Archaeologia Islandica - 01.01.2015, Blaðsíða 42

Elín Ósk Hreiðarsdóttir, Guðrún Alda Gísladóttir,
Kristborg Þórsdóttir And Ragnheiður Gló Gylfadóttir
erosion (e.g. Arnalds 1988, 24; Geirsdóttir
et al. 2012). Rangárvellir is a good example
of this.
Prior to human colonisation the Ice-
landic ecosystem had seen soil erosion and
changes in woodland cover (Ólafsdóttir
& Guðmundsson 2002) but these pale in
comparison to the drastic changes the
ecosystem underwent after settlement.
Colonisation was accompanied by massive
deforestation, reducing woodlands by up
to 80%, resulting in rangeland degradation
and soil erosion which became exacerbated
by overgrazing and climate change. How
much and how fast is still debated but a
conservative estimate suggests that prior to
settlement, vegetation covered about 65%
of the country and forest 25-30%. At the
end of the 19th century vegetation covered
only about 25% and forest about 1% (see
e.g. Arnalds 1988, 13; Friðriksson 1987,
167-86; Ólafsdóttir 2001).
The effects of eruptions on erosion vary
greatly depending on the type and amount
of tephra, the state of the vegetation and the
time of the year the eruption occurs. When
tephra forms thick layers it can sometimes
kill all vegetation underneath leaving the
soil vulnerable to erosion by wind and wa-
ter. The 1510 eruption marked a threshold
in the history of soil erosion of Rangárvellir.
Soil sections show that in the aftermath of
this eruption, erosion increased markedly
in the upper half of the district. It has been
suggested that this can be explained by the
coarseness of the 1510 tephra (the coars-
est of all previous historic Hekla tephras),
weaker soil composition than before and
lesser vegetation cover in the area than
in the centuries before (Jóhannesson &
Einarsson 1990, 133-34). To make things
worse the fall-out of the 1510 eruption was
to the southwest over the settlements in
Rangárvellir, in contrast to earlier tephra-
falls from Hekla which in historic times
had had a northerly direction. The erosion
most likely had a major impact on settle-
ment in Rangárvellir which hereafter was
characterized by instability and retreat. The
1510 eruption marked the beginning of a
protracted and severe erosion phase which
reached a peak in the 17th-19th centuries
when many farms were abandoned and/
or moved (Friðriksson 1988, 10; Jóhannes-
son & Einarsson 1990, 129, 133-34). The
erosion contributed to the formation and
expansion of deserts in the area (e.g. Hellu-
vaðssandur and Hofssandur1) and addi-
tionally it created erosion channels in many
parts of Rangárvellir (Guðmundsson 1954,
93-94).
As this brief summary shows, Rangár-
vellir district has been significantly aífected
by the eruptions in Hekla since the end of
the Viking Age. Contrary to what might be
assumed however, the eruptions themselves
1 Hofssandur is mentioned in a 13th century source suggesting that parts of Rangárvellir were already denuded
before rapid change began in the 16th century (Islenzk fornrit XII, 185).
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