How many volcanoes erupt each year?

How to get close to this number

Work from the standing rate. The explanation gives around twenty erupting on any given day, and eruptions last weeks to months. Twenty concurrent eruptions with an average duration of a few months implies a few dozen distinct eruptions starting each year.

The always-on figure is the part that surprises: twenty volcanoes are erupting right now. Eruptions feel like rare events because only the destructive ones are reported, but most are continuous low-level activity at remote or ocean volcanoes that never make news. Newsworthiness and frequency are almost unrelated.

The exposure figure is the one that matters: an estimated eight hundred million people live within a hundred kilometres of a potentially active volcano. Volcanic soil is exceptionally fertile, so populations have always concentrated around the hazard — the same trade-off that puts cities on floodplains and fault lines.