Geometric columns such as those found at the Giant’s Causeway in Northern Ireland and Devils Postpile (USA) have inspired mythologies and legends.Columnar joints are amongst the most amazing geological features on Earth but their formation hasn’t been known.
Now, for the first time, geoscientists at the University of Liverpool have identified the temperature at which cooling magma cracks to form these geometric columns.
Columnar joints in Iceland. Credit: University of Liverpool
Liverpool geoscientists undertook a research study to find out how hot the rocks were when they cracked open to form these spectacular stepping stones.
Yan Lavallée, Liverpool Professor of Volcanology who headed the research, said: “The temperature at which magma cools to form these columnar joints is a question that has fascinated the world of geology for a very long time. We have been wanting to know whether the temperature of the lava that causes the fractures was hot, warm or cold.”
The study that performed on basaltic columns from Eyjafjallajökull volcano, Iceland, showed that hot temperature is responsible for the process. These new experiments demonstrated that the rocks fracture when they cool about 90 to 140˚C below the temperature at which magma crystallises into a rock, which is about 980˚C for basalts.
This means that columnar joints exposed in basaltic rocks, as observed at the Giant’s Causeway and Devils Postpile (USA) amongst others, were formed around 840-890 ˚C.
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 results are published in the journal Nature Communications.