Tenerife's reality as a volcanic Island has been made apparent throughout history due to a number of eruptions, some of which took place after the conquest and were therefore documented. The eruption that took place in 1704 and 1705 was a fissure eruption with three different emission centres: Fasnia, Siete Fuentes and Volcán de las Arenas. Shortly afterwards, in 1706, came the eruption of Montaña Negra in Garachico, which lasted nine days and is the only eruption known to have caused significant damage. The history of Garachico is therefore marked by the event.
The eruption of Pico Viejo, also known as Chahorra, occurred on the edge of Teide National Park. It began on 9 June 1798 and lasted until 8 September that year, making it the longest eruption on record. The last eruption to trouble Tenerife was on 18 November 1909 by the Chinyero volcano, which went from having nine mouths to just three.
The eruptions of Arafo, Siete Fuentes and Fasnia left their mark on the landscape in the north-east of Las Cañadas, and it is there that a fascinating trail sets out to reveal the geological history of Tenerife. The trail explores the pools and tongues of lava created by the eruptions by tracing paths that are lined with phonolite, pumice and obsidian rock, all set against the backdrop of the mighty Teide and Montaña Blanca.
Mount Teide, despite being the undisputed highlight on Tenerife's skyline, is geologically a rather young volcano at just 200,000 years old. When measured from sea level, it stands 3,718 m (12,198 ft) tall, but if measured from its base under the ocean floor, it is the world's third highest volcano after the Hawaiian peaks of Mauna Kea and Mauna Loa. This stratovolcano-type volcanic edifice stands over a massive ancient crater-like depression comprised of two semi-craters that are separated by the Roques de García rock formations. Mount Teide is topped by El Pilón de Azúcar, which still shows traces of activity in the form of fumaroles and sulfataras issuing gas at 86º C (186 ºC, which is water boiling temperature at that altitude).