天皇海山群
The islands are the exposed peaks of a great undersea mountain range known as the Hawaiian–Emperor seamount chain, formed by volcanic activity over a hotspot in the Earth's mantle. The archipelago formed as the Pacific plate moved slowly northwestward over a hotspot in the mantle at about 32 miles (51 km) per million years. The islands in the northwest of the archipelago are older and typically smaller, due to longer exposure to erosion. The age of the archipelago has been estimated using potassium-argon dating methods. It is estimated that the northwesternmost Kure Atoll is the oldest at approximately 28 million years, while the southeasternmost Hawaiʻi Island is approximately 400,000 years old and still subjected to ongoing volcanism—one of the most active hotspots on Earth.