Erosion

Erosion is a level behaviour that causes lava to spread over time. Only certain terrain can erode, which are the following: Erosion can only occur on a tile that has started eroding or a tile that is next to lava. If the tile is erodable, it will then go through 4 stages of erosion, each with a more lava-like appearance, until the tile finally turns into lava. At that point, there is no way to turn the tile back into ground.
 * Ground
 * Rubble
 * Power paths
 * Building paths

Timing
The timing or each erosion tile depends on the level. Each tile in the level can have its own erosion time, ranging between 2 and 600 seconds. Each tile's delay is random in a specific span even if its erosion time is the same as its neighbours. The random delay will be consistent between playthroughs, drawn from a stream of random numbers generated by hashing the level file.

The timing can be altered further by including the level parameter "erosionscale:X" in the section "levelinfo", where X is replaced by a floating point number such as 0.2, which would result in the lowest erosion time becoming 0.4.

Erosion repair
When a tile starts eroding, a new option will appear if you click the tile: Erosion repair. This option orders your miners to repair the damage using 2 pieces of Ore. This action follows the build queue and will always be done before any other buildings. After reparation, the tile will turn into gruond and Erosion will remain dormant for 120 seconds before restarting its erosion cycle. If the tile was an in-progress Power Path or a completed Power Path, it will also turn into a fully fixed Power Path upon repair!