A cooling system for a subterranean power line may include a cooling tube configured to house a fluid. Heat generated by the subterranean power line may be radiated and/or conducted to the cooling tube and absorbed by the fluid within the cooling tube. As the fluid heats up, it may change phase from a liquid to a gas. The hot gas may rise to a heat-exchanging condenser configured to dissipate the heat and condense the fluid back into a liquid. The cool, condensed liquid my return from the heat-exchanging condenser to the cooling tube. Risers, gas transport tubes, pressure regulation systems, fluid storage tanks, and other components described herein may increase the efficiency of the cooling system and/or otherwise improve the viability of the cooling system for subterranean power lines.