How Northern Ireland's tectonic past formed our highest mountain range
My first close encounter with the rough granite tors of the High Mournes was on top of Slieve Binnian when a buddy and I were having an all night photo shot. Although it was in the heart of the summer, with temperatures at sea level in the high 20s the afternoon we set out, by 2.00 am exposed to a biting wind on the top of a 2500 ft mountain, we needed somewhere to shelter for an hour's kip. So there I was, pressed in close to the rough stone surface, lying back on the soft grass and gazing up past the tor to the Milky Way stretched above me as I drifted off to sleep. I was thankful of the shelter of the tor that night.
But these exposed rock outcrops, strewn all across the Mourne landscape, are a reminder of a rather more violent and somewhat more threatening origin to these mountains. Rewind around 50 million years, to a time when Ireland was found slap bang in the middle of one of the earth's tectonic plate margins. Unimagineably powerful convection currents streaming out from the earth's mantle were pushing apart the crust. North America and Europe were slowly being separated and the very early signs of what would become the Atlantic Ocean were beginning to be seen.
And in the heart of these huge tectonic processes lay little Northern Ireland. Towards the north, huge fissures spewed out lava which built up in thick layers to form the Antrim Plateau (and, of course, the Gaint's Causeway) This lava cooled quickly to form the characteristic dark grey/black colour of basalt.
But to the south east, the ancient sedimentary shale rock found there was collapsing downwards into the crust. And the hot magma was rising up into the gaps created, eventually forming a cap over the shale. This magma cooled more slowly, allowing the larger crystals that formed to interlock with each other tightly. And the light grey granite was produced, a hard and resistant mass of rock just underneath the surface of the ground.
Now fast forward 50 million years to today. In the meantime, rivers, the weather and a series of colossal glacial ice sheets have eroded away much of the surrounding weaker rock, and the granite peaks are now thrust proudly skywards. The characteristic rounded mountains have been shaped themselves by the erosive power of the ice ages, yet still these young mountains remain the tallest mountain range in Northern Ireland. And, although they have been rounded, they are certainly not smoothed. Unlike your polished granite kitchen worktops, these rocks have a very appropriate rough, sandpapery quality to them.
Today, when you walk through this captivating landscape, the granite outcrops, tors and screes are a constant reminder of this geologic history. And they can also make for some handy foreground interest for the budding landscape photographer who is always looking for that close up element to act as a juxtaposition for the far distant and epic mountain heights!
The photo at the top of this blog is of one of the granite outcrops on the top of Doan. With the light of the setting sun blazing right at me from between the clouds, I took shelter once more behind a tor and set up just in time to catch the warmth of the last of the sun's light paint the straight side of another granite boulder. With the straightness of the side and the warmth of the orange glow, it was almost as if someone had sliced through this granite rock - only to find that in it's heart it retained something of that tectonic glow. A reminder that this stunningly beautiful landscape had much more violent magmatic origins. The tors weren't always quite so friendly...