All the islands have been built up in submarine eruptions and consist of alternating layers of palagonite tuff and lava.
2.
"' Palagonite tuff "'is a tuff composed of sideromelane fragments and coarser pieces of basaltic rock, embedded in a palagonite matrix.
3.
The internal structure of this volcano, which is in height above sea level ( at Pico das Cruzinhas ), is marked by layers of basaltic pyroclasts of various thicknesses ( between centimetres and metres thick ) forming a lithificated palagonite tuff.
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