The Giant's Causeway, Northern Ireland's most iconic landmark, has attracted millions of curious travelers over the centuries. Some 40,000 strange, interlocking columns form a "road" of stepping stones that lead from the coastal cliffs down into the sea. The edges of each column line up so perfectly they look like the work of a skilled Inca mason. Legend has it that Irish giant Finn MacCool built the causeway so he could travel across the sea to fight a challenger in Scotland without getting his feet wet. (Similar columns rise from the sea in the Scottish Isles.) Evolutionary geologists say the causeway was formed by massive volcanic eruptions 50–60 million years ago.
How Did It Really Happen?
The first clue is that these columns are made out of basalt, a rock formed from cooling lava. When we observe lava cooling today, it shrinks and cracks. Under the right conditions—uniform mineral content and slowly falling temperatures — the cracks follow geometric patterns.