Hikurangi subduction zone expedition #375 – blog 5

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 fifth blog from Aliki Weststrate, IODP (International Ocean Discovery Program) Outreach Educator. This is her account of a voyage full of excitement, challenges and science!

Bad weather hits expedition #375

This week was dominated by weather. We heard on Tuesday that big swells were heading our way due to a cold southerly screaming up the country. The captain was out in this same location in November 2017 on expedition #372 when they were caught out with 10 m waves – so big they hit the bridge.

To avoid this kind of weather again and look after this relatively old ship (JOIDES Resolution was built in 1985), he chose to head north to shelter near Tauranga in the Bay of Plenty, well away from the southerly and its worst effects. On the daily ship reports to staff, they call this WOW – waiting on weather.

The transit back to the research site took longer than expected because we encountered gale headwinds and big seas.

It was a pretty sleepless night for most of us, with the waves and anchor slamming into the bow near our cabins.

Aliki Weststrate

We lost 3 days out of our schedule because of the storm. The two Co-chief Scientists say this is to be expected on a 2-month voyage and that we are actually still tracking well for achieving all our science objectives at the Hikurangi subduction zone.

There are so many things out of your control on a science expedition in the open ocean. It means everyone has to be very good at problem solving and adapting.

What does the crew do when there is no core to analyse?

The storm meant we could not drill and collect new core samples. This gave scientists some much-needed downtime. They had been working long hours at our previous site analysing the core from the seamount. Working 12-hour shifts with no weekends off gets tiring by week 5! Apart from writing their site reports and doing presentations on this, they spent the time playing table tennis, going to the gym, eating and watching movies.

The sum is greater than its parts

Each science group produces a report and presentation for every site. The six science teams on this expedition studying different aspects of the Hikurangi subduction zone focus on:

• geochemistry
• structural geology
• sedimentology
• physical properties
• palaeomagnetics
• palaeontology.

Each team has 2–4 people in it, and they are all specialists in their field of Earth science. The team leaders have usually sailed before and are very experienced in their area, but the teams also include early-career geologists doing a PhD. It’s a great learning experience for them. The wonderful thing about this multidisciplinary team is that they all bring different perspectives and knowledge.

As a team, they are putting the various parts of the puzzle together, which they could not do in isolation.

Aliki Weststrate

This multidisciplinary approach is the best way to solve the challenging questions we have about slow slip earthquakes, large earthquakes and tsunamis at the Hikurangi subduction zone.

Other JOIDES Resolution expeditions studying climate change also have a team of oceanographers and sometimes marine biologists on board as well.

The calm after the storm

We transited back to the East Coast quite quickly on Friday to arrive at our third site, U1519.

At this site, we are installing New Zealand’s second sub-seafloor observatory, and because it is simpler than the first, it should only take us a week to deploy it 280 m under the seafloor.

Blog 3 details how the first observatory under the seafloor was installed.

The geology of site U1519

The location of our second and less-complex observatory is 33 km from the coast and only 5 km above a known slow slip zone in the harder rock mass of the Hikurangi subduction zone. This is an area called the upper plate or upper slope and is mid-slope on a sedimentary basin. It sits quite close to the shallow continental shelf that is attached to the east coast. At 1,003 metres, the water is not so deep here as our previous sites.

My next blog will be focused on attaching the pressure and temperature sensors to the rope that will be lowered into the borehole and then sealing it shut.