The Terceira volcanic complex results from overlapping strato-volcanoes built over a geologic line called the Terceira Rift. These volcanic areas include the Cinco Picos, Guilherme Moniz, Pico Alto, and Santa Barbara volcanic aggregates.
The western part of Terceira Island has more vegetation than the eastern part due to the prevailing westerly winds and greater precipitation. Other geographical areas of interest include the plains of Achada, the hills near Santa Barbara, and the small lagoon of Lagoa das Patas.
The northern coast is an area marked by evidence of volcanic activity with several “misterios” (lava fields) and the swimming pools of Biscoitos. The center of the island features the dormant volcanic caves of Algar do Carvao: a popular fixture with tourists.