11. Lava of the unstable dome may occasionally create minor pyroclastic flows, explosions and eruption columns . 12. Originally, the dispersal index was considered a function of the height of the eruption column . 13. An eruption column rose into the atmosphere and deposited ash in 11 U . S . states. 14. Eruption columns are not usually visible on weather radar and may be obscured by cloud or night.15. Large eruption columns formed, causing numerous pyroclastic flows down the heavily populated slopes of the volcano. 16. The eruption column caused a large pumice-fall deposit to the east of the source area. 17. The eruption was the strongest of the three lava dome forming eruptions and formed an eruption column high. 18. The solid or liquid material in an eruption column is lifted by processes which vary as the material ascends: 19. The Krakatoa ( Indonesia ) eruption of 1883 produced an eruption column which rose to more than 50 km. 20. Explosive activity with eruption columns of height may result in ashfall in Arica and Putre depending on the season.
