What is symbolic about the opening of the fissure in the wall at the end of The Fall of the House of Usher?

The opening of the fissure in the wall is symbolic of the final collapse and deterioration of the Usher family and their home. It represents the ultimate disintegration of the family's sanity and the supernatural forces that have plagued them. The fissure serves as a physical manifestation of the emotional and psychological decay that has been building throughout the story.