Documentation and monitoring of active structures at El Hierro: potential of flank collapse from the present seismo-volcanic crisis and eruption

After four months of low magnitude seismic activity and continuous deformation, the Island of El Hierro in the Canarian Achipelago erupted on 10 October 2011. Since that date, seismic activity has been slowly increasing in magnitude, with more than 34 Ml>3 earthquakes (four of which have Ml> 4) occurring since 1 November. The largest, a Ml 4.6, intensity (EMS) IV-V earthquake occurred on the 11/11/11 and was felt across El Hierro as well as in the neighbouring Tenerife and La Palma Islands. The current eruption has also extended, with activity now taking place from several vents describing an approximate north-south alignment a short distance offshore. Most ominously this alignment parallels a prominent band of young cinder cones and possible rifting that extends northwards across the island and this area has now been placed on red alert status. Moreover, this alignment parallels the pattern of present seismicity that bisects the island, as well as apparently structurally controlled segments of the cliffed coastline. El Hierro, although the smallest island in the Canary group, represents just the uppermost 1500 metres of a very large volcano that extends more than three kilometres below sea level. Its distinctive scalloped coastline is the result of at least four large-scale flank collapses, occurring as recently as 15 thousand years ago, and the current deformation and seismic activity could trigger a new flank collapse or reactivate one of the older collapses. The official Spanish agency (IGN) responsible for monitoring the seismicity also installed 4 GPS stations in mid July 2011 to record variations in distance between these points, while thekey local group for volcanological research (INVOLCAN) focuses mainly on geochemical monitoring (CO2 and radon emissions) but has a further 6 GPS stations, some pre-dating the crisis, which measure absolute movement of the stations, with data processed by personnel from Nagoya University inJapan. These datasets, although valuable, only provide information from scattered points, and do not represent the integrated structural documentation and analysis of recent and potential future overall deformation presently proposed. This structural analysis needs to be carried out urgently, to seize the scientific opportunity to capture baseline data and to provide a volcano-tectonic framework in which to place the monitoring data outlined above. In this way the progression of potential flank instability can be documented and modelled, work that is crucial to understanding this widespread and potentially catastrophic phenomenon, yet presently does not exist.
On 27 October 2011, a meeting took place of the members of the scientific committee set up as a result of the present crisis. This meeting, attended by the PI, confirmed that no group is investigating active fractures and other structures in the field, emphasising the urgency of,
1) establishing this baseline structural framework and,
2) enacting monitoring networks and procedures to record the pattern and rate at which this framework deforms.
We therefore propose in this project a field campaign to map and analyse active volcano-seismo-gravitational structures on the island and to set up a control system that will monitor the evolution of these structures. The work will contribute principally to modelling and understanding the overall deformation of volcanic edifices during eruptions and the generation and evolution of areas of instability. Additionally, the work has the potential to make predictions and warnings useful in the current crisis. Once the initial field campaign is finished, repeat measurements will be performed by personnel from the relevant Spanish agencies, INVOLCAN and ITER. The ultimate aim is to further collaborate with these colleagues in a follow-up multi-disciplinary project proposal.

In addition to the academic beneficiaries outlined in the relevant section, the project has direct application and benefit to a wider community of government and non-government stakeholders.
In the short term, the assessment of the structural integrity of El Hierro (with special emphasis on its vulnerability to sector collapse due to the current eruption) that this study will produce, is of paramount importance for disaster risk managers, as the local and international media are requesting information on the potential of El Hierro for catastrophic collapse and associated tsunami (see a selection of web pages at the end of this section)
The social importance of possible large-scale tsunami-generating flank collapse from Canarian volcanic edifices can be gauged by the high level of international media coverage this topic receives. This was demonstrated, most notably, following publication of modelling studies suggesting devastating tsunami generated by flank collapse on the Cumbre Vieja volcano in La Palma, some 100 km north of El Hierro. Public awareness has of course been further heightened by the Indian Ocean tsunami in 2004, and the Japan tsunami in March 2011. Such disasters extend their effects well beyond the site of tsunami generation; the modelling for a La Palma collapse, for example, predicted a 6 metre tsunami along the south coast of England. Less appreciated by the media, there are a number of ocean-island volcanoes in the world that also have the potential for flank collapse and tsunami generation and to which this project will benefit too. For example, Stromboli, to the north of Sicily, has produced four large-scale flank collapses in the last 13000 years, and Santorini in the Aegean is thought to have generated a tsunami in 1650 BC. A repeat of these events would have disastrous consequences for Mediterranean holidaymakers in coastal resorts, many of whom are from the UK. Britain also retains administrative responsibilities for several small volcanic islands, for example in the Caribbean and south Atlantic, whose flanks are prone to collapse events. Understanding structural movements leading up to these events will be vital for an appropriate response.
Beyond government agencies responsible for disaster preparedness, wise land-use planning, and advice to UK citizens travelling abroad, the proposed project will also inform decision-making at the local level. This would include setting up alarm systems for vulnerable coastal zones, on El Hierro and neighbouring Canarian islands in particular. This has has been done on Stromboli, for example, where a very small landslide from the volcano flank in December 2002 created a localised tsunami with waves up to 10 metres high that did extensive damage to coastal infrastructure. The monitoring network that we propose to deploy will also warn of relatively small but threatening areas of instability , allowing apporpiate protective steps to be taken promptly.
The commercial sector also stands to gain from improved knowledge of the progression of volcano flank instability, through better costed and evaluated business and investment decisions. Benefit-cost analyses of developments in potentially vulnerable coastal zones would be more accurate and comprehensive, as would risk and reward analyses performed by the insurance industry in deciding competitive insurance quotations.
http://www.theweek.co.uk/environment/natural-disaster/1449/canary-islands-eruption-triggers-us-tsunami-fears
http://www.dailymail.co.uk/news/article-2042873/Earthquake-swarm-Canary-Island-El-Hierro-sparks-fears-volcanic-eruption.html
http://www.telegraph.co.uk/news/worldnews/europe/spain/8795750/Volcano-threat-sparks-evacuation-in-Canaries.html
http://www.myweathertech.com/2011/08/01/worries-of-mega-tsunami-720-earthquakes-on-el-hierro-in-one-week/