Volcanoes currently pose no danger to Ireland’s residents, but the island is known for its re-occurring history of volcanic eruptions and is surrounded by extinct volcanoes, writes Paula Redmond.
The Earth’s surface consists of a rocky outer crust. This ranges from approximately five miles in depth under the oceans, to approximately twenty-five miles deep under the continents.
The crust is not static, but made up of rigid plates – known as tectonic plates – that move in relation to one another. Where the plates meet is called a fault and when plates collide this can result in an earthquake. Movements in plates also form mountains. Beneath the crust is a layer of rock called the mantle.
Movements in the earth’s plates can cause this rock to rise upwards, and as it does it can melt to form molten rock or ‘magma’. The word magma is derived from the Greek meaning ‘thick unguent’. It is the currents in this flowing molten rock that cause the plates to form in the upper crust of the earth. The mantle is about 1,800 miles deep.
When magma erupts onto the earth’s surface it is known as lava. When thick magma and gas build up under the earth’s surface, they can explode, expelling lava, rock and ash into the air. The mountain-like mounds that we call volcanoes are in fact the hardened deposits expelled during the eruption.
Volcanoes can be highly dangerous. The lava expelled through openings, known as vents, can reach 1,250 degrees Celsius, burning everything in its path. Volcanic ash can cover and destroy whole towns, while dangerous gases can damage lungs.
Pompeii in Italy is a famous example of this. Once a thriving Roman town, an eruption from nearby Mount Vesuvius in 79AD sent a plume of gas, rock and volcanic ash so high into the sky it could be seen for hundreds of miles. Over the coming days it covered the town and its remaining inhabitants in ash and toxic gases, killing approximately 2,000 people.
Many people in Ireland might be surprised to find that they are living near an extinct volcano. The Giant’s Causeway in Co. Antrim is an example, as is the County Wicklow quarry known as The Rock, in Arklow.
There are two main ages of ancient volcanic activity preserved in Ireland, Ordovician (c. 480-450 million years ago) and Paleogene (‘Early Tertiary’, c. 60-50 million years ago).