Stranded passengers. Grounded aircraft. Closed airports. The cause: an obscure volcano in Iceland with an unpronounceable name rocked aviation and transport in the Northern Hemisphere.

Now we’re eleven years on, and another volcano in Iceland is spewing hot lava and gasses: Fagradalsfjall of the Krýsuvík-Trölladyngja volcanic system on the Reykjanes Peninsula, not far at all from the capital Reykjavik. But… no flights cancelled, no passengers stranded. What’s the difference? Why could one vo...