Need To Know

How was the Giant’s Causeway formed?

On the north-east coast of County Antrim in Northern Ireland
lies an unusual rock formation which draws in millions of
visitors from around the world every year. They flock to see
a vast plateau of polygonal basalt columns – which are commonly
known as the Giant’s Causeway – which looks like a carpet of
enormous stepping stones extending out into the Irish Sea. The basalt
pillars that make up this amazing rock formation dramatically range
in size from a matter of centimetres to several metres high. Although
the Giant’s Causeway is so-named due
to an ancient legend, its formation
actually began up to 65 million years
ago during the Tertiary period when
volcanic activity forced tectonic plates
to stretch and break. This caused
magma to spew up from inside the
Earth and spill out across the surface
as lava. The temperature of erupting
lava can range from between 700
and 1,200 degrees Celsius (1,292 and
2,192 degrees Fahrenheit). However,
upon contact with the surface it will
immediately begin to cool. At first this
cooling is extremely rapid and this
results in a hardened crust forming on
top of the superhot substance, which
insulates the still liquid lava below. Because the lava is now insulated
the cooling becomes increasingly slow over time. While you could
probably walk on the crust after just half an hour or so, thick lava
fl ows can take a number of years to cool completely and solidify all
the way through. While the temperature falls the lava begins to dry
out, and it’s this drying that causes the solidifying lava to crack and
form regular pillars of basalt rock. The size and shape of each column
is ultimately determined by the rate at which the lava actually cools
and dries, and therefore the speed at which what’s called the ‘drying
front’ moves. Scientists from the University of Toronto discovered that
the slower the cooling rate the larger the basalt columns that formed.

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