kolumnaarinen

Kolumnaarinen is a term used in Finnish geology to describe columnar jointing in volcanic rocks. It refers to the regular, polygonal fracture pattern that forms as hot lava or magma cools and contracts, producing vertical, closely spaced columns. The columns are commonly hexagonal in cross-section, but other polygonal shapes are also found.

Formation occurs when thick lava flows or lava lakes solidify. Shrinkage during cooling causes fractures to propagate from the surface inward, creating a system of polygonal joints that extend into the rock and often produce vertical walls or cliffs. The size of the columns varies with cooling rate, lava viscosity, and thickness of the solidifying body, typically ranging from a few decimeters up to meters.

Distribution and examples: Columnar jointing occurs globally, especially in basaltic rocks, and is visible at sites such as Giant's Causeway in Northern Ireland and Svartifoss in Iceland. Similar structures are reported in other regions. In Finland, the term kolumnaarinen is used to describe such textures when encountered in local igneous rocks.

Significance: Kolumnaarinen joints provide clues about past cooling rates and volcanic history. They influence rock strength, weathering patterns, and landscape development, and are a common subject of study in structural geology and geomorphology.