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 seventh and final blog from Aliki Weststrate, IODP (International Ocean Discovery Program) Outreach Educator. This is her account of a voyage full of excitement, challenges and science!
We’ve met all our science objectives
It’s our last week now at the Hikurangi subduction zone. In some ways, the 2-month voyage has gone very slowly, and in other ways, it has sped by.
Compared to other expeditions, we have had very little down time to wait on weather or major mechanical issues, so we have achieved all our science objectives already. This has allowed us to do some extra coring, a real bonus for the scientists. But it has also meant we are exhausted from working 55 days in a row, 12 hours per day, with no weekends off!
We don’t know when a science drilling vessel like JOIDES Resolution will be back to the subduction zone, so everyone is keenly aware we have to make the most of it, even though we’re all pretty tired.
Aliki Weststrate, IODP Outreach Educator
When a seamount meets a subducting plate interface
Our last site, U1526, is on top of a seamount. As you can see on the map, there are a number of seamounts in this area, and they are being slowly ‘dragged’ westward on the subducting Pacific plate, underneath the Australian plate to the west.
Site U1526
A bathymetric map of expedition #375 last location (U1526) on top of a seamount.
The seamount – the Tūranganui Knoll – that we are drilling into the top of rises almost 900 m, from a depth of 3,600 m to 2,740 m. It is sitting on the margin of the Hikurangi Plateau approximately east-south-east of Gisborne.
A seamount is an underwater mountain formed by volcanic activity. This one is now extinct but might hold some clues to what happens to seamounts when they meet a plate boundary.
Laura Wallace, Co-chief on expedition 375
We have been close to this seamount a few weeks ago to collect core from its western flank. Now, we aim to sample and describe the age, physical characteristics and properties of the top portion.
We believe that other seamounts in the Hikurangi subduction zone have been subducted under already, and some hypotheses are that they may affect slow-slip events or perhaps trigger local tsunamis when they collide with the Australian plate (see the JOIDES Resolution blog).
We hope to answer these questions at site U1526:
- Is there sedimentary cover at the top, and if so, how thick is it?
- What is its architecture and assemblage?
- How will any sedimentary cover and underlying igneous rock behave when it later moves west towards the main subduction zone and decollement?
Think of this as understanding the ‘before and after’ process. We need to quantify and test this seamount material before it is subducted to understand what might happen to it afterwards.
Seamounts might cause added friction as they are dragged under the Australian plate (subducted) or break apart in unusual ways, so we can simulate these pressures and temperature effects in the lab on this original basement material.
Making memories
Everyone will have different things they remember most about this once-in-a-lifetime science voyage.
Ekant Desai, a publications specialist working on JOIDES Resolution, says, “There was one sunrise that was just so magical, I will remember it forever. The clouds were perfectly spaced, the colours were incredible. I don’t know why it stood out so much in a way, but that one did for me.”
Geochemist Pierre Malie says, “[A highlight is] working with inspirational, humble scientists from many different cultures, many of whom are world recognised in their field but are so self-effacing.”
For me, I think it will be the ocean and animals we’ve seen. I have never lived out on the open ocean before, and I just love watching the albatross, the swell roll by in lines and the incredible sunrises we have seen in Tairāwhiti.
The other thing I have loved seeing is core samples. Some have been less than 500,000 years old and were deposited quickly on the seafloor then buried over time, while others are from the Cretaceous period 80 million years ago and have been laid down slowly over millennia. This was when dinosaurs roamed the Earth!
It’s so amazing to know we are the first humans ever to see and touch them. It is fascinating listening to the scientists work out their ideas of how the contents of the core samples got to be where they are too. It’s just like detective work.
Core samples from sites 1 and 4
The first cores we brought up from site 1 were from right inside an active fault that sits above the main Hikurangi megathrust. The sediments were laid down very quickly in this area and showed signs of faulting and folding.
In sharp contrast, the cores from site 4 show volcaniclastic rock with beautiful rounded clasts (stones of differing colours). The colour differences are due to the different minerals inside the rocks.
Goodbye to expedition 375 and hello to expedition 376
We’re scheduled to pull in to Auckland Port and be met by the tugboat at 7.00am on 5 May 2018. I will take some ship tours that day with Auckland University students and then catch a plane home to my family. And some rest!
The next expedition crew boards the day after we leave. They get trained on the lab equipment and then set sail for the Brothers Volcano in the Kermadec Trench for 2 months. Another adventure begins!
Nature of science
There is so much we have yet to uncover, discover and understand about our world. The more curious we are, the more we will discover. Learning never ends.
Related content
Find out more information about seamounts in the southern seas in this article.
In this video clip, NIWA scientist Malcolm Clark explains how seamounts offer habitats to communities of organisms.
Read about how an international team of scientists may have uncovered the biggest volcano on Earth under water.
Find out more about tectonic plates, volcanoes and earthquakes.
Read Aliki’s other blog articles here.
Activity idea
In this activity, students build a model seafloor and create a map of it through taking depth readings.
Useful links
Hikurangi on the move – a look at the origins of the huge Hikurangi Plateau.
Piecing together the Hikurangi subduction zone – read about the different types of scientific data we are using to find out about New Zealand’s largest fault.
Acknowledgement
This article was written by staff at GNS Science working as part of the ANZIC IODP Consortium.
