Deep fjords indent the coasts of Iceland, particularly in the north and west. The island itself is a geologically young basalt plateau, averaging 2,000 ft (610 m) in height (Öraefajökull, c.6,950 ft/2,120 m high, is the highest point) and culminating in vast icefields, of which the Vatnajökull, in the southeast, is the largest. There are about 200 volcanoes, many of them active; among them are Katla (4,961 ft/1,512 m), Hekla (4,892 ft/1,491 m), and Laki (2,684 ft/818 m). The eruptions of Iceland's volcanoes have at times also affected the rest of Europe, as with the sulfur-dioxed haze produced by Laki's 1783 eruption, and the ash ejected into the atmosphere during the 2010 eruption of Eyjafjallajökull interfered with air travel in much of Europe. Hot springs abound and are used for inexpensive heating; the great Geysir is particularly famous. The watershed of Iceland runs roughly east-west; the chief river, the Jökulsá, flows N into the Axarfjörður (there are several other rivers of the same name).
The climate is relatively mild and humid (especially in the west and south), owing to the proximity of the North Atlantic Drift; however, N and E Iceland have a polar, tundralike climate. Grasses predominate; timber is virtually absent, and much of the land is barren. (Some of this is a result of human habitition, which led to deforestation and overgrazing.) Only about one fourth of the island is habitable, and practically all the larger inhabited places are located on the coast; they are Reykjavík, Akureyri, Hafnarfjörður, Siglufjörður, Akranes, and Isafjörður.
The population, until recently largely homogeneous and isolated, is descended mainly from Norse settlers and their slaves. (This homogeneity, combined with longstanding genealogical records, has made Icelanders the subject of fruitful genetic study.) More than 85% of the people belong to the established Lutheran Church, but there is complete religious freedom. The national language is Icelandic (Old Norse), although English, other Nordic languages, and German are also spoken. Virtually all Icelanders are literate; they read more books per capita than any other nation.