Mapping hydrothermal alteration products on Mt Tongariro using multispectral satellite data, XRD analysis and reflectance spectroscopy : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science, at Massey University, Palmerston North, New Zealand
The threat of a major collapse/landslide from a volcanic cone is a primary hazard of
concern in the Tongariro National Park. The geologic record at Ruapehu and
Tongariro volcanoes shows that past debris flows (lahars) have often contained a
high proportion of alteration products. The present flanks of volcanoes in the
Tongariro National Park have several hydrothermally altered zones that could be
sources of future collapses. The purpose of this study was to assess the overall
extent of alteration products and map altered zones on Mount Tongariro using field
spectroscopy, X-Ray Diffraction analysis and analysis of satellite data.
Hyperspectral data from the Hyperion sensor on the EO1 satellite and multi-spectral
data from the Aster sensor on the EOS (Terra) satellite platform were acquired for
the study area. The low signal to noise ratio of the Hyperion dataset meant the data
was not suitable for analysis. The Aster data was chosen as it contains bands above
1500nm, the wavelength range where diagnostic abosorptions for minerals appear.
There were analysis issues with the Aster scene but once the questionable bands
were removed, areas of hydrothermal alteration were successfully identified and
Mineral samples were collected from a variety of visually unique areas and
reflectance spectra recorded using a portable spectroradiometer, along with the GPS
locations. These samples were identified in the laboratory using the Spectral Analyst
tool in ENVI and comparing them to the USGS, JPL and JHU mineral spectral libraries.
The identification results from the field spectra and traditional X-Ray Diffraction
(XRD) analysis of the samples were used to ground truth the satellite data. XRD was
used to identify the alteration products and confirm the findings of the field spectra
analysis. This enabled the selection of accurate end-members that were used to
perform a classification of the imagery of the study area. The XRD and field
spectroscopy data correlated well, and only the problem of several mixed minerals
hindered a direct corelation.
The alteration products form some of the least stable zones on the volcano. Smectite
was identified in many of the samples which is a swelling/shrinking clay associated
with volcanic faluire. Identifying these zones provides crucial information in the
production of a new lahar hazard map for the Tongariro National Park. The northern
flank of the Te Maari craters was found to contain hydrothermal alteration products
and this areas has generated many colapses in the past.
Identifying large areas or mapping out larger zones of hydrothermal alteration
products was not possible due to the small surface expression of some of the
hydrothermal fields and also the atmospheric/signal to noise interference with the
main satellite sensors. The mixed method approach used in this study remains useful
and ongoing attempts at working with new hyperspectral data as it comes available
should be investigated.