Volcanic Activity in Lake Rotoiti # 2

Understanding the Affects of Under Water Volcanic Activity on Lake Rotoiti

Rotoiti, the freshwater paradise in Rotorua’s backyard, has a deep secret. A field of geothermal vents, over a hundred metres under the surface at Hauparu Basin, releases near- constant streams of bubbles that rise through the waters. The lake, her ecosystem, and all the life that surrounds her, are shaped by this activity.

As they rise, volcanic bubbles interact with freshwater and exchange elements: acids and metals from the volcanic gas dissolve into the water and are replaced by oxygen as the bubbles race to the surface. Carbon dioxide acidifies the lake, changing the availability of nutrient for life in the lake to breath.

Yearly, the seasonal cycle of the temperate climate in Aotearoa changes the physical structure of some lakes, as heat from the summer sun can only reach a certain depth. Due to the temperature induced barrier, bottom water that is rich in dissolved CO2, is colder and denser than the warmed surface layers and is stopped from escaping to the surface. Because of this, Carbon dioxide accumulates deep in the waters of Rotoiti: but is this a potential resource or a danger?

At lake Nyos, a volcanic lake in Cameroon, the sudden ‘explosion’1 of Carbon Dioxide from the lake killed thousands, now they pump bottom water to the surface to reduce risk. Another volcanic lake, Lake Laach (or the Laacher Sea), has been utilised as a commercial CO2 resource for Vulkan Brauerei.

This research found that, as the summer stratification traps CO2, winter mixing releases it to the air. A maximum accumulation was found in April, where the oxygen rich, warm surface waters were completely isolated from the acidified, cooler, deep waters. Over two years this research found that the natural environmental cycling of the seasons is responsible for risk mitigation, as annual cooling, through June, allows CO2 to leave the lake relatively rapidly, but not instantaneously.

As noted in the previous newsletter on this research, we wonder about the impact of climate change on these processes. As summers get longer, hotter, and/ or drier, will the Lake’s dissolved CO2 processes change, could more intense stratification lead to a higher risk? We are currently moving to a second stage of investigation: modelling CO2 behaviour and looking to publish the data from this research in an Open Access journal. I would like to implement home and community-based measures, in the next stage of research, including air CO2 monitors at Marae and houses around Hauparu & Tapuwaekura Bays. We are working to fund this endeavour: if you live near the lake at one of these bays, please be in touch.

Alongside this research, I have been given the opportunity to share korero at consecutive ‘Te Tukohu Ngawha' Science and Design fairs, as well as at multiple kura in the region. If you are a teacher, parent, or student who would like to learn more, please be in contact and we can work to organise a presentation on a range of science and engineering topics.

You can contact me at: aj.marshall@vuw.ac.nz OR 02885139659, any time, with Patai regarding this research or requests for educational outreach.

Open access resources:

Nyos- type (Explosive CO2) eruptions: An overview of the structure, hazards, and methods of investigation of Nyos-type lakes from the geochemical perspective. Be patient - this link takes some time to open up.....

LAWA’s monitoring platform of Rotoiti’s lake health, water quality, and swimability.

BoP Regional Council’s water monitoring platform of lake physiochemical properties.

AJ’s research blog with the latest updates, publications, and resources.