Text Box: Hawaiian Islands Introduction | Geologic Development | Hawaii | Volcanic Rock Aquifers | Maui | Molokai | Lanai | Kahoolawe | Oahu | Kauai | Niihau | Climate and Resources                                                       The Hawaiian Islands are composed of a chain of about 132 volcanic and coral islands, including many atolls, rock reefs and coral reefs, as well as shoals, near the middle of the North Pacific Ocean.  This archipelago extends approximately 1,600 miles in a southeast-northwest direction from the island of Hawaii at the southeastern end to the island of Kure (also called Kure Atoll and Ocean Island) at the northwestern end.  The state of Hawaii extends the entire 1,600 miles, excluding the two small Midway Islands (Atoll), which were administered by the U.S. Navy as a territory until being turned over to the U. S. Department of the Interior in 1996; only Alaska extends over a greater linear distance.  Above-sea-level areas and maximum elevations of the eight largest islands, all at the southeastern end of the archipelago, are shown in Table 4.                                                                           TABLE 4 Island                             Area (square miles)                            Maximum Elevation (feet)   Hawaii                                     4,030                                                        13,796 Maui                                          728                                                         10,023 Oahu                                          604                                                           4,025 Kauai                                         555                                                           5,170 Molokai                                     260                                                           4,970 Lanai                                          141                                                          3,370 Niihau                                          72                                                          1,281 Kahoolawe                                   45                                                          1,477   Using the same criteria as applied to the other geomorphic provinces of the United States, the Hawaiian Islands could be divided into several provinces, but to be consistent with most previous classifications they are treated here as one province.    General Characteristics The portion of the archipelago northwest of the eight major islands consists of a few very small volcanic islands, including Nihoa, Necker Island (Mokumanamana), and Layman Island, but much of the above-water parts are atolls, including Kure Atoll and Midway Atoll, shoals, such as French Frigate Shoals, and coral reefs.  The majority of the coral reefs in the United States are here.  All of these features in this portion of the archipelago are included in the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, most of which is extremely restricted in terms of human visitation.  All of the main islands, which are in the southeastern part of the state and are not in the reserve, are composed of basalt lava.  Hawaiian lavas are among the hottest on Earth, and the high temperatures, coupled with a relatively high gas content, produce lava that often spreads over many miles in individual layers that rarely exceed 30 feet in thickness.  Pyroclastic materials are much less common than lava on the islands, comprising less than 5 percent of the volume of Hawaii, the largest island.  The lava hardens into two main types.  These two types differ essentially only in appearance, having the same basic chemical composition, and may occur in different parts of the same lava flow.  Pahoehoe (Hawaiian for smooth or ropy) lava results from very hot, relatively fast flowing basalt that congeals into a smooth, billowy layer most often less than 10 feet thick.  The second main type of lava, aa (Hawaiian for rough), has a very rugged, jagged surface.  Aa lava may develop in different ways.  It may form directly by the cooling of thick, less hot, slowly moving lava, or may result from a pahoehoe flow converting into aa by a change in the initial gas content and viscosity, or by a pahoehoe flow hardening and then experiencing additional movement, breaking the flow into angular chunks.  Aa lava has a dull luster because its rough texture absorbs much sunlight, whereas pahoehoe has a shiny appearance because of its smooth reflective surface.  Individual flows of aa lava typically are 10-30 feet thick.  Sometimes mixed in with these two types of lava are Pele’s tears and Pele’s hair.  The former result when droplets of fountaining lava are propelled into the air and solidify before landing.  Pele’s hair occurs from the airborne droplets being drawn into very fine strands resembling hair.  Despite being among the hottest lavas on Earth, some Hawaiian lava solidifies enough to be walked on (with special-soled boots) within 10 hours of being extruded.  Within a month, and sometimes sooner, the lava may have cooled sufficiently to be cool to the touch.    Hawaiian Islands Introduction | Geologic Development | Hawaii | Volcanic Rock Aquifers | Maui | Molokai | Lanai | Kahoolawe | Oahu | Kauai | Niihau | Climate and Resources