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

Abstract

ABSTRACT. The long-term monitoring ofLewis Glacier on Mount Kenya serves as a basis for the study of glacier evolution in response to climatic forcing through mode ling of its ice flow and mass budget. Following up on an earlier modeling and prediction study to 1990, this paper examines the ice-mass and flow changes in relation to the net-balance conditions over 1986-90. A model experiment using as climatic forcing the observed 1978-86 vertical net-balance profile yielded a volume loss and slow down of ice flow more drastic than observed during 1986-90. The causes of this discrepancy were examined in successive model experiments. Realistic simulations of mass-budget and thickness changes over 1986-90 are obtained using as input the net-balance forcing for the same period rather than for the preceding 1978-86 interval, and approximate flow velocities. With the same net-balance forcing and a completely stagnant Lewis Glacier, the elimination of mass redistribution by ice flow acts to mitigate the loss of volume and thickness in the upper glacier, and to accentuate it in the lower glacier. Accordingly, the observed 1986-90 net-balance profile along with the 1990 ice-flow velocities provide suitable input for the modeling ofLewis Glacier changes to 1994. Under continuation of the 1986-90 climatic forcing, ice thinning ranging from less than I m in the upper glacier to more than 7 m in the lower glacier, and a total volume loss of order 57 X 10 4 m 3 , are anticipated over the 1990-94 time interval.