Jäähdytysmuodostumat

Jäähdytysmuodostumat, known in English as cooling formations, are geological features formed by the contraction of rock due to cooling. These structures are commonly observed in igneous rocks, particularly basaltic lava flows and sills. As molten rock cools, it shrinks, creating tensile stresses within the solidifying mass. When these stresses exceed the rock's strength, fractures form.

The most characteristic type of cooling formation is columnar jointing. This results in the development of polygonal columns, often hexagonal in shape, that extend through the rock mass. These columns form as cooling progresses inward from the exposed surface and the underlying contact. The joints typically grow perpendicular to the cooling surface.

Another type of cooling formation is known as sheeting joints or exfoliation. These are large, curved fractures that develop parallel to the exposed surface of a rock mass, often granite. They are thought to form due to the release of confining pressure as overlying rock is eroded, combined with thermal expansion and contraction cycles. The characteristic onion-like peeling of rock layers in granite landforms is a result of sheeting joints.

The scale of cooling formations can vary greatly, from small cracks to massive columns hundreds of meters long. They are important indicators of the cooling history of igneous bodies and play a significant role in the weathering and erosion processes of rock formations. Examples of well-known columnar jointing can be found at Giant's Causeway in Northern Ireland and Svartifoss waterfall in Iceland. Sheeting joints are prominent in many mountainous regions with large granitic intrusions.