https://www.cnet.com/how-to/fortnites-volcano-event-heres-everything-we-know-so-far/

Players began "feeding" the volcano items and materials, which caused a meter in the rune itself to fill and made the volcano more active. Later, the volcano stopped accepting items, which players assumed would be the end of the event, but it instead reset, requiring players to deposit even more items. 

Thanks to data miners -- people who dig through the game's data files for clues on what's coming up -- there's further evidence the volcano event might be right around the corner.