The Floor is Lava

The Floor is Lava is a Limited Time Modes in Fortnite: Battle Royale that was introduced in Update v8.20.

LTM Rules and Gameplay

 * Lava gradually rises from the lowest parts of the map, and it’s hot! Drop in and quickly loot and gather materials so you can be the first to reach the high ground.
 * A few minutes into the match, the lava will begin to rise.
 * The lava moves at a steady speed until the entire map is covered.
 * Touching the lava will apply damage directly to your health and bounce you up in the air.
 * You can build on the lava.
 * Players will be given a small number of materials every second, to help out in those "entire map is on fire" situations.

Trivia

 * Grefg's Floor is Lava is a remake of this LTM but with a different Loot Pool.