A primitive planet where Kirk saves both Spock and the native population from a volcano at the start of Star Trek Into Darkness.
Nibiru is an inhabited planet with a pre-warp civilization, visited by the Enterprise in the opening of Star Trek Into Darkness. A massive volcano threatens to destroy the native population, and Spock is lowered into it with a device to halt the eruption.
The operation goes wrong, and to rescue Spock, Kirk raises the Enterprise from its hiding place beneath the ocean in full view of the natives, violating the Prime Directive. As a result, Kirk is relieved of command of the Enterprise.