Midway

Midway Atoll is part of a chain of volcanic islands, atolls, and seamounts extending from Hawaii up to the tip of the Aleutian Islands and known as the Hawaiian–Emperor seamount chain. It consists of a ring-shaped barrier reef nearly five miles in diameter[8] and several sand islets. The two significant pieces of land, Sand Island and Eastern Island, provide a habitat for millions of seabirds. The island sizes are shown in the table above. The atoll, which has a small population (approximately 60 in 2014,[9] but no indigenous inhabitants), is designated an insular area under the authority of the United States Department of the Interior.

Midway was formed roughly 28 million years ago when the seabed underneath it was over the same hotspot from which the Island of Hawaii is now being formed. In fact, Midway was once a shield volcano, perhaps as large as the island of Lana'i. As the volcano piled up lava flows building the island, its weight depressed the crust and the island slowly subsided over a period of millions of years, a process known as isostatic adjustment.

As the island subsided, a coral reef around the former volcanic island was able to maintain itself near sea level by growing upwards. That reef is now over 516 feet (157 m) thick[10] (in the lagoon, 1,261 feet (384 m), comprised mostly post-Miocene limestones with a layer of upper Miocene (Tertiary g) sediments and lower Miocene (Tertiary e) limestones at the bottom overlying the basalts). What remains today is a shallow water atoll about 6 miles (9.7 km) across. Following Kure Atoll, Midway is the 2nd most northerly atoll in the world.

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