A map created by ESRI, a company specialized in geographic information systems, shows known volcanic eruptions in the past 10,000 years. The dynamic map displays the location of the eruption and associated Volcanic Explosivity Index (VEI), a relative measure of the explosiveness of a volcanic eruption running from 0 to 8 (the 1980 eruption of Mount St. Helens has a VEI of 5).
Most active volcanoes occur at the boundaries between tectonic plates where the Earth’s crust is either created in rift zones (where tectonic plates move slowly apart, like happening in East Africa) or destroyed in subduction zones (where plates collide and one is pushed below the other, like happening along the east coast of the U.S.). Volcanoes located along subduction zones have the potential to be highly explosive as their magma contains large amounts of volatile gases and water vapor. Some active volcanoes occur in the interiors of tectonic plates above mantle “hot spots”, like the Hawaiian volcanic chain and Yellowstone in the U.S.
In total there are 1,551 volcanoes in the Smithsonian Institution database, used for the map, of which 866 are known to have erupted in the last 10,000 years. The map contains some minor mistakes, like the supposed eruption in Tuscany (Italy), as it is still a work in progress. The database also doesn’t cover volcanic activity on the seafloor, rarely recorded before underwater monitoring systems (like underwater microphones) became available. Geological, historical and dating records for volcanic eruptions on land become less complete further back in time. Since 1500 AD, there are 596 volcanoes that are known to have erupted. The record since 1950 is believed to be almost complete with 2,208 eruptions recorded from 347 volcanoes. The average number of eruptions ongoing per year since 1950 is 63, with minimum of 46 and maximum of 85 eruptions recorded per year. On average 34 of these are new eruptions beginning each year.
Today more than 800 million people are living within 100 kilometers (60 miles) of an active volcano. In general, there is an increasing probability of fatalities with increasing VEI, for example, all recorded VEI 6 and 7 eruptions since the year 1600 have caused fatalities. The two largest disasters in terms of fatalities were caused by the largest eruptions of Tambora in 1850 and Krakatau in 1883. Nevertheless, small to moderate eruptions can be devastating, the modest eruptions of Nevado del Ruiz (VEI 3) and Mont Pelée (VEI 4) being good examples. Between the years 1500 and 2017, more than 278,000 people were killed during a volcanic eruption.