This special type of eruption destroyed the city of St. Pierre in 1902 . In other cases hot material from the volcano can melt snow and ice at the volcano summit and the whole mass of mud and lava can sweep rapidly down the mountain, destroying everything in its path. This type of flow is called a lahar . There have been some spectacular eruptions in Earth history. This is an image of the eruption of Mt. Pinatubo.
Some eruptions only contain lava and hot gas.
These lavas move slowly, at walking speed or slower. Other eruptions contain lava accompanied by clouds of ash , bombs, lava fragments, as well as hot gases. In some eruptions, ash and lava, carried by hot vapors, can pour down a volcano with speeds of about 100 miles per hour. This special type of eruption destroyed the city of St. Pierre in 1902 in a matter of minutes. In other cases, the eruption can melt snow and ice at the peak of the volcano, and a mass of mud and lava can sweep rapidly down like a river, and destroy everything in its path.