| Term: | Response time |
| Definition: |
The e-folding time scale for the transition of a glacier, following a step change in mass balance, from one steady state to another. Response times have been formulated for various attributes of the glacier such as volume and length. They can be confused easily with the mass-turnover time; the reaction time; and the growth time. The volumetric response time is the most commonly seen formulation. Here the glacier changes from an initial volume V1 to a later volume V2, and the response time is the time needed for the volume to change by (V2 V1) (1 e-1), where e = 2.71828... Is the base of natural logarithms. The response time is much shorter than the time required to attain volume V2. Indeed, in this formulation the time to attain volume V2 is infinite. The change between state 1 and state 2 is assumed to be 'small'. The response time for volume is somewhat shorter than that for length, that is, for the length to change by (L2 L1) (1 e-1). The response time is an idealization. The essence of the idea is that the glacier 'remembers' its earlier steady state because it adjusts its size and shape by flow. The volume response time is often estimated with an expression due to J IHPGlacierMassBalance
GCW |