Hope Spring bubbles were discovered by Kaikōura
a week after the damaging 7.8 magnitude earthquake which struck the
north eastern South Island in November 2016.
a couple of days, engineering geologist Matthew
from the University of Canterbury, was on-site inspecting the
bubbles, which the kayak guides reported had a sulphurous smell.
bubbles are 50-60 metres offshore in Whaler’s Bay in 3-4-metre deep
water. Matthew describes them as sheets of bubbles that extend for
about a hundred metres. They were being released from the seabed
along with some warm water, about 18°C.
first impression was just how beautiful and surreal and amazing it
seemed,” said Matthew.
my second major impression was that this was a major geologic feature
that had been created by the earthquake.”
Matthew thought the bubbles might be coming from a local source. He
knew there had been some fracturing of rocks which was liberating
groundwater and the gas dissolved in it, but he wasn’t sure exactly
what the gases were.
was keen to investigate further.
who is also at the University of Canterbury, had the knowledge and
equipment required, having already studied other warm spring systems
around New Zealand.
they devised a simple way of collecting gas from the bubbles, and in
December 2016 Matthew headed back to Kaikōura to collect some gases.
said Travis analysed the isotopic signature of carbon atoms collected
from carbon dioxide.
able to tell how much Carbon-12 there is – the most common and
abundant form of carbon – compared to Carbon-13,” said Matthew.
ratio of Carbon-12 to Carbon-13 can tell us from which depth,
approximately, carbon molecules originated.”
from the deep
said the data he and Travis have collected is still preliminary, but
suggesting two major sources. The first is what we call the
metamorphic source – this is carbon originating from lower down in
the earth’s crust, possibly the upper mantle.
is essentially being evolved from metamorphosed rocks at depth and
under extreme pressures and high temperatures.”
said they can’t put an exact figure on the depth, but the warm
water containing the carbon dioxide is starting tens of kilometres
below the seafloor.
said there is another biogenic carbon source which is from
hydrocarbons – “essentially oil and gas.”
and Travis suspect that water from the deep source, which contains
carbon dioxide dissolved under pressure, passes through rock layers
containing hydrocarbon deposits on its way to the surface. The
geology of the area suggests the hydrocarbons might be about 2-3km
below the surface.
the water nears the sea floor the dissolved carbon dioxide is
released as bubbles. Matthew said a good analogy is a bottle of fizzy
drink – taking the lid off releases the pressure and produces
are other deep hydrothermal systems around New Zealand such as Hanmer
Springs and Rapaki
Lyttleton Harbour. Rapaki Springs began producing gas as well as
larger quantities of warm water following the February 2011
in the water
from NIWA, has also measured levels of methane in seawater samples
that Matthew collected from Hope Springs.
is “an awful lot of methane dissolved in the seawater,” said
Matthew, “the highest levels in New Zealand seawater that Cliff’s
ever measured.” This may be because the Hope Springs are in much
shallower water than other similar spring systems, and the methane
hasn’t been diluted by passing through a deep water column.
methane supports the carbon isotope evidence for the presence of
said the liberation of gas from the seafloor following an earthquake
is not that unusual, but what makes the Hope Springs unique is that
they are in such shallow water and very accessible to the shore.
is planning further analysis, including mapping the bubbles with a
heat-sensitive thermal camera and calculating the amount of gas being
released. And he hopes the bubbles will continue to offer geo-tourism
opportunities for a small community still struggling to recover from