The Marshall Islands

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The Marshall Islands lie on the eastern edge of Micronesia in the west central Pacific Ocean, approximately halfway between Hawaii and northern Australia. Depending on how terms are defined, the island nation called the Republic of the Marshall Islands consists of 34 coral atolls or 29 atolls and five isolated low coral islands. Geographically they are roughly divided into two chains of atolls, the eastern Ratak or sunrise and the western Ralik or sunset chains, that run from southeast to northwest.

Weather is definitely tropical. Year-round temperatures on Kwajalein hardly change from summer to winter, varying from daytime highs of 86 to 88 degrees F to nighttime lows of 78 to 80. Occasionally it will go a degree or two above or below these ranges. Ocean water temperature ranges from about 80 degrees F in the winter to 85 degrees in the summer. Tradewinds from the east through northeast, usually ranging from about 12 to 20 knots, blow from late fall (usually starting in November) through early summer (often through June or even into July). The rest of the summer and early fall usually see lighter winds, from becalmed to 10 to 15 knots. It is during this period that winds will often come out of a direction other than northeast.

The largest atoll in the Marshalls--indeed, the largest in the world--is Kwajalein Atoll in about the center of the Ralik chain. As shown in the map above, Kwajalein Atoll is irregularly boomerang shaped and stretches approximately 106 km (66 miles) in a straight line from Kwajalein Island in the southeast to Ebadon in the northwest. Kwajalein, like Enewetak Atoll at the northwestern edge of the Marshalls, was fortified by Japan during World War II and captured by invading American forces in 1944. Remnants of the Japanese occupation and American invasion can be found on a number of islands, particular Roi-Namur at the northern tip of the atoll.

After the war, Enewetak and another northern Marshall Islands atoll, Bikini, were used by the US for nuclear testing in the late 1940s and 1950s. Kwajalein supported those efforts, and is currently the site of a US army base engaged primarily in radar research and tracking.

Kwajalein's ring of mostly shallow reef is dotted with low islands called motus and interrupted in various places by passes. The lagoon within the ring is mostly about 50 meters (about 160 feet) deep dropping in places to a bit over 60 meters (200 feet). The lagoon bottom is mostly fine coral sand, often with thick growths of Halimeda algae and innumerable coral knolls that range from mere bumps in the bottom to steep-sided pinnacles that reach to the surface of the water. The seaward reef gradually deepens from the intertidal moving outward until it drops off into the ocean depths. On the eastern side, the seaward reef front tends to be wider, with the knee of the drop at about 15 to 25 meters (50 to 80 feet), and the slope of the deeper coral-covered drop typically 45 to 60 degrees. On the leeward reef, the reef front is narrower, with the knee of the drop typically around 6 to 8 meters (20 to 25 feet) and the outer slope steeper, 60 degrees or more and even vertical in some areas. The leeward reef front is also often cut by steep-sided channels opening on the outer slope and narrowing back in towards the intertidal reef.

With little land for run-off, atoll waters are mostly very clear, with visibilities often exceeding 45 meters (150 feet) on the seaward slopes. Visibility within the lagoon tends to be less, but it is not too unusual to be able to see at least 30 meters down from the surface. Marine life is abundant in most areas. Some of richest communities of corals and fish are on the lagoon pinnacle reefs, particularly those that get washed by tidal currents during the twice daily rising and lowering tides. Sharks, particularly gray reef sharks, abound, most often on the lagoon pinnacles and seaward reef areas farther away from lots of diving traffic; we suspect that extensive diving activity tends to push the sharks out. Other big animals are mostly seen on the seaward slopes, although mantas are more common along some lagoon reef cleaning stations.

The lagoon, particularly around the southern island of Kwajalein and the northern island of Roi-Namur, is littered with the wreckage of war, mostly numerous Japanese ships sunk in the days leading up the American invasion of the atoll in 1944 and many American aircraft, particularly in the north, scuttled after the end of the war. There is also the German Heavy Cruiser Prinz Eugen, which survived two nuclear tests at Bikini only to develop a leak and sink at Kwajalein while awaiting final disposition. Dave Fortin's website gives an indication how nice a place Kwaj is for shipwreck diving.

Kwajalein does not have everything. There are few sea grasses and no mangroves or muddy flats that further west in the Pacific support numerous interesting creatures. The lush and colorful tree-like Dendronephthya soft corals so prevalent on reefs such as the passes at Pohnpei, on the shipwrecks of Chuuk lagoon, and on many reefs in places such as Indonesia and the Solomon Islands, are present but scarce in the Marshalls.

But there is a lot of marine life. Photos on this web site and in the videos produced by In-Depth Images Kwajalein barely scratch the surface.

Kwajalein Underwater Home

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