Columnar Joints

Fingal’s Cave is a sea cave on the south side of the Isle of Staffa, Scotland. The island (which is only 0.33 square Km) is made entirely of igneous rock. This was formed in the volcanic episodes when the continents Laurentia and Eurasia separated in the Early Cenozoic, creating the North Atlantic Ocean. The cave is made up of fine, black, hexagonally-jointed, basalt columns which are similar to those seen at the Giant’s Causeway in Ireland. In Irish mythology Finn (or Fingal) built a causeway of stone to connect Ireland and Scotland. The columns formed from a Palaeocene (66.5-55.8 million years ago) lava flow that cooled from both the top and bottom. This cooling pattern caused contraction and fracturing of the flow into a blocky pattern. As cooling spreads through the lava flow the cracks move through the middle forming long columns. The cave was formed when a mild tilting event caused concentration of pressure above the current mouth of the cave. This caused a fissure to form and since then the waves have been eroding and opening up this beautiful structural.

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