The rift aftermath is like a dump, and I was wondering, what was the cause of all this?
From the official map description found https://www.ea.com/games/apex-legends/maps
However, all dreams come to an end, and this one ended explosively: an accident in an experimental research facility led to the creation of the Phase Rift (a massive bubble of Phase energy), and the Outlands’ best and brightest quickly abandoned the city.
A failed experiment caused the rift tunnel to explode and create this bubble. This may have something do with Horizon, as she was able to re-route the phase runner for her season 7 story event. Since it's a new map and a new storyline, we'll just have to wait and see what Respawn has in store for Olympus.