Minecraft wiki entry for Chunk, associated text: Block changing on the edge of a ticking area can spread updates to blocks outside the ticking area and respond appropriately.
Flowing water or lava can spread to the first adjacent block in an outside chunk, but the flow becomes suspended there until the outside chunk becomes active.
Fire can spread to the first adjacent flammable block outside the ticking area. Like water and lava, it becomes suspended there; although visible, its animation does not run, and it cannot spread further until the outside chunk becomes active.
Grass and mycelium can spread to the first adjacent block in an outside chunk, but the affected block does not actually change its appearance until its chunk becomes active; it then changes instantly. Grass and mycelium cannot spread beyond the first such block, nor from such a block into the ticking area until the outside chunk becomes active.
Pumpkin and melon stem growing on the edge of a ticking area can place their fruits on an adjacent block in an outside chunk.
An entity (mob, minecart, arrow, etc.) that attempts to move into an outside chunk becomes suspended as soon as it leaves the ticking area. It remains visible but motionless. When the outside block becomes active, the entity resumes moving.
Exploding TNT can damage or destroy blocks in an inactive chunk, and unlike other events, its effects are not limited to adjacent blocks. However, secondary effects in the outside chunk are suspended until the chunk becomes active. For instance, if an explosion destroys a block that supported sand or gravel, the sand or gravel does not fall immediately. The same thing happens with items that were attached to destroyed blocks, such as item frames and Redstone torches; they do not drop until the chunk is activated.
Primed TNT launched into an inactive chunk is suspended in mid-air within the first outside block it enters. It disappears until the outer chunk becomes active, at which time it resumes its flight and countdown.