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Photo ID: 977
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Photo Title: Caldera de Pinos de Galdar, Gran Canaria, Canary islands.
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Keywords:
caldera de pinos de galdar, gran canaria, canary islands, oceanic islands, macaronesia, atlantic islands, atlantic ocean, western highlands, fontanales, valleseco, montañón negro, hondo de fagagesto, sao, los berrazales, barranquillo del brezal, pinos de galdar, caldera, holocene, rejuvenation stage, fracture, fissure, volcano, lava flow, pyroclastic cone, cinders, lapilli, scoria, strombolian eruption, phreatomagmatic, surge, ground water, vesicular, porphyritic, basanite, olivine, ultramafic, mafic xenoliths, hydrothermal alteration,
Description:
Interior view of the Caldera de Pinos de Galdar is located at 1350 metres above sea level, on the western tip of Gran Canaria’s north western highlands, to the south of the small town of Fontanales and close to the forested area known as the Pinos de Galdar. This volcano is one of several volcanoes including, Valleseco, Montañón Negro, Hondo de Fagagesto, Sao and Los Berrazales, to have formed along a NW-SE structural fracture of 9 km long and are all of Holocene age, forming part of the most recent eruptions to have taken place on the island of Gran Canaria. The Caldera de Pinos de Galdar has been dated as 2830 years old, whilst the Berrezales lavas may be less than 1000 years old. The circular volcano is embedded in the side of the mountain and within the abundant pyroclastic fallout from the previous eruption of nearby Montañon Negro, which erupted some 140 years earlier. The volcano is characterized by a strombolian cone, several lava flows and the caldera itself which is of a deep crater measuring 300 metres across and 150 metres in depth, whose vertical walls give way to more gentle lower interior slopes created by the erosion and infill of the surrounding materials. The volcano was formed by both strombolian eruptions and explosive phreatomagmatic surges as is the case with many recent volcanos whose magmas have come into contact with ground water. The fallout materials which are widely dispersed are composed of lapilli, bombs and scoria, stratified within compacted layers of reds and blacks. Along the upper parts of the volcano’s crater and across the road from the viewpoint are the remains of the phraetomagmatic surges interbedded with the pyroclastic fallout lapilli. Lava flows of basanitic composition were emitted from two fissures within the base of the volcano and channeled down the Barranquillo del Brezal merging with the lava flow from the earlier Montañon Negro. The porphyritic rocks contain abundant phenocrysts of fresh bright yellowy-green olivine, together with a lesser amount of augite-diopside ( SiO2 43.2% and sum of alkalis 5%) They also contain a certain amount of ultramafic and mafic xenoliths and cumulates. In contrast to many other volcano’s, the rocks and pyroclastic fallout around and within the crater are highly oxidised, the red tones created by the alteration of iron within the rock by the residual hot, water vapour rich gases escaping from the crater after the eruptions had ceased. (hydrothermal alteration)
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