One of the most amazing Natural Wonders of the United Kingdom, the Giant’s Causeway was declared a UNESCO World Heritage Site in 1986. Located on the northern coast of County Antrim, near Bushmills (yes, whiskey Bushmills!) Giant’s Causeway is a must see for anyone.

Being a geologist, it was only a matter of time before I would marvel at this natural volcanic landscape for myself.  It’s a bit of a “Busman’s Holiday”, but it is stuff like this that got me interested in rocks in the first place!  My husband and I (he’s a Geologist too) made the pilgrimage, last August, as a day trip from our base just outside the town of Donegal.

It was a soft drizzle that escorted us from the visitor centre down the road to the main site on the shore.  We were able to enjoy it for long enough and walk back up the hill, before the rain started falling more heavily.  We, lazy folks that we are, decided not to walk along the cliff-top pathway to get a view from the top.

We were also getting “slightly” ticked off with people who would barge up to the information boards, that were on rotating drums about a horizontal axis (would you believe??), spin them around to the board they wanted to read without any consideration for those still reading the previous board!  I like to think that I am quite smart and can read up-side down, but frustration turns out to be quite a hindrance!

Just enough tourists for my liking - no more please!

Anyway, since then – I have had the pleasure of reading up what I want to, and for how long I want to take over it on the internet 🙂

So to share with you – here’s The Giant’s Causeway in a nutshell:

In a period of intense volcanic activity about 62 million years ago, associated with Mid Atlantic Ridge activity (think current day Iceland & recent eruptions), molten lava erupted through chalk beds in three phases – resulting in the Lower, Middle and Upper Basalts.

The Amphitheater

The lateral spread of these lavas would have originally been much greater than the present day’s extent.  Through processes of erosion they have been reduced to a mere 3800km2, yet they are still Europe’s most extensive lava field.

Chimney Tops

The first eruption, which resulted in the Lower Basalts (itself a collective of up to 11 individual lava flows), would have long since cooled, solidified and have been subject to thousands of years of erosion by water and ice before the second eruption of Middle Basalts.  The resulting undulating topography included deep river channels, which would have allowed the lava from the Middle Basalts to pond in greater thicknesses (up to 100m) than the average depth of lava flow.  The consequence of this greater depth is that it takes longer to cool than lava that is closer to the edges of the flow.

It is this slow cooling and contracting process which results in the formation of columnar joints that is seen at the world famous sites such as the Giant’s Causeway and Fingal’s Cave on the Isle of Staffa, which I visited some 20 years ago!

The Organ - perfect columns, topped with "jumbled" columns are most likely the result of water percolating down through the cooling lava before the columns were "set".

These two sites are not only linked geologically, they are also linked by mythology.

Two giants, Finn McCool from Ireland and Benandonner from Scotland, challenged each other to a trial of strength (i.e a big scrap).  Never having set eyes on each other, Finn started to build a causeway from County Antrim across the Sea of Moyle to Benandonner’s Lair, at Fingal’s Cave.

Only, he fell asleep halfway across. D’oh!

Mrs McCool, otherwise known as Oonagh and a giantess in her own right, heard the thunderous step of Benandonner and saw how much larger he was compared with her husband.  Quickly, she whipped out a bonnet and blanket (as you do) and disguised her, still sleeping, husband as her baby.

Benandonner, believing this to be so, wondered at the size of the father if this was the size of a baby and fled back to the Isle of Staffa – ripping up the causeway as he went so that Finn couldn’t follow him home.


Wikipedia: Giant’s Causeway / Fingal’s Cave & Queen’s University Belfast & Giant’s Causeway Official Guide

Not all hexagonal - definitely polygonal..

August, 2010


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