I’m trying to wrap my head around something that appears far more complex than I first thought. I don’t understand the explosive elements and chemistry that drives ash production and the heat to create the eruption column. I’m aware of how molten metal behaves in a foundry crucible with flux and degassing required. So I understand how magmas can have a tremendous amount of dissolved elements that can release like CO2 from a shaken soda bottle being opened. I can picture this kind of pyroclastic flow easily; the “shaken soda bottle” type.
I don’t have a very good grasp of how the ash column can reach enormous heights and then collapse, or how composition impacts this kind of collapse. I just can’t picture in my mind how this type of collapse results in a flow, like some kind of avalanche or pronounced river of material as opposed to more of a micro-regional rain like ash fall event that is very intense and superheated. What is the trigger and how does it overcome any hotter material lower in the column?