How many active volcanoes are there?
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. The number is also dependent on what time scale is included, and if only confirmed eruptions are counted, or uncertain eruptions and the opinions of volcanologists are considered. Because dormant intervals between major eruptions at a single volcano may last hundreds to tens of 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 numbers will change as new research is published, new age dates are acquired, or new criteria are applied and volcanoes are reviewed.
Here are a few statistics (at last database update):
- Volcanoes erupting now: 41
- Volcanoes that erupted during 2017: 68
- Volcanoes with confirmed historical eruptions: 568
- Volcanoes with confirmed Holocene eruptions: 870
- Volcanoes thought to have Holocene eruptions: 1,436
The definition of "volcano" is as important in answering the number question as the definition of "active." Usage has varied widely, with "volcano" applied to individual vents, volcanic edifices, or volcanic fields. We have tended toward the broader definition in our compilations, allowing the record of a single large plumbing system to be viewed as a whole, but this approach often requires careful work in field and laboratory to establish a common magmatic link. Perhaps the most honest answer to the number question is that we do not really have an accurate count of the world's volcanoes, but that there are at least a thousand identified magma systems--on land alone--likely to erupt in the future.
Note that the figures above do not include most eruptions (and undescribed volcanoes) on the deep sea floor. Estimates of global magma budgets suggest that roughly 75% of the lava reaching Earth's surface does so unnoticed at submarine midocean ridges. Some estimates of young seafloor volcanoes exceed a million.
Global Volcanism Program, 2013. Volcanoes of the World, v. 4.7.0. Venzke, E (ed.). Smithsonian Institution. Downloaded 25 Jun 2018. https://doi.org/10.5479/si.GVP.VOTW4-2013