Iceland and Eyjafjallajökull

Iceland sits on the Mid-Atlantic Ridge, a divergent boundary, and on a mantle plume. New oceanic crust is made here. Thingvellir is a rift you can walk. The island is the ridge plus extra magma from the hotspot — which is why it stands above water when most of the ridge does not.

Eyjafjallajökull in 2010 was a subglacial, explosive eruption of relatively evolved magma. Ice plus silica-rich melt made fine ash. High-level winds carried it over Europe. Aviation avoids ash because it damages turbine blades. UK specifications treat the eruption as a tectonic and atmospheric case. The ridge itself is the plate story; the ash is the hazard story.

Compare the Himalaya: continent–continent convergence, crust stacked, not made. Compare Hawaii: a hotspot without a plate boundary. Compare Cascadia: subduction, not divergence. Three colours of boundary, plus a plume, cover the exam list.

Seafloor spreading on either side of Iceland lays down magnetic stripes. The seafloor-spreading lab is that tape recorder. Iceland is where the tape is a country.