The activity of some volcanoes is characterized by violent explosions that break the magma into fragment of different size. Those bits of magma are launched high and then fall down at very high speed, like a burning cloud that hits the ground from far-away distances. In 1902, a 800 °C burning cloud came out of the La Pelèe volcano, Martinica, at 100 km/h speed. In just a minute and without any warning, it hit Saint Pierre city and killed 29,000 people.
Also the eruption of Nevado de Ruiz volcano in Colombia in 1985 was a terrible catastrophe. The explosive activity was anticipated by a series of earthquakes, secondary eruptions, avalanches and landslides. On 13th November the explosion formed a burning cloud with a radius of 11,000 kilometres. But there was another problem, as the top of the volcano was covered by snow that suddenly melted. The water formed a mud avalanche that ran over 22,000 people, 5,150 houses, 50 schools, 2 hospitals, 200 kilometres of roads, 18 kilometres of railways network, 10 kilometres of long-distance power lines, 58 factories, 3 pipelines, 5,000 hectares of fertile soil, 343 handicraft activities and the waterworks that supplied water to 50,000 people.