https://www.pcgamer.com/fortnite-comet-destroys-dusty-depotrisky-reels-and-hop-rocks-new-for-season-4/

Fortnite's long-teased comet has landed—destroying Dusty Depot, not Tilted Towers, in the process. In its place remains a crater, filled with glowing Hop Rocks—consumables which let players "lift off with low gravity." Away from the crash site stands Risky Reels, a new location situated on the map's eastern corner, north of Wailing Woods. It's all go in Fortnite Season 4.  

Courtesy of Fortnite Intel, here's Hop Rocks in practice: