Terceira Island is noteworthy for its abundance of effusive silicic products. The island consists of four polygenetic volcanoes and a fissure zone that crosses the island from NW to SE. Santa Bárbara and Pico Alto are large polygenetic volcanoes with calderas filled, and at some places over-spilled, by the products of recent silicic eruptions. Their flanks are also covered by numerous silicic extrusions, arranged along well-defined alignments as the NW-SE to WNW-ESE regional trend. 166 effusive silicic eruptive centres were identified, distributed by 3 of the 4 polygenetic volcanoes. The effusive silicic extrusions studied are low lava domes, most of them with aspect ratios ranging between 4 and 7, and coulées with a wider dispersal of aspect ratios, ranging from 10 to 47. Regarding their size, about 70% of the studied structures plot on a field defined by the maximum area of the domes and the maximum height of the coulées flow-front.