Terceira is one of the central islands of the Azores. It is the third largest in the archipelago (401 km2) and the highest at 1,021 m (Pico de Santa Barbara). The geomorphology is dominated by three massifs: Serra do Cume, Serra do Morião and Santa Barbara, with their respective calderas. All are the result of recent volcanism, and historical and sub-historical lava flows are located in various sectors of the island. The last eruption occurred in 1761. The coastline is rugged in some parts and rises to 150 m, particularly in the west, but is mainly undulating and features broad lava platforms that disappear into the sea. The most important promontories are Ponta do Queimado, at the western tip, Ponta dos Biscoitos and Ponta do Mistério, in the north, and Praia da Vitória, at the eastern tip. On the southern side is the islet of Ilhéu das Cabras, an old volcano heavily eroded by the sea and split in two, and Monte Brasil, a volcano that was originally separated from the main island but is now linked by a tombolo or bar of sediments. Aside from the massifs, the island is mainly flat with a few volcanoes dotted along the east-west alignment.
Average annual rainfall in low-lying areas is round 1,100 mm, but in the mountains and central regions it can rise to 2,500 mm, which again shows how relief and vegetation density can significantly affect precipitation. Like the other islands, sunny days are few and far between, except on the coast and in summer. The pattern of rainfall favours the growth of ample pasturelands, which remain green practically all year round.
The current population of the island numbers 56 000 and is mostly concentrated in the capital, Angra do Heroísmo, and Praia da Vitória, the second largest town. Terceira (‘third’ in Portuguese) was the third island—after the easternmost Santa Maria and São Miguel—to be discovered, hence its name. The first colonists settled here around 1450 and the port of Angra do Heroísmo soon gained regional importance, mainly due to the natural protection provided by Monte Brasil. Angra do Heroísmo is certainly one of the best preserved cities in all the archipelagos of Macaronesia and was declared a World Heritage Site by UNESCO in 1983. One of the seven seats of the Universidade dos Açores is located here. A dramatic event took place in 1980 when a great earthquake seriously damaged the capital, causing the total or partial destruction of many buildings, killing 51 people and wounding many more. The effect was a rise in the traditional emigration to the USA and Canada.
The local economy is mostly based on the primary sector. Livestock farming is especially important and extensive areas are given over to pastures. Cows are mainly used to produce milk, since the Azores provide a high percentage of all milk production in Portugal. Fishing is also significant, which is true of the archipelago as a whole. In recent decades, the rise of tourism has led to a gradual increase in the importance of the tertiary sector, on a par with the other islands, and several museums and visitors centres have been opened. Interestingly, the civilian facilities at Lajes airport are also an American military base, now used by NATO forces.