Volcanic hazards mapping using aircraft, satellite, and digital topographic data: Pico de Orizaba (Citlatepetl), Mexico

Pico de Orizaba (Citlaltepetl) is a hazardous volcano located in the easternmost part of the TransMexican Volcanic Belt. Similar to other dormant stratovolcanoes, several population centers are at risk from gravity-driven volcanic flows, including debris avalanches and debris flows. The volcano has produced numerous debris avalanche/flow deposits in the past. Some were related to hydrothermal alteration and catastrophic edifice collapses, while others were triggered by eruptions and earthquakes.; This four-part study demonstrates the combined use of multispectral/hyperspectral image processing, laboratory spectral analysis of samples, digital terrain analysis, GIS modelling and fieldwork for both assessing and mapping debris avalanche/flow-related hazards at Pico de Orizaba. Of particular use was aircraft hyperspectral data such as Airborne Visible/Infrared Remote Imaging Spectrometer (AVIRIS), satellite multispectral data in the form of a Landsat TM scene and digital topographic data in the form of a National Imagery and Mapping Agency (NIMA) DEM.; Part one of this study focuses on the characteristics and origin of a historically large debris flow northeast of the volcano. This debris flow devastated populated areas in the Huitzilapan-Pescados River valley and was triggered by a tectonic earthquake in the upstream karst source area. The origin of the clay-sized fraction of this cohesive debris flow was halloysite- and opal-bearing andisols that overlay mafic lava flows and rhyolite ash deposits.; Part two of this study uses AVIRIS data to map hydrothermal alteration zones on the edifice of Pico de Orizaba. Areas containing advanced-argillic alteration mineral assemblages correspond to the modern summit cone and the remnants of the second constructional phase of the volcano. Areas containing silicic alteration mineral assemblages were identified mainly by the presence of abundant secondary iron-bearing minerals. These areas correspond to the remnants of the first constructional phase of the volcano.; Part three of this study uses digital topographic data to map cross-sectional extents and magnitudes of debris flow terrace deposits in several drainages around the volcano. This information is used to forecast potential inundation levels at cities and towns located along river valleys that have been affected by debris flows of various sizes in the past.; Part four of this study investigates the origin of the three largest debris avalanche/flow deposits east of the volcano. This was done by using several analytical methods including: X-Ray Diffraction (XRD), Infrared reflectance spectroscopy (IR-Spectra) and Scanning Electron Microscopy (SEM), to compare clay-sized fractions of the deposits with hydrothermally altered source areas on the volcano.