HISTORY of VOLCANISM
The islands of the Atlantic Ocean created by the volcanism of the Mid
Atlantic Ridge are The Azores,
The Canary Islands,
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 North
American- and Eurasian systems move to the northwest across
the hot spot.
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 the 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 Hekla, the
Mt. Eyjafjallajokull, Mts
Laki Area, 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 (flank zones) 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 Faroe Islands and Eastern
Greenland where it left
basaltic regions and submarine ridges in both directions.
The 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
regions. The largest volcano and caldera of the country are probably
contained under the ice cap of the Hofsjokull glacier.
with 100% molten lava and areas of 100-1000 km³ are present at
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
depth of 3 km and above it the magma chamber at the 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
the 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 deeper
10% of the structure of the country consist of rhyolite, dasite and
other acid rock types. 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 between them.
age of the basaltic strata from west to east is 16 – 10 million years.
Eight central volcano systems are recognizable by light coloured
rock types (gabbro) and high temperature systems.
The structure of the island Hrappsey on the
is anorthosite, the light coloured type of rock on the moon (the other
type is norite).
When oxygen was first produced as a waste product by certain plant
cells some three billion years ago, it created a crisis for all
other life on earth. Those plants were polluting the environment,
exhaling a lethal gas. Earth eventually had an atmosphere
incompatible with life. Nevertheless, life on earth took care of
itself. In the thinking of the human being a hundred years is a long
time. Hundred years ago we didn't have cars, airplanes, computers or
vaccines. It was a whole different world, but to the earth, a
hundred years is nothing. A million years is nothing. This planet
lives and breathes on a much vaster scale. We can't imagine its slow
and powerful rhythms, and we haven't got the humility to try. We've
been residents here for the blink of an eye. If we're gone tomorrow,
the earth will not miss us.
Michael Crichton, "Jurassic Park"