1. Natural and social conditions
There are about 4,000 islands in the sea areas of Viet Nam. The offshore islands are about 3,000 with a total area of over 1,600 km2. Of these 3,000 islands, three islands are larger than 100 km2, 23 islands larger than 10 km2, and 82 have an area over 1 km2. Almost all sections of the coast are sheltered by individual or groups of islands. Viet Nam has two offshore archipelagos, which are Hoang Sa and Truong Sa.
The islands are not distributed equally on the sea. Over 2300 islands (with a total area of over 800 km2) are located off the coast of North Viet Nam. Over 250 islands (with a total area of over 170 km2) are located off the coast of Central Viet Nam. Over 200 islands (with a total area of over 679 km2) are located off the coast of South Viet Nam.
The large islands are: Phu Quoc (Kien Giang province, 567 km2), Cai Bau (Quang Ninh province, 200 km2), Cat Ba (Hai Phong, 149 km2), Con Dao (Vung Tau, 56.7 km2), Hon L6n (Khanh Hoa province, 45 km2), Hon Tre (Khanh Hoa province, 32 km2), Phu Quy (Binh Thuan province, 32.5 km2), Vinh Thuc (Quang Ninh province, 32 km2), Co To-Thanh Lan (Quang Ninh province, 23.4 km2), Cai Chien (Quang Ninh province, 10.9 km2).
Most of the islands are concentrated in the following seas of Viet Nam: the northeastern sea of North Viet Nam, the northern and southern seas of Central Viet Nam and the southwestern sea of South Viet Nam. There are two archipelagos of Hoang Sa and Truong Sa.
Islands and archipelagos are often divided into groups according to the significance of their location and their geographical and population conditions. These groups are:
– the group of outpost islands which are especially important for national construction and defence. Bases for controlling the sea, maritime airspace, ship and boat operations may be established on islands and archipelagos like Hoang Sa, Truong Sa, Chang Tay, Tho Chu, Phu Quoc, Con Dao, Phu Quy, Ly Son, Con Co, Co To, Bach Long Vi, etc.
– the group of large islands with favorable conditions for socio-economic development. These islands are: Co To, Cat Ba, Cu Lao Cham, Ly Son, Phu Quy, Con Dao, Phu Quoc etc.
the group of inshore islands with favorable conditions for fishing and sea tourism. These islands are also bases for protecting security and keeping order on the sea and in coastal areas of Viet Nam. They are the islands of the island districts of Cat Ba, Bach Long Vi (Hai Phong City), Phu Quy (Binh Thuan province), Con Son (Ba Ria-Vung Tau province), Ly Son (Quang Ngai province) and Phu Quoc (Kien Giang province).
Over 97% of inshore islands are small ones (less than 0.5 km2 in area). These islands, or rather island clusters, are mainly concentrated near the coastline of Bac Bo Gulf. They are small limestone mountains (limestone rocks) located on a low and much weathered terrain. Unique shapes, steep slopes and sharp peaks are characteristics of these islands. Islands may even be huge heaps of broken rock blocks. Wave-cut caves and grottos of offshore rock islands have created the famous karst landscape highly valued from the viewpoint of geology and geomorphology. The Ha Long Bay Natural World Heritage is also located in such karst topography.
Slopes of these islands, especially the leeward ones, are often gentle. They are little affected by the sea’s dynamic forces. Slopes may rest on even or slanting stone layers, or on eroded stone steps of different heights of 20 meters, 30 meters, 50 meters, 70 meters, 100 meters, 200 meters and 300 meters. In the foothills of Co To, Ngoc Vung, Cai Bau, Phu Quy and Phu Quoc Islands there are concave coastal sections where ideal beaches were formed on the ground of accumulated thin quartz. These beaches have different sizes from 20 meters length to 200 meters length (even up to 2000 and 3000 meters length). At the windward side of these islands are abrupt cliffs (steep inclines of 30-60°). These cliffs are much affected by the sea’s dynamic forces and local tectonic movement, creating a spectacular geological landscape. In particular, on sharp cliffs of the granite rocks along the coast of Central Viet Nam (such as Hon Kho, Hon Lao, Cu Lao Cham, and the islands of Nha Trang and Khanh Hoa) are cracks and hollows where sea swallows make nests.

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