Open Session - SWISS GEOSCIENCE MEETINGs

Figure 1: Schematic flowchart and details of the glacier bed modelling.
6.1
Transient response of idealized glaciers to climate variations
Martin Lüthi
VAW Glaciology, ETH Zürich, CH-4092 Zürich (luethi@vaw.baug.ethz.ch)
Variations of glacier length and volume under climate variations are investigated with model glaciers on a simple bedrock
geometry. Under periodic climate oscillations the well-known phase lags of length and volume are obtained, after initial
transients have died out. The relation between glacier mass balance (local or total) and climate is strongly influenced by the
transient response for forcing periods shorter than the volume time scale. These transients are surprisingly large, and lead
to unexpected trajectories in phase space. Under periodic oscillations the local ice thickness follows the climate forcing with
a typical phase delay of 60˚ (accumulation area) to 180˚ (glacier terminus), while glacier length is completely out of phase
for forcing periods below the volume time scale. The evolution of the model glacier can be approximately described with a
forced, linearly damped harmonic oscillator which is typically underdamped. Approximate expressions for the volume- and
area time scales are explicitly derived, as are volume-length scaling relations.
Phase space diagram of volume change vs. length change of a model glacier under climate forcing with 50 year period. Only after 5 cli-
mate cycles the glacier response approaches the limiting cycle around the steady state (black dot). Obviously climate and glacier reaction
are not closely related.
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Symposium 6: Apply! Snow, ice and Permafrost Science + Geomorphology