Minecraft wiki entry for Creeper, associated text: When within 3 blocks of a player, a creeper stops moving, hisses, flashes and expands and explodes after 1.5 seconds, destroying blocks in the area as well as significantly damaging the player. A creeper's detonation can be halted if the player leaves the blast radius, including by knocking it back, going out of the creeper's sight, or if the creeper is killed before the explosion. The distance with the player at which a creeper cancels its explosion is greater at higher difficulties. Normal creeper explosions have a power of 3.