The bulk of the volcanism of a Hawaiian volcano is made up by the shield stage during which tholeiitic lavas are erupted. This stage is after between 250,000 - 2,500,000 years followed by a post-erosional or rejuvenated stage during which lavas of alkali basalt, melilitite and nephelinite composition; such volcanism has been observed on Koolau, Kauai and Niihau and covers large parts of the Hawaiian Islands even though it makes up less than one percent of their volume. The North Arch volcanic rocks resemble the composition of these rejuvenated stage volcanics of Hawaii such as the Honolulu Volcanics, and another unit of these volcanics forms the South Arch volcanic field south of Kilauea, and have been deemed peripheral lavas of the Hawaii hotspot. In fact, it has been proposed that the rejuvenated volcanics of Niihau, Kauai, Oahu and Molokai might actually be part of the North Arch volcanic field. Other volcanic units of a probably similar nature have been found between Oahu and Kauai.