Watching Ruapehu Crater Lake: What does this tell us about an active volcano?

Ruapehu is an active volcano in New Zealand, with all historical eruptions having occurred from its Crater Lake. By watching and photographing the Crater Lake, we attempted to better understand the lake and see if watching the lake could indicate when and how Ruapehu may erupt in the future.
Published in Earth & Environment
Watching Ruapehu Crater Lake: What does this tell us about an active volcano?
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BioMed Central
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Observations of Ruapehu Crater Lake (Te Wai ā-moe) and implications for lake dynamics and volcano monitoring - Journal of Applied Volcanology

All historical eruptions at Ruapehu have occurred from its Crater Lake, Te Wai ā-moe. This study aims to better understand Crater Lake dynamics by using visible light and long wavelength infrared images of the lake. Over 10,000 images from 1902 – 2021 were analysed to produce a time-series of lake observations. Our results show that visible light observations reveal colour changes on the entire Crater Lake surface from blue to grey, and localised grey, yellow, and black discolourations. Grey discolourations are interpreted as localised upwellings of lake-floor sediment, and yellow and black material to comprise vent-hosted sulphur/sulphides, both transported by volcanic fluids from subaqueous vents to the surface. The locations of upwellings were used to identify five vent locations beneath Crater Lake, three more vents than were previously recognised. Upwellings appeared and disappeared in 10 min. Steam above the lake surface was controlled by both lake temperature and cloud conditions. Blue lakes were most common in summer and autumn, implying a relationship with ice or snow melt entering the lake. Grey lakes were observed in the month before 97% of eruptions, suggesting a correlation between a grey lake and eruption precursors.Crater Lake processes are illustrated by three regimes. Regime 1, a vigorously convecting grey lake associated with steam, eruptions, and more frequently the high end of recorded lake temperatures (within the range of 7 – 69 °C). Regime 2, a blue lake to occasionally green that typically occurs in summer and autumn when ice or snow melt is significant and is associated with generally the low end of lake temperatures and reduced volcanic fluid input. Regime 3, a blue-grey lake, the most observed lake colour in this study and effectively a balance between volcanic and seasonal processes. We suggest that an array of cameras would be useful additions to the current volcano monitoring network at Ruapehu.

Ruapehu is a large stratovolcano located in the North Island of New Zealand, known mainly for the snow sports enjoyed on its mountain slopes during winter. Ruapehu has a large lake near the volcano's peak, known as Crater Lake, or to local tribes as Te Wai ā-moe. All historical eruptions at Ruapehu have occurred from volcanic vents found beneath the Crater Lake, with the most recent significant eruption in 2007 severely injuring a hiker camping near the lake. Ruapehu Crater Lake varies in temperature, colour, and steam conditions over time, which provide an insight into how the volcano works. Studying how the lake has visibly changed before past volcanic eruptions can also improve understanding of when and how Ruapehu may erupt in the future.

Left: Ruapehu Crater Lake. Right: Ruapehu Crater Lake and summit area covered in volcanic debris after the 2007 eruption. Both images courtesy of GNS Science.
Left: Ruapehu Crater Lake. Right: Ruapehu Crater Lake and summit area covered in volcanic debris after the 2007 eruption. Both images courtesy of GNS Science.

I began this study by looking at thousands of images of the Crater Lake that had previously been obtained by GNS Science, local iwi Ngāti Rangi, and various other sources. For every image I documented the lake colour, discolourations on the lake surface, and if steam was visible. Yes, this is as painful as it sounds. I looked at ways to automate this process, however due to differing camera angles and cloud conditions, and lack of consistent reference points, this proved difficult. Thankfully, some analysis had already been completed by GNS Science, so I built on this previous work. By chance, while I was on Ruapehu for a university field trip, my professor and I decided that I should climb to the Crater Lake and observe it. We found that the Crater Lake surface had numerous yellow and grey discolourations that changed location in a matter of minutes, something previously unknown to us. This was important as these discolourations were thought to indicate material being carried from the vents at the floor of the lake to the surface by volcanic processes, and could indicate where the volcano may erupt from in the future. We decided that systematic fieldwork with an array of cameras was necessary to better understand the location and timing of these volcanic processes.

We recruited the help of scientists from GNS Science, the Department of Conservation, various universities, and local iwi, to help with data collection and analysis. Fieldwork involved carrying camera equipment, food, and hiking gear from the bottom of Whakapapa ski field to a vantage point overlooking Crater Lake, named Dome, a total of 20 times. This was a three hour walk with a heavy pack, including carrying a laptop to power an infrared camera, so I was always exhausted by the time I made it to Dome. I set up an array of ‘normal’ visible light, multispectral, and infrared cameras to capture images at 10 second intervals, left the cameras for a few hours, and then descended back down the mountain. I later collated the images together to create timelapse videos showing how the Crater Lake surface changed over time.

Camera arrays during fieldwork consisting of (a) visible light, (b) visible light and multispectral, and (c) infrared and visible light cameras.

From the visible light images of the Crater Lake, we identified entire changes in lake colour from blue to grey, localised circular grey discolourations that we referred to as upwellings, localised elongate yellow discolourations identified as sulphur and referred to as sulphur slicks, and varying amounts of steam above the lake surface. The infrared imagery showed no useful information due to steam and the low angle view from Dome obscuring the lake temperature.

Ruapehu Crater Lake images of (a) upwellings, (b) sulphur slicks, (c) no steam, (d) very intense steam. Vent locations are shown as central (yellow), western (red), central-northern (black), eastern (blue), and northern (green). (a, b) Images courtesy of GNS Science.

Circular grey upwellings are interpreted to be lake-floor sediment carried to the lake surface by volcanic fluids. These upwellings varied from metres to hundreds of metres in diameter, and either appeared and disappeared in less than 10 minutes, or remained present for hours. The locations of upwellings were used to identify five vent locations beneath the Crater Lake, three more than were previously known. Upwellings from the central vent were much larger than the other 4 upwelling locations, suggesting that a grey lake only resulted from central vent activity. Yellow or black elongate sulphur slicks are composites of thousands of small bubbles coated in sulphur, and are produced by volcanic fluids rising through a layer of liquid sulphur at the bottom of the lake and then being carried to the surface. Steam above the lake surface was only seen when the lake temperature was over 30 °C, with it being more abundant on cloudy days. The shape of the steam was circular during low wind conditions, and in high winds it formed sheets of steam blown across the lake.

We analysed the Crater Lake colour before historical volcanic eruptions at Ruapehu, finding that the lake colour was grey in the month before 97% of eruptions. This suggests that grey lakes may appear prior to eruptions in the future. Entire lake colour changes to grey are caused by volcanic fluids stirring sediment throughout the whole lake, as illustrated in Regime 1 below. Colour changes to blue are caused by ice or snow meltwater entering the lake and travelling across the surface, which was often observed in Summer and Autumn, and is shown in Regime 2 below. A blue-grey lake is the most commonly observed lake colour, and results from a balance between volcanic and meltwater processes. Based on the correlation between lake colour and past eruptions, we recommend that a visible light camera be deployed to monitor Ruapehu Crater Lake.

Regime 1 illustrating a grey lake with significant volcanic fluid input.
Regime 2 illustrating a surficial blue lake due to meltwater input.

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Community voices and volcanic risk reduction: co-production, participatory research, and community-led approaches to risk

This Collection will highlight research and case studies that adopt participatory, community-led, or co-produced approaches to volcanic risk and resilience.

Experience and research into effective volcanic risk reduction highlights the importance of community involvement and community-led approaches to understanding and anticipating risk, as well as effective response, and recovery. Systems and solutions that do not include community needs, can reduce their efficacy, and, at worst disengage those communities, wasting resources and creating risk. Identifying approaches to volcanic risk reduction in partnership with communities can foster community ownership, empowerment, and control; enhancing the resilience of those communities. Co-production of risk knowledge and risk solutions not only result in outcomes that are more meaningful, relevant, and successful, but can also lead to improved understanding of volcanic risk for all parties.

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In this Collection we seek to highlight community participation initiatives in volcanic contexts and capture this emerging knowledge. We are interested in articles that address the spectrum of approaches and challenges. This encompasses the spectrum of community engagement from wholly community-led initiatives, through knowledge co-production, to novel examples of successful engagement led by volcano scientists or managers of risk. We particularly welcome reflections on pitfalls and challenges, and even examples of failure. We will also consider many definitions of community: from local communities and populations, through to communities of stakeholders and decision-makers. We thus seek contributions from the broad communities involved in understanding and managing volcanic risk: including physical and social scientists, indigenous researchers, practitioners, policy and planners, emergency managers, central and local government, and local community leaders.

We encourage authors to share experiences and methods for empowering local communities, authorities and partnerships, engaging multiple and diverse stakeholders, understanding local expressions of hazards and risk, and sharing responsibilities, as beacons for the core goals of the SENDAI Framework. Volcanic risk settings are inherently multi-hazard, and can present outstanding exemplars of means to “leave no-one behind” in the context of sustainable development and global environmental change. This speaks directly to the aspirations of both the SENDAI framework and the UN Sustainable Development goals which seeks to eliminate poverty (Goal 1) and share knowledge and education (Goal 4) with all (Goals 5 and 10), for the development of inclusive and sustainable settlements (Goal 11). As such, we also welcome contributions that consider implications of this work for sustainable development in other contexts.

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