lavalagen

Lavalagen is a geological term used primarily in Swedish geology to denote a layer composed of cooled and solidified lava that erupted at the Earth's surface. It marks a discrete lava-flow event within a volcanic sequence and can form continuous sheets or stacked flow units. The rock type depends on the magma’s composition and cooling rate, ranging from basalt and andesite to rhyolite; textures may be aphanitic, porphyritic, or vesicular, and large flows can exhibit columnar jointing.

Stratigraphically, lavalagen can serve as a horizon for correlating rocks across outcrops, and it is distinct from pyroclastic deposits (such as tuffs) and from intrusive units. It is not a formal, internationally standardized stratigraphic unit, but a practical field description used in Nordic geology.

Occurrence and significance: Lavalagen appears in many volcanic regions worldwide as part of layered volcanic histories. In field studies it is often subdivided into individual lava flows or flow units and may interleave with sedimentary rocks or other volcanic facies.

See also: Lava flow, Igneous rock, Basalt, Andesite, Rhyolite, Volcanic stratigraphy.