Jökull - 01.12.1986, Blaðsíða 68

continual fog, sleet and rainy weather caused by the
ice” (B.S. Húrmvatnssýsla). Another severe year fol-
lowed in 1757, but in 1758 the run of severe years
which had lasted through the decade came to an end
with a winter and spring that were much milder than
previous seasons. The summer this year was mainly
good everywhere and the autumn average to good.
The 1740s and 1750s may well have been the
coldest decades of the century. Of equal severity (see
Figure 2) were the 1690s and 1630s. Previous works
(for example, Koch, 1945; Bergþórsson, 1969) have
suggested that the 1750s were more severe than the
1740s and, certainly in terms of human suffering, this
would seem to be so (Vilmundarson, 1969; Ogilvie,
1981). In the index for the whole of Iceland presented
here, however, the 1740s appear to have been slightly
colder (see Figure 2). This is because, although more
seasons were described as very cold in the 1750s,
more seasons were described as good as well. The re-
gional indices for the north and west of Iceland (Fig-
ure 3) follow this pattern; indeed, in the west, the
1740s appear far colder than the 1750s, but in the
south, it is the 1750s which are the coldest decade in
the period 1601 to 1780.
1761-1770
The following decade, 1761 to 1770, was undoubt-
edly milder than the previous two in the north, south
and west. During the 1760s, only two winters were
recorded as severe in most districts: 1761 and 1770.
Flowever, western sources also give 1764 and 1766 as
very cold winters. 1767 was said by Jón Jónsson to
have been severe in the east, although it was mild and
calm in the north. A high proportion of winters were
judged to be mild this decade. In the north: 1762,
1763, 1767, 1768, 1769; in the south: 1762, 1763,
1765, 1768, 1769; in the west: 1763 and 1768. Spring
was severe in the south and west in 1761, but good
this year in the north. The spring of 1764 was cold in
the north and west, as was 1766. In the latter year, a
western source stated: “The winter weather lasted
until 5 June with continual frost and keen northerly
winds” (B.S. Dalasýsla). 1769 was very cold in the
south and west, but tolerable in the north. 1770 was
recorded as cold in the north. 1763 was a mild spring
in the north and west and 1768 in the north and
south.
The summers this decade were mainly variable,
although some stand out as interesting. 1761 was cold
in the north, south and west, and 1766 in the east and
elsewhere. In this latter year “few people in the north
and in Múla district went to the Alþing because of the
severity” (íslands Árbók). Later on, the weather be-
came better, at least in the north. Dry summers were:
1762 (north, south, west), 1763 and 1768 (west), 1769
(south). 1762 was also regarded as being good in the
south and west. 1767 and 1768 were good in the
north. 1768 was very wet in the south, and 1764 in
the west. There is very little information on the
autumns this decade but four could be described as
good or favourable in the north (1761, 1762, 1763
and 1768). 1762 was also good in the south and west.
1764 and 1766 were very cold in the north.
During 1761 to 1770, there was sea ice present in
1764, 1766, 1767, 1769 and 1770. 1766 was a fairly
heavy ice year, but the ice seems not to have pen-
etrated beyond the northern and northwestern coasts.
The outstanding environmental event of the decade
was the Hekla eruption which began in 1766 and
lasted for two years. Jón Jónsson described the effects
of the ash cloud from the eruption which was first
seen by him on 5 April. The cloud “took away the
colour of snow in the mountains” and the fall of ash
had adverse effects on grass and livestock.
1771-1780
The thermal index for the whole of Iceland (Figure
2) suggests that the 1770s were colder than the 1760s.
Nevertheless, on a regional scale there were large
areas where the climate was probably milder in the
1770s than it had been at any time since the 1730s.
The overall situation is reflected in the south and
north, but in the west the 1770s were milder than the
1760s.
Seven winters were described as severe, at least in
part, in one or more districts in the 1770s. These
were: 1772 (north), 1773 (north and east), 1775
(south), 1777 (west), 1778 (north), 1779 (south, west),
1780 (north, east, west). Southern sources say the
winter of 1780 was mild to around mid to late
February, when severe weather with frost and snow
set in. Four winters were mild: 1775 (north and west),
1776 (north and west), 1777 (north), and 1779 (north
and east). It can thus be seen that 1775, 1777 and
1779 were years with marked spatial contrasts in the
severity of their winters. Only one spring was de-
scribed as mild in this decade: 1776, in the north.
However, this may well reflect lack of data for these
years rather than the true picture. (As early meteoro-
Iogical observations exist for some years from the
1770s onwards, it may eventually be possible to fill in
gaps in the historical data.) Five springs were de-
scribed as severe: 1773 (north), 1774 (west), 1775
(north), 1777 (north, west), 1779 (north), 1780 (every-
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