Mount Ranier

Dominating the skyline south of Seattle is a magnificent volcano, which last erupted a few minutes ago, geologically-speaking, in 1854. Although currently dormant, it is monitored daily, because an eruption would cause mass destruction brought about by its huge glacial ice.

It's twice as big as Mt.St.Helens, 80 kilometres to the south, so an eruption would be impressive, but moreso because of Lahars which would quickly engulf life downstream. Moving at tens of metres per second, and up to 140 metres deep, the glacial ice would melt, mixing pyroclastic flow with rocks and water. Three and a half million people live in its path.