At night of June 8,1991, the 2nd lava dome collapse and neck or vent of this dome are crop out. Then a magmatic explosion was occured and the pyroclastic flow down to the foot of volcano about 3.5km.
Fig-1 Animation of just explosion by dome colapse on Jun. 8, 1991.
This animation was made from tharmal video camera, taken by Kyusyu branch of minstry of construction from Fukae town. ( in "Volcanic hazard of Unzen eruption", 1993 [Japanese] ).