Watch: Hawke’s Bay gas seep draws international scientists for study

What looks like a mini volcano complete with a bubbling centre has drawn international scientists to Hawke’s Bay to study it.

Known as a gas seep, the phenomenon happens when methane and other gases bubble up through springs – not like a mud pool or geyser – but much more gently and from much deeper underground.

There are four known gas seeps in Hawke’s Bay. This one is in Raukawa Valley, about 30km from the coast and scientists from the US, Chile and Italy joined Hawke’s Bay Regional Council groundwater scientists, including Tom Wilson, to collect water and gas samples.

Wilson said while the earliest research study he had seen on this gas seep was 1989, locals had known about it for a long time.

“At the Raukawa site, the gases are bubbling up through an old hand-dug well. Not all gas seeps occur at wells.

“In 1920 the landowners tried to use the gas to light their home but that fell through,” Wilson said.

“It’s likely that the gas flux (the volume of gas going up out of the ground) was too low to be useful.”

He said the international scientists reached out to HBRC to ask to come and see it.

“We are all still learning about them and it’s a great way of sharing knowledge.”

To collect gas samples from the seep, a tube is inserted into the underwater bubbling area, allowing gas and water to rise together through it. Once a steady flow is established and the system is fully flushed, valves connected to in-line evacuated sampling bottles are opened to draw in the gas. The bottles are sealed to preserve the samples for analysis

Wilson said the samples were taken for the specific needs of the overseas scientists.

Hawke’s Bay Regional groundwater scientists Tom Wilson. Photo / Hawke’s Bay Regional Council

“Samples collected included basic water chemistry data (i.e. concentrations of the main naturally occurring mineral components), radiocarbon and tritium for an estimate of the groundwater age, stable water isotope compositions, physical and chemical properties (e.g. temperature, electrical conductivity, pH), eDNA testing (used for understanding what microbes live in these systems) and gas samples. Gas samples are used for measuring the gas composition, which scientists use to help understand where the gas comes from and what geological processes it is associated with.”

He said some of it probably comes from very deep down, even the mantle (the largest layer of the Earth, situated between the crust and the outer core).

“This research aims to improve scientists’ understanding of the geological processes happening along the Hikurangi tectonic margin, where the Pacific Plate is forced beneath the Australian Plate beneath Hawke’s Bay. The sampling is part of a broader campaign across the North Island to study these processes.”

Wilson said there were four known sites in Hawke’s Bay. The other three were in Waipuka, Kahuranaki, and Puhokio (between Poukawa and Ōtāne ).

“I imagine the more you look the more you will find. That’s common in science.”

LDR is local body journalism co-funded by RNZ and NZ On Air.