"You need a volcano that has the energy to inject that fine aerosol and those particles into the high atmosphere," [Bill Buhay] said. "Normally the mixing happens in the lower atmosphere."

Buhay said it's important for the particles to be smaller than the wavelengths of light for the light to scatter. Once those particles are in the stratosphere, "then you've got this potential for lots of light scattering when the sun goes down, and some beautiful sunsets," he said.