New gas sensors confirm gas output continues from Te Maari (Tongariro)
Following the August 2012 eruptions from Te Maari large amounts of volcanic gas were emitted. Sometimes the output of sulphur dioxide (SO2) was over 5-8 kg per second (430-700 tons per day). However with time this decreased and we were not able to measure it from our standard airborne platform. We needed to find a new ground based technology. Based on our experiences from White Island (Whakaari) we chose to go with scanning FLYSPEC, a new version of the miniDOAS that we have at White Island. The new equipment has been installed collaboratively by DOC and GeoNet. Data from this type of equipment is used by our volcano team to assess the status of the volcano and set the Volcanic Alert Level.
Volcanic gas is derived from the molten material (magma) that drives an eruption, so it is one of the few data that can give us direct information about the magma under an active volcano. The types of gas present and the amounts are very useful. Detecting and measuring gas is not easy. A correlation spectrometer (COSPEC) which was initially designed to measure industrial pollutants, are now routinely used by volcano observatories to measure volcanic gas emissions.
The spectrometer is designed to measure the concentration of sulphur dioxide (SO2) in the volcanic plume that is emitted from the volcano. The miniDOAS and FLYSPEC are adaptions of this technology into smaller instruments. They work by analysing the ultraviolet light absorbed by the SO2 molecules in the volcanic plume. Hence we have to install them ‘under the plume’ to get data. The variable wind directions in NZ make this a challenge.
At Te Maari we have installed two scanning FLYSPECS to improve our chances of detecting the SO2 in the volcanic plume. When the local wind is blowing the gas plume over our instruments we are able to get data and work out how much gas is coming from the active vents. We get useable data about 40-50% of the time. Since September 2015 the gas output has dropped below 0.1 kg per second (8.6 tons per day) and is often just at the limits of detection. This is good for Tongariro National Park users as it confirms the volcano is slowly going back to sleep and risk from eruptions has decreased.
Tongariro is a large andesitic volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu volcano) to Te Mari crater (including vents at the present-day location of Ngauruhoe) were active during several hundred years around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. North Crater stratovolcano, one of the largest features of the massif, is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the NW side by a small explosion crater. The youngest cone of the complex, Ngauruhoe, has grown to become the highest peak of the massif since its birth about 2500 years ago. The symmetrical, steep-sided Ngauruhoe, along with its neighbor Ruapehu to the south, have been New Zealand’s most active volcanoes during historical time.
April 22 , 2016.Tongariro , New Zealand :
Sources : Geonet ( Brad Scott) , GVP.
Photos : Photovolcanica