The Botany of Iceland - 01.12.1949, Page 11

THE FLORA OF REYKJANES PENINSULA
9
areas, not deflation areas. At the time when loess originated, there was
a greater deflation area which was bare. The inland ice was probably
not so great in those times as it is nowadays. The Icelandic loess
originated—according to I w a n—in a period climatically quite diffe-
rent from the recent one. The actual period may be designated as ablation
period. The accumulation period has, according to I w a n—a dry, cold,
moderately windy climate.
Icelanders think (erroneously in Iwan’s opinion) that the chief
factors influencing destructively the loess cover of the Island are man
and his sheep. This is a false conclusion (according to Iwan); the
destruction of the loess cover is due to climatic chánges: the area in-
fluenced by man is too small to explain the whole of the catastrophe.
The deflation period began already before the colonisation of Iceland.
Nowadays no new loess originates, the winds transport only the old
material to the sea.
I w a n ’ s study is very interesting, very original, and brings much
new material. But I do not agree with him on the point of the origin
of the Icelandic loess. I w a n regards the problem exclusively from the
geological point of view; thus he comes to overlook the biological
factors, especially the influence of vegetation. Vegetation existed on
lceland long before I w a n ’ s “Loess-period” began. It cannot be denied
that the vegetation was present from the beginning of the loess period.
When we discuss the loess problem, it is therefore vitally necessary
also to consider the influence of the vegetation. It seems e. g. im-
possible to visualise the sedimentation of aeolic sand on loess without a
plant cover. If remains of the loess cover (“Fetzen”) are distributed
evenly over the whole Island—as I w a n affirms—how can a deteriora-
tion of the climate (in the sense of this becoming more atlantic) be
responsible for this destruction; for while the SW of Iceland has a
truly atlantic climate the NE has a continental climate?
If in some places morainic deposits are covered by loess or blown
sand, it is not necessary to assume that all moraines were covered by
aeolic sediments, forming a part of the zone of accumulation.
An excursion to Pingvellir and Sandkluftir (near Langjökull)
throws much light on the question of the loess problem. Sandkluftir is a
defile extending to an amphitheatre built by palagonite formation and
morainic material. On sunny days the air in this amphitheatre becomes
very warm; an air depression originates in this place. Then the cold
air from the Langjökull ice sheet streams to the amphitheatre, drying
up wet rocks. Temperature differences between day and night are
The Botany of Iceland. Vol. V. Part I. 2