Final answer:
The supporting detail for the main idea about lava land ownership in Hawaii is that newly created land by lava solidifying in the ocean belongs to the state.
Step-by-step explanation:
The sentence that serves as a supporting detail for the main idea that ownership of lava lands in Hawaii is split between the state and existing property holders is: "Where lava hit the ocean and hardened, adding completely new land along the coast, it belongs to the state." This sentence clarifies how property rights are determined in the case of new land created by volcanic activity, specifically the 2018 eruption of the Kilauea Volcano in Hawaii. It explains that the newly formed land due to lava solidifying upon reaching the ocean falls under state ownership, whereas land that was previously owned before being covered by fresh lava retains its original ownership despite the diminished property value.