Author: Tehnuka

PhD student Jordanka Chaneva has a new paper, ‘Monotonic and cyclic undrained behaviour and liquefaction resistance of a pumiceous, non-plastic sandy silt’ published in the journal Soil Dynamics and Earthquake Engineering. Please contact us if you would like a copy.

This paper is based on her lab work, testing the properties of Tuhua tephra (one of the younger tephra layers in our study). In addition to contributing more broadly to understanding the undrained behaviour and liquefaction resistance of similar soils (pumiceous silts), Jordanka’s work helps us understand the response of Tuhua tephra in the Hamilton Basin lakes to earthquake shaking, by analysing its liquefaction potential.

Many thanks to Ngāti Wairere and the Department of Conservation for field site access, and to MBIE, Marsden, QuakeCoRE, EQC, and Waikato Regional Council for funding.

Jordanka also attended the 2023 Disastrous Doctorates symposium last week, hosted by the Joint Centre for Disaster Research at Massey University, where she presented a three-minute talk about this research.

Two weeks ago, some of the Tephra Seismites group attended the IAVCEI (International Association of Volcanology and Chemistry of the Earth’s Interior) 2023 Scientific Assembly in Rotorua. The conference, with the University of Waikato a major sponsor, was originally scheduled for February 2021. Twice postponed due to COVID, it was a relief that the meeting could proceed (with 860 in-person and 203 virtual participants) despite the wet weather and temporary closure of Auckland Airport.

We presented two talks on behalf of the group, in the session ‘Tephrochronology: new methods and applications for chronostratigraphy and beyond’.

The first was a broad overview of the project, covering some of our recently published work, and our work with X-ray CT to identify and characterise tephras and seismites: ‘Tephra seismites preserved in unconsolidated organic lake sediments in the Hamilton lowlands, New Zealand, indicate paleoearthquake activity since 17.6 ka’ (presented by Tehnuka).

The next talk focused on our work at Rotoroa/Hamilton Lake, and findings from Richard Melchert’s thesis: ‘Using ground-penetrating radar and X-ray computer tomography to survey and characterise distal tephras in lake sediments, Hamilton lowlands, New Zealand’ (presented by David).

Tehnuka also gave an ECR (Early Career Researcher) Plenary, showing how we can unravel volcanic gas data to understand both magmatic and non-magmatic processes.

One of the pre-conference workshops was also tephra-related: ‘From field apps to data repositories: Improving tephra data discoverability, access, and workflows to support next generation research’, organised by Steven Kuehn, Kristi Wallace, Ellen Nelson, Andrei Kurbatov and Kerstin Lehnert. This workshop was a continuation of an ongoing project under the auspices of the Commission on Tephrochronology entitled ‘Community established best practice recommendations for tephra studies—from collection through analysis’, with a milestone paper published last year.

For a field visit and a chance to try out the Strabo app for field data collection, David, Josh, Richard, and Tehnuka arranged an excursion to a tephra outcrop at a nearby pumice quarry. The deposits here include the Rotorua and Waiohau tephras we are familiar with from lake coring around Hamilton, although they are much thicker, since this site is far closer to the source. Our field guide contains more details. Many thanks to the RNL pumice quarry owners for permission to visit.

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.

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.

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.

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. 

A short newsletter on research progress was recently emailed to partners, supporters and stakeholders, and can also be viewed below. If you’d like to receive any future updates directly, please feel free to contact us.

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.

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

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.

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).

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.