How did vertical columns form at Giant's Causeway in Northern Ireland?

Question

How did vertical columns form at Giant's Causeway in Northern Ireland?

Answer 1

millions of years ago, northern ireland was highly volcanic. lava spilled across the land. as this lava cooled, mineral deposition forced the basalt to become fractured and contract. as the crystal bonding was worn away by the elements, the basalt columns were left behind.

Answer 2

I have seen pictures of Giant's Causeway, and this is what I think:  I have been to Devil's Tower in Wyoming and saw the same thing there ON the tower.  The Tower is the inner cone of a volcano, and has columns and columns of basalt formed upon slow cooling when the volcano was active some long time ago.  I believe that Giant's causeway is a remnant of a volcano, and that those vertical columns reach down 100 feet or more from their surface.  If you like, try Wikipedia for both of these places and see if the geology is the same.