The emission of POISONOUS GASES rather than the direct effects of lava flows or ash showers are the greatest reason for loss of life.
An example is the eruption from the Laki volcano in 1783 (see first link below) in which an estimated 25% of the population of Iceland was killed.
"The system erupted over an 8 month period during 1783-1784 from the Laki fissure and the adjoining Grímsvötn volcano, pouring out an estimated 14 km3 (3.4 cu mi) of basalt lava and clouds of poisonous hydrofluoric acid & sulphur dioxide compounds that killed over 50% of Iceland's livestock population, leading to famine which killed approximately 25% of the population. The Laki eruption and its aftermath has been estimated to have killed over six million people globally, making it the deadliest volcanic eruption in historical times. The drop in temperatures, due to the sulphuric gases spewed into the northern hemisphere, caused crop failures in Europe, droughts in India, and Japan's worst famine."
Similarly, people have been overcome & suffocated from poisonous gases emitted by volcanoes in South America & the eruption of Krakatoa, Indonesia in 1883. The Krakatoa eruption was also responsible for indirect deaths from related tsunamis & earthquakes. As stated above, there may be indirect loss of life from crop failures & also from flooding as a result of lava melting Iceland's ice caps.
The 'nuée ardente' volcanic cloud from Mount Pelée on Martinique in 1902 (see second link) killed an estimated 28,000 people in the town of St Pierre. Here there was a pyroclastic surge travelling at 130 metres / second at a temperature of between 200 & 500 degrees centigrade. This eruption was similar to the Vesuvius eruption that buried Pompei in 79AD but these types of eruptions are very rare.
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