The large triangular island of Tenerife is composed of a complex of overlapping Miocene-to-Quaternary stratovolcanoes. The NE-trending Cordillera Dorsal volcanic massif joins the Las Cañadas volcano on the SW side of the island with older volcanoes, creating the largest volcanic complex of the Canary Islands. The origin of the 10 x 17 km Las Cañadas caldera, partially filled by the Teide stratovolcano, has been variably considered to be due to collapse following multiple major explosive eruptions or as a result of a massive landslide (in a manner similar to the earlier formation of the massive La Orotava and Guimar valleys), or a combination of the two processes. The most recent stage of activity beginning in the late Pleistocene included the construction of the Pico Viejo and Teide edifices. Tenerife was perhaps observed in eruption by Christopher Columbus, and several flank vents on the Canary Island's most active volcano have been active during historical time.