Fissure Flames

Volcanic fissures form primarily along divergent plate boundaries or zones of crustal extension, where tectonic plates pull apart and create fractures that allow magma to ascend from the mantle.

At mid-ocean ridges, such as the Mid-Atlantic Ridge, decompression melting of mantle material generates basaltic magma that erupts through linear fissures, building new seafloor.

On continents, like in Iceland’s rift zones or the East African Rift, similar extensional forces thin the lithosphere, and dike intrusions—vertical magma-filled cracks—propagate along these weaknesses, often producing curtain-like eruptions rather than centralized cones.

These fissures reflect zones of high tectonic stress release, and their geometry and length are controlled by the regional stress field and magma pressure, making them key markers of plate dynamics and crustal deformation.