which statement accurately describes a pyroclastic flow? responses pyroclastic flows occur when the snow and ice of the summit are melted and mix with the ash and mud on the mountain. pyroclastic flows occur when the snow and ice of the summit are melted and mix with the ash and mud on the mountain. pyroclastic flows move slowly and are rarely deadly. pyroclastic flows move slowly and are rarely deadly. pyroclastic flows move very quickly but are relatively cool. pyroclastic flows move very quickly but are relatively cool. pyroclastic flows move at speeds of more than 100 km/hr (up to 500 km/hr) and usually have temperatures of over 1000 degrees c (over 500 deg f). pyroclastic flows move at speeds of more than 100 km/hr (up to 500 km/hr) and usually have temperatures of over 1000 degrees c (over 500 deg f).