islands of the Atlantic Ocean created by the volcanism of the Middle
Atlantic Ridge are
Tristan da Cunha,
and others. The
divergence of the ridge started in the north about 150 million years
ago and 90 million years ago in the south.
Iceland is the largest island on the ridge because of the
additional volcanism caused by the hot spot under the country, which
moves slowly towards the northwest across it.
These unique circumstances on the ridge probably are the
reason for the country’s existence, because the tectonic movement of
the plates and the related volcanism would not have sufficed.
The country probably would have looked very differently if the
hot spot were the sole reason for its creation, probably something
similar to Hawaii. The
plate tectonics move the plates apart, towards east and west, and both
the American- and Eurasian systems move to the northwest across the
It is possible to trace the tracks of such hot spots because
the plates move across them like steel plates across a fixed blowtorch
flame. On top of the hot spot is a 20-100% molten layer at a depth of
5-20 km, which supplies more than sufficient material for eruptions. This hot spot causes eruptions
within the southern volcanic
zone including volcanic systems such as
Mt. Eyjafjallajokull, Mt. Tindfjoll, the
Fishing Lake Area,
and the western sub-glacial part of the
This volcanic zone has gradually moved to
the southeast from the present Graben, or the continuation of the
ridge across the country.
The lateral rift system across the Snaefell Peninsula and
the Huna Bay ceased being active about seven million years ago.
About 60 million years ago, when it was active, it was situated
near the present Faeroe Islands and Eastern Greenland where it left
basaltic regions and submarine ridges in both directions.
present centre of the hot spot lies under the Trolladyngja shield
volcano, where it reaches depths of 275-375 km and probably stretches
underneath the mainstay of the Vatnajokull and Hofsjokull regions. The
largest volcano and caldera of the country are probably contained
under the ice cap of the Hofsjokull glacier.
Magma reservoirs with 100% molten lava and areas of 100-1000 km³
are present at a depth of 10 km under the volcanic zones (the Graben),
and they feed the shallower and smaller magma chambers under the
central volcano systems.
The shape of those magma reservoirs is rather obvious on the surface,
such as under the Krafla system, where it is situated at a depth of 3
km and above it the magma chamber at a depth of about 700 m.
Mt. Hekla does not have any magma chamber, but the magma
reservoir under the volcanic system is estimated to be at a depth of 8
km and about 40 km long.
Chambers usually are 10% of the size of reservoirs.
When the Krafla system erupts, the magma chamber feeds it, but
eruptions of the Gjastykki system, further north, are fed by the
Approximately 10% of the structure of the country consist of
rhyolite, dasite and other acid rock formations.
The most common type of basaltic rock is thoelite, which is divided
into many subtypes. The
Ice Age ended about 9000 years ago.
The 3 million years long Ice Age was divided into 30 glaciation epochs
of almost 100.000 years, and about 10.000 years long warmer epochs
The age of the basaltic strata from west
to east is 16 – 10 million years.
Eight central volcano systems are
recognizable by light coloured rock (gabbro) and high temperature
The structure of the island Hrappsey on
the Breidafiord Bay is anorthosite, the light coloured type of rock on
the moon (the other type on the moon is norite).