Home » Spike Island emergence – The natural formation of Ireland’s historic island

Spike Island emergence – The natural formation of Ireland’s historic island

Choosing a point from which to start the story of an island like Spike Island is as difficult as choosing a starting point for the tale of humanity itself.  From its very creation, the island has a rich story that is worth sharing. While the story really ramps up with the arrival of the British Military in 1779, and subsequent fortress and prison use, it is well worth starting the journey from the island’s formation and emergence from the Celtic Sea.

To begin at the very beginning, there has been an endless ebb and flow of time since our planet coalesced from big bang remnants, some 13.6 billion years ago, into a hard-molten ball stable enough to allow for geological processes.  Over countless mega-annum, this swirling superheated work led to massive upheavals of great shifting tectonic plates, eventually forming what we recognise today as the earth’s islands and continents. 

This furious period of fire and cooling was interspersed with billions of years of tides, winds, rain and ice, performing their slow sculptural work.  The tools of nature’s masonry work, they work on a truly grandiose scale, carving in this corner of the Emerald isle one of the world’s largest natural harbours. 

At some distant point in our past, too remote to be recalled, these forces conspired to produce a harbour so fitting for modern human purposes, that it appears to be made that way just for us.  Shaped and crafted by a thoughtful celestial creator, with our happiness and well-being in mind. 

The story and shape of the present-day Island begins 420 million years ago, when the two halves of Ireland (2) that had formed on different continents fused together, and were edging as one further away from nearby landmasses.  Ireland’s present shape was largely defined 23000 years ago, when the last great ice age was transforming the land and altering the presiding way of life for the myriad inhabitants of Europe. 

The end result of this endless upheaval and rising sea levels was the ‘teddy bear’ shape island that we identify on our maps today, alone and adrift on the edge of the world. 

The dark broken line indicates the ‘two halves’ of Ireland

Land bridges still connected Ireland, Britain and Europe at this distant point, when sea levels were much lower than today, as the water was drawn into the land ice.  In parts, the sea level dropped by an astonishing 121 meters.  Regardless of what was exposed or covered, the shape we recognise as modern Ireland today was fully formed, complimented by temporary arteries and appendages that extended to the United Kingdom and Europe. 

The advances and retreats of this ice age had been going on for millennia, but the cold snap of the last glacial maximum, approx 23000 years ago (3), was so severe it forced an evacuation of Ireland and Britain by many mammals along the aforementioned land bridges.  Much of modern-day northern Europe saw a retreat, sending humans and animals to warmer southern climates, and killing or driving out species that would never return to Irish shores. 

The long winter was here, as a glacial invasion from the frozen north prompted global temperatures to plummet, the polar opposite climate actions to today’s warm temperature extremes.  One-kilometre-deep ice sheets crushed much of the country under the weight of millions of tonnes of snow, ice and debris. 

Despite the ice age ending over 10000 years ago, parts of the northern half of Ireland are still ‘springing up’, from the effects of the geologically recent weight of over a kilometre of ice forcing the land down.  The whole island of Ireland is at something of a tilt from North to South, as the land continues to recover.  So much for the solid ground we all take for granted. 

At one point, just 107 square kilometres of Ireland’s modern 85000 square kilometres is estimated to have been above the ice (4) (5).  Only the highest peaks and mountain ranges, areas known as ‘nunataq’ by the Inuits – peaks of mountains that protrude through the ice.  More moderate areas suitable for wildlife refuge likely existed (6) to allow early Irish animals to survive in nearby temperate pockets, but there is no question Ireland’s diversity was hard hit. 

It would be another 8000 years after the onset of this cold snap, or 15000 years ago from today, that temperature began to rise to favourable, habitable conditions for humans, and an increased variety of wildlife.  Northern Europe was re-colonised in a mass migration of the hunters and the hunted.  It’s likely that Spike Island of today was unrecognisable at this distant point, as it sat in a very different Cork harbour. 

A glacier buried the future sites of nearby towns Ballincollig and Cork city under a mountain of ice (7; 8), and extended along the Lee valley as far as Ringaskiddy and Great Island, close to the island.  It launched out toward the harbour entrance like a great white snake, slithering a path to the sea.  Stopping short of the harbour mouth, it released its runoff in great channels and streams that ploughed deep furrows, creating a tundra landscape similar to those found in Iceland today.

It was far from lifeless during this time, but by today’s standards, Ireland must have seemed a stark, desolate and unwelcoming place.  The warm winds of change were blowing, and with every millennia that passed, conditions in Ireland became more favourable to a growing body of would be inhabitants. 

Irish Elk, the largest deer to have ever lived

Over the coming centuries, as the ice retreat gathered pace and sea levels rose to their present conditions, Cork harbour began to take its modern outline which created the modern safe haven that is well utilised today.  For Spike Island, the filling of the harbour and eventual settling of sea levels resulted in its present 104 acre outline sitting exposed, open and inviting, available to all of the living inhabitants of southern Ireland. 

Fast forward to today and the island sits surrounded by water as an awkwardly oval shaped 104 acre outcrop, where seemingly static beaches and coastline do not betray an ever-changing topographical past.  The now smooth sloped island is believed to have once had something of an uneven pyramid shape, leading to a ‘spike’ at its centre which may have influenced its name. 

This feature is now missing, as the British used first manpower and eventually dynamite to carve out a hole for the 19th century fortress that crowns the island summit today.  While sometimes rudimentary in its approach, it was an impressive feat of Victorian engineering, on a scale seldom repeated. 

The smooth sloped ‘Glasis’, the man made rising hill leading to the fort to slow down attacker.

Also gone from the island of 10000 years ago are the rough, weather hewn sloped sides of the first island incarnation, which were pockmarked with trees, shrubs and grasses.   The trend in 19th century fortress protection was to build a long steep hill or ‘Glacis’, the French word for slope, which was a deliberate flat rise that attackers would need to scale to get to the forts walls.  This exhausted would be invaders, and exposed them at all times to mortar and cannon fire, making it a simple yet highly effective intervention. 

The modern island has been extensively remodelled to meet the whims of its inhabitants, but there are areas to the east and south that show the more natural state of the landmass, pockmarked as they are now with modern whims like World War one training trenches, convict cemeteries and concrete lookout posts. 

Before extensive human intervention in either Cork harbour or Spike Island, it is likely the coastal regions were popular with the returning forms of life, mammals and birds that progressed north along the remaining land bridges following the glacial retreat. 

The sheltered confines of Cork Harbour held appeal for human and animal settlers

The ice age had taken a toll on the diversity of Ireland’s wildlife (9), with as much as three quarters of the large ice age animals believed to have died out or left by 15000-13000 years ago when the ice retreat began.  Ireland’s current wildlife is a reflection of those that remained, or those that travelled to the exposed land mass before land bridges disappeared entirely, giving Ireland less diversity than mainland Europe, or even nearby Britain.

It is easily overlooked now but striking to remember that some 20000 – 40000 years ago, animals as exotic as hyena, reindeers and wolf would have shared the Irish landscape (10). 

More recent residents include animals as impressive as woolly mammoths, saber toothed tiger cats and giant brown bears, creatures so magnificent that had they been around today, they would be the stand out attractions of the Irish wildlife scene.  If not quiet the most welcome neighbours for suburban dwelling homosapiens.  Imagine the work commute, or putting out the bins? 

Such considerations are not so farfetched when you consider that current research has placed woolly mammoths living on an island in Alaska as phenomenally recently as 5000 years ago.  This was when the sun and star worshippers of Newgrange, an Irish archaeological site older than the pyramids, were building and manning their impressive Irish temple.  We are all not so far removed.   

Perhaps the first mammal to walk Spike Island’s shores after the ice retreat was something as sizable as a woolly mammoth, its great tusks interfering with the early island trees and foliage.  It may have been a humble mouse, crossing a mud bank at low tide, unaware that the returning waters could render a return journey impossible.  They would unwittingly become the first prisoner on an island destined for a career in incarceration. 

Irrespective of who arrived first, it is certain the island was well utilised prior to human arrival in Cork harbour.  The eventual disappearance of the larger and more dangerous of these early animal inhabitants made the island, and Ireland, a far more hospitable place to human kind.

The harbour as it appears today from a 1700’s map

The cause for the disappearance of some of these larger beasts is debated between human over hunting and climate change (11) (12), but irrespective of the reason, their removal brought opportunities for others.  Humans were well placed to replace the old colossal mammals, and begin our journey towards world domination.  It is likely the two traded places, and there may have been a brief skirmish for dominance over the tiny emerging mass of land that became Spike Island, a desirable speck in the Celtic Sea. 

For the hungry homosapiens who made their way north and west from Britain and France, the nutrient rich waters of Cork harbour were inviting, an attractive proposition for would be settlers.  Coasts held appeal due to the diversity they offered, so the area around Spike Island was a notable prize. 

This desirability would become a characteristic of Spike Island for the entirety of its history, as it emerged from under the glaziers and icy waters of Ireland’s largest harbour. We have to fast forward several thousand years to 635AD to find the first recorded use of Spike Island, as an Island Monastery.


Content and full references in authors upcoming title on Spike Island Cork.

1. The story of Spike Island. Coleman, James. 1, s.l. : Journal of the Cork Historical and Archaeological Society, 1893, Vol. 2.

3. Scientists Project Precisely How Cold the Last Ice Age Was. McGreevy, Nora. August, s.l. : Smithsonian Magazine, 2020.

4. F.H.A. Aalen, Kevin Whelan and Matthew Stout. Atlas of the Irish rural landscape. 2011.

5. Various publications – Consultant with Talamireland. Meehan, R.T. 1996, 1997, 1999, 2001, http://www.talamhireland.ie/pdf/dr_robert_meehan_publications.pdf .

6. Woodman, Peter Charles. Ireland’s First Settlers Time and the Mesolithic. s.l. : Oxbow books, 2021.

7. Geology of the Ballincollig-Crookstown Area, County Cork. McCarthy, Ivor. s.l. : Journal of Muskerry Local History Society , 2012, Vol. 10.

8. Late Pleistocene-Holocene Buried Valleys in the Cork Syncline, Ireland. Tara Davis, Ivor A. J. Maccarthy , Alistair R. Allen & Bettie Higgs. s.l. : Journal of Maps, , 2006, Vols. 2:1, 79-93.

9. Ward, Peter D. The call of distant mammoths. s.l. : Copernicus, 1997.

10. New radiocarbon evidence on the extirpation of the spotted hyaena (Crocuta crocuta (Erxl.)) in northern Eurasia. Stuart AJ, Lister AM. s.l. : Quaternary Science Reviews, 2014, Vol. 96.

11. The impact of climate change on large mammal distribution and extinction: evidence from the last glacial/interglacial transition. Lister AM, Stuart AJ. 340, s.l. : Comptes Rendus Géosciences, 2008.

12. Pleistocene to Holocene extinction dynamics in giant deer and woolly mammoth. Stuart AJ, Kosintsev PA, Higham TFG, Lister AM. 431, s.l. : Nature, 2004.

Content taken from authors upcoming title on the history, or related research. May be shared - used with quotation - links