Basalt lava flow, Antrim

Huge lava flows like this one, (which also forms the Isle of Staffa, in western Scotland) show that about 60 million years ago north-west Britain was volcanically very active, like Iceland is today. The lava flows were erupted on land -there was no sea here then - and flowed across a wide area of what is now western Scotland, Northern Ireland, and East Greenland!

As the newly-formed basalt lava cooled, contraction cracks produced regular columns in the lower part of the flow. The columns are divided by dish-shaped cracks, forming domes and basins - which in this photograph are partly filled by rainwater.

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