Jökull - 01.01.2012, Page 171

Structural evolution of the 1890 Brúarjökull end moraine
Figure 1. A) The location of Brúarjökull at the northern margin of the Vatnajökull ice cap in Iceland. B) Digital
elevation model of the central forefield of Brúarjökull in Kringilsárrani. Points S-0 to S-3 indicate excavated
cross-sections in the 1890 end moraine. The area is approximately 8 km across. UTM coordinates are in metres.
– A) Kort af rannsóknasvæðinu við sporð Brúarjökuls. B) Hæðarlíkan af framlandi Brúarjökuls í Kringilsár-
rana. Punktar S-0 – S-3 tákna þversnið sem kortlögð voru í jökulgarðinum frá framhlaupinu 1890. Jökulgarðar
framhlaupanna 1810 og 1964 eru einnig merktir. Svæðið er um 8 km í þvermál. UTM hnit eru í metrum.
fore, the numbers obtained on the horizontal shorten-
ing and décollement depth can be regarded as mini-
mum and maximum numbers, respectively.
THE 1890 END MORAINE AS A PART
OF A DUAL MARGINAL LANDFORM
During the 1890 surge, the ice was coupled to the
overall fine-grained bed, as evident from strong clast
fabric in flutes and significant subglacial deformation
(Kjær et al., 2006). Overpressurized porewater in the
substrate lowered the effective pressure and favoured
decoupling at the substrate-bedrock interface, as in-
dicated by laminated dewatering structures that drape
the bedrock surface but unconformably truncate the
overlying layers of the substrate (Kjær et al., 2006).
Due to the decoupling, the substrate was dislocated
downglacier, resulting in high sediment influx to the
marginal zone. During the downglacier transport,
the subglacial sequence was deformed compressively
through multiple folding. To accommodate the sed-
iment surplus in the marginal zone, a ∼500 m long
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