The Caroline Islands form an archipelago just north of the equator in Micronesia, western Pacific. At various times in the past, the Caroline Islands encompassed all the islands that now comprise the Federated States of Micronesia (FSM), the Republic of Belau (formerly known as Palau), Guam and the southern Mariana Islands, and the southwestern islands of the Republic of the Marshall Islands (Fig. 1). Today, the name Caroline Islands refers to only the islands of the FSM and Belau (sometimes referred to as Palau).
The earliest settlement of Micronesia is thought to have occurred about 2000 years ago, when immigrants from
the south arrived on the western mountainous islands. In 1525, Portuguese explorers landed on Yap and Ulithi Islands (FSM) during their search for the Spice Islands (Indonesia). Subsequent Spanish expeditions made the first European contacts with the rest of the Caroline Islands, which were named the Carolinas in 1526 by Toribio Alonso de Salazar. Although visited many times through the years, Spain did not formally occupy the Carolinas until 1886. In 1899, Spain sold the islands to Germany, and then they were taken over by Japan in 1914 and mandated to Japan by the League of Nations in 1920. The United States occupied the islands in 1944-1945, and the United Nations placed them under U.S. administration as Trust Territories in 1947. The FSM gained independence in 1986, as did Belau in 1994; both have Compacts of Free Association with the United States.
The Caroline Islands have a tropical climate, and crops include taro, yams, breadfruit, coconuts, sugarcane, tapioca, and pepper. Copra and tapioca are important exports, as are handicrafts and fish, mostly dried bonito. The cultures of the FSM are as varied as the islands. Eight different languages are spoken, and nine Micronesian and Polynesian ethnic groups inhabit the FSM. Populations on Nukuoro and Kapingamarangi Atolls are mostly Polynesian; those on the remaining islands are mostly Micronesian. Belau is about 70% Micronesian, with the remainder of the population being Filipino, Chinese, or of another Asian ethnicity.
The Caroline Islands include several high islands, which are the erosional remnants of long-inactive volcanoes, now partially submerged. The degree of submergence has determined in part the types of reefs surrounding the islands. For most of the islands, the volcanic edifice subsided completely, and only a limestone platform or coral atoll remains above sea level.
The FSM consists of 607 islands and islets comprising a total land area of 702 km2. The islands vary from high mountainous islands (Pohnpei, Kosrae, Yap, and part of Chuuk) to low-lying coral atolls. More than half of the population of approximately 110,000 lives in Chuuk State, which consists of seven major island groups, the largest group being Chuuk proper. The Chuuk group is a complex of 98 islands and islets, 14 of which are volcanic, surrounded by a barrier reef that encloses a large lagoon. Pohnpei, the largest island in the FSM, is mountainous (Mt. Totolom, 791 m high, and Mt. Nahna Laud, 798 m), with 342.4 km2 of land. The impressive ruins at Nan Mandol on islets off southeastern Pohnpei date from about AD 1200. This extensive array of ancient structures was constructed from columnar basalt quarried on the main island.
Belau consists of about 300 islands and islets, with a total land area of 460 km2; nine of the islands are permanently inhabited. The Belau chain extends for about 240 km. Babeldaob, the largest island in Belau, has a maximum elevation of 287 m; a ring road has recently been built around the island. The Belau archipelago is encircled by a part-barrier, part-fringing reef, except for the northernmost island, Ngcheangel (formerly Kayangel), and the southernmost island, Ngeaur. Ngcheangel constitutes an atoll, and Ngeaur is an uplifted coral platform with a maximum elevation of 56 m.
The ocean crust on which the Caroline Islands rest can be divided into two broad geologic provinces. The first is a complex array of ancient volcanoes and ridges that make up the 2500-km-long Caroline Ridge (Fig. 1). The second is a volcanic-arc/subduction-zone system comprising the Yap and Belau trenches, the Yap and Belau volcanic arcs, and the Philippine Sea back-arc area.
The eastern third of Caroline Ridge, from Kosrae Island to Chuuk Atoll, consists of isolated atolls and sea-mounts formed at a hotspot that was active between 12 and 1 million years ago. Central Caroline Ridge, Chuuk Atoll to Tamang Bank, consists of atolls and large submarine carbonate banks. The western third of Caroline Ridge, Tamang Bank to the Yap trench, consists of a large ridge bounded by narrow troughs created by strike-slip faults (southern margin) and normal faults (northern margin). The western two-thirds of Caroline Ridge is generally at less than 2500 m water depth, and it formed about 28 to 24 million years ago. This part of the ridge has been variously interpreted to be a relict volcanic arc, a transform fault along which volcanism occurred, a transform fault combined with a hotspot trace, or an extinct spreading-ridge/transform-fault system.
The Yap arc and trench represent a 34- to 1.8-million-year old subduction zone that is anomalously narrow between the arc and the trench compared to other western Pacific volcanic-arc systems. It has been suggested that subduction ended about 5 million years ago and that back-arc-basin crust was obducted (uplifted) onto the volcanic arc; however, subduction likely occurs at a very slow rate along the Yap trench.
The Belau volcanic arc began forming about 40 million years ago as the Pacific plate was being subducted beneath the Philippine plate. The arc remained volcanically active until about 20 million years ago, when subduction ceased; subduction continued further northeast along the Yap and Mariana trenches. The Belau arc is now part of the Belau-Kyushu Ridge, an extinct volcanic arc located for the most part in the Philippine Sea back-arc basin.
Gold occurs on Maap (also spelled Map) and Gagil-Tomil Islands in the Yap island group, but it has yet to be mined. Copper ore was mined on Gagil-Tomil and Maap Islands during the Japanese occupation. Also during that time, nickel-rich laterite was mined from an open pit on Gagil-Tomil Island.
In Belau, bauxite (aluminum ore) was mined on Babeldaob Island between 1938 and 1944 from two (Ngardmau, Ngeremlengui) of the dozens of prospects, and proven reserves still exist. A gold deposit occurs at Rois Malk on southeast Babeldaob Island, but it has yet to be mined. Locally, the rocks in the same area are highly enriched in organic matter, constituting lignite (coal) deposits. The lignite was briefly mined during World War II, along with interbedded layers of kaolinite (white clay), which was used for ceramics. Phosphate was mined on Ngeaur, Beliliou, and Mecherchar (Eil Malk) Islands, and proven phosphate reserves are still present on those islands as well as on Tobi, Pulo Anna, and Sonsorol islands.
Atolls / Coral / Exploration and Discovery / Pacific Region / Seamounts, Geology
- Marine mineral resources of Pacific islands—a review of the Exclusive Economic Zones of islands of U.S. affiliation, excluding the State of Hawaii. U.S. Geological Survey Circular 1286. , , and . 2005.
- U.S. Office of Insular Affairs, Federated States of Micronesia, http://www.doi.gov/oia/Islandpages/fsmpage.htm.
- U.S. Office of Insular Affairs, Palau, http://www.doi.gov/oia/Islandpages/palaupage.htm.
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