Ice dynamics

The dynamics of plateau icefields are controlled by the ice provenance and thermal regime experienced during either extensive regional to full glacial conditions where the topography is submerged and ice-sheet-surface slopes control ice-flow directions, or local- to regional-scale glaciation when ice accumulation is centred on plateaux, occurring during interstadials/interglacials. With the onset of full glacial conditions newly forming or expanding plateau icefields are likely to be, or become, cold-based, thereby 'freezing' and thus preserving the plateau surface. As ice masses thicken, plateau ice will likely remain cold-based, whereas ice in surrounding valleys may reach the PMP (pressure melting point), overdeepening existing valleys and perhaps cutting through-valleys, in the classic style of 'selective linear erosion' (Sugden, 1974).

During local- to regional-scale glaciation, plataeu ice thicknesses are reduced and controlled by the plateau dimensions (Rea

Figure 20.1 Land elements and units that comprise the plateau icefield landsystem. Plateaux surfaces that show no signs of glacierization must be evaluated for a potential ice cover by an area altitude approach. Reprinted by permission of Hodder Arnold.

et al., 1998). Simplistically, below a critical summit size, the smaller the plateau the higher it must be above the regional firn line to support an icefield, and so the lower will be the ice temperature. Thus, the potential for producing a clear geomorpho-logical signature varies directly with plateau size (thicker warmer ice) and inversely with plateau altitude above the regional firn line (colder protective ice). In polar regions even large icefields are unlikely to reach the PMP. If present, plateau icefields may contribute mass to valley glaciers, by direct connection or avalanch-ing, thus having an impact upon climate reconstructions based on glacier equilibrium line altitudes (ELAs).

Was this article helpful?

0 0

Post a comment