The Botany of Iceland - 01.12.1914, Blaðsíða 39

PHYSICAL GEOGRAPHY
223
Large areas of Iceland are, moreover, covered with volcanic
ashes, slags and bombs ejected by volcanoes. During the eruptions,
the fine ashes are often spread out over a large part of the country
and are sometimes carried by tlie wind across the Atlantic Ocean.
During tlie Katla eruption in 1625, the aslies were carried to Bergen
in Norway, and in 1845, ashes frorn Hekla were carried as far as
to Germany, and during the Askja eruption in 1875 the volcanic
dust was carried to llie west coast of Norway in eleven hours forty
minutes, and in another ten hours tliey travelled as far as Stock-
holm. Ashes and slag are thrown up into the air to a great height;
on April 21, 1766, the ash-column of Hekla liad a height of 5000
metres above the summit of the mountain, and it has often been
higher still. Lava fragments and bombs are shot into the air to a
great height and often fall at a distance from the place oferuption;
during the Hekla eruption in 1510, a man was killed by a volcanic
bomb at Skálholt, 45 km. from the volcano; during the eruption
of the same mountain in April 5, 1766, a volcanic slag, as big as
a man’s fist, was hurled to Viðivellir in Skagafjörður, 165 km. from
the mountain. The íine dust which íills the air during great erup-
tions, causes peculiar refraction-eífects in the air; thus, during the
Laki eruption of 1783, dust-clouds and unusually brilliant sunsets
were common over the whole of Europe, North Africa and a part
of western Asia. The aslies fell in such quantities in Caithness in
Scotland as to destroy the crops; that year is still spoken of by
the inhabitants as “the year of the ashie.” The shower of ashes,
togetlier with the red-hot scoriæ ejected in an eruption, often causes
considerable damage to tlie inhabited land. Pastures are buried
beneath them or are scorched, and the coppice-woods often suffer
severely. Whether the damage done by the ashes to pastures is
perinanent or not greatly depends upon their nature; the heavy
basaltic ashes are especially injurious, as they can only witli diffi-
culty be carried away by the rain or by irrigation. When, however,
the layer of ashes is thin it gradually is absorbed into the soil, by
the grass growing up above it. In the neighbourhood of larger
volcanoes, several layers of ashes, one above the other, are found
in the soil. Tlie light, liparitic pumice-ash, which is rarer, is less
injurious, as it is quickly carried away by water. Sometimes the
ashes discharged by a volcano contain a great quantity of acids;
during the Laki eruption of 1783, the ashes were so acid that they
burnt lioles in the burdock leaves, and left black patches on the