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It happened between 840 and 890° C: researchers find out how Giant’s Causeway in Northern Ireland was formed

Giant’s Causeway, a tourist attraction at the coast of Northern Ireland about 80 km from Belfast.

Study identifies the temperatures of lava when it carved striking geometric columns which at first sight can only be done by titans from mythology

A new study by geoscientists at the University of Liverpool has identified the temperature at which cooling magma cracks to form geometric columns such as those found at the Giant’s Causeway in Northern Ireland and in many places around the globe.

Geometric columns occur in many types of volcanic rocks and form as the rock cools and contracts, resulting in a regular array of polygonal prisms or columns.

Liverpool geoscientists undertook a research study to find out how hot the rocks were when they cracked open to form columnar joints looking like stepping stones.

According to a paper published in Nature Communications, researchers and students at the University’s School of Environmental Sciences designed a new type of experiment to show how as magma cools, it contracts and accumulates stress, until it cracks.

The study was performed on basaltic columns from Eyjafjallajökull volcano, Iceland.

Scientists and students designed a novel apparatus to permit cooling lava, gripped in a press, to contract and crack to form a column. These new experiments demonstrated that the rocks fracture when they cool lies about 90 until 140° C below the temperature at which magma crystallizes into a rock (which is about 980° C for basalt).

This means that those columnar joints exposed in basaltic rocks were formed between 840 and 890° C.

Scientists have long been wondering whether the temperature of the lava that causes the fractures was hot, warm or cold.

Columnar joints in Iceland.

Yan Lavallée, Liverpool Professor of Volcanology who headed the research, said: „Now, with this study, we have found that the answer is hot, but after it solidified.“
The challenge had been how to design the right experiment to find this out.

Dr Anthony Lamur, for whom this work formed part of his doctoral study, added: „The experiments were technically very challenging, but they clearly demonstrate the power and significance of thermal contraction on the evolution of cooling rocks and the development of fractures“.

Dr Jackie Kendrick, a post-doctoral researcher in the Liverpool group said: „Knowing the point at which cooling magma fractures is critical, as – beyond leading to the incision of this stunning geometrical feature – it initiates fluid circulation in the fracture network. Fluid flow controls heat transfer in volcanic systems, which can be harnessed for geothermal energy production. So the findings have tremendous applications for both volcanology and geothermal research.“

Understanding how cooling magma and rocks contract and fracture is central to understand the stability of volcanic constructs as well as how heat is transferred in the Earth.

The study was published in Nature Communications doi:10.1038/s41467-018-03842-4.

University of Liverpool

Source: University of Liverpool

(23.04.2018, USA: 04.23.2018)