In 1984, Tonga's Home Reef shot a 12km-high plume into the sky and built an island. 42 years later, the growing volcanic island has gained nearly 20 acres of land. The submarine volcano has repeatedly created and lost islands since the 19th century. Recent eruptions have expanded the island. Satellite images help experts monitor changes, ash, lava flows and water plumes while scientists study possible effects on marine life and birds.