How many active volcanoes are there in the world?
The answer to this common question depends upon use of the word “active.” At least 20 volcanoes will probably be erupting as you read these words (Italy’s Stromboli, for example, has been erupting for more than a thousand years); roughly 60 erupted each year through the 1990s; 154 in the full decade 1990-1999; about 550 have had historically documented eruptions; about 1300 (and perhaps more than 1500) have erupted in the Holocene (past 10,000 years); and some estimates of young seafloor volcanoes exceed a million. Because dormant intervals between major eruptions at a single volcano may last hundreds to thousands of years, dwarfing the relatively short historical record in many regions, it is misleading to restrict usage of “active volcano” to recorded human memories: we prefer to add another identifying word (e.g. “historically active” or “Holocene volcano”). The definition of “volcano” is as important in answering the number question as the definition of “active.” Usage has varied w
