Hikurangi subduction zone expedition #375 – blog 2
In March 2018, JOIDES Resolution, a large scientific research vessel, headed out to sea to research the Hikurangi subduction zone on expedition #375. This article is the second blog from Aliki Weststrate, IODP (International Ocean Discovery Program) Outreach Educator. This is her account of a voyage full of excitement, challenges and science!
A double rainbow over JOIDES Resolution
A faint double rainbow over JOIDES Resolution’s drill tower (called a derrick) about 70 km east of Gisborne.
Getting into the swing of ship life
Week 2 on board the science vessel JOIDES Resolution has definitely been easier. We’re all sleeping better as we adjust to the movement of the ship. I’m finding it easier to wake up at 11.30pm for my 12-hour shift too, which is midnight to noon. Most people have a pattern of going to the gym, working, then going up to the top deck for some sun or watching a movie in the lounge.
We haven’t seen any whales or dolphins, but we do see lots of albatross and fish. One day, I came out to see a double rainbow behind the derrick – it was beautiful.
Connecting with schools
One of the reasons I am on the midnight to noon shift is that schools from around the world can Zoom us (like Skype) in their daylight hours. My job as an Outreach Officer is to take them on a tour of the ship, showing them the amazing drill tower (derrick), the lifeboats and inside to the high-tech laboratories on board the research vessel.
Students connect with the IODP Outreach Educator on board JOIDES Resolution
Students at Waingaro School are involved in a ship-to-shore experience and are asking Aliki questions about the ship during their live broadcast .
Where are we?
We are located about 70 km off shore of the east coast of New Zealand – near Tolaga Bay above Gisborne. The main purpose of this site is to take core samples from under the seafloor, and this will give clues in order to understand how the layers change from the top, through the fault zone to the bottom of our drill hole. We are looking at the sediment to understand its chemistry and what that tells us, its physical properties (how dense, how wet, how brittle), its temperature and whether it contains fossils that help us date it.
A 3D image of the Hikurangi trench off the east coast of New Zealand
A 3D image showing the location of JOIDES Resolution in the red circle. The land on the east coast is in green to the left of the image. The image shows the contour of the seafloor is dropping down deeper, just like hillsides on land.
What have the scientists been looking at?
We spent the first week at site 1 busily coring down under the seafloor to about 500 metres (in 2,700 metres of seawater). The core comes up faster than the scientists can analyse it, so it was only in the first part of week 2 that they split in half the cores from the actual fault. The excitement and discussion about the fault zone cores was intense. It is not often we can access core samples of a fault from under the ocean.
The excitement and discussion about the fault zone cores by the scientists and engineers was intense. It is not often we can access core samples from under the ocean of a fault
Akiki Westrate
Site 1 is where the frontal thrust of the Hikurangi subduction zone is located. This is a fault that splinters off from the main Hikurangi subduction zone fault below, and it runs vertically almost all the way to the seabed. It is sometimes called a hanging wall because it sits above.
A seismic reflection map of the Hikurangi trench taken from JOIDES Resolution
This seismic reflection map is similar to an ultrasound and shows scientists the inside of the Earth as a cross-section. The black line at U1518 is the first drill site for expedition #375 on board JOIDES Resolution. The line shows how deep the drill went – it crosses the red fault that stretches up to the seafloor. By drilling here, scientists can pull up sediment directly from the fault zone to study.
This whole area is part of the Hikurangi subduction zone where two huge tectonic plates collide – the Pacific plate is diving down under (subducting) the Australian plate. The image above is a seismic map. It is similar to an ultrasound and shows scientists the inside of the Earth as a cross-section. The black line at U1518 is the first drill site. The line shows how deep the drill went – it crosses the red fault that stretches up to the seafloor. By drilling here, scientists can pull up sediment directly from the fault zone to study.
Our site and this whole area near Gisborne is interesting because, just after the M7.8 Kaikōura earthquake in 2016, it set off a slow-slip event here. This set the whole region shaking slowly like jelly in a bowl, but so slowly that people couldn’t feel it – only GPS could. It is also one of the shallowest subduction zones in the world, making it possible for an Earth science ship like JOIDES Resolution to drill into and study it.
Next mission – launch an observatory!
Later in the week, I spoke to people who are doing the final preparation of the CORK observatory, which we will finish installing next week. It’s such an amazing instrument – it will sit 450 m under the seabed, and the measuring equipment is designed to sit exactly in the fault zone itself (which is only about 20 m wide). It is a mixture of ancient mariner knowledge, modern materials, science and technology.
CORK observatory, top part
Te Matakite is the top part of the CORK observatory. It will sit just above the Hikurangi Subduction Zone main fault, in an area which we know experiences slow slip earthquakes. It will remain down there for the next 5 years measuring temperature, pressure and chemistry changes during earthquakes.
It is essentially an outside steel casing lowered down into a predrilled hole, and inside are three different ‘packages’ of equipment. Each package is designed to sit exactly at the right depth to measure chemistry, temperature and fluid pressure through the fault zone for the next 5–10 years. Installing it while the ship is moving and in a water depth of 2,700 m is not easy! Each package has to sit inside the other, like a Russian doll, so it goes down in three stages. An engineering feat for sure!
Free-fall tunnel part of the CORK observatory
The free-fall funnel is the first part of the CORK observatory that was installed during the JOIDES Resolution expedition #375. It was lowered through the moonpool all the way to the seafloor. The moonpool is a 5 m diameter circle or hole in the middle of the boat that the drill pipe and camera go down. This equipment will measure earthquakes along the Hikurangi Trench.
Activity idea
In this activity, students use (or observe the teacher using) a small coring tool to make a core sample from a convenient site and examine the resulting sample for features such as particle size, colour variation and layering. It is an opportunity to discuss similarities and challenges between drilling on land and drilling in the ocean.
Related content
This article gives some background to the scientific research vessel JOIDES Resolution.
Read Aliki’s other blog articles here.
Useful links
Watch this YouTube clip about JOIDES Resolution and its research.
Learn more about the international science vessel JOIDES Resolution.
How do you drill a hole in the seafloor?
Get more information on the International Ocean Discovery Program (IODP).
See these GNS press releases for information on the JOIDES Resolution expeditions around New Zealand in 2018–2019.
Acknowledgement
This article has been written by staff at GNS Science working as part of the ANZIC IODP Consortium.
GNS Science
GNS Science, Te Pū Ao, is New Zealand’s leading provider of Earth, geoscience and isotope research and consultancy services. Its purpose is to understand natural Earth system processes and resources and to translate these into economic, environmental and social benefits.
