A lavacast is a structure made of cobblestone created by repeatedly pouring water over lava, generally used to quickly grief a large area. The landscape of Spawn has mostly been replaced by numerous lavacasts over the years. They most often resemble mountains or pyramids but can take on many different shapes depending on the manner in which they were created. Lavacasts often contain small air pockets. They are also sometimes used to create walls, towers, and other large structures. A rare but well-known usage of lavacasts is to create huge symbols, the most famous example of which is the giant cobblestone swastika. The word itself is also commonly used as a verb (eg: "He lavacasted the base.")
chezhead's screenshots show that lavacasts had been made by April 27, 2011.
Spawn began to get lavacasted more than ever in 2016, in response to the Rusher Invasion and War.
Lavacasts can be made in several different ways, but the two main types are staircases and cobblestone monsters. The end structure is always the same though, a giant cobble stone structure.
- Staircase: The quickest and easiest way to build a lavacast. Simply build a staircase and pour lava down it, and then pour water on top. If made in a straight line it will form a triangle shaped lavacast, but you could also twist and turn the staircase or branch off from it to make more complex shapes. Lava and water can be poured multiple times to increase the thickness. You could also make several staircases all meet at a central point to make a sort of pyramid.
- Cobblestone monster: This method takes the longest but produces the biggest lavacasts. Build a tower out of dirt or something and remove every other block. Pour lava into the bottom space, wait for it to spread, then pour water into the next space. Remove the water and place lava there again, basically building up your lavacast layer by layer. If done all the way to height limit the resulting lavacast can be incredibly large. This method has been used to leave a nearly permanent mark on several bases and monuments, and is also what created the many giant mountains of cobblestone around spawn.
- The Penny Dropper
- Gape 1.0
- Jared Town
Squid Base Old Town
- Fort Creatonism Corner
- 8k8k (currently the largest lavacast on the server, measuring around 600+ blocks from end to end)
Valley of Wheat (itself considered to be the second greatest grief apart from spawn)
- Cobblestone penis, a penis made out of 16 large cobblestone monsters next to each other (coords: 13,750 -18,750)
200 150 (Armorsmith's Spawn Base) -300 -300 (Octocast)
- Carolina Memorial (Largest Staircase lavacast at the End's Spawn located at 0, -200) 
- Wassrige Holle (Nether lavacast)
- 1 million +X milestone
- 1 million -Z milestone