lavblokk

Lavblokk is a Norwegian geological term referring to a fragment of solidified lava that forms within or at the margins of a volcanic lava flow. The blocks are typically angular to subrounded and can vary in size from centimeters to several meters across. They originate when the crust of a flowing lava body thickens and fractures as the interior continues to move or when the lava begins to break apart during cooling. In viscous lava flows, such as those of andesitic or rhyolitic composition, the surface crust commonly breaks into blocks that can be carried downslope by the flow or accumulate at the flow front.

Lavblokker can be vesiculated or dense, depending on cooling rate and gas content. Their presence provides clues about past flow dynamics, including instability of the crust, extrusion rate, and rheology of the lava. In field observations, a concentration of lavblokker at a flow margin or toe can indicate a period of crust formation followed by continued extrusion or fragmentation.

The term is used mainly in Norwegian-language geology, but the concept corresponds to what English-language sources would describe as lava blocks or block lava fragments. Lavblokk is thus a descriptive term for a common feature of solidified lava within and at the edges of lava flows, contributing to interpretations of volcanic activity and landscape formation.

See also: lava flow, a'a lava, pahoehoe, lava block, volcanic fragmentation.