Jökull - 01.12.1981, Page 82

segja, að Guðrún Larsen hefur tjáð mér, að
hún hafi fundið það á Búrfellshálsi NV af
Heklu, rétt ofan á lagi, sem skv. C14 aldurs-
ákvörðun er ég fékk gerða fyrir löngu, er um
2700 ára. Nú er móhellan miklu eldri en eldra
trefjalagið, líklega svo þúsundum ára skiptir.
Það virðist því auðsætt, að yngri sandhóla-
myndunin á Hellnaskaga er miklu eldri en
svo, að hún geti verið frá mótum járn- og
brónsaldar. Mætti geta þess til, að hún væri
frá upphafi síðara birkiskeiðs fyrir um 5000
árum, en hún kynni að vera allmiklu eldri.
Samanburður á gjóskulagasniðunum á 18.
mynd bendir til þess, að myndun yngri sand-
hólanna hafi tekiö stuttan tíma.
ABSTRACT
Miscellanea from excursions
through South Iceland
After their first year of geoscience studies at the
Umversity of Iceland the students take part in a com-
pulsory one-week excursion through South Iceland.
This paper presents some observations and measure-
ments made mainly during these excursions.
I. KIRKJUGÓLF
Kirkjugólf (Church floor) is the name of a famous
site of jointed basalt near Kirkjubœjarklaustur in the
Sída district. The floor (Figs. I and 7) is the surface
of a jointed basalt lava layer, which has been eroded by
ice or/and abraded by the sea and, ultimately, polished
by sandstorms. It has irregular outlines (Fig. 1 and
6), covers an area of about 80 m2 and is composed of
about 1060 pillars. The percentage distribution of the
pillars with regard to the number of their sides and
average diameter is shown in Table 1 and in the
diagrams on Figs 3 and 4. The Kirkjugólf was long
thought to be a real church floorfrom Catholic time, or
to have been used as such, although natural. The
interstices between the pillars, formerly interpreted by
many observers as cement, are in reality a few mm
thick surface layer on the sides of the pillars. This
layer tends to separate from the pillars, through
weathering, as a thin layer immediately inside it is
more vesicular than the rest of the pillars (Fig. 5).
II. BLOCKS OF ANKARAMITE
ON SÓLHEIMASANDUR
S. Steinthórsson has descnbed an outcrop of basic
highly porphyritic rocks at the base of Hvammsmúli in
the Eyjafjöll dislnct, South Iceland. He classified
these rocks as ankaramite. As the main road through
the Eyjafjöll district has recently been moved some-
what southward from this outcrop it is pointed out
that this interesting rock type can be studied injökul-
hlaup-transported blocks on Sólheimasandur near the
eastern head of the bridge across Jökulsá (Fig. 9).
These blocks originate from a layer of ankaramite lava
north-west of the snout of Sólheimajökull.
The rock knoll Arnarhóll on the NW-side of the
lagoon Holtsós is built up of similar rocks as those at
the base of Hvammsmúli.
III. SOLIFLUCTION TERRACES ON
THE SOUTH SLOPES OF PÉTURSEY
Contrary to most other talus slopes m Iceland, those
in the distnct Vestur-Skaflafellssýsla are covered by
humus soil andgrass-grown up to the rockwalls above
them. On many of these slopes, especially in Mýrdalur
and Sída, the surface layer of the soil is regularly
folded in a washboardlike fashion. An impressive
example of this folding is seen on the south slope of
mount Pétursey in Mýrdalur, as shown on the photos
Figs. 10—12. The talus slope on Fig. 10isabout75
m high, the average angle of the slope 35° and
average vertical distance between the terraces 67 cm,
the horizontal distance about 1 m. Figs. 11 and 12
show details of the slope.
IV. ONTHE AGEOFTHE
HELLNASKAGI DUNES
On some stretches of the sandy south coast of Ice-
land there are rather large fossil dunes. Hellnaskagi
in Reynishverfi (Fig. 13) is a row of such dunes,
forming a rather narrow ridge running westward from
the Reynisfjall mount. Its seafacing side is almost
vertical and at its base are some caves formed by wave
erosion. A partly man-made cave, Bæjarhellir, is
higher up in the south wall (Figs. 13— 15). In this
cave Reverend Jón Steingrímsson, the renowned de-
scriber of the Lakagígar eruption in 1783, spent the
winter 1755/56. In the back wall of the cave
80 JÖKULL 31.ÁR