Gasses bubbling up in Auckland waters prior to an eruption–this isn’t an unlikely scenario. Thanks to a high (and rising) sea level, over a third (35%*) of the Auckland Volcanic Field is under shallow water.
A lot of gas (typically CO2, H2O, H2S, SO4, HCl, and HF) is dissolved in magma–just like CO2 is dissolved in Coke. As magma rises from deep in the Earth–or we open the cap of a Coke bottle, the pressure decreases, and gasses can escape more easily. In an eruption, we would expect some of the volcanic gasses to reach the surface before the magma does. This means that we can use gas emissions in Auckland as a monitoring tool during eruption crises. It’s important to note that no volcanic gasses have been found in Auckland–yet.
Thanks to a previous survey of soil gas, we know what a ‘normal’ gas reading in Auckland looks like. We can use these previous survey results as a comparison during eruption crises and when we notice something unusual.
And people have found unusual activity in Auckland. Just recently, some kayakers reported constant bubbling in Tamaki River from one spot. They wanted to know: is it volcanic?
Here is the bubbling in the Tamaki River:
A still photograph of the bubbling:
To figure out what the gas is, we (at the University of Auckland) use gas meters. They tell us what gas we are measuring, and how much of it there is. We mainly look for an abnormal amount of CO2, as this gas is one of the first to escape from rising magma. There is also usually more of it in magma than the other gasses, so it is more likely to be detected. If we do find CO2 levels above normal concentrations, or it is venting in an unusual way, we collect samples of the carbon dioxide in special bags and figure out if it is the type that is found in magma (volcanic CO2 has a special signature). In this case, we didn’t find anything unusual in the air bubbling up through the water, so no samples were taken. We also went looking for other reasons that gas may bubble up as bubbling doesn’t always come from volcanic activity.
Sometimes, all it takes is some detective work to explain what is happening. I visited the site again at low tide, and this is the same location as the bubbling shown above (marked with an arrow):
There is a drain pipe directly underneath where the bubbles are occurring. Looking around, the pipe can be seen again here:
A quick search of the Auckland Council GIS Viewer reveals that this is an abandoned pipe. It is likely venting during high tide for some reason.
The simplest answer is often the right one. The matter was reported to the Auckland Council and the case is considered solved.
Whew. We can rest easy for now–there are still no volcanic gasses rising in Auckland. Happy holidays, everyone!
*Agustín-Flores, J., Németh, K., Cronin, S. J., Lindsay, J. M., & Kereszturi, G. (2015). Construction of the North Head (Maungauika) tuff cone: a product of Surtseyan volcanism, rare in the Auckland Volcanic Field, New Zealand. Bulletin of Volcanology, 77(2), 1-17.