Press Releases‎ > ‎

Press Release: El Hierro


22nd January 2015

 

Fossils survive volcanic eruption to tell us about volcano origins

 

The most recent eruption on the Canary Islands – at El Hierro in 2011 – produced spectacularly enigmatic white “floating rocks” that originated from the layers of oceanic sedimentary rock underneath the island. Despite being violently transported through the volcano, some of these rocks contain microscopic fossils of delicate single-celled marine organisms, making the survival of these fossils all the more extraordinary. A new study published today in Scientific Reports, an open access journal of the Nature Publishing Group, by a team of scientists from the universities of Uppsala (Sweden), Las Palmas de Gran Canaria (Spain), Lisbon (Portugal), and the Research Council of Spain, uses these fossil time-travellers to date the sedimentary layers beneath El Hierro and, in turn, shed new light on the long-standing puzzle about the origin of the Canary Islands.

The origin and life cycle of oceanic volcanoes, such as the Canary Islands, has long been a source of debate among natural scientists. There are two competing models for the origin of the Canaries – one in which ocean floor fractures control the location of volcanic activity, and another in which an anomalously hot plume of molten rock from the Earth’s mantle feeds island growth from below. A cornerstone of the debate concerns the validity of an age-progression along the island chain. A fixed mantle plume under the roughly eastwards moving African tectonic plate would cause the islands and the pre-volcanic ocean sediments underlying them to become progressively younger towards the westernmost island of El Hierro. The fracture model, in turn, would give rise to randomly distributed island ages.

Fossils and volcanoes are not usually compatible with each other, which is what makes these samples so special. The newly published study in Scientific Reports by a research group led by Prof. Valentin Troll from Uppsala University, Sweden, offers a unique perspective on the plume versus fracture model debate for the origin of the Canary Islands. The fossils are de facto witnesses of the pre-island environment. Researchers can now place constraints on the ages of the sedimentary strata present before island-building and, indeed, on the initiation of island-building itself. In combination with known sediment ages from the east of the archipelago, it is now clear that the oceanic sediments become younger towards the west of the island chain, thus verifying an age-progression among the islands. These findings are in strong agreement with the mantle plume model for the origin of the Canary Islands and thus contribute to our wider understanding of ocean island volcano genesis.

For more information please contact Prof. Valentin R. Troll, Chair in Petrology at Uppsala University, valentin.troll@geo.uu.se

Publication details: Zaczek, K., Troll, V. R., Cachao, M., Ferreira, J., Deegan, F.M., Carracedo, J.C., Soler, V., Meade, F.C., Burchardt, S. 2015. Nannofossils in 2011 El Hierro eruptive products reinstate plume model for Canary Islands. Scientific Reports 5:7945. DOI 10.1038/srep07945.

This project was initiated by Prof. Valentin Troll (Uppsala University, Sweden), Dr. Mario Cachao (University of Lisbon, Portugal), and Prof. Juan Carlos Carracedo (University of Las Palmas de Gran Canaria, Spain) and forms part of the doctoral thesis of Kirsten Zaczek at Uppsala University. The research was supported by an international team of co-workers from institutions in Spain and Portugal and by the Royal Swedish Academy of Sciences (KVA), the Center for Natural Disaster Sciences (CNDS) at Uppsala University and through the Swedish Science Foundation (VR).

 

(a) View of the white “floating rocks” on the sea surface off the coast of El Hierro in 2011. (b) View of a white “floating rock” covered with black lava. Image source: Carracedo et al. 2012, Geology Today 28, 53-58.

(a) Close-up view of a white “floating rock” with sedimentary relicts highlighted with red circles. Published under license by the Nature Publishing Group. (b) Example of a single-celled microscopic fossil (“coccolithophore”) Scale bar is 1 mm. Source: Wikipedia.

(a) Sketch of the sub-surface structure of El Hierro island at the time of the 2011 eruption. The sketch shows how magma travelling from the mantle to the surface picked up pre-volcanic sediments, some of which contain fossils. Image source: Carracedo et al. 2012, Geology Today 28, 53-58. (b) Sketch cross section through the Canary Islands showing how the islands were built upon progressively younger sedimentary rock. Published under license by the Nature Publishing Group.