Jökull - 01.01.2012, Síða 165

Surge fingerprinting of cirque glaciers
Figure 10. Landsystems model for small surge-type cirque glaciers in Iceland, inspired from an overall landsys-
tems model for surging glaciers, (Evans and Rea, 1999; 2003). Distal zone, terminal moraine is formed of
pre-surge sediment and dump of sediment of the surge front. The moraines are often small, and hummocky
moraine often continues from their proximal slope. Proximal zone, it extends from the terminal moraine on to
the glacier margin, dead-ice and hummocky moraine are often widespread with occurrence of landforms such
as crevasse-fill ridges, backslump niches, medial moraines, and flutes. 1) glacier snout 2) rocks and sediment 3)
basaltic bedrock 4) subglacial sediment 5) supraglacial and englacial sediment 6) dead-ice 7) terminal moraine
8) hummocky moraine 9) crevasse-fill ridge 10) medial moraine 11) flute. – Landmótunarlíkan fyrir framhlaup
skálar-/hvilftarjökla á Íslandi. Líkaninu er skipt í innra svæði og ytra svæði þar sem ýmis landform finnast.
1) jökuljaðar 2) grjót og set 3) berggrunnur 4) set undir jökli 5) set á og í jökli 6) dauðís 7) endagarður 8)
haugaruðningur 9) sprungufyllingar 10) urðarranar 11) jökulkembur.
Proximal zone: Coarse and angular sediment is
prominent with numerous boulders on the surface.
Hummocky moraine is prevalent, sometimes contin-
uing from the distal zone. Small-scale crevasse-
fill ridges occur scattered in the area. Crevasse-fill
ridges are considered to be representative for surge-
type glaciers (Sharp, 1985a, 1985b, 1988b; Evans and
Rea, 1999). Such ridges are preserved because the
marginal zone of surge-type glaciers is usually stag-
nant after a surge terminates. As the stagnant ice
melts down, the ridges are preserved. In front of Búr-
fellsjökull and Teigarjökull well defined crevasse-fill
ridges occur randomly in the proximal area. They re-
late mainly to drift formations from the 1900s; how-
ever some indistinct ridges occur on the surface of
older drift sheets, indicating poor preservation poten-
tial. The abundance of supraglacially and englacially
transported debris can in some cases bury or obscure
crevasse ridges. Boulder trains or medial moraines
can be traced from the ablation zone of the glacier
into the forefield. Occasionally, flutes occur in the in-
ner zone. Dead-ice and associated landforms are com-
mon, particularly in the younger drift sheets.
The landsystems model from the Tröllaskagi
peninsula (Figure 10) describes the geomorphology
of surge-type cirque glaciers in alpine environments.
The lowland surge-type glacier landsystem model by
Evans and Rea (1999, 2003) does not cover alpine en-
vironments. The present study shows that this geo-
morphological environment is not as diverse in sed-
iments and landforms as the forefields of the larger
surge-type glaciers in Iceland, as it lacks e.g. most
glaciofluvial landforms that characterize the surging
glacier landsystem (pitted sandar, concertina eskers).
The alpine surge-type glacier landsystem has, how-
ever, unique fingerprinting in the sheet-like geome-
try of surge debris that is defined by the clear hum-
mocky terrain linking to the proximal sides of ter-
minal moraines. Crevasse-fill ridges and hummocky
moraine predominates the proglacial area in front of
the surge-type cirque glaciers in Tröllaskagi, whereas
annual moraines only occur in front of the non-surge
JÖKULL No. 62, 2012 163