siirtolohkot

Siirtolohkot is a Finnish geological term describing rock blocks that have been displaced with respect to surrounding rocks by tectonic movement. The word combines siirtää (to move or transfer) and lohko (block), and is used to denote discrete, map- or cross-section–bounded masses of bedrock whose boundaries are controlled by faults or shear zones.

Formation and characteristics: Siirtolohkot form when blocks are offset along faults during regional deformation. They may rotate, tilt, or translate relative to neighboring rocks, producing distinct structural boundaries and sometimes contrasting lithologies. On the landscape they can appear as discrete blocks or as stepped topography when interpreted in geological maps and cross-sections. Boundaries are typically defined by fault planes, fractures, or zones of differing rock properties.

Distribution and significance: In Finland and other Nordic regions, siirtolohkot feature in structural geology and tectonics studies as units that help interpret fault geometries and deformation history. They can influence local drainage patterns, erosion, and soil formation, and their study contributes to broader models of transform- or oblique-slip tectonics and post-glacial crustal movements.

See also: tectonics, fault block, strike-slip fault, structural geology.