Working group on mid-ocean ridge islands and seamounts
Motivation
The populations of isolated islands are particularly vulnerable to threats from weather or geological events, as illustrated by the recent disruptions caused by hurricanes and earthquakes in the Caribbean. Their submarine areas also host a varied fauna (of which many island communities depend economically) that is at risk from climate change and catastrophic events, such as slope failure, volcanic eruptions, earthquakes and extreme storms. Although there has been much progress by individual groups towards understanding these problems, the diversity of their subject areas has led to a lack of communication. Importantly, many marine data- and sample-sets that have recently been collected could provide valuable information if combined or provided to researchers working in the other subject areas.
An InterRidge WG is now needed to study volcanic islands and seamounts lying near mid-ocean ridges to bring these dispersed groups together in a workshop, other meetings and online. This will allow us to refine or modify the key gaps in our understanding, datasets and modeling capability that need to be filled going forward to addressing their risks. In addressing hazards primarily, this effort will also help move forward a wide range of other science concerning MOR islands and seamounts, as illustrated by the science questions below. This WG will expand significantly the relevance of InterRidge to a broader community of researchers, as well as produce results of more general societal importance and interest.
Scientific background
The failure of massive sectors of volcanic edifices is known to occur in oceanic islands. Although this process is less well known in volcanic islands and seamounts near mid-ocean ridges, recent work has found several landslide scars and debris fields amongst the Azores islands, and others have been found at Ascension, Tristan da Cunha and other islands. Furthermore, while these large events have captured much attention, there has been less interest in smaller upper-slope landslides, although they are likely more frequent and hence potentially represent an on-going threat to local populations because of the waves (tsunamis) they produce. These hazards compound the vulnerability already known from weather events and, especially for the Azores, earthquakes and volcanic eruptions. The science of island hazards could be moved forward by combining the wealth of marine geophysical and geological datasets gathered recently with geohazards work on land.
Ocean islands are also important for understanding the generation and extraction of melt from Earth’s mantle. Although the geochemical changes associated with melting of Earth's mantle have been developed over decades, there has been comparatively little systematic sampling of near-ridge seamounts to address how migration and higher-level differentiation of melts affect the geochemistry of lavas erupted at seamounts. Given the effort required to sample and date these lavas, the frequency of submarine eruptions is poorly known compared to subaerial eruptions. Some island groups are particularly active seismically and melt penetration and eruption may be linked to tectonic activity or to structural features.
Abruptly changed seabed conditions associated with landslides and submarine eruptions potentially allow us to see how and how fast submarine fauna colonize new areas. The fauna and flora adapted to a particular ambient temperature, acidity, current and light conditions will also likely be affected by climate changes. New biological datasets that have now been collected around many islands provide an important benchmark with which to evaluate future changes. Recent discoveries of giant rhodolith beds (coralline red algae nodules) in the Azores, for example, suggest an important role of island shelves in carbon burial and acidity regulation. Seamounts and islands affect many different physical-oceanographic flows, leading to complex fluid dynamics and ultimately potentially affect how nutrients and food particles become available to organisms, as well as affecting dispersal of species and speciation. Seamounts and islands disrupt larger-scale oceanic flows, such as meso-scale eddies, but also are predicted to affect or create sub-mesoscale eddies, internal tides and lee-wave eddies. Now that physical oceanographic modeling is becoming accurate, more integrated efforts could be very fruitful, combining work on substrate geology, sediments, physical oceanography and marine biology to understand these complex systems.
Science questions
The following is a preliminary set of questions to be addressed, which will be refined with the input of participants of the workshop and other meetings, and online contributions.
* How frequent is catastrophic failure in submarine slopes? How important are small compared with large movements in terms of net volume? What are the implications of these disturbances for ecosystem functioning on island slopes? Does it lead to significant burial of organic carbon? Can we link faults already mapped on land with signs of recent deformation in shallow-marine geophysical data to improve estimates of earthquake risk to local populations?
* Can we relate changes in plate tectonic regime with changes in magmatic extrusion in an individual magmatic system? How do mantle plumes affect a mid-ocean ridge where the mantle buoyancy flux is small? To what extents do tectonic processes affect formation and movement of melts? How do magmatic activity and styles of eruption relate to mantle composition, tectonic setting and local geology?
* How do fauna and flora vary from deep spreading centres to shallow depths of ocean island shelves and coasts, in response to varying temperature, pressure, substrate geology, currents and ambient light? How do seabed populations change with time after catastrophic events and with other changes, such as associated with climate change? How do topographically controlled fluid dynamics and sediment disturbances affect the distribution of Fe-Mn crusts on island and seamount slopes? How do the depths and distributions of sedimentary deposits on the shelves of volcanic islands relate to ocean physical conditions, in particular, waves? What roles do island shelves and, in particular, rhodolith beds have in carbon cycling and regulating water properties?
Planned activities and outcomes
2018: special session on the Azores islands already established for EGU 2018 (Beier, Mitchell)
2019: 3-day workshop on islands and seamounts to be hosted by the Instituto Hidrográfico, Lisbon, with input for non-attendees via Skype or other video-conferencing (Quartau, Mitchell, Ramalho etc.)
2019: Review article identifying the gaps in our data, knowledge and modeling capabilities, with recommendations for how the community can make progress to address them (Mitchell et al.).
2020: special sessions at AGU, EGU, Goldschmidt, etc.
Group members:
Neil Mitchell (Manchester, UK)
Rui Quartau (Instituto Hidrográfico, Lisbon, Portugal)
Christoph Beier (Univ. Erlangen-Nürnberg, Germany)
Telmo Morato (University of the Azores, Portugal)
David Barnes (British Antarctic Survey, Cambridge, UK)
Eric Fielding (Jet Propulsion Laboratory, Pasadena, USA)
Robert Turnewitsch (Scottish Marine Institute, Oban, UK)
Pedro Afonso (University of the Azores, Portugal)
Christian Hübscher (University of Hamburg, Germany)
Katrin Linse (BAS, Cambridge, UK)
Ricardo Ramalho (Instituto Dom Luiz, Lisbon, Portugal)
Simon Morley (BAS, Cambridge, UK)
Ulrich Küppers (volcanology, LMU Munich, Germany)
José Madeira (University of Lisbon, Portugal)
Dmitry Aleynik (Scottish Assoc. of Marine Science, UK)
Chester Sands (British Antarctic Survey, Cambridge, UK)
Christian Mohn (Aarhus University, Denmark)
Zhongwei Zhao (University of Manchester, UK)
Thor Hansteen (GEOMAR, Kiel, Germany)
Julia Crummy (British Geological Survey, Edinburgh, UK)
Michael Bizimis (University of Southern Carolina, USA)
Susumu Umino (Kanazawa University, Japan)
Bryndís Brandsdóttir (University of Iceland)
Jo Whittaker (University of Tasmania, Australia)
Carmen Gaina (University of Oslo, Norway)
Paraskevi Nomikou (University of Athens, Greece)
Christine Meyzen (University of Padova, Italy)
Cedric Hamelin (University of Bremen, Norway)
Kamesh Raju (National Institute of Oceanography, India)
DelWayne Bohnenstiehl (North Carolina State University, USA)
