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Drilling the seabed for answers to earth's mysteries

Drilling the seabed for answers to earth's mysteries


​Dr Aggeliki Georgiopoulou (UCD School of Earth Sciences) and Dr David McNamara (NUI,Galway, Earth and Ocean Sciences) are currently on board an International Ocean Discovery Programme vessel near New Zealand.


IODP facilitates international research on 'big questions'. To do this, the programme tries to find the most representative, the most appropriate places on the planet to answer these questions. IODP does not focus on impacts for any specific country, it's all about Science and understanding how our planet works.


For a country's scientists to be able to apply to sail, the country has to be paying into the programme. As Geological Survey Ireland is a contributing member, Irish scientists can apply to take part in IODP expeditions. This provides opportunities for high impact scientific research but also new collaborations. Scientists work globally rather than locally and are part of a larger operation serving science and fundamental understanding.


JOIDES Resolution is a drill ship with similar technologies and capabilities as drill ships that drill for hydrocarbons. It has very high derrick, and barrels upon barrels upon barrels to get down to the seafloor. Each barrel is almost 10m long and they are slid from horizontal to vertical, lowered through the moon pool into the water, fixed to the next barrel and that's how it gets longer and longer. There are two main ways to drill and the one is fit for soft sediments (APC) and the other is fit for hard rock (XCB). Often when they have to drill several hundreds of meters below which means that they will eventually get to hard rocks, they'll start with drilling the soft sediments, and then bring the drill bit up to swap it for the XCB.


Scientists will also collect LWD data and not just from one site but several. LWD stands for Logging While Drilling and it does what it says on the tin, as the drill bit is drilling into the seafloor, an assembly of instruments making up a long barrel is fixed behind the drill bit and all these instruments are measuring different properties of the sediments as they go down. These will also help understand the sediment behaviour. They will also help better understand the earthquakes that occur here and in similar geological settings around the world. This is the other objective of the expedition; to understand the behaviour of the sediments and how the Pacific Plate subducts, glides below the Australian Plate.


Dr Aggeliki Georgiopoulou's work on board focusses on landslides off New Zealand, the Tuaheni Landslide Complex, is that they seem to be slowly creeping instead of catastrophically collapsing and moving like avalanches on the seafloor. The reason for this behaviour appears to be the fact that the sediments of the slide contain gas hydrates. (You can think of gas hydrates like ice, only formed by methane and other gases, not water, in the pores of the sediments, the empty spaces between the grains).

"This association of underwater landslides being generated by gas hydrates has long been hypothesized because of evidence we see on seismic data, which are remotely acquired images using acoustic waves. To confirm this relationship it would require long drilling equipment as conventional, academic coring cannot reach such depths below the seafloor as is required. We are going to drill 200 m below the seafloor surface and we will acquire sediment cores, a continuous sequence of the sediments from the seafloor surface to 200 m below. JR has the capacity to get even 1000m of core if we needed to but we don't and it is a time consuming process. This depth will allow us to get to the gas hydrate zone that we see on the seismic, it will allow us to get to the base of the slide and see the surface on which it glides and hopefully then we'll be able to understand what it is about this surface that the sediments like to move on and we will also get to the sediments below the slide. This is enough for us, this 200m interval will help us understand a lot of things". 


Dr Georgiopoulou's work is also relevant to Ireland: "What I want to work on is figuring out whether what we consider large landslides, in terms of volume and impact, are indeed as large as we think or merely made up of smaller events. Submarine landslides can cause tsunamis, so the implications are that instead of having one big wave from a large landslide you have several smaller waves. This is work that I have started with a landslide complex offshore Ireland, the Rockall Bank Slide Complex, but had even begun considering as part of PhD, with landslides south of the Canary Islands. The more I look at these processes the more I think it's the latter, but I need to find ways to tell them apart and that is what the IODP data will help with".


Dr McNamara's work focusses on understanding fault systems. By drilling in to the rock, scientists can collect information about the crust and the behaviour of 'slow slip' earthquakes recorded in the region. (These events happen over a period of time, usually about two weeks). We can therefore better understand the tectonic regime. "These slow-slip earthquakes, or 'silent earthquakes' have been recorded in New Zealand since 2002, taking place roughly every two years,".


Link to Irish Times article (opens in a new window).