HARDLY A TREMOR BENEATH THE PLAINS OF KILDARE

by jdurney on January 12, 2012

Hardly a tremor beneath the plains of Kildare

The earthquake which devastated northern Japan is a reminder of the powerful forces deep within the earth’s crust. Volcanoes, earthquakes and tsunamis have become the headline words which represent the unleashing of natural forces against which even the most technologically advanced societies have few defences.
 From an Irish viewpoint such catastrophes are regarded as being terrible but at a safe distance. The rocks underlying the island of Ireland are, on the face of it, stable and steady. However when it comes to dealing with nature there are no guarantees. Last May, a tremor off the west coast of Ireland rattled the residents of the Clare coast. It surprised seismologists – scientists who study earthquakes – too because the rock off Ireland’s Atlantic coast had been regarded as supremely stable. Not so the east coast where a band of frequent seismic activity has been recorded extending across the Irish Sea. Many Kildare residents felt the July 1984 earthquake which had its epicentre in north Wales – this column recalls a sensation similar to hearing a truck rumbling down a road. 
The effects of more distant quakes can be felt in the bedrock across thousands of miles. Sensitive equipment can detect the echoes and vibrations of earthquakes on opposite sides of the world. In May 2008 a school in Baltinglass equipped with a seismometer for measuring earth tremors picked up the echoes of an earthquake which just a few minutes earlier had devastated the Sichuan province of China. The school – Scoil Conglais – was taking part in an exciting programme known as ‘Seismology in Schools’ run by the Geophysics section of the Dublin Institute of Advanced Studies which maintains the network of recording stations for earthquake measurement in the Irish bedrock.  For some years a measuring gauge at the Lyons Estate near Celbridge was a component of the Irish seismic network.
The speed at which earthquakes waves travel through the bedrock is astounding – it  took just twelve minutes for the vibrations of the Japanese earthquake to show up on the Irish seismic measuring gauges. The geological history of Co. Kildare bears little witness to the great collisions of the continental plates which happened many billions of years ago. The terrain of the county is shaped by more recent forces of nature – powerful in their own way but perhaps not as dramatic as the volcanoes and earthquakes which left their mark on the more rugged parts of the island of Ireland.
The generally flat landscape which characterises most of the county’s terrain is a product of the ice age (about 1.5 million years ago) when melting glaciers deposited vast quantities of glacial soils and gravels. The glaciers had gouged chunks out of the underlying limestone rock and ground it down into particles. Floods from the melting glaciers created some of Kildare’s best known terrain features. The five thousand acres of the Curragh and its adjoining farmlands are the surface terrain of an extremely thick deep deposit glacial sandy soils. Geologists have measured depths of seventy metres or more of sandy soil before the limestone bedrock is reached. Even this bedrock is the result of relatively gentle processes: this part of Ireland was immersed by seawater for many millions of years. Over this period deposits of marine life drifted to the bottom of the sea building up layers of rock rich in the calcium which in time would nurture the ideal grazing conditions for bloodstock. More than three-quarters of the landscape of the county is underlain by limestone rock produced by this gradual process of seawater deposition.
However in parts of the county traces of older rock can be found which bear witness to the kind of violent earthquakes and eruptions seen in modern times in the Pacific and the Caribbean. What is now the landmass of Ireland is made of two halves – one attached to the north American continent, the other to the European continent. Great movements of the continent plates  brought the two halves together. The Hill of Allen which protrudes above the Bog of the same name was formed from a volcanic eruption triggered as the ancient continental plates collided. However there is no need for alarm at the mention of a volcano in mid Kildare … it is an unimaginable 500 million years or more since the last eruption and there is no sign of any resumption of volcanic activity beneath the old rocks of Kildare. Series no: 221.

Liam Kenny in his ‘Looking Back’ column in the Leinster Leader of 22 March 2011 reassures us that the plains of Kildare are safe from earthquakes. Our thanks to Liam

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