Are you talking about how areas of the world are covered with fire and some places have cracks in them?
The could possibly be because as he caused the cataclysm from rising from Deepholm it shook the entire earth. Cracking certain parts of the land (Barrens). The shit on fire is from him flying over it, well, the burned stuff in Wetlands. Everything probably caught fire from the cracks spewing out magma.