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What causes fissure eruptions in Iceland?

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tectonic basins and rift valleys Escarpments of the Great Rift Valley rising above the plain north of Samburu Game Preserve, central Kenya. Beisa oryxes graze in the foreground.

Fissure eruptions in Iceland are primarily caused by the continuous divergence of lithospheric plates along the Mid-Atlantic Ridge.12

As these plates pull apart, the process is intermittent rather than steady, similar to a rubber band being stretched until it snaps. When the stress from this tectonic movement exceeds the strength of the near-surface rocks, the crust fractures along steeply dipping cracks that run parallel to the rift zone. These fractures, known as dikes when filled with magma, provide a pathway for basaltic magma to rise from depths of several kilometers to the surface.32

The resulting volcanic activity is characterized by long, linear vents that produce voluminous flows of fluid basaltic lava. Because these eruptions often occur from new, parallel fractures offset from previous ones, they typically build up thick lava plateaus rather than forming a single, traditional volcanic mountain.2