It is important to note from the outset that meltwater not only flows through glaciers but that it can also be stored within a glacier in a number of ways. Storage occurs as ice, snow and water at a number of different spatial and temporal scales. For example, in subglacial settings, meltwater can be stored in cavities, in the pore space of subglacial sediments and in subglacial lakes. It can also be stored within the ice in englacial water pockets, tunnels and cavities, and on the glacier surface as snow and firn, and in supraglacial lakes. Water can also be stored adjacent to a glacier in proglacial and ice-marginal lakes.
Water storage in glaciers occurs at three time-scales (Figure 4.3). Long-term storage (years to centuries and longer) occurs as glacier ice and firn. This storage affects the long-term water balance of glacierised catchments and has the potential to influence global sea level. Intermediate-term storage (days to years) includes the seasonal storage and release of snow and water. Intermediate-term storage affects the runoff characteristics of glacierised catchments and their downstream river-flow regimes. Short-term storage (hours to days) includes the daily effects of drainage through a glacier including meltwater routing through snow and firn, as well as englacial and subglacial pathways. In addition to these time-dependent
processes there are also event-driven storage releases, including floods released by glacier surges and the drainage of subglacial, moraine-dammed or glacier-dammed water bodies (see Box 2.3).
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