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

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.

Diagnosing the imbalance of Yanamarey Glacier in the Cordillera Blanca of Peru

“…The following treatment of ice flow dynamics is in part repeated from Hastenrath [1989] and is further based on a series of earlier papers [Budd, 1969;Bhatt et al, 1980;Hastenrath and Kruss, 1982;Kruss, 1984]. Directly pertinent here are only the relationships, described in (5)…”

Ice-flow and mass changes of Lewis Glacier, Mount Kenya, East Africa, 1986–90: observations and modeling

“…From the glaciological (net-balance stakes) and the geodetic (repeated mapping of ice-surface topography) methods, the uncertainty in the volume change of the entire glacier during 1986-90 is estimated at order 5 (range 69-4 m 3 • For the glacier as a whole, this translates into a thickness equivalent of 0.2 m. For an individual 100 m band or a particular grid poin t, the uncertainty in thickness change would be of order 0.5 m. For the vicinity of 400-500 m, small changes were in fact obtained from the 1986 to 1990 mapping; the effect may in part be real in this location just below a steep surface slope, and in part be a shortcoming due to the fresh snow cover in the 1990 mapping (Hastenrath and Rostom, 1990) . The 1986-90 changes in flow velocity are determined to within 0.1 ma-I.…”

“…The 4 year (1986-90) mean vertical net-balance profile is plotted in Figure 2 as curve "b" . The glacier was mapped by aerial photogrammetry at a scale of I : 2500 in March 1986 and March 1990 (Hastenrath and Caukwell, 1987;Hastenrath and , Rostom, 1990), which allows the assessment of changes in ice thickness and volume over this 4 year time span for various domains of the glacier (Fig. 1).…”

“…Kruss (1984a, b) pioneered an ice-flow model specific to Lewis Glacier, adapting the model described by Budd (Hastenrath and Caukwell, 1987;Hastenrath and Rostom, 1990 J enssen (1975) and also used by Allison and Kruss (1977) . Kruss's (1984a, b) Lewis Glacier specific model has proven realistic in a series of earlier studies in producing ice thickness and flow velocity consistent with observation (Bhatt and others, 1980;Kruss, 1981, 1982;Hastenrath, 1989), and is further used here.…”

Continued Decrease of Ice-Flow Velocity at Lewis Glacier, Mount Kenya, East Africa

“…The ice-flow velocity pattern in Lewis Glacier and its long-term variations have been the topic of a series of papers Kruss, 1979, 1982;Hastenrath, 1983;Kruss and Hastenrath, 1983). These works have borne out a mono tonic and drastic slow-down of ice flow from the turn of the century to January 1982, demonstrably as a direct consequence of unfavorable climatic changes, the prevailingly negative net balance, and the concomitant thinning of the glacier (Hastenrath and Kruss, 1982;Hastenrath, 1984, p. 170-95). Moreover, based on the numerical modeling of the ice dynamics and the net balance during the budget year March I 979-March 1980, the following changes were predicted from the 1978 to the 1985 datum (Hastenrath and Kruss, 1982): a reduction of the ice-flow velocity by nearly a half and of the maximum mass flux by more than half; an up-glacier displacement of maximum velocity, maximum mass flux, and of the transition zone between longitudinal crevasses in the lower glacier and transverse crevasses in the upper glacier; a flattening of the velocity and mass-flux maxima, and less well-defined contrasts in crevasse orientation; and a terminus retreat of the order of 50 m. It was further anticipated that continued negative net balance and diminishing ice movement would lead to the terminus retreat becoming increasingly determined by the ill-situ net balance rather than the mass economy and flow dynamics of the glacier as a whole.…”