Graciosa is a stratovolcano with a caldera. The caldera is about 5,000 feet (1,500 m) long, 2,600 feet (800 m) wide, and 300 feet (100 m) deep. Pumice deposits blanket the slopes of the volcano. Graciosa is famous of a large cave nearly 600 feet (200 m) wide near the bottom of the caldera. There is a lake within the cave and solfataras.
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.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.