The island is chiefly notable for its "mysterious" prehistoric ruins, its once-extensive deposits of phosphatic guano, its former use as the site of the first British H-bomb tests, and its current importance as a protected area for breeding seabirds.
The island is designated as the Malden Island Wildlife Sanctuary. In 2014 the Kiribati government established a 12-nautical-mile fishing exclusion zone around each of the southern Line Islands.
Malden Island is located 242 nautical miles (278 mi; 448 km) south of the equator, 1,530 nautical miles (1,761 mi; 2,834 km) south of Honolulu, Hawaii, and more than 4,000 nautical miles (7,000 km) west of the coast of South America. The nearest land is uninhabited Starbuck Island, 110 nautical miles (204 km; 127 mi) to the southwest. The closest inhabited place is Tongareva (Penrhyn Island), 243 nautical miles (450 km; 280 mi) to the southwest. The nearest airport is on Kiritimati (Christmas Island), 365 nautical miles (676 km; 420 mi) to the northwest. Other nearby islands (all uninhabited) include Jarvis Island, 373 nautical miles (691 km; 429 mi) to the northwest, Vostok Island, 385 nautical miles (713 km; 443 mi) to the south-southeast, and Caroline (Millennium) Island, 460 nautical miles (852 km; 529 mi) to the southeast.
The island has roughly the shape of an equilateral triangle, with 8 km (5 mi) on a side, aligned with the southwest side running northwest to southeast. The west and south corners are slightly truncated, shortening the north, east and southwest coasts to about 7 km (4 mi), and adding shorter west and south coasts about 1 to 2 km (½–1 mi) in length. A large, mostly shallow, irregularly shaped lagoon, containing a number of small islets, fills the east central part of the island. The lagoon is entirely enclosed by land, but only by relatively narrow strips along its north and east sides. It is connected to the sea by underground channels, and is quite salty. Most of the land area of the island lies to the south and west of the lagoon. The total area of the island is about 39.3 square kilometres (15 sq mi).
The island is very low, no more than 10 metres (33 ft) above sea level at its highest point. The highest elevations are found along a rim that closely follows the coastline. The interior forms a depression that is only a few meters above sea level in the western part and is below sea level (filled by the lagoon) in the east central part. Because of this topography, the ocean cannot be seen from much of Malden's interior.
There is no standing fresh water on Malden Island, though a fresh water lens may exist.
A continuous heavy surf falls all along the coast, forming a narrow white to gray sandy beach. Except on the west coast, where the white sandy beach is more extensive than elsewhere, a strip of dark gray coral rubble, forming a series of low ridges parallel to the coast, lies within the narrow beach, extending inward to the island rim.
Because of Malden's isolation and aridity, its vegetation is extremely limited. Sixteen species of vascular plants have been recorded, of which nine are indigenous. The island is largely covered in stunted Sida fallax scrub, low herbs and grasses. Few, if any, of the clumps of stunted Pisonia grandis once found on the island still survive. Coconut palms planted by the guano diggers did not thrive, although a few dilapidated trees may still be seen. Introduced weeds, including the low-growing woody vine Tribulus cistoides, now dominate extensive open areas, providing increased cover for young sooty terns.
Malden is an important breeding island for about a dozen species including masked boobies (Sula dactylatra), red-footed booby (Sula sula), tropicbirds (Phaethontidae), great frigatebird (Fregata minor), lesser frigatebird (Fregata ariel), grey-backed tern (Onychoprion lunata), red-tailed tropicbird (Phaethon rubricauda), sooty terns (sterna fuscata) It is also an important winter-stop for the bristle-thighed curlew (Numenius tahitiensis), a migrant from Alaska; and other migratory seabirds (nineteen species in all).
Two kinds of lizards, the mourning gecko (Lepidodactylus lugubris) and snake-eyed skink (Ablepharus boutonii) are present on Malden, together with brown libellulid dragonfly.
Cats, pigs, goats and house mice were introduced to Malden during the guano-digging period. While the goats and pigs have all died off, feral cats and house mice are still present. Small numbers of green turtles nest on the beaches, and hermit crabs abound.
Malden was rediscovered on 30 July 1825 by Captain The 7th Lord Byron (a cousin of the famous poet). Byron, commanding the British warship HMS Blonde, was returning to London from a special mission to Honolulu to repatriate the remains of the young king and queen of Hawaii, who had died of measles during a visit to Britain. The island was named for Lt. Charles Robert Malden, navigator of the Blonde, who sighted the island and briefly explored it. Andrew Bloxam, naturalist of the Blonde, and James Macrae, a botanist travelling for the Royal Horticultural Society, joined in exploring the island and recorded their observations. Malden may have been the island sighted by another whaling captain William Clark in 1823, aboard the Winslow.
At the time of its discovery by Europeans, Malden was found to be unoccupied, but the remains of ruined temples and other structures indicated that the island had at one time been inhabited. At various times these remains have been speculatively attributed to "wrecked seamen", "buccaneers", "South American Incas", "early Chinese navigators", etc. In 1924, the Malden ruins were examined by an archaeologist from the Bishop Museum in Honolulu, Kenneth Emory, who concluded that they were the creation of a small Polynesian population which had resided there for perhaps several generations some centuries earlier.
The ancient stone structures are located around the beach ridges, principally on the north and south sides. A total of 21 archaeological sites have been discovered, three of which (on the island's northwest side) are larger than the others. These sites include temple platforms, called marae, house sites, and graves. Comparisons with stone structures on Tuamotu atolls show that a population of between 100 and 200 natives could have produced all of the Malden structures. Maraes of a similar type are found on Raivavae, one of the Austral Islands. Various wells used by these ancients were found by later settlers to be dry or brackish.
In the first half of the nineteenth century, during the heyday of American whaling in the central Pacific, Malden was visited on a number of occasions by American whalers.
In 1918, schooner Annie Larsen, infamous for her role in the Hindu-German Conspiracy, was stranded at Malden Island.
Malden was claimed by the U.S. Guano Company under the Guano Islands Act of 1856, which authorized citizens to take possession of uninhabited islands under the authority of the United States for the purpose of removing guano, a valuable agricultural fertilizer. Before the American company could begin their operations, however, the island was occupied by an Australian company under British license. This company and its successors exploited the island continuously from the 1860s through 1927.
Beatrice Grimshaw, a visitor to Malden in the guano-digging era, decried the "glaring barrenness of the bit island", declaring that "...shade, coolness, refreshing fruit, pleasant sights and sounds: there are none. For those who live on the island, it is the scene of an exile which has to be endured somehow or other". She described Malden as containing "a little settlement fronted by a big wooden pier, and a desolate plain of low greyish-green herbage, relieved here and there by small bushes bearing insignificant yellow flowers". Water for settlers was produced by large distillation plants, since no fresh-water wells could be successfully dug on the island.
The five or six European supervisors on the island were given "a row of little tin-roofed, one-storeyed houses above the beach", while the native laborers from Niue Island and Aitutaki were housed in "big, barn-like shelters". Grimshaw described these edifices as being "large, bare, shady buildings fitted with wide shelves, on which the men spread their mats and pillows to sleep". Their food consisted of "rice, biscuits, yams, tinned beef, and tea, with a few cocoanuts for those who may fall sick". Food for the white supervisors consisted of "tinned food of various kinds, also bread, rice, fowls, pork, goat, and goat's milk", but vegetables were hard to come by.
Indentured laborers on Malden were contracted for one year, paid ten shillings per week plus room and board, and repatriated to their home islands when their contracts expired. Salaries for the supervisors were described as "quite high". Work hours were 5 am to 5 pm, with one hour and 45 minutes given off for meals.
The guano diggers constructed a unique railroad on Malden Island, with cars powered by large sails. Laborers pushed empty carts from the loading area up the tramway to the digging pits, where they were then loaded with guano. At the end of the day, the sails were unfurled, and the train cars whisked back to the settlement by the prevailing southeastern winds. While cars were known to jump the tracks more than once during these excursions, the system seems to have worked fairly well. Railroad handcars were also used. This tramway remained in use on Malden as late as 1924, and its roadbed still exists on the island today.
Although guano digging continued on Malden through the early 1920s, all human activity on the island had ceased by the early 1930s. No further human use seems to have been made of Malden until 1956.
In 1956 the United Kingdom selected Malden as the "instrumentation site" for its first series of thermonuclear (H-bomb) weapons tests, based at Kiritimati (Christmas Island). British officials insisted that Malden should not be called a "target island". Nevertheless, the bombing target marker was located at the south point of the island and three thermonuclear devices were detonated at high altitude a short distance offshore in 1957. The airstrip constructed on the island by the Royal Engineers in 1956–57 remained usable in July 1979.
Malden was incorporated in the British Gilbert and Ellice Islands Colony in 1972, and included in the portion of the colony which became the Republic of Kiribati in 1979. The U.S. continued to dispute British sovereignty, based on its nineteenth century Guano Act claims, until after Kiribati became independent. On 20 September 1979, representatives of the United States and Kiribati met on Tarawa Atoll in the Gilberts group of Kiribati, and signed a treaty of friendship between their two nations (commonly referred to as the Treaty of Tarawa of 1979) by which the United States recognized Kiribati's sovereignty over Malden and thirteen other islands in the Line and Phoenix Islands groups. This treaty entered into force on 23 September 1983.
The main value of the island to Kiribati lies in the resources of the 200-nautical-mile (230 mi; 370 km) Exclusive Economic Zone which surrounds it, particularly the rich tuna fisheries. Gypsum deposits on the island itself are extensive, but do not appear to be economically viable under foreseeable market conditions, mainly due to cost of transportation. Some revenue has been realized from ecotourism; the World Discoverer, an adventure cruise ship operated by Society Expeditions, visited the island once or twice annually for several years in the mid-1990s.
Malden was reserved as a wildlife sanctuary and closed area, and was officially designated as the "Malden Island Wildlife Sanctuary", on 29 May 1975, under the 1975 Wildlife Conservation Ordinance. The principal purpose of this reservation was to protect the large breeding populations of seabirds. This sanctuary is administered by the Wildlife Conservation Unit of the Ministry of Line and Phoenix Islands Development, headquartered on Kiritimati. There is no resident staff at Malden, however, and occasional visits by foreign yachtsmen and fishermen cannot be monitored from Kiritimati. A fire in 1977, possibly caused by visitors, threatened breeding seabirds; this remains a potential threat, particularly during periods of drought.