Afterglow

[6] Specifically in volcanic occurrences it is light scattered by fine particulates, like dust, suspended in the atmosphere.

[citation needed] Sunlight reaches Earth around civil twilight during golden hour intensely in its low-energy and low-frequency red component.

During this part of civil twilight after sunset and before sundawn the red sunlight remains visible by scattering through particles in the air.

Backscattering, possibly after being reflected off clouds or high snowfields in mountain regions, furthermore creates a reddish to pinkish light.

An enormous amount of exceedingly fine dust were blown to a great height by the volcano's explosion, and then globally diffused by the high atmospheric winds.