The Physics of a Waterfall
Svartifoss, or "Black Fall," is a 20-meter (66-foot) high waterfall in Iceland's Vatnajökull National Park. The name comes from the dark basalt columns that frame the cascade. These columns are the result of a geological process called columnar jointing. When a thick flow of basalt lava cools, it contracts and fractures. To relieve the thermal stress most efficiently, the cracks form a hexagonal pattern, similar to the way mud cracks as it dries.
The perfection of these columns depends on the cooling rate. A thick lava flow that cools slowly, insulated by the ground below and rock above, allows stress to distribute evenly. This slow process results in the formation of large, well-defined hexagonal columns known as a colonnade. Faster, uneven cooling, often caused by exposure to air or water, creates smaller, more irregular fractures called entablature. Svartifoss is a colonnade, where the slow solidification of magma created a near-perfect geometric structure. The columns have horizontal grooves, or striations, spaced 5 to 20 cm apart, which mark the successive stages of the fracture's propagation as the lava cooled. At the base of the falls, a pile of sharp-edged rocks consists of column sections that have broken off over time.
From Geology to Architecture
The distinct geometric forms of Svartifoss have influenced Icelandic national architecture. Guðjón Samúelsson (1887-1950), Iceland's former State Architect, frequently drew inspiration from the country's natural geological formations. He integrated the shapes of basalt columns into several of his most important building designs.
The main example is Hallgrímskirkja, the famous Lutheran church in Reykjavík. The church's concrete facade matches the cascading, tiered structure of the Svartifoss columns. Commissioned in 1937, the church took 41 years to build, and Samúelsson did not live to see its completion. He also used the basalt motif in the design of Iceland's National Theatre (Þjóðleikhúsið) and the main building of the University of Iceland. This architectural style, which blends natural forms with modernism, became a signature of Icelandic design in the first half of the 20th century. The influence remains, with the glass facade of the Harpa Concert Hall in Reykjavík also referencing the country's basalt geology.