This video clip was taken from "Understanding Volcanic Hazards", © 1995, International Association of Volcanology and Chemistry of Earth's Interior (IAVCEI). The following was taken from the video:
Lava flows are formed by molten rock that erupts in fountains like these, or pours across the ground from a vent. Molten rock can erupt from several vents at the same time merging together to form a fast moving river of lava. On steep ground these rivers can flow as fast as 30 kilometers per hour. On flatter ground lava flows spread out in broad sheets up to several kilometers wide and usually move less than one kilometer an hour.