance and Yosemite

LAB 7Simple Changes to ELA, Mass balance Input Parameters

GC2D/Ice Component

• Task: to calculate glacier evolution.• Needs: climate and DEM characteristics• Provides: Ice thickness and Melt rate

• Original Developers: Mark Kessler & Bob Anderson, code was in Matlab; in the CMT tool a simplified version of GC2D is an “Ice” component in the Hydrology project.

Mountain Glaciers

Valley Glacier

Snow-Sourced

Delivers sediment & waterto pro-glacial river

Avalanche-Sourced

Glacier Evolution ModelSome Theory……..

1. What is ELA?

2. Basic mechanism of glacier evolution.

ELA

By definition, the line separating the ablation area of a glacier from the accumulation area is the equilibrium line (Meier, 1962). The net or annual specific balance is zero along this line and its elevation is denoted by ELA.

Glacier equilibrium line altitude (ELA) combined with the DEM determines the area of the basin covered with glaciers, and thus area contributing to ice accumulation and ice melt.

60 % of Ag> ELA = zero mass balance

Mass Balance

From McGregor et al., 2000

Mass Balance = Precipitation – Melt

Precipitation === CONSTANTAir Temp === Sine function of a year

Ice Flux Calculations:

Ud = Ice deformationUs = Basal sliding

• MODEL SETTINGS• Sierra Nevada, California experiments:• ELA = 3170 m• Mass balance = 0.01 m/yr/m• Maximum positive balance = 2 m/yr

• T ~6deg cooler, P ~ 2X higher

• Reproduces King Canyon 38 km, Eastern Sierra glaciers about 6 km.

GC2D; an Sierra Nevada Example

Westward draining glaciers 7 x longer than eastward draining glaciers; topographic asymmetry attributes for most of the length differences (Kessler et al, 2006).

Simulation Wiring

Note that the component acts without dynamic input of meteorology/snow melt

Time Stepping Issues

This is almost like a debugging assignment!

ELA and Mass Balance SettingsSet the number of rivers to two distributary channels. If you can adjust the bedload exponent, the channel with the shortest route to the coast will receive a higher proportion bedload.

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References on GC2D

• MacGregor, K.R., Anderson, R.S., Anderson, S.P., Waddington, E.D., 2000. Numerical Simulations of Glacial-Valley Longitudinal Profile Evolution. Geology, 28, 11,1031-1034.

• Kessler, M.A., R.S. Anderson, and G.S. Stock (2006), Modeling topographic and climatic control of east-west asymmetry in Sierra Nevada Glacier length during the Last Glacial Maximum, J. Geophys. Res., 111, F2, F02002, doi:10.1029/2005JF000365.

• Mark A. Kessler, Robert S. Anderson, Jason P. Briner, 2008. Fjord insertion into continental margins driven by topographic steering of ice. Nature Geoscience 1, 365-369 (11 May 2008) doi:10.1038/ngeo201 Letter

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Theoretical References

• Cuffey, K.M., Paterson, W.S.B. 2010. The Physics of Glaciers, Fourth Edition

Braithwaite, R.J., Muller, F., 1980. On the parameterization of glacier equilibrium line altitude World Glacier Inventory –

Proceedings of the Riederalp Workshop, September 1978: IAHS Publ. no. 126, 1980.