Jökull - 01.01.2013, Blaðsíða 56

Da̧bski and Tittenbrun
Figure 1. Location of the Fláajökull marginal zone
and the rate of retreat along the Hólmsárgarður profile
(Sigurðsson, 1998; Da̧bski, 2002, 2007, modified).
– Kort af jökulgörðum við jaðar Fláajökuls ásamt
þversniði yfir sjö framrásargarða austan Hólmsár.
Jökuljaðarinn við lok litlu ísaldarinnar er sýndur
með punktalínu.
These methods are generally known in geomorphol-
ogy (Hubbard and Glasser, 2005), however, a new in-
strument was used in this study to determine micro-
roughness. Additional lichenometric dating of the
oldest moraine ridge of Fláajökull was performed.
The Handysurf E35-B electronic profilometer al-
lows the measurement of very subtle increases in sur-
face micro-roughness and displays micro-roughness
parameters with a vertical resolution of 0.01 µm.
Therefore, a hypothesis was put forward that short-
term (post-LIA maximum) time-dependent surface
deterioration of basaltic surfaces, result in micro-
roughness increase, and can be recorded by the elec-
tronic profilometer. It was assumed that weathering
processes also result in gradual thickening of weather-
ing rinds and decrease in Schmidt hammer R-values.
These indices have the potential to differentiate the
age of the moraines, thereby providing the opportu-
nity to critically assess the possible early 19th c. age
of the LIA maximum at Fláajökull suggested by Ch-
enet et al. (2010).
USE OF SURFACE ROUGHNESS,
WEATHERING RIND THICKNESS AND
SCHMIDT HAMMER IN GLACIAL
GEOMORPHOLOGY
Previous measurements of rock surface roughness
in studies of glacial transport and relative dating of
glacial landforms were performed on gneiss within
the Storbreen marginal zone and in Oldedalen, Nor-
way (McCarroll, 1992; McCarroll and Nesje, 1996).
A hand profilometer was used which enabled mea-
surement of relative heights of micro-depressions
and micro-elevations with a vertical resolution of
0.01 mm, and the amplitude of micro-relief was usu-
ally 0.5–6 mm. Results proved that there are dif-
ferences in surface roughness of glacially abraded
rocks exposed since about 250 BP (LIA) and those
exposed about 9000 BP, allowing for a great differ-
ence in weathering time. A different approach to rock
surface roughness was employed by Hubbard et al.
(2000) in the marginal zone of the Glacier de Tsan-
fleuron in Switzerland. They used a micro-roughness
meter (MRM) and an electro-optical distance meter
(EDM) and found that roughness at all horizontal
56 JÖKULL No. 63, 2013