Stevens, N.F.; Scott, B.J. 2002 Changes in the Ngauruhoe summit fumarole field, 1999-2001, from Landsat data . Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 2002/30 11 p.
Abstract: Observations during field visits in recent years suggested that the Ngauruhoe fumarole field was growing. In this study, the usefulness of archived visible satellite data was explored for measuring planimetric changes in snowmelt coinciding with the Ngauruhoe fumarole field. Landsat 7 ETM+ images from September 29th 1999, August 14th 2000 and September 9th 2001 were examined, using an image processing methodology designed for discriminating snow from bare rock. The extent of the snowmelt is clear in the 1999 and 2001 images, and the Ngauruhoe fumarole field has expanded northwards. Negligible snowmelt was observed in the August 14th 2000 scene, although an aerial photograph taken the following day shows snowmelt clearly. This difference in snow cover is perhaps due to a large deposit of snow recorded on August 13th-14th 2000, which may not have melted through until August 15th 2000, and demonstrates one of the drawbacks of this methodology. Although the expansion of the fumarole field between 1999 and 2001 does not necessarily signify an imminent eruption, monitoring for future changes is important. Future acquisition of Landsat 7 (or similar) data is a possibility, but a more reliable method to track such changes in snowmelt would be to acquire photographs during autumn, winter and spring, during the routine flights about the Tongariro Volcanic Centre. (auth)