Locality 2.4 Barranco del Azúcar

Figure 4. Click on the panorama to enlarge it. Click here for the full size, unlabelled image. In this panorama:

• contacts have been marked as dashed lines - their position is approximate;
• intervals between contacts are assigned letters (A to F);
• sub-localities are numbered (loc 2.4.1 etc.). This should enable you to match up individual outcrop photos to the overall section shown on this panorama.

Figure 5.

View of the lowest unit in the section, west of the bridge. These are breccias of the Helecho Formation (interval A), and their base is not exposed here - record this as base not seen on your log.

On the right, the dashed line through the section east of the bridge marks the inclined base of interval B, which overlies the Helecho Formation.

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Figure 6. Outcrop is approximately 6m high.

This deposit is very widespread on southern Tenerife. It has been described and interpreted by Davila Harris et al. (2011) This short article is well worth reading.

Figure 7. Detail of the right-hand part of Figure 6. Note: the fracture pattern in the large block between the two geologists is a result of blasting during road works.

• This is a very coarse fragmental deposit: describe it as you would any other clastic rock, following the description scheme.
• Grain size, sorting, shape and support are important.
• Are the clasts all of similar composition, or is there a range of compositions?

Figure 8. Click on the picture to enlarge it or here for the full-size image.

View of the contact between intervals A and B.

• Can you see any change in the attitude of the bedding in interval B?
• Explain your answer.

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Figure 9. Pen is 15 cm long, and rests on the A\B contact.

• Describe the contact and the units above and below it in detail

Figure 10. 1 metre pole for scale. The A\B contact is arrowed.

• From the information in this and later photos, would you subdivide interval B into 2 or more units?

Figure 11. 1 metre pole for scale. Close-up of Figure 10. The sub-vertical lines are artificial: they were made by an excavator.

Figure 12. Detail of the top unit in Figure 11. Metal tip of pen is 10 mm long.

Your detailed description should enable you to interpret how this material was emplaced.

Figure 13. 1 metre pole for scale (centre).

View of intervals B, above the road, and F, at the top of the outcrop; the intervals between are hidden by the wall and vegetation (including Opuntia - prickly pear cactus).

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Figure 14.

Another view of interval B. This lithology is commonly carved out to make storage spaces, though the purpose of this one is unknown.

Figure 15. Full size image

A close-up of the outcrop in Figure 14, ~ 1 m above the road.

Figure 16. Click on the picture to enlarge it or here for the full-size image.

This is a view down the section from loc 2.4.5 to loc 2.4.4.

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Figure 17. Full size image.

This is the left side of the alcove seen on the left side of Figure 16.

Figure 18. Pole is 1m long.

The right side of the alcove in Figure 17. The roof of the alcove is the base of interval C.

• Study the detail of the section beside and above the pole, looking for significant surfaces.
• Colour may be an important clue.

Figure 19. Visible part of pole is 42 cm long.

Detail of Figure 18.

Figure 20. Pole from top of handle to base of red section is 50 cm long.

The base of interval C is at neck level of the two geologists. The overhanging base of D is in shadow, just above their heads.

Figure 21.

Interval C is seen at the base of the outcrop on the left. Interval D forms most of the outcrop. The base of E is difficult to see in this view: it is roughly at the level of the base of the electricity pole.

Figure 22.

Detail of Figure 21, showing part of interval D. The white surfaces are small faults.

• Look carefully at clast shape and size. Do they vary from bottom to top of this view?

Figure 23. Pole is 1 m long. This, and Figures 24 -26 are from around the km 64 post, between sub-localities 2.4.4. and 2.4.5.

The large dark clasts consist of obsidian with a phonolite composition.

• Carefully describe their shapes and sizes, and think about the significance of your observations.

Figure 24. Coin is 20 mm in diameter.

• Besides the black glassy clasts, can you identify any other components in this rock (look also at Figures 25 and 26)?
• Describe its sorting and support.

Figure 25. Coin is 20 mm in diameter.

• Zoom in and describe the petrography of the various clasts.

• Look closely at the area to the right of the coin, and describe and identify the components.

Figure 27.

The streaky rocks seen in interval D are quarried at several locations in the Bandas del Sur, and sawn into blocks to use as ornamental building stone all over Tenerife..

This block has been sawn perpendicular to bedding.

Look also at Figure 28, then answer these questions

• What can you say about the 3-D shapes of the black glassy clasts?
• How did they acquire this shape, and under what conditions? (hint: perhaps they were initially a different shape).

Figure 28.

This block has been sawn parallel to bedding.

• Study and describe this spectacular rock in thin section.
• Give the rock a name, based on its texture and composition.

Figure 29. Full-size image.

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Figure 30. Pole from top of handle to base of red section is 50 cm long.

The base of interval E overhangs and is in shadow, ~ 50 cm above the road.

Figure 31. Rubber handle grip is 13 cm long.

• Fully describe the deposit shown in this image and Figure 30, using the description scheme for clastic sedimentary rocks. Pay particular attention to texture.

Figure 32. Detail of the left-centre part of Figure 29. Backpack on right is ~50 cm tall.

Figure 33. Pole (centre right) is 1 metre long.

The left-hand (northern) part of the outcrop.

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Figure 34.

Detail of the right-hand part of Figure 33.

Figure 35. Pole from top of handle to base of red section is 50 cm long.

Detail of the area above the geologists' heads in Figure 34.

• There are two lithologies here. Describe them, and explain the possible relationship between them.

Figure 36.

The right-hand (southern) part of the outcrop.

• As in Figure 35, we can see two lithologies. Describe the distribution of these, and show them on your log.

Figure 37. Pole is 1 metre long.

• Zoom in and describe any structures you can see.
• What do these structures tell us about the properties of the lava?

Figure 38. Pen is 15 cm long.

Close-up of the structures in Figure 37, seen on a weathered surface.

This is clearly a lava flow. Chemical analysis shows that its composition is mugearite.

Close examination of the outcrop reveals rare small blue crystals of the mineral sodalite. You won't see it in any of these photos, however.

• What do the rock composition and the presence of sodalite in this rock tell us?

Our section stops here, without seeing the next unit above interval F. Record this as top not seen on your log.

Figure 39.

Close-up of the structures in Figure 37, seen on a fresh surface.

Figure 40. Close-up of the top centre part of Figure 34.

• Describe and identify the structures, and explain how they formed.

Whilst we're in Tenerife, let's take full advantage of the culture as well as the geology. The barraquito is a local speciality, and a tasty restorative after a long day in the field, especially if the weather on the volcano was a bit chilly.

Recipe