Exactly the same way it affects the way ketchup comes out of a bottle or treacle comes out of a tin. Compare it with water poured from a glass and see the difference ...that’s viscosity.
Although in volcanic terms viscosity has more to do with lava flow after the eruption than before.
The more viscus the lava, the more explosive the eruption!
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.