2025年6月19日

Svartifoss waterfall basalt columns, Vatnajökull National Park, Iceland

Svartifoss is one of several Icelandic waterfalls flanked by distinctive hexagon-shaped basalt columns so smooth they're seemingly carved by the Norse gods themselves. OK, they may not have their origins with Odin's kin, but the science behind them is remarkable. Columnar joints are formed as lava flows cool and buckle under stress, with cracks penetrating deep into newly formed rock. The path of least resistance places these cracks at 120-degree intersections. So as the cracks run deeper, their shape averages out to a near-perfect hexagon—exposing neat geometric columns when the rock face eventually shears off.