Geology
Main article: Hawaii hotspot
Pāhoehoe, or smooth lava, spills into the Pacific Ocean, forming new rock off the coast of the Island of Hawaii.
The Hawaiian islands were formed by volcanic activity initiated at an undersea magma source called the Hawaii hotspot. The process is continuing to build islands; the tectonic plate beneath much of the Pacific Ocean continually moves northwest and the hot spot remains stationary, slowly creating new volcanoes. Because of the hotspot's location, all currently active land volcanoes are located on the southern half of Hawaii Island. The newest volcano, Lōʻihi Seamount, is located south of the coast of Hawaii Island.
The last volcanic eruption outside Hawaii Island occurred at Haleakalā on Maui before the late 18th century, though it could have been hundreds of years earlier.[47] In 1790, Kīlauea exploded; it was the deadliest eruption known to have occurred in the modern era in what is now the United States.[48] Up to 5,405 warriors and their families marching on Kīlauea were killed by the eruption.[49] Volcanic activity and subsequent erosion have created impressive geological features. Hawaii Island has the third-highest point among the world's islands.[50]
On the flanks of the volcanoes, slope instability has generated damaging earthquakes and related tsunamis, particularly in 1868 and 1975.[51] Steep cliffs have been created by catastrophic debris avalanches on the submerged flanks of ocean island volcanoes.[52][53]