Gas

When molten material (magma) moves into a volcano it gives off volcanic gas emissions which are measured regularly at our volcanoes. There are several techniques which include measurement done from an aircraft and on the ground. The four primary techniques, two airborne and two ground-based are outlined below.

The COSPEC mounted to the port side of a light aircraft.

Diagram showing how COSPEC looks up at the plume.

The Lycor and InfraScan equipment.

Diagram showing how the aircraft tracks through the gas plume for Lycor measurements.

Making soil gas measurements.

MiniDOAS installation at White Island.

Airborne Gas Monitoring

COSPEC

A Correlation Spectrometer (COSPEC) measures the absorption of ultraviolet light by SO₂, so the SO₂ content of the volcanic gases is determined by flying under the gas plume (at right angles to the wind direction) and looking up through it.

Plume Contouring

The aircraft flies through the volcanic gas plume at different altitudes. A pump inside the aircraft sucks in the gases and the Lycor and Infrascan instruments measure the concentration of carbon dioxide (CO₂), sulphur dioxide (SO₂) and hydrogen sulphide (H₂S).

Ground Based Gas Monitoring

Soil Gas Flux Measurements

Gas emitted by volcanic systems can also seep up through the soil in the area surrounding a volcano. These soil gas emissions are measured with a soil gas flux meter. A round metal accumulation chamber is placed on the ground and the gas emitted from the soil is measured in the back-pack analyser. The soil gases we measure are carbon dioxide (CO₂) and hydrogen sulphide (H₂S).

Soil gas flux measurements can be used to track changes in the volcano. Regular measurements are made at White Island. Measurements of soil gas flux have also been used at Raoul Island, Ngauruhoe and Tongariro in response to eruptions or signs of volcanic unrest.

Soil gas flux measurements are also used in geothermal areas such as Rotorua to map the geothermal area and determine the risks to public health posed by gases.

MiniDOAS

Sulphur dioxide (SO₂) emissions at White Island are also measured by a permanent MiniDOAS installation (Miniature Differential Optical Absorption Spectrometer). The MiniDOAS instrument uses a UV spectrometer to measure the absorption of ultraviolet light by SO₂ gas in the atmosphere. At White Island, two MiniDOAS instruments work together to profile the plume.