Counting volcanoes around the world | Number Theory

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Indians generally do not care much about volcanoes. And for good reason. There are only two of them in India and none on the mainland. But when the eruption of the Hayli Gubbi volcano in Ethiopia on November 23 sent an ash cloud to India – it did create some disruption to air traffic – volcanoes did grab our attention. This makes it worthy to do understand the world’s volcanoes and the world of volcanoes. Data compiled by the Global Volcanism Program (GVP) run by the Smithsonian Institution is useful here.

A satellite image shows ash rising from the eruption of the Hayli Gubbi volcano in Ethiopia on Sunday. (NASA handout via Reuters)

Counting volcanoes around the world

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  Which countries have the most volcanoes?

  The answer to this question depends on how one defines a volcano. GVP uses a relatively loose definition, counting multiple vents or fissures within a 10 km distance from which magma eruptions occur as one volcano. The database lists 1,230 volcanoes on land (there are also sub-sea ones) that have erupted in the Holocene period, which is the period of roughly the past 12,000 years. This list includes the Hayli Gubbi volcano, the year of whose last known eruption (before the eruption of this week) is unknown. The countries with the highest number of such volcanoes – counting only volcanoes in mainland locations – are the US, Japan, and Indonesia, which have 165, 105, and 101 volcanoes. These are also the only countries with more than 100 volcanoes. To be sure, volcanoes are sometimes also located in overseas territories or at national boundaries. If such multiple-territory volcanoes are added to the list of each of those countries, Russia, with 94 volcanoes in mainland locations, would be ranked third instead of fourth and Indonesia would be ranked fourth. Ethiopia, where Hayli Gubbi is located, is ranked sixth using both criteria, although its volcano count increases from 46 in the former criteria to 50 in the latter. India has only two volcanoes and is ranked 52nd among 90 territories (counting multiple territory volcanoes as separate territory) with volcanoes.
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  How many volcanoes are active right now?

  The answer to this question can also change depending on the time-frame . It can also change with research because some eruptions may go unobserved, or because the date of older eruptions is not clearly known. Among the 1230 Holocene volcanoes on land, 524 have erupted 1800 onward, 440 from 1900 onward, 359 from 1950 onward, and 230 from 2000 onward. Indonesia is ahead of the US and Japan on each of these time-frames. While the last eruption of one of India’s two Holocene volcanoes (both in the Andaman and Nicobar Islands) is unknown, the Barren Island volcano may have erupted as recently as November 25, leading to an advisory from the Darwin Volcanic Ash Advisory Centre (VAAC) -- one of nine VAACs across the globe for the aviation industry -- which says a pilot noticed ash emissions rising up to 2.4 km above sea level. Its previous eruption was on July 30-31 this year.
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  How many volcanoes are erupting currently?

  As of November 25 – GVP had not updated its Holocene list with Hayli Gubbi’s 2025 eruption on the date – 58 volcanoes had their last eruption listed in 2025. However, 44 of these 58 are what GVP calls volcanoes with continuing eruptions. These are volcanoes that don’t take breaks of three months or longer between eruptions, and Indonesia has the highest number (eight) of these as well, as of September 19 (the last update). Among the three Darwin VAAC advisories on November 26, two were for such continuously erupting volcanoes, both in Indonesia. “There are typically 40-50 continuing eruptions, and out of those generally around 20 will be actively erupting on any particular day,” GVP says.
• Which volcanic eruptions are a threat to aviation?

  Any volcanic eruption would be a threat to aviation if a flight is in the path of an eruption. However, forecasts are possible for eruptions based on observations of tremors and changes in gravity and magnetic fields. Disruption from ash clouds from volcanoes, on the other hand, depends on a wide range of factors. These include the amount of ash thrown up by an eruption, the altitude to which the ash rises, and how it is carried by the wind.