Giant's Causeway - geology
Basalt
The rocks at Giant?s Causeway are
formed of basalt. This mineral is the
result of volcanic action.
Lava that flows swiftly because it is thin
cools off at the open air and becomes
solid below a temperature of
approximately 1000 degrees centigrade.
Therefore it contracts.
Depending on the speed of cooling, cold
basalt can take different forms.
Sometimes it cracks into hectagonal
columns, the cracks only appearing
vertically. This usually happens if Lava
cools off in the open air, not under the
sea.
Development
Giant?s Causeway developed during the
Paleogene period, around 60 million years
ago. Then the area was situated near the
equator under hot and humid conditions.
Actually, there are 3 layers of basalt from
3 successive periods of eruptions. During
the periods between the eruptions, which
lasted for millions of years, layers of
basalt eroded to form a layer of red rock
called ?Laterite?. The basalt columns
result exclusively from the second period
of eruptions.
Geology:
giantscauseway.com, Giant’s Causeway Visitor Centre, Bushmills, Antrim, 13 Oct 2006
Giant's Causeway Official Guide, at: giantscausewayofficialguide.com; 16 Oct 2006