How can there be snow on erupting volcanoes?

Answer 1

In some cases hot gasses, lava, and ash do not make it very far from the vent or rise above the volcano before they have a chance to melt much snow.

Answer 2

Snow can accumulate on the higher elevations of volcanoes where temperatures are colder, even while the volcano is erupting. The heat from the eruption may melt the snow temporarily, but since snowfall continues at higher altitudes, it can still accumulate on the volcano. Additionally, volcanic ash and debris can cool the surrounding area, allowing the snow to remain despite the heat from the eruption.