It might be land area affected ? if they get enough warning , people could be moved , but nature doesn’t always cooperate . If not , then a big chunk of population will be wiped out . Thats another thing about our infrastructure , or the lack of it . people will be trying to get away from the ash states away from the volcano .
Even if they can , then the population density in the unaffected areas will grow beyond capacity to care for them . That leaves Canada and Mexico as far as logical places to put them , but who really knows .