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North face of Pico taken from S. Jorge Island. Photo by Dr. Eduardo Tereso
This Space Shuttle image shows the islands of Fayal (left) and Pico (right). The island of Pico (42 km long) is made of two volcanic strutures, the tall basaltic stratovolcano, also called Pico on the west, and an older volcanic ridge to the east. Pico is considered the youngest island in the Azores because of its many young lava flows. The approximate locations of basaltic lava flows from the three historic eruptions are outlined on the Shuttle photo. The bare, lava-covered slopes of the stratovolcano show as a brownish tone, and a line of small cones that define an east-west fissure along the volcanic ridge is just visible.
An interesting thing to consider is that Pico is a typical stratovolcano, with slopes as steep as 40°, and yet it is made of basaltic lava. Most stratovolcanoes are constructed of more silica-rich lavas such as andesite. The steep slopes of Pico probably result from its lava flows being erupted slowly, so that they did not travel far from their source before cooling and stopping - thus they would tend to pile up around the vent, constructing a stratovolcano.
Historic volcanic activity at Pico based on van Padang and others (1967).
Sources of Information:
Neumann van Padang, M., Richards, A.F., Machado, F., Bravo, T., Baker, E., Le Maitre, W., 1967, Part XXI, Atlantic Ocean: Catalogue of the active volcanoes of the world, International Association of Volcanology, Rome, Italy, 128 p.
Woodhall, D., 1974, Geology and volcanic history of Pico Island volcano, Azores. Nature, vol. 248, p. 663-5.