Here "bread" represents food in general. Food coming out of the ground is a metaphor for food growing out of the ground. AT: "the earth, where food grows" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-metaphor]])
Possible meanings are that 1) people made fires under the ground to break apart the rock. AT: "it is broken up below by the fires that the miners make" or 2) "turned" is a metaphor for changed. AT: "it is broken up below so much that it appears that it was destroyed by fire"