Something interesting as an explanation for all this would be that the entire planet was infused with so much arcane energy that it became a ball of raw energy itself.

I'm thinking like Arcane Tectonic Plates that are constantly moving around like the creation of the earth and whenever they clash, the earthquakes release huge amounts of 'mana' (instead of exploding in lava). These Manaquakes could do anything that arcane spells could think of. A lot of the ideas already came up.

And the Arcane Tectonic Plates could be small and have significant gaps between them so that the manaquakes are frequent and quick. The party would have to find ways to cross these chasms as wide as the Grand Canyon which fall into the raw arcane core.