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America's Coasts

Hawaiian Coast

The Hawaiian Archipelago extends from the large island of Hawaii across the central Pacific Ocean to tiny Kure Atoll, 2,450 km away. The 8 main islands of the state of Hawaii at the southeast end of the archipelago comprise 99% of the land area. About 20% of the 1,650 km of shore on the main islands is sandy beach. Aside from manmade structures, the remainder of the shore consists primarily of outcrops or boulders of lava, but also includes muddy shores, gravel beaches, beach rock, raised reefs and lithified sand dunes.

Although the coastlines of the Hawaiian Islands are geologically young, wave erosion and the growth of coral reefs have modified most of the shores. Coastal plains have formed around the base of some volcanoes and between others. The plains are partly alluvial and partly raised reefs. The greater parts of the Hawaiian coasts are sea cliffs, some as high as 1,000 meters on the windward side of the islands.

There are also extensive beaches, the best of which tend to be on the western sides of the islands, protected from waves generated by the northeast trade winds. On southwestern Kauai near Kekaha, there are prograding beach ridges. Surprisingly, most of the beaches are composed not of volcanic debris but primarily of biogenic sediment. The rare volcanic sand beaches are at the mouths of the large rivers or along coasts where recent lava flows have killed the coral reefs.

Map of United States showing Hawaii


Hawaiian Coasts

Many Hawaiian beaches are undergoing serious erosion. Finding suitable sources of sand for renourishment has been difficult. This is a critical problem because tourism is a major part of the Hawaiian economy and the beaches are among the great attractions.