The Great Rift is manifested by the power of the magic Green Emerald of Khufu. When the jewel is worn, it creates great anger inside its user, poisoning their heart and filling it with evil. The more fighting that the wearer engages in, the more power that is transferred into the Great Rift, making it more powerful and solid over time.
The Green Emerald of Khufu somehow ended up in Mesmaria over the years, where the beast was eventually summoned and reduced the once glorious city to dust.
The Great Rift was released nce more when Queen Deluca began fighting with her brothers for power but after Aladdin and his friends destroyed the cursed green emerald, he disappeared.