How can melting ice make Icelandic volcanism spike instead of calm down?

Answer: Ice unloading melts mantle

Cool meltwater feeds magma — Meltwater can trigger local steam explosions if it reaches hot rock, but that is not the long-term Iceland mechanism here. The big effect of an ice sheet is its weight. Remove that load, and hot mantle can decompress, which favors more melting even though the surface is getting less icy.

Ice unloading melts mantle ✓ — Ice is heavy enough to press down the crust and mantle. When it retreats, pressure drops; hot mantle can cross the melting threshold without needing extra heat, a process related to pressure-release melting. That is why less ice can mean more magma, the opposite of the easy 'ice cools fire' intuition.

Ice seals seafloor cracks — Ice can cover or dam a vent, but sealing cracks would tend to suppress eruption, not explain a post-ice volcanic pulse. The Reykjanes debate instead asks whether retreating ice removed pressure and helped volcanism resume. In geodynamics, unloading is not passive; it changes the force balance below.