El Hierro, the youngest Canary.
Island of landslides

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Text: Annemieke van Roekel, geoscience journalist
www.vuurberg.nl.

This article was first published in Gea Magazine (September 2022).

Hydromagmatic eruptions
On El Hierro some examples of hydromagmatic eruptions, from the third volcanic phase, can be seen, when magma comes into contact with (sea) water and the eruptions are more explosive due to rapid cooling and steam production. During this process, the volume increases by a factor of a thousand.

The result is the characteristic yellow/orange color of the tephra, caused by the formation of palagonite (a mixture of phylosilicates and zeolite). This can be seen at the crater of Hoya de Fireba (fig. 7 and 8), which is also a geosite. A second example is found near the beach of Verodal, an outcrop of part of a tuff ring (fig. 9).

 

Fig. 7. Crater of La Hoya de Fireba (450 diameter, 160 m deep), the result of both strombolian and hydromagmatic eruptions, located at the center of the three axes, on top of the cliff of El Golfo. Fig. 8. Detail of yellow lapilli on the crater rim. Fig. 9. Outcrop of a tuff ring in the far west of El Hierro. Photos by A. van Roekel.

Sand from the red beach of Playa Verodal
At the foot of the El Vallito cliff, at the end of the northwestern rift (NWR on Fig. 5), lies the "red beach" of Verodal (Fig. 10). At the top of the cliff is a red cone of lapilli: Montaña de los Charcos. Although from afar the beach looks gray at first glance, up close the sand has a tinge of red and you also notice how coarse the sand is.

The macro photographs of the Verodal sand clearly match the sources: the lava (cliff) and lapilli (from the cone above it), which enclose the beach. The grains are black, dark gray and red and consist of unaltered to partially oxidized basalt fragments (Figs. 11). Fig. 12 shows olivine grains isolated from the sand sample.



 

Fig. 10. Playa del Verodal, enclosed by the El Vallito cliff. The beach sand is a mixture of red and gray, rather coarse grains. Fig. 11. Macro photos of the 'red sand' of Playa del Verodal. Gray/black: basalt; red: oxidized basaltic lapilli, with clearly visible gas bubbles; green: olivine. Fig. 12. Isolated olivine grains. FOV: 8 mm. Photos by Jacques Feijen.

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Copyright: Annemieke van Roekel
Last update: December 28, 2022