Thursday, 25 June 2015

Day 3 - A little guided jaunt around Tenerife

Today our trusty guide Ignacio is to give us a tour of the island, so off we go! 

Travelling north along the eastern side of the island, stopping at several locations along the way, then over the top and down the west side, finally heading in land to the main attraction, Mount Teide.

The first location was a visit to The Arch!

Sitting above a currently dried up, deeply incised river bed, this arch is a result of aeolian processes. The arch has been carved in to the only ignimbrites on Tenerife. These phonolitic  ignimbrites have been associated with a caldera collapse approximately 273Ma and form part of the Bandas del Sur Group (Brown and Branney, 2004).

Ignimbrite arch, with Ignacio for scale!

Construction of the road has provided a fabulous opportunity to observe the dykes that are found in huge densities around the island. These dykes vary in width from approximately 10 cm to several meters. The extend upwards towards the peaks of the island and down towards the sea. Over 3000 meters long (high), plus consider what may have been eroded away over time, they are pretty impressive. These dykes would have been the feeders to the volcanic activity on the island over millions of years. No major eruption has occurred on Tenerife since approximately 1600 AD (Smithsonian Institute, GVP).

Hannah and Ariane checking out a large dyke

We stopped off at a natural pool for a refreshing dip, even though it was a little overcast, it was still pretty warm. Though the Atlantic water that fills the pool is nowhere near warm!

The Gang! Minus me - well someone had to take pictures!

This was followed by the second coffee stop of the day. The coffee on Tenerife is amazing, especially when you are away from the tourist trail.

Now to explore one of my favourite geological features (though there are many!). Lava tubes.
We got to explore two small ones. The first still had a roof and we had to stoop low to get in. Once at the far end we could stand up.

Lava tube opening, once inside it was possible to stand up.

They are strangely eerie places I think. To know that you are stood where once upon a time lava, hot lava, upwards of 1200°C lava, lava that could toast your toes - just slightly, ran; and could run again! But great fun to explore.

The second tube had partially collapsed, so although still impressive, the light coming in meant some of the effect was lost. However the roof of this lava tube, where still intact was much higher and the walls had features that looked like partially cooled lave had peeled away from the wall of the tube before completely cooling, leaving behind these odd curled up features around the walls.

Following this we started to head towards Teide, stopping along the way to observe the surprisingly poorly vegetated 1798 eruption centre and lava flow and an empty lava channel. Finally arriving at Las Canadas caldera.

Las Canadas caldera

Where Las Canadas is now, there was once a huge volcano that formed an ocean island similar to what we see today. Beneath the surface of the volcano there was a network of unstable fractures. Approximately 170,000 years ago, a huge landslide occurred along many of these fractures. The landslide took away the top of the island and its volcano, resulting in a submarine debris avalanche and tsunami. The resultant depression we see today is horseshoe in shape and approximately 17km across. Highly resistant dykes and volcanic necks surround a feature known as Roques de Garcia.
The landslide was followed by volcanic activity that is still active today, currently in the form of fumaroles. The lava from these eruptions has gradually filled the depression left behind by the landslide, though it is still quite clear to see today.

On leaving the location we observed multiple areas where hydrothermal alteration had changed the rocks from browns, yellows and greys to greens, blue's purple and white. Here is where I took the below image.

Long road to Teide

Our final stop before heading back to El Medano was to observe some lavas that have formed what is known as 'onion skin'. This is a weathering feature. When lava cools it fractures forming small blocks of now cold lava. The corners of these lava blocks weather faster than the rest of the rock that results in a spherical shaped 'blob' of rock that has layers peeling away giving the onion skin appearance.

Onion skin weathering

Every day is an adventure!

Buenas noches de La Palma!

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