The Giant's Causeway in northeast coast of Northern Ireland, is an area
of about 40,000 interlocking basalt columns, the result of an ancient
volcanic eruption. The majority of the columns are hexagonal, but some
have four, five, eight or even ten sides, measuring approximately 12
inches wide. The tops of the columns form stepping stones that lead from
the cliff foot and disappear under the sea. The Giant’s Causeway has
often been described as the Eighth Wonder of the World and was declared
as Ireland’s first World Heritage site by UNESCO in 1986.
Sixty-one million years ago, geological activity caused a series of
volcanic eruptions, and molten lava flowed from cracks in the ground,
causing valleys to burn and killing all vegetation. Then the basalt lava
rapidly cooled, which caused it to shrink and crack into even polygonal
shaped rocks (blocks). This in turn caused column-type joints to form
beneath the earth. Fifty-eight million years ago, another series of
volcanic eruptions produced a lava flow with a different chemical
composition. When this lava cooled, it did not form columns as definite
and staunch; it cloaked the well-defined, durable column structures
beneath the surface. At the end of the Ice Age, 15,000 years ago, the
frozen ocean chiseled its way past the high basalt elevations, eroding
the shoreline and unveiling the cliff of columns, which resulted in the
Giant’s Causeway.
Source :- http://www.unbelievableinfo.com/2013/11/the-giants-causeway.html
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