Geology help please

[Morph]

I took this pic at Gigantes, Tenerife some years ago, what I would like to know is what are the vertical protrusions. I know Tenerife is a volcanic island so my first thoughts were it was lava from later eruptions filling into cracks in the ground, but some if you look finish at differing heights and are narrower at the top than the bottom.

[ChrisJB]

Originally Posted by Morph

I took this pic at Gigantes, Tenerife some years ago, what I would like to know is what are the vertical protrusions. I know Tenerife is a volcanic island so my first thoughts were it was lava from later eruptions filling into cracks in the ground, but some if you look finish at differing heights and are narrower at the top than the bottom.

Hi Morph. They do look like dykes to me (magma sheets filling cracks perpendicular to strata, as opposed to 'sills', which are intrusions parallel to strata), of later magma intrusions through the volcanic layers. The fact they appear to end at different heights doesn't matter. That just depends on how much magma is available at source, magma temperature and viscosity, etc (a greater amount of magma at source and the hotter it is, then it should be able to be injected further into the surrounding rock). Size and availablity of cracks and weaknesses in the rocks would also determine how far the emplacement of dykes can go.
The Tertiary volcanic complexes of the NW Highlands of Scotland illustrates this beautifully.

Regards, Chris

[Morph]

Thanks for clearing that up.