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Rhyolite lava flow, Barranco de Tirajana, Gran Canaria.

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Photo ID: 625
Gallery ID: 62
Photo Title: Rhyolite lava flow, Barranco de Tirajana, Gran Canaria.
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Keywords:
rhyolite lava flow, barranco de tirajana, gran canaria, canary islands, geological history, geology, rhyolite, rhyolite lava, rhyolite lava vl, lava, magma, volcano, caldera de tejeda, miocene, caldera, hydrothermal alteration,
Description:
This part of the Barranco (canyon) de Tirajana is specially interesting in that the erosion has revealed part of the most dramatic geological history of the island of Gran Canaria. Some 14.1 million years ago, there was a catastrophic volcanic explosion, which created an elliptical caldera, 18 x 28 kilometres in size and up to 1000 metres deep, the Caldera de Tejeda. Over the following million years eruptions continued at intervals of 30 – 50,000 years from ring fractures around the caldera’s periphery, largely refilling this caldera with trachy-rhyolitic ignimbrites and rare lava flows, which is known as the Mogan formation. Then at around 13 million years ago, there was a resurgence of the island’s volcanism comprising of magmas of a chemically different composition and which instead of the eruptions being from ring fractures inside the caldera’s periphery, the focal point of activity moved to the centre of the caldera, with the formation of a high stratovolcano. The ignimbrites and lava flows emitted from this volcano between 13 and 9 million years ago, at intervals of around 50,000 years, were to completely bury most of the remains of the caldera and overflow its flanks, building huge accumulations of lava flows which reached the coastline to the north and south of the island. It is during this period when the early paleo-canyons began to take their shape, owing to the increased erosion caused by the new high central volcano and the long time periods between eruptions. Following this there was a long period with little or no volcanic activity, when erosion really began to carve out the rock formations, only that these paleo-canyons were not in the same location as they are today, but slightly offset. Between 4.6 and 3 million years ago there was yet another new period of very large scale volcanic activity, the Roque Nublo Cycle which was again to build a stratovolcano in the centre of the island. The lava flows and breccia sheets emitted during this time were to fill in the previously carved out canyons, forming new ridges of volcanic materials. Finally after all these events, and whilst volcanic activity continued along the north east of the island, there was to be no more volcanic activity in the south and south-western area and for over 3 million years now erosion has been the only factor involved, shaping the canyons into what they are today. Here within the Barranco de Tirajana, the erosion has been so intense that the rock formations dating back to the caldera period have been exposed. This is the entrance to the lower part of the canyon below the Tirajan reservoir, where a 13.97 million year old rhyolitic lava flow has been cut through, these reddish coloured rocks once having been situated on the inside of the caldera wall and are this colour because of having undergone hydrothermal alteration. The more grey coloured rock formations in the centre of the image (on horizon) are of the same lava flow except situated outside of the caldera wall and unaltered.
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