Náttúrufræðingurinn - 2012, Blaðsíða 47

47
Tímarit Hins íslenska náttúrufræðifélags
SUMMARY
Formation of the Hraukar 1890
surge end moraine in Kringils-
árrani, Brúarjökull, Iceland
This paper describes the formation of
Hraukar – a prominent end moraine in
Kringilsárrani, east Iceland, formed dur-
ing the 1890 glacier surge of Brúarjökull,
a northern outlet of the Vatnajökull ice
cap. The sediment distribution proximal
to the moraine is investigated, along
with the morphology, sedimentology,
and tectonic architecture of the 1890 mo-
raine in order to increase current under-
standing on the interplay between a
fast-flowing ice and its forefield.
During the 1890 surge of Brúarjökull,
high porewater pressure developed in
the fine-grained subglacial sediment
sequence. This caused decoupling at
the substrate-bedrock interface and dis-
placement and compressive deforma-
tion of the subglacial sequence, result-
ing in gradual thickening downglacier
and the formation of an upglacier ta-
pering sediment wedge in the marginal
zone. The formation of the wedge oc-
curred during the last five days or so of
the surge. During the last day of the
surge, approximately, a moraine ridge
developed on the distal end of the
ridge as submarginal porewater pres-
sure dropped and substrate-bedrock
decoupling was established. This lead
to increased friction at the substrate-
bedrock interface and stress transfer up
into the sequence, which commenced
as brittle deformation in the final phase
in the moraine ridge formation. Three
excavated cross-sections show that
ductile deformation was the dominat-
ing style of deformation within the
wedge and moraine. A sequential mod-
el of subglacial and ice-marginal proc-
esses operating during the surge illus-
trates the stepwise formation of the
marginal sediment wedge and the end
moraine – a dual, inseparable marginal
end product of the 1890 surge.
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Um höfundinn
Ívar Örn Benediktsson (f. 1978 ) lauk BS-prófi í náttúru-
landfræði frá Háskóla Íslands 2003, meistaraprófi í
sömu grein frá Kaupmannahafnarháskóla 2005 og
doktorsprófi í jarðfræði frá Háskóla Íslands 2010.
Hann hefur starfað sem nýdoktor á Jarðvísindastofnun
Háskólans frá 2010 og sinnt stundakennslu í jarðfræði
við HÍ frá 2006. Hann starfar sem lektor við Háskólann
í Lundi frá 2012.
Póst- og netfang höfundar/Author’s address
Ívar Örn Benediktsson
Jarðvísindastofnun Háskólans
Öskju, Sturlugötu 7
IS-101 Reykjavík
iob2@hi.is