Lava flows

Lava flows are streams of molten rock that will travel down valleys on the slopes of volcanoes.
 The distance they travel depends on the viscosity of the lava, output rates, volume erupted, steepness of the slope, topography and obstructions in the flow path. Basalt flows have low viscosity (flow easily) and have been recorded to travel more than 50 km from a volcano but usually only flow 5-10 kilometres. Andesite flows are more viscous and rarely travel more than 5 kilometres. Dacite and rhyolite lavas have high viscosity and typically form short, thick flows or domes.
 Lava flows will seldom threaten human life because of their slow rate of movement. However, the steep fronts of flows may became unstable and can collapse, causing small pyroclastic flows. Lava flows will causes total destruction of buildings and other infrastructure in their path.