Meaning
This flag stands for Heard Island and McDonald Islands, an uninhabited Australian territory in the far southern Indian Ocean. The islands have no flag of their own and use the flag of Australia.
Heard Island is topped by an active volcano wrapped in glaciers, so the emoji mostly appears in science news, documentaries and remote-places trivia, with 🌋 or 🧊. “Imagine an active volcano covered in ice 🇭🇲🌋”