<P> This chain of islands, or archipelago, developed as the Pacific Plate moved slowly northwestward over a hotspot in the Earth's mantle at a rate of approximately 32 miles (51 km) per million years . Thus, the southeast island is volcanically active, whereas the islands on the northwest end 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 . From this study and others, it is estimated that the northwestern most island, Kure Atoll, is the oldest at approximately 28 million years (Ma); while the southeastern most island, Hawai ʻi, is approximately 0.4 Ma (400,000 years). The only active volcanism in the last 200 years has been on the southeastern island, Hawai ʻi, and on the submerged but growing volcano to the extreme southeast, Lo ʻihi . The Hawaiian Volcano Observatory of the USGS documents recent volcanic activity and provides images and interpretations of the volcanism . </P> <P> Almost all of the magma of the hotspot has the composition of basalt, and so the Hawaiian volcanoes are composed almost entirely of this igneous rock . There is very little coarser - grained gabbro and diabase . Nephelinite is exposed on the islands but is extremely rare . The majority of eruptions in Hawai ʻi are Hawaiian - type eruptions because basaltic magma is relatively fluid compared with magmas typically involved in more explosive eruptions, such as the andesitic magmas that produce some of the spectacular and dangerous eruptions around the margins of the Pacific basin . </P> <P> Hawai ʻi island (the Big Island) is the biggest and youngest island in the chain, built from five volcanoes . Mauna Loa, taking up over half of the Big Island, is the largest shield volcano on the Earth . The measurement from sea level to summit is more than 2.5 miles (4 km), from sea level to sea floor about 3.1 miles (5 km). </P> <P> The Hawaiian Islands have many earthquakes, generally caused by volcanic activity . Most of the early earthquake monitoring took place in Hilo, by missionaries Titus Coan, Sarah J. Lyman and her family . From 1833 to 1896, approximately 4 or 5 earthquakes were reported per year . </P>

Which island of the hawaiian island chain is the youngest