But new technology and a volcanic eruption in Iceland has changed that. Or has it?
But is it a volcanic dyke as found subsea or like the more famous 'ancient' dykes that are visible on land, Shiprock New Mexico for example?
The dyke stretches for more than 45 kilometres, from the Bárðarbunga central volcano to the Holuhraun site, where magma has been erupting since the summer.
The dyke mostly formed in the two weeks before the main eruptive activity began. Its average opening is approximately 1.5 metres wide, focused from just beneath the surface to six kilometres down. The dyke volume grew to 0.5 cubic kilometres before the main eruption began. A model for the dyke also explains the unusual and varying direction of dyke segments that relate to interaction of topography and stresses in the ground caused by divergent plate movements in Iceland.
New understanding of how magma moves underground
Volcano dykes - Shiprock, New Mexico
Is Shiprock, New Mexico the harder rock remains while the rest of the land has eroded away?
Can you get limestone dyke swarms?