Field and lab update

The Tephra Seismites have had a particularly busy couple of months. Our coring fieldwork was completed in September, with cores collected from six further lakes.

Photo of part of a lake. An inflatable boat and pontoon raft are lashed together in the middle of the lake. Three people sit on the boat, facing the raft, where two people are standing, holding a long rod that projects through the centre of the raft into the lake.
Coring at Ngārotoiti. Left to right: Dr Marcus Vandergoes, Henry Gard, Joe Butterworth, Dr Vicki Moon, Dr Tehnuka Ilanko. Photo: D. Lowe.

We have since completed X-ray Computer Tomography (CT) scans of all these new cores. Over the past few weeks, we cut, opened, and described all remaining cores from both of our 2022 field campaigns. This came to a total of 51 separate logs! As well as making detailed descriptions of key tephras and any deformation features, we collected samples for grainsize analyses.

In the coming weeks, will continue labwork on these samples and study the 3D imagery provided by the CT scanning.

A sincere thanks to all those involved with this most recent work, including our GNS Science and Lakes380 colleagues Dr Marcus Vandergoes and Henry Gard for their expert coring support; skipper Joe Butterworth; Ngā Iwi Tōpū O Waipā, private landowners, the Department of Conservation, and Waipā District Council, for fieldwork and access permission; and Nic Ross and Hamilton Radiology for CT scanning.

Tephra Seismites group seminars

The Tephra Seismites team at Waikato held a half-day meeting today to present progress on different aspects of the project, and discuss next steps. 

Josh presented preliminary results from paleoseismic trenching and geomorphology of the Te Puninga Fault segment, Hamilton lowlands.

Richard, in his talk on ‘Soft sediment deformation structures (SSDS) in Rotoroa/Hamilton Lake’, presented observations from CT scans, grainsize analyses, and scanning electron microscope imagery of core samples.

Richard presents CT and grain size data from a core taken at Rotoroa.

Danche gave a talk on findings from her labwork, ‘Pumice content quantification of Tuhua tephra using different approaches’, ahead of her presentation at the QuakeCore annual meeting.

In Max’s presentation, ‘Implications of tephra thickness and grain size properties for the occurrence of soft-sediment deformation structures in lacustrine tephra layers, Hamilton lowlands’, he considered the relationship between tephra properties and the occurrence of soft sediment deformation over multiple lakes in the Hamilton Basin. 

Tehnuka discussed computational analysis of core CT scans for estimating volumes of tephra layers and associated soft-sediment deformation structures.

Finally, David’s talk, ‘Origin and development of lakes in the Waikato region’, gave us an overview of different types of lakes according to their formation mechanisms and relationship with the surrounding landscape, illustrated by examples from Waikato. 

Wānanga with Wiremu Puke and CT scanning update

At the start of June, the team met at Hamilton Gardens for a wānanga led by Wiremu Puke (Ngāti Wairere, Ngāti Porou). This began with an introduction to mātauranga Māori in geosciences research – particularly as it relates to Ngāti Wairere, as mana whenua for much of the area in which we are working. Wiremu also shared some of the history of Ngāti Wairere, and took us on a tour of Te Parapara Garden. We were lucky to have Wiremu, as one of the leaders of its planning, and construction, explain the significance of the garden design and layout, especially to the direct descendants of Ngāti Wairere, as well as visitors.

An article about Te Parapara is available on the web, and the abstract is free to read.

The team at Te Parapara, with the whatarangi (storehouse) visible in the background. From L to R: Wiremu Puke, Vicki Moon, Tehnuka Ilanko, Richard Melchert, Danche Chaneva, Toby Kluger (our website designer), and Josh Hughes.

We have also completed CT scanning of all remaining cores from our March field campaign, with the help of Nic Ross at Hamilton Radiology. This means we can identify tephras and avoid cutting through them when we begin the next stage – opening and describing the cores. Masters student Richard Melchert has already been working on the cores from Rotoroa (Hamilton Lake). When we look at the CT scan images in more detail, they will show us the structures of any tephra seismites in 3D. We remain very grateful to Nic and Hamilton Radiology for their generous support.

CT scanning at Hamilton Radiology. L to R: Danche, Nic Ross (seated), Max Kluger (standing), Vicki, Richard.

New paper and conference presentation

Tephra Seismites PhD student Jordanka Chaneva attended two conferences in Sydney earlier this month: the International Young Geotechnical Engineers Conference (7iYGEC), and the 20th International Conference on Soil Mechanics and Geotechnical Engineering (ICSMGE). As well as presenting a paper at 7iYGEC, she participated in a victorious debate between ‘Young’ and ‘Experienced’ engineering teams on the future of geotechnical engineering!

Jordanka’s ten-minute presentation recorded for 7iYGEC describes the results of her research testing the geotechnical properties of tephra samples from local lakes. The associated paper, ‘Geotechnical properties of liquefied pumiceous layers in lakes’, is also now available to read

Jordanka (second from left) seated with team members at the 7iYGEC debate.

Lake coring and GPR fieldwork

The Tephra Seismites team has had a busy month, with successful field campaigns conducting ground-penetrating radar (GPR) at Rotoroa/Hamilton Lake with Dr Andrew Lorrey and John-Mark Woolley (NIWA), and sediment coring at seven Hamilton Basin lakes with Dr Marcus Vandergoes and Henry Gard (Lakes380 and GNS Science).

This follows fieldwork with Dr Pilar Villamor and Genevieve Coffey (GNS Science) in February to continue investigating Te Puninga Fault, also using GPR.

Richard Melchert and Drew Lorrey set off for canoe-based GPR of Rotoroa/Hamilton Lake. Photo: David Lowe
The GPR field team (L to R): Drew Lorrey, John-Mark Woolley, Max Kluger, Richard Melchert. Photo: David Lowe
Richard Melchert (left), Marcus Vandergoes (right) & Henry Gard (back) coring on Rotoroa. Photo: Chris Morcom.

Thank you to our collaborators, and all those who helped with fieldwork permission and access.

Triaxial testing

While we plan for fieldwork later this summer, some of our team members have also been busy in the lab with triaxial testing to characterise the mechanical properties of pumiceous sands and tephras. These tests will tell us more about the conditions under which the tephras in our lake cores have liquefied.

August update

In recognition of having submitted the first of our papers from the project, and a lot of hard work thus far, our group and supporters met for a special lunch last Friday (13 Aug).

Tephra seismites group and supporters at lunch
Several local members of the Tephra Seismites group, along with supporters and advisors.

Triaxial tests in the lab, led by Danche, got underway earlier this week – though these are now on hold with the latest lockdown! There is plenty to do from home, however. The team are working on abstracts for the forthcoming Geoscience Society of NZ annual conference at Massey University (Palmerston North) later this year, and on the first report to our Marsden funders. As we head into spring, we are also looking forward to resuming our fieldwork.

First newsletter and team meeting

Our first newsletter update on research progress went out to colleagues and stakeholders this month. A copy can be found below.

Last week we also had a visit from Auckland-based team member Professor Rolando Orense for our first in-person meeting, before he gave a New Zealand Geotechnical Society presentation.

Some of the Tephra Seismites team (left to right). Back: David Lowe, Richard Melchert, Max Kluger; Front: Rolly Orense, Danche Chaneva, Vicki Moon, Tehnuka Ilanko. (Team members unable to be present include Pilar Villamor, Rich Johnston, Josh Hughes, Wiremu Puke).

Tephra sampling fieldwork

Late last month, the Tephra Seismites team went to visit one of our field sites and collect tephra samples for lab testing, to better understand how and why they might liquefy in an earthquake.

Tori and Max at the sampling site

We found Tuhua (Mayor Island) tephra (7.6 cal ka) and Mamaku tephra from the Okataina caldera (8.0 cal ka), which are the upper and lower tephras respectively in the photo below. Jordanka will be using these in her geomechanical tests.

Tuhua (upper) and Mamaku (lower) tephras in lake sediment