COME AND VISIT CARLOW’S VERY OWN VOLCANO!
The banks of the Slaney River at Kilcarry Bridge contain evidence of Carlow’s
volcanic past! The district was covered with deep sea water when lavas were
spewed out onto the seafloor. There was probably a single vent somewhere near
Kilcarry but no trace remains. However the lavas are well preserved as
predominately green rocks in cliffs on either side of the river. Minor amounts of
metals accumulated on the warm seabed and while some old workings are
evident no viable mining has taken place.
By the time the volcanic action stopped, the seas here were less deep and
distinctive sands (locally lime-rich) accumulated. But time was running out for
this unique Carlow environment: on a larger scale it became caught up in the
stresses between colliding tectonic plates – and evidence of those stresses can
still be traced in the rocks today. They were folded into complex shapes and
muddy sediments developed into slates (some were quarried for roofing near
Bunclody).
A final act in the stressful Carlow history was the emplacement of the major
Leinster Granite, exposed from the coastline in south County Dublin to beyond
Graiguenamanagh in County Kilkenny. It can be seen in Monaughrim Glen just
north of Kilcarry Bridge. It formed from very hot magma which welled upwards
from depth along fractures in the Earth’s crust. As it cooled a series of veins
formed in its margins – and a small percentage have potential resources of
lithium and tantalum, both essential to power our mobile phones.
The Earth’s crust in Carlow has a long-term memory preserved in its rocks. The
fractures that facilitated the volcanic lavas to form also controlled how the
tectonic plates merged with each other, how the seas retreated, and how the
granite was subsequently emplaced. These fractures must have been active for
at least 100 million years and would have been the focus of extensive earthquake
activity.
Does Carlow still quake? This part of Ireland has a destinctive level of seismic
activity. But no need to worry, it is still at a low level. However it reflects a more
violent past which affected the landscape of this region, gradually elevating much
of it. The Slaney eroded its bed downwards in this changing scenario so that it
now flows through a rocky gorge here.
All of these topics, and more, will be discussed during a guided walk to mark Irish
Heritage Week. All are welcome to assemble at Kilcarry Bridge at 14.30 on
Saturday 30 August 2008. The walk will take 2-3 hours, and although not
suitable for disabled access, the terrain is not difficult. The easiest approach to
Kilcarry Bridge is from the Carlow-Enniscorthy road (N80). About 3km north of
Kildavin village turn off eastwards (signposted “Clonegal 5km”) to reach the
Bridge after 2km. Car parking will be available: please follow instructions on
arrival.
Bring warm waterproof clothes and we won’t have to worry about the weather.
Also strong comfortable footwear. I am happy to answer any queries on 087226-2519 (including on the day). I wish to thank Fiona Conlon and Kathleen
Nolan for facilitating access. Please respect the properties we visit. Also, thanks
to Dermot Mulligan, Carlow County Museum, for enthusiastically supporting the
event in many ways.
Peadar McArdle, Geological Survey of Ireland
E-mail: peadar.mcardle@gsi.ie, Office: 01-687-2730