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On the Secular Variation of Ice Flow Velocity at Lewis Glacier, Mount Kenya, Kenya

  • Stefan Hastenrath (a1) and Phillip Kruss (a1)

Abstract

Measurements at various epochs in the course of the twentieth century indicate a slowing down of surface ice flow velocity. This is consistent with the numerical modeling of the secular glacier recession, which furthermore shows a gradual upward shift of the regions of highest velocity and mass flux. Crevasse orientation is transverse above, and longitudinal below, the velocity maximum. The secular change in the longitudinal velocity profile seems to affect the crevasse pattern. Net balance in the next five years is a major factor in future changes of the glacier. With this reservation, model calculations for a possible extreme scenario indicate a drastic overall velocity decrease, and a moderate further displacement of the velocity and mass-flux maxima up-glacier, by the mid 1980’s.

Sur la variation seculaire de la vitesse de la glace au Lewis Glacier. Mount Kenya, Kenya. Des mesures à différentes époques au cours du vingtième siècle montrent un ralentissement de la vitesse superfieielle de la glace. Ceci est cohérent avec la modélisation numérique de la régression séculaire du glacier qui, de plus, montre une remontée progressive en altitude des régions de plus forte vitesse et de plus gros bilans. L’orientation des crevasses est transversale au-dessus et longitudinale au-dessous du point de vitesse maximum, Le changement séculaire du profil de vitesse longitudinal semble affecter la disposition des crevasses. Le bilan glaciaire des cinq prochaines années est le facteur majeur des changements futurs du glacier. Sauf cette réserve, les calculs sur modèle pour un scénario extrême montrent une forte diminution globale de la vitesse, suivie d’un déplacement modèré vers le haut de la vitesse et des flux maximum de glace, vers le milieu des années 1980.

Zusammenfassung

Die säkularen Änderungen der Fliessgeschwindigkeil des Eises am Lewis Glacier, Mount Kenya, Kenia. Messungen zu verschiedenen Zeitpunkten im Laufe des zwanzigsten Jahrhunderts lassen eine Abnahme der Fliessgeschwindigkeit des Eises erkennen. Dies passt zur numerischen Modellrechnung des säkularen Gletscherrückgangs, die ausserdem auf eine allmähliche Verlagerung der Gebiete höchster Geschwindigkeit und Massenbewegung nach oben schliessen lassen. Die Orientierung der Spalten verläuft oberhalb des Geschwindigkeitsmaximums quer, unterhalb desselben jedoch parallel zur Fliessrichtung. Die säkulare Änderung im Geschwindigkeitslängsprofil scheint das Spaltenmuster zu beeinflussen. Die Nettobilanz der nächsten fünf Jahre wird ausschlaggebend für zukünftige Veränderungen des Gletschers sein. Mit dieser Einschränkung deuten Modellrechnungen unter extremen Annahmen auf eine drastische Abnahme der Gesamtgeschwindigkeit und eine weitere, mässige Verlagerung der Maxima von Geschwindigkeit und Massenfluss gletscheraufwärts um die Mitte der 80er-Jahre hin.

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References

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Allison, I. F., and Kruss, P. 1977. Estimation of recent climate change in Irian Jaya by numerical modeling of its tropical glaciers. Artic and Alpine Research, Vol. 9, No. 1, p. 4960.
Caukwell, R. A., and Hastenrath, S. 1977. A new map of Lewis Glacier, Mount Kenya. Erdkunde, Bd. 31. Ht. 2. p. 8587.
Charnley, F. E. 1959. Some observations on the glaciers of Mt. Kenya. Journal of Glaciology, Vol. 3. No. 26. p. 48092.
Hastenrath, S., and Caukwell, R. A. 1979. Variations of Lewis Glacier, Mount Kenya. 1974–78. Erdkunde, Bd. 33. Ht. 4. p. 29297.
Hastenrath, S., and Kruss, P. [1981.] Dynamics of crevasse pattern at Lewis Glacier, Mount Kenya. Zeitschrift für Gletscherkunde und Glazialgeologie, Bd. 15, Ht. 2, 1979, p. 20107.
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On the Secular Variation of Ice Flow Velocity at Lewis Glacier, Mount Kenya, Kenya

  • Stefan Hastenrath (a1) and Phillip Kruss (a1)

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