Mass Balance - Theory and Application

8/2/2019 Mass Balance - Theory and Application

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Mass Balance:Mass Balance:

Theory andTheory andApplicationApplication

Steve Wilson South Cascade Glacier - 1928


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South Cascade Glacier - 20


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Outline

Basics

Methods Stratigraphic

Annual Hydrologic

Photogrammetric

Flux Gate (IceSheets)

South CascadeGlacier Comparative

Methods

Dynamics


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Mass Balance Basics

Wavering between the profit and theloss.

-T.S. Eliot, Ash Wednesday

The bank account model

Bn vs. bn

Measurements made

twice a year

Net balance (~October 1)

Winter balance (~May 1)

Summer balance(calculate)

c a

n n n

S S

B b d S b d S= +

n w sB B B= +


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Stratigraphic Method

Similar to annualmass balancemethod

Directmeasurement ofaccumulation andablation

Very laborintensive


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Terminology

Stratigraphicbalance vs. annualbalance

Mass balance is atime transgressiveprocess using timedependent

variables andmethods

from Mayo et al. (1972)


7/22from Mayo et al. (1972)


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Measurement Tools

Selectingrepresentativepoints

Mapping transientsnow line

Measurement tools

Surface areaestimations

R. Hock (2008)

Calculated massbalance can

depend on glacieroutlines, number ofmeasurements,human error, and

other factors.


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Measurement Points

Established positions Stakes/pits should covereven elevationdistribution

Account for velocity

from Kaser et al. (2003)


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Transient Snow Line

Early Season Late Season


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ELA

Low ELA/sharplydefined

High ELA/sharply

defined ELA separated

from ice by old firn

+Bn

Increasedaccumulationfollowing years of Bn

Bn more negativethan in precedingyears


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Measurement Tools

Probes, stakes,pits, and cores

Material properties

from Kaser et al. (2003)


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Surface Area

1992 1993


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Hydrologic Method

(square = )

Where is theglacier?

Accounts forinternal waterstorage

Primarily used inconjunction withother methods

from Krimmel (1995)

nB P Q E S

= V


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Photogrammetric Method

Requires highaccuracy

Works on ice,

difficult on snow Elevation change

at a specific pointdue to multipleprocesses

Timing is critical

Still requires

snow/firn densities


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Flux Gate

Primarily used onice sheets

Accumulation

Total accumulationover grounded ice

Ablation

Annual ice fluxacross groundingline


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South Cascade Glacier

Benchmark Glacier

Multiple massbalance methods

used andcompared

Long termglaciological andmeteorologicalrecords


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South Cascade Glacier:Mass Balance


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Internal Consistency

Meier andTangborn (1965)

use three methods

on South CascadeGlacier (squares = )

Photogrammetricvalues and directlymeasured balance

should be equal Can be checked

against hydrologicdata to check for

consistency orwater storage

1

S S

M h dS b dS

= = V V


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Emergence Velocity

Describesrelationshipbetween net

balance, flow, andthickness changesSubmergence inthe accumulation

areaEmergence in theablation areaCrossover

point=equilibrium


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Be carefulwhere youdig!!!

The End


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References

Fountain, A.G., Krimmel, R.M., Trabant, D.C., A Strategy for Monitoring Glaciers: United StatesGeological Survey, Circular 1132, 25 p.

Hock, R., Hulth, J., Pettersson, R., 2008, Mass Balance of Storglacieren: American Geophysical

Union, Fall Meeting 2008, abstract #C11D-0527

Kaser, G., Fountain, A.G., Jansson, P., 2003, A Manual for Monitoring the Mass Balance of MountainGlaciers: Technical Documents in Hydrology, UNESCO, no. 59, 137 p.

Krimmel, R.M., 1995, Water, ice, and meteorological measurements at South Cascade Glacier,Washington, 1994 balance year: U.S. Geological Survey Water-Resources Investigations Report 95-4162, 41 p.

Krimmel, R.M., 1994, Runoff, precipitation, mass balance, and ice velocity measurements at SouthCascade Glacier, Washington, 1993 balance year: U.S. Geological Survey Water-ResourcesInvestigations Report 94-4139, 34 p.

Krimmel, R.M., 1993, Mass balance, meteorological, and runoff measurements at South CascadeGlacier, Washington, 1992 balance year: U.S. Geological Survey Open-File Report 93-640, 38 p.

Mayo, L.R., Meier, M.F., and Tangborn, W.V., 1972, A System to Combine Stratigraphic and AnnualMass Balance Systems: A Contribution to the International Hydrological Decade: Journal ofGlaciology, v. 11, no. 61, p. 3-14.

Meier, M.F., and Tangborn, W.V., 1965, Net budget and flow of South Cascade Glacier, Washington:Journal of Glaciology, v. 5, no. 41, p. 547-566.

Paterson, W.S.B., 1994, the Physics of Glaciers, Third Edition: Butterworth-Heinemann, Oxford, pp.

26-52.