Sills are buried magma sheets. Why can Siberian sills pose more risk than lava?

Answer: They cook gas-rich rocks

They cook gas-rich rocks ✓ — Right. A sill is magma injected between rock layers, so it can bake coal, carbonates, evaporites, and organic-rich sediments like an underground kiln. USGS links the end-Permian extinction onset to widespread Siberian sill emplacement. The scary part is that the deadliest gas factory may be invisible at the surface.

They send ash skyward — Ash matters in explosive surface eruptions, but a buried sill is not mainly an ash cannon. Its power comes from contact metamorphism: heat changes surrounding sediment chemistry and liberates greenhouse or toxic gases. The hazard is chemical amplification underground, not just visible material thrown into the sky.

They spread lava farther — Farther lava spread would increase the visible footprint, but it still may miss the global trigger. The Siberian-sill idea is sharper: magma intruded gas-rich layers and made extra gases before much of the damage reached ecosystems through air and ocean chemistry. Invisible plumbing can outweigh visible lava.