Study area

Field investigations were carried out on the northern part of the Br0gger Peninsula, NW Spitsbergen (78°55' N, 12° 10' E, Fig. 1). The study area is mountainous and supports a number of valley glaciers, like midre Lovenbreen, austre Lovenbreen and vestre Lovenbreen. Active sandurs (outwash plains) occupy the zone between arcuate terminal moraine complexes and fjord coastline (Fig. 2).

Fig. 1. Map showing Svalbard and the location of the study area in West Spitsbergen

From: Harris, C. & Murton, J. B. (eds) 2005. Cryospheric Systems: Glaciers and Permafrost. Geological Society, London, Special Publications, 242, 111-117. 0305-8719/05/$15.00 © The Geological Society of London 2005.

Slâttofjellet

Metamorphic rocks Limestone bar

Terminal moraine L.I.A, Proglacial area T7! Vegetalized sandur

J Sandur with active runoff Ur-^1 Runoff B881 Marine terrace Shoreline 0 French camp

Kongsfjorden

Source : aeriai photography NPI 16-0B-1990 (S90-5789) OD. MERCIER

Gluudneset

Fig. 2. Geomorphological map of the proglacial area (austre Lovenbreen and midre Lovenbreen), Spitsbergen

Metamorphic rocks Limestone bar

Terminal moraine L.I.A, Proglacial area T7! Vegetalized sandur

J Sandur with active runoff Ur-^1 Runoff B881 Marine terrace Shoreline 0 French camp

Kongsfjorden

Source : aeriai photography NPI 16-0B-1990 (S90-5789) OD. MERCIER

Slâttofjellet

Gluudneset

Fig. 2. Geomorphological map of the proglacial area (austre Lovenbreen and midre Lovenbreen), Spitsbergen

The barrier coastline at the seaward end of the outwash plains constitutes a paraglacial coast in which the nearshore sediment budget is dominated by inputs of reworked glacigenic sediments transported by glacial meltwater streams. Forbes & Syvitski (1994) defined paraglacial coasts 'to be those on or adjacent to formerly ice-covered terrain, where glacially excavated landforms or glacigenic sediments have a recognizable influence on the character and evolution of the coast and nearshore deposits'.

Mass-balance investigations on the local glaciers indicate a negative net balance since the end of the Little Ice Age (Lefauconnier et al. 1999; Nesje & Dahl 2000). Small glaciers (around 8 km2 in area) have been retreating throughout the twentieth century, although in 1907 austre Lovenbreen, midre Lovenbreen and vestre Lovenbreen were at their maximum, with domed fronts associated with the outermost frontal moraines, as we can see on Isachsen's photos (Isachsen 1912). In 1936, these glaciers were still very close to their terminal moraines (Fig. 3). Rippin et al. (2003) calculated mean annual mass balance of —0.61 m/a (water equivalent) for Midre Lovenbreen between 1977 and 1985. This glacier retreat is correlated with the current climatic change. During 19751996 in Ny-Alesund, 25% of the precipitation was rain, 44% was snow and 31% was mixed, sleet or combination of rain and snow (F0rland & Hanssen-Bauer, 2000), with the trend for snow being negative and that for mixed precipitation positive. The annual mean temperature at Svalbard Airport has increased by 0.14°C per decade since 1912 and annual precipitation has

Fig. 3. Aerial photographs of northern part of Br0gger peninsula (1936-1999)

Fig. 3. Aerial photographs of northern part of Br0gger peninsula (1936-1999)

increased highly significantly by 2.8% per decade during the twentieth century (Hanssen-Bauer 2002). Statistical relationships between negative mass balance and meteorological parameters have been investigated (Lefauconnier & Hagen 1990; Hansen 1999; Lefauconnier et al. 1999; Nesje & Dahl 2000). Glacier retreat reflects in part a decrease in winter snowfall and a concomitant increase in rainfall. Hansen (1999) calculated the response time of midre Lovenbreen to climate change during the twentieth century to be 31 years. One consequence of these changes in climate and glacier mass budget is that seasonal meltwater discharge has been increasing (Hagen & Lefauconnier 1995). Current summer meltwater discharge amounts to about 107 m3. Increased water discharge has resulted in increased sediment mobilization. Sediment transport has been estimated to be between 478 and 2009 t/km2/a for the austre Lovenbreen catchment (Geoffray 1968; Griselin 1982) and around 940 t/km2/a for vestre Lovenbreen catchment (Etzellmiiller 2000). Paragla-cial sediment reworking, particularly by meltwater runoff, is therefore increasing in importance. Changes in glacifluvial sediment input have important consequences in terms of the dynamics of the paraglacial barrier coastline (Boulton 1990; Dowdeswell & Scourse 1990), which experiences local progradation where sediment input is augmented, but local retreat where sediment input is reduced.

0 0

Post a comment