Hawaii is the only U.S. state that is surrounded by water. It is one of two states that do not share a border with another U.S. state (Alaska being the other). It is the southernmost part of the United States.

In addition to possessing the southernmost point in the United States, it is the only state that lies completely in the tropics. One of two states outside the contiguous United States, it is the only state without territory on the mainland of any continent. It is also the only state that continues to grow in area because of active extrusive lava flows, most notably from Kilauea. Because it has more endangered species per square mile than anywhere else, Hawaii is considered the endangered species capital of the world.

The Hawaiian Archipelago comprises nineteen islands and atolls extending across a distance of 1,500 miles (2,400 km). Of these, eight high islands are considered the “main islands” and are located at the southeastern end of the archipelago. These islands are, in order from the northwest to southeast, Ni?ihau, Kaua?i, O?ahu, Moloka?i, Lana?i, Kaho?olawe, Maui and the Island of Hawai?i.

All of the Hawaiian Islands were formed by volcanoes arising from the sea floor through a vent described in geological theory as a hotspot. The theory maintains that as the tectonic plate beneath much of the Pacific Ocean moves in a northwesterly direction, the hot spot remains stationary, slowly creating new volcanoes. This explains why only volcanoes on the southern half of the Island of are presently active.

The last volcanic eruption outside the Island of Hawaii happened at Haleakala on Maui in the late 18th century. The newest volcano to form is Lo?ihi, deep below the waters off the southern coast of the Island of Hawai?i.

The isolation of the Hawaiian Islands in the middle of the Pacific Ocean, and the wide range of environments to be found on high islands located in and near the tropics, has resulted in a vast array of endemic flora and fauna. The volcanic activity and subsequent erosion created impressive geological features.

Hawai?i is notable for rainfall: Mount Wai?ale?ale, on the island of Kaua?i, has the second highest average annual rainfall on earth: about 460 inches (11.7 m). The Big Island of Hawai?i is notable as the world’s fifth highest island. If the height of the island is measured from its base, deep in the ocean, to its snow-clad peak on Mauna Kea, it can be considered one of the tallest mountains in the world.