The Comoros archipelago consists of four main islands aligned along a northwest-southeast axis at the north end of the Mozambique Channel, between Mozambique and the island of Madagascar. Still widely known by their French names, the islands officially have been called by their Swahili names by the Comoran government. They are Njazidja (Grande Comore), Mwali (Mohéli), Nzwani (Anjouan), and Mahoré (Mayotte). The islands' distance from each other--Njazidja is some 200 kilometers from Mahoré, forty kilometers from Mwali, and eighty kilometers from Nzwani--along with a lack of good harbor facilities, make transportation and communication difficult. The islands have a total land area of 2,236 square kilometers (including Mahoré), and claim territorial waters of 320 kilometers.

Njazidja is the largest island, sixty-seven kilometers long and twenty-seven kilometers wide, with a total area of 1,146 square kilometers. The most recently formed of the four islands in the archipelago, it is also of volcanic origin. Two volcanoes form the island's most prominent topographic features: La Grille in the north, with an elevation of 1,000 meters, is extinct and largely eroded; Kartala in the south, rising to a height of 2,361 meters, last erupted in 1977. A plateau averaging 600 to 700 meters high connects the two mountains. Because Njazidja is geologically a relatively new island, its soil is thin and rocky and cannot hold water. As a result, water from the island's heavy rainfall must be stored in catchment tanks. There are no coral reefs along the coast, and the island lacks a good harbor for ships. One of the largest remnants of Comoros' once-extensive rain forests is on the slopes of Kartala. The national capital has been at Moroni since 1962.

Nzwani, triangular shaped and forty kilometers from apex to base, has an area of 424 square kilometers. Three mountain chains--Sima, Nioumakele, and Jimilime--emanate from a central peak, Mtingui (1,575 meters), giving the island its distinctive shape. Older than Njazidja, Nzwani has deeper soil cover, but overcultivation has caused serious erosion. A coral reef lies close to shore; the island's capital of Mutsamudu is also its main port.

Mwali is thirty kilometers long and twelve kilometers wide, with an area of 290 square kilometers. It is the smallest of the four islands and has a central mountain chain reaching 860 meters at its highest. Like Njazidja, it retains stands of rain forest. Mwali's capital is Fomboni.

Mahoré, geologically the oldest of the four islands, is thirty-nine kilometers long and twenty-two kilometers wide, totaling 375 square kilometers, and its highest points are between 500 and 600 meters above sea level. Because of greater weathering of the volcanic rock, the soil is relatively rich in some areas. A well-developed coral reef that encircles much of the island ensures protection for ships and a habitat for fish. Dzaoudzi, capital of Comoros until 1962 and now Mahoré's administrative center, is situated on a rocky outcropping off the east shore of the main island. Dzaoudzi is linked by a causeway to le Pamanzi, which at ten kilometers in area is the largest of several islets adjacent to Mahoré. Islets are also scattered in the coastal waters of Njazidja, Nzwani, and Mwali.

Comoran waters are the habitat of the coelacanth, a rare fish with limblike fins and a cartilaginous skeleton, the fossil remains of which date as far back as 400 million years and which was once thought to have become extinct about 70 million years ago. A live specimen was caught in 1938 off southern Africa; other coelacanths have since been found in the vicinity of the Comoro Islands.

Several mammals are unique to the islands themselves. The macao, a lemur found only on Mahoré, is protected by French law and by local tradition. Another, Livingstone's fruit bat, although plentiful when discovered by explorer David Livingstone in 1863, has been reduced to a population of about 120, entirely on Nzwani. The world's largest bat, the jet-black Livingstone fruit bat has a wingspan of nearly two meters. A British preservation group sent an expedition to Comoros in 1992 to bring some of the bats to Britain to establish a breeding population. Humboldt's flycatcher is perhaps the best known of the birds native to Comoros. .

Partly in response to international pressures, Comorans in the 1990s have become more concerned about the environment. Steps are being taken not only to preserve the rare fauna, but also to counteract degradation of the environment, especially on densely populated Nzwani. Specifically, to minimize the cutting down of trees for fuel, kerosene is being subsidized, and efforts are being made to replace the loss of the forest cover caused by ylang-ylang distillation for perfume. The Community Development Support Fund, sponsored by the International Development Association (IDA) and the Comoran government, is working to improve water supply on the islands as well.

The climate is marine tropical, with two seasons: hot and humid from November to April, the result of the northeastern monsoon, and a cooler, drier season the rest of the year. Average monthly temperatures range from 23° C to 28° C along the coasts. Although the average annual precipitation is 2,000 millimeters, water is a scarce commodity in many parts of Comoros. Mwali and Mahoré possess streams and other natural sources of water, but Njazidja and Nzwani, whose mountainous landscapes retain water poorly, are almost devoid of naturally occurring running water. Cyclones, occurring during the hot and wet season, can cause extensive damage, especially in coastal areas. On the average, at least twice each decade houses, farms, and harbor facilities are devastated by these great storms.