<P> The volcanic explosivity index (commonly shortened to VEI) is a scale, from 0 to 8, for measuring the strength of eruptions . It is used by the Smithsonian Institution's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows . It operates in a way similar to the Richter scale for earthquakes, in that each interval in value represents a tenfold increasing in magnitude (it is logarithmic). The vast majority of volcanic eruptions are of VEIs between 0 and 2 . </P> <P> Volcanic eruptions by VEI index </P> <Table> <Tr> <Th> VEI </Th> <Th> Plume height </Th> <Th> Eruptive volume * </Th> <Th> Eruption type </Th> <Th> Frequency * * </Th> <Th> Example </Th> </Tr> <Tr> <Td> 0 </Td> <Td> <100 m (330 ft) </Td> <Td> 1,000 m (35,300 cu ft) </Td> <Td> Hawaiian </Td> <Td> Continuous </Td> <Td> Kilauea </Td> </Tr> <Tr> <Td> </Td> <Td> 100--1,000 m (300--3,300 ft) </Td> <Td> 10,000 m (353,000 cu ft) </Td> <Td> Hawaiian / Strombolian </Td> <Td> Fortnightly </Td> <Td> Stromboli </Td> </Tr> <Tr> <Td> </Td> <Td> 1--5 km (1--3 mi) </Td> <Td> 1,000,000 m (35,300,000 cu ft) </Td> <Td> Strombolian / Vulcanian </Td> <Td> Monthly </Td> <Td> Galeras (1992) </Td> </Tr> <Tr> <Td> </Td> <Td> 3--15 km (2--9 mi) </Td> <Td> 10,000,000 m (353,000,000 cu ft) </Td> <Td> Vulcanian </Td> <Td> 3 monthly </Td> <Td> Nevado del Ruiz (1985) </Td> </Tr> <Tr> <Td> </Td> <Td> 10--25 km (6--16 mi) </Td> <Td> 100,000,000 m (0.024 cu mi) </Td> <Td> Vulcanian / Peléan </Td> <Td> 18 months </Td> <Td> Eyjafjallajökull (2010) </Td> </Tr> <Tr> <Td> 5 </Td> <Td>> 25 km (16 mi) </Td> <Td> 1 km (0.24 cu mi) </Td> <Td> Plinian </Td> <Td> 10--15 years </Td> <Td> Mount St. Helens (1980) </Td> </Tr> <Tr> <Td> 6 </Td> <Td>> 25 km (16 mi) </Td> <Td> 10 km (2 cu mi) </Td> <Td> Plinian / Ultra-Plinian </Td> <Td> 50--100 years </Td> <Td> Santa Maria (1902) </Td> </Tr> <Tr> <Td> 7 </Td> <Td>> 25 km (16 mi) </Td> <Td> 100 km (20 cu mi) </Td> <Td> Ultra-Plinian </Td> <Td> 500--1000 years </Td> <Td> Tambora (1815) </Td> </Tr> <Tr> <Td> 8 </Td> <Td>> 25 km (16 mi) </Td> <Td> 1,000 km (200 cu mi) </Td> <Td> Supervolcanic </Td> <Td> 50,000 + years </Td> <Td> Lake Toba (74 k.y.a.) </Td> </Tr> <Tr> <Td_colspan="6"> * This is the minimum eruptive volume necessary for the eruption to be considered within the category . * * Values are a rough estimate . They indicate the frequencies for volcanoes of that magnitude OR HIGHER † There is a discontinuity between the 1st and 2nd VEI level; instead of increasing by a magnitude of 10, the value increases by a magnitude of 100 (from 10,000 to 1,000,000). </Td> </Tr> </Table> <Tr> <Th> VEI </Th> <Th> Plume height </Th> <Th> Eruptive volume * </Th> <Th> Eruption type </Th> <Th> Frequency * * </Th> <Th> Example </Th> </Tr>

When do the most violent volcanic eruptions occur
find me the text answering this question