Volcano mapping using hyperspectral remote sensing

 


By Dr Gabor Kereszturi, Massey University

 

 

New Zealand is not short of composite volcanoes that can produce volcanic hazards from a range of eruption styles, pyroclastic density currents, rockfall and ballistics, lahars, and flank collapses, among others. Based on the geological record, Mt Ruapehu and Mt Tongariro have produced many of these impactful hazards in their pasts, including larger-scale flank instabilities leading to far-reaching debris avalanches.

Flank collapses and instability are linked with hydrothermal alteration. Hydrothermal alteration is due to the circulation of hot and acidic fluids making their ways to the surface within a volcano. On Mt Ruapehu, this is often manifested as a heat-up of the Crater Lake (Figure 1) however, the current and past extent of such hot fluid’s pathways are practically unknown. 

 

Figure 1: Thermal image of the Crater Lake in March 2020
Figure 2: Field photo of hydrothermally altered rocks

These fluids can change the primary physical and chemical characteristic (Figure 2), making it weaker and weaker over time. The mineralogical is spatially highly heterogenous, complicating our ability to quantify volcanic hazard around composite volcanoes.

Hydrothermal alteration forms new minerals that can absorb light at wavelength beyond visible light. Hyperspectral imaging is a versatile technology that measures upwelling radiation from the surface of the Earth at hundreds of narrow and overlapping spectral bands.

When a hyperspectral sensor is mounted on a low-flying aircraft, we can acquire a seamless image with detailed spectral information associated with every image pixel. This wealth of spectral information can help to constrain the extent and type of dominant alteration mineralogy at every pixel, allowing a fast way to quantify the spatial patterns and degree of hydrothermal alteration on the surface of volcanoes.

New alteration mineral maps have been produced for Mt Ruapehu with this exciting technology for the first time, highlighting areas of intense alteration in the geological past (e.g. in purple in Figure 3). Our understanding of the evolution of such highly altered areas can vastly improve our capability to implement numerical modelling to forecast initiation and run-out distance of resultant debris avalanches that can travel 20-40 km from the volcanoes.

 

Figure 3: Mineral map derived from hyperspectral imagery, showing the Upper Whangaehu valley

Hyperspectral scanning is, however, not limited to airborne, or satellite application. Still, it can be used in well-constrained laboratory condition, providing opportunities in the future to combine hyperspectral data with other datasets (e.g. engineering geology). This is a promising future research direction that can help better understanding hydrothermal alteration on volcanoes at a centimetre smaller scale, as opposed to the 1-10 meters resolutions of airborne and satellite hyperspectral images, respectively.

These new datasets can decipher how rock-mass behaves and change their mechanical properties with hydrothermal alteration, contributing to highlights areas of potential future failure zones on New Zealand’s most iconic volcanoes.

 

Dr Gabor Kereszturi was a recipient of a 2020 Rutherford Discovery Fellowship for his research on hyperspectral remote sensing of volcanoes. 

Impact case study:

Model and tools for decision-making

 


How did Resilience Challenge research have an impact in 2019-2020?

 

Central to our mission to accelerate natural hazard resilience is the development of new models and tools to quantify hazards and impacts in more realistic ways, providing better assessments of resilience options to decision-makers.

Development of new models is iterative, requiring repeated testing and validation, and their application usually comes at the end of an extensive period of development. RNC is driving meaningful enhancements and innovations in this area, building on work in Phase 1, the Natural Hazards Research Platform, and leveraging existing New Zealand tools such as RiskScape and MERIT.

Updated hazard map for Whakapapa skifield. Credit: GNS Science

Earlier this year, Volcano programme research was integrated into updated hazard posters  for Turoa and Whakapapa skifields, as part of a collaboration with the Department of Conservation. Researchers were also commissioned by Ruapehu Alpine Lifts to produce a technical report on potential lahar hazard in the Whakapapa ski area. A new lahar simulation model, calibrated to previous lahars, was used to estimate the lahar footprint and impact for a range of scenarios. Results of the report have been used to develop safety measures for the new Sky Waka gondola.

 

 

Dr Nicky McDonald and colleagues from ME Research produced economic modelling utilising the MERIT (Measuring the Economics of Resilient Infrastructure Tool) capability developed in Phase 1, to assess the economic consequences of fuel outage scenarios following the Auckland-Marsden Point fuel pipeline failure. MERIT was applied to five disruption scenarios, which were then evaluated with and without mitigation options to better understand the impact of disruption and potential value of mitigation actions for New Zealand. The report was prepared for MBIE and findings also contributed to the Board of Inquiry into the 2017 Auckland Fuel Supply Disruption.

As part of our Coastal Flooding project led by Prof Karin Bryan (University of Waikato) and Dr Scott Stephens (NIWA), Dr Shari Gallop and Masters student Akuhata Bailey-Winiata (Te Arawa, Ngāti Tūwharetoa) carried out a summer project to determine the proximity of coastal marae (located within 2km of the coast) to coastal and river waterbodies. They found that 93% of coastal marae are located in the North Island; over 45% of coastal marae are within 200 meters of the coastline; and approximately 70% of coastal marae are located below 20 meters elevation relative to mean sea level. Data will be used as a baseline for determining risk and vulnerability of coastal marae to coastal hazards and sea-level rise. Akuhata’s research was recognised by the New Zealand Coastal Society who awarded him with a Māori and Pacific Island Research Scholarship in July 2020. 

Our Built Environment programme has completed new hazard maps for Bay of Plenty marae (showing fault lines, flooding, geothermal, liquefaction, and tsunami zones) using data from Rotorua City Council and Environment Bay of Plenty. The maps were provided to Te Arawa Lakes Trust collaborators, and are intended to be used to catalyse conversations with marae regarding adaptation and preparedness planning.

Part of our Weather and Wildfire programme involves the modelling of credible ‘what-if’ scenarios. What if the path of ex-Tropical Cyclone Cook (which did much damage in eastern Bay of Plenty in 2017) had been further west and hit our biggest population centre, Auckland? Weather scenario modelling at such fine-grid resolutions is a first for New Zealand, and allows detailed impact modelling to be carried out for a variety of coincident weather, flood, and landslide hazards, building a credible worse-case impact scenario for Auckland and surrounding districts. The early modelling is highlighting the potential for extreme impacts in Auckland, and in other areas well away from Auckland such as the higher elevations of the Kaimai ranges.

 

New modelling shows what could have happened if ex-TC Cook has tracked over Auckland. Credit: Ian Boutle, 2020

The primary goal of our Earthquake-Tsunami programme is to generate synthetic earthquakes using computer models. Big earthquakes and tsunamis (thankfully) don’t happen very often. A downside of this infrequency is that limited information from past earthquakes makes the job of forecasting future earthquakes and tsunamis challenging. One way of getting over these limitations is to generate synthetic earthquakes over millions of years using computer programs.

The team, led by Dr Bill Fry and Prof Andy Nicol, now has a first iteration of a synthetic seismicity model for New Zealand that incorporates all of the faults used for the National Seismic Hazard Model. This is a successful proof of concept. Further, through extended international collaboration, they have produced basic ground motion predictions from this model. This is an exciting and important stepping-stone in a programme of work that aims to improve future earthquake, tsunami and landslide hazard models in New Zealand.

 

This case study was submitted to the Ministry of Business, Innovation and Employment as part of our 2019-2020 annual reporting. 

 

Impact case study:
Responsive science for national emergencies

 


Resilience to Nature’s Challenges (RNC) has a unique role among National Science Challenges, with obligations under the National Civil Defence Management Plan (2015) to enable coordination of post-event research activity. As we have demonstrated in 2019-20, we’re able to add significant value by linking and coordinating across the science system, and supporting the direct input of science into decision-making during natural hazard emergencies.

In December 2019, six days of heavy rain caused the Rangitata River to overtop its banks, causing extensive flooding of farmland and roads. The event had significant national consequences, cutting off State Highway 1 and disrupting the national electricity grid. Our Built Environment team collected empirical data alongside other agencies to better understand the impacts of such an event, and University of Auckland postgraduate students supervised by Assoc Prof Liam Wotherspoon are developing a case study database in collaboration with affected network owners. This will inform other RNC projects by adding to the wider database of case history evidence of infrastructure component performance.

In Southland in February 2020, a month’s rainfall in a single day washed out roads and bridges and caused flooding and landslides. Fiordland was hit hard, with hundreds of tourists trapped in Milford Sound and on tramping tracks. The Rural programme’s science leadership in the AF8 (Alpine Fault magnitude 8) programme contributed to the Fiordland Hazards Group planning for disruptive events over several years prior to the floods. The flooding response was enhanced by these existing relationships, and the response planning efforts already in place. The evacuation of Milford Sound was the largest ever conducted in New Zealand. The Rural programme is leading innovative research to understand tourist risk exposure using geospatial tools, which will continue to support emergency managers in effective response planning.  

 

Road damage in Fiordland. Credit: Milford Road Alliance

The tragic Whakaari eruption on December 9th was the start of an unexpectedly busy period for a number of RNC researchers who assisted with the eruption response, providing regular expert commentary in the media, supporting GeoNet with risk assessments and risk communication, working with local iwi, providing specialist advice to agencies such as NEMA, MOH and MPI, and coordinating the identification of science and research priorities.

COVID-19 has been a significant event for many of our programmes. We mobilised early to provide integrated advice to the Department of Prime Minister and Cabinet as part of their strategic recovery planning, compiling short summaries of lessons from past natural hazard events to identify a set of issues that could be anticipated in medium-and longer-term recovery planning. 

RNC programmes also mobilised to contribute to the COVID-19 research effort. Our Resilience in Practice co-leader Dr Nick Cradock-Henry and colleagues identified the convergence of winter/spring flood risk and COVID-19 economic impacts in rural communities as a driver for increased social inequities, providing targets for stimulus investment. This analysis has been applied to consideration of investment in enhanced flood protection schemes through the ‘Shovel-Ready’ government stimulus, supported by the DIA Community Resilience Programme. This modelling capability is now being drawn on by Te Punaha Matatini to integrate social and economic impact modelling into overall COVID-19 scenario modelling.

RNC researchers have been active contributors to the national dialogue about priorities for the COVID-19 recovery stimulus. In numerous opinion pieces and media appearances, Prof Iain White and Prof Ilan Noy advocated for transformative change that boosts our local and national resilience to future disruptive events including climate change.

The multiple dimensions of the pandemic and economic recession are also informing our natural hazard resilience research, in the areas of multi-hazard modelling, consideration of livelihoods, the political dimensions of risk, and adaptation to multiple stressors. Several RNC programmes have brought an additional COVID-19 dimension to their work through new funding from MBIE, the Health Research Council, and Te Punaha Matatini.

Our Phase 2 Rural programme, as designed, featured a strong focus on tourism and disasters. COVID-19 has now extinguished the international tourist market for the foreseeable future, rapidly shrunk a sector that was set to be a key partner in our research programme, and exposed its vulnerability to international events. Rural programme researchers Dr Joanna Fountain, Dr Caroline Orchiston and others have been part of an emerging dialogue about the need for a ‘reimagined’ tourism system that will lead to a more sustainable and resilient industry.

The agility demonstrated in these examples is possible because of the collaborative network of researchers committed to the RNC mission, and well-established relationships with research users and decision-makers.   

This case study was submitted to the Ministry of Business, Innovation and Employment as part of our 2019/20 annual reporting.