At the start of the eruption, a large Plinian column rose above the Bridge River Vent, creating its bowl-shaped volcanic crater. This explosive eruption might have been followed by the collapse of a former lava dome based on the existence of a thick cover of welded vitrophyric breccia. The Plinian column is estimated to have had a height of to . Its height has been calculated by comparing the size and density of rugged pumice fragments away from the vent area. However, the eruption column was likely higher than the estimated data indicates because it does not include the highest portions of the column. During this time of the eruption, tephra spread into the stratosphere and parts of the mushroom-shaped ash column collapsed, devastating nearby areas with heavy pyroclastic fall which deposited tephra on Meager's steep flanks. A pyroclastic fall deposit up to thick consists largely of light grey pumice grains that range in diameter from to . About 1-5% of the pumice grains contain white to dark grey bands.