Roques de Garcia are a group of rock formations (pinnacles) in the Las Cañadas caldera. This caldera is a large depression (16 km) that surrounds the highest peak of Tenerife (El Teide or Mount Teide) that rises 3718 meters above the sea level. The caldera floor itself is about 2000…2300 meters above sea level.
The caldera of the Las Cañadas formed 200,000 years ago as a result of the collapse of the volcano with the same name1. The collapse was probably multi-staged and was not typical vertical collapse which is how calderas usually form. The caldera of the Las Cañadas is a result of a lateral flank collapse. Evidence of it lies on the seafloor north of Tenerife as an extensive debris avalanche deposit2. Hence, the caldera has no northern rim. The Las Cañadas caldera is one of the two calderas after which all other calderas are named. The other being in La Palma (Caldera de Taburiente). The term “caldera” was first used in geological sense by a German geologist Christian Leopold von Buch who visited the Canaries in 1815.
The focus of this post are the pinnacles at the foot of the Mount Teide which exhibit weird shapes and are therefore one of the most important tourist attractions of the island. I recommend to arrive early in the morning because later you will have difficulties to find a parking place. I knew that and therefore arrived early and enjoyed the landscape without huge crowds. It is also good idea to arrive early because light conditions for photography are better. Light at noon is generally too harsh for landscape photography.
It must be said, though, that the vast majority of people only take a look of The Cinchado and its surroundings right next to the car park. But there is much more than that to those who are interested in geology. There is a very scenic hiking trail around the Roques. It should not take more than one hour to walk it through but I had so much to look at there that it took at least three times as much time for me. I am sharing some of the photos I took there with you below.
Tenerife has been restless after the collapse which is clearly manifested by the magnificent peak of El Teide which rises prominently about 1500 meters above the floor of the caldera. All of it had to form during the last 200,000 years. The volcano is active. Its last eruption took place a little more than 100 years ago (1909) but this timespan is nothing special to volcanoes. El Teide will undoubtedly erupt again in the future. The pinnacles of the Roques de Garcia are on the lower right.
The pinnacles of the Roque de Garcia are the remnants of the collapse which are later modified by erosion. Most of them are composed of polylithic and generally matrix-supported volcanic breccia3. Such breccias are fairly common in the Canaries and demonstrate the gravitational instability of these islands. The most likely reason for this is the common development of near-surface magma chambers in the Canaries2 and quite possibly also highly evolved alkaline magma which brings along explosive volcanic eruptions.
By far the most famous of these pinnacles is The Cinchado. It is evident that sooner or later it will collapse under its own weight but fortunately the base of the structure seems to be still strong enough for many generations to enjoy the sight.
The Cinchado from another angle. There are many different layers of breccia and there seems to be two dikes near the top.
Close-up of a matrix-supported breccia. Width of view 1.7 meters.
Some breccia layers are clast-supported. Width of view 2 meters.
This pinnacle is a remnant of a dike with a phonolitic composition. It is me with my wife Tuul for scale. This pinnacle is actually very modest in size. Most of them are much taller.
Pinnacle composed of breccia with a pahoehoe-like lava flow in front of it.
There are lots of dikes cutting through the breccia beds.
Here is one dike nicely exposed at the surface.
And here it gets really magnificent. Dikes are forming huge thick walls of rock.
Trachybasaltic pahoehoe lava flow from The Teide cascading down the breccia cliff.
Lava flow and the peak of Mount Teide itself in the background.
It may not be easily understood from this photo but there are three pinnacles in this photo. The middle one is behind the other two and it is an igneous intrusion which is demonstrated by columnar jointing. Columns are always perpendicular to the cooling front. So it can be used to determine the orientation of the intrusion.
Here again is a nice example of columnar jointing but this time we can see the ends of the columns which give us a hint that this intrusion may be a neck (former volcanic vent or other pipelike intrusion).
A view from The Roques to the caldera floor which is covered by alluvium and aa lava. The rim of the caldera in the background.
References
1. Hoernle, Kaj & Carracedo, Juan-Carlos (2009). Canary Islands, Geology. In: Encyclopedia of Islands (Encyclopedias of the Natural World)
(Ed. Gillespie, Rosemary G. & Clague, David A.). University of California Press. 133-143.
2. Schmincke, Hans-Ulrich (2005). Volcanism
. Springer.
3. Gill, Robin & Thirlwall, Matthew (2012). Tenerife Canary Islands: Geologists’ Association Guide: No.49
. The Geologists’ Association.
Images 7, 9 and 10 are of “Cone Sheets” which are a feature of caldera formation the other immediately obvious feature are “Ring dykes” Cone sheets dip into the centre of the volcano like the letter “V” whilst cone sheets dip outwards with their point of junction being higher than the observer like this: “/\.” Another feature often seen in the Las Canadas Caldera are radial dykes which as the name suggest radiate outwards from the centre of the volcano – like the spokes of a wheel. Otherwise some very nice images.
That symbol should look like opposing “/ \” not the “/.” as it is shown in my earlier post.