This story appears in the August 2018 issue of National Geographic magazine. Indonesia has 127 active volcanoes. Only the U.S. (168) and Russia (144) have more. Essential packing list: We landed ...

Millions of people around the world live near one of the roughly 1,500 active volcanoes on Earth—from Italy’s Campi Flegrei to Indonesia’s Merapi to the United States’ Mount Rainier.

That tectonic pandemonium has led to the formation of spiderweb-like fault zones and myriad volcanoes ... a submarine volcanologist at the National Oceanography Centre in Southampton, England.

“Glaciers cover about 12 percent of Iceland and there are quite a few volcanoes beneath ... past found almost nowhere else,” says National Geographic fellow Jonathan Tourtellot, who ...