The eruption column may collapse due to decreasing gas content in the magma or failure of the column to entrain enough air.
A collapse can occur if the eruption column becomes too dense, leading to instability. This density can be caused by the accumulation of dense volcanic materials like ash and pumice. When the column collapses, it can create a fast-moving pyroclastic flow that travels downslope, posing a significant hazard to surrounding areas.
That would be a matter of opinion, but a reasonable choice might be the eruption of Vesuvius that destroyed and buried Pompei in 76 CE.
If it is an effusive eruption, the lava can burn living organisms. In an explosive eruption pyroclastic flows can sweep away, bury and/or burn living organisms. Ash can poison the soil and cause animals to suffocate. Plants and animals alike may be exposed to toxic gasses.
The Heimaey eruption might have caused problems, but no one died.
The reasons stadiums doesn't just collapse is because there are pillars to hold it. It might collapse when someone bombs or break the pillars.
Your lungs might collapse
Polution maybe?
no there were not
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Global temperatures might cool by several degrees
Volcanic mountains can get smaller through erosion, where wind, water, and ice gradually wear down the volcano's surface over time. They can also decrease in size through volcanic collapse, where the eruption of magma causes the structure of the volcano to weaken and collapse inward.