Proglacial hydrology

The proglacial hydrology is relatively complex owing to several water inputs, an irregular topography and 200-300 m of per-

.5 2.0 2.5 Kilometres

Contours at 10 metre vertical Intervals \ (labelled at 50 metre vertical Intervals)

Watershed

Moraines

• 148 Heights In metres above sea level

Lakes Channels

Figure 15.1 Map of the proglacial zone of Finsterwalderbreen, showing glacier terminus. (See www.blackwellpublishing.com/ knight for colour version.)

mafrost. Main water inputs derive from snowmelt, rainfall and active layer melt. These accumulate in active layer sediments, forming lakes in topographic depressions in the moraine (5% of the proglacial area). These groundwaters drain through the summer along a topographic gradient to the proglacial floodplain via ephemeral streams. The streams dry out and water takes a subsurface routing as the active layer deepens and with progressive evaporative loss through the summer. Evaporative losses represent the greatest output from the proglacial hydrolog-ical system, accounting for 70% of water inputs from snow and rain.

Glacial bulk meltwaters act as a significant water input locally in near-channel environments. They flow through the proglacial zone in two major channels originating on the eastern and western glacier margins (eastern and western ice-marginal channels: Fig. 15.1). Together, they form a braided stream network that floods a significant area of the proglacial zone during summer. This network finally reforms as a single channel, discharging meltwaters to the fjord ca. 1.5 km from the glacier terminus. The glacial bulk meltwater stream and the proglacial active layer groundwater system are closely coupled in the near-channel zone. Glacial meltwaters are forced out into fluvial sediments and moraines as bulk meltwater discharge rises and drain back to the main channel as discharge falls. These channel and active-layer groundwater interactions are evident in stage records of wells emplaced in active-layer sediments bordering the main channel (Fig. 15.2). Periods of high bulk meltwater discharge give rise to high groundwater levels, with a decreasing effect with distance from the main channel (Wells 1 to 3). This channel-groundwa-ter coupling contrasts with observations in some other proglacial environments where the lack of an active layer, less complex topography and smaller groundwater reservoirs lead to very little interaction between glacial meltwaters and proglacial sediments (Fairchild et al., 1999).

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