Preliminary report on the July 10–11, 2015 explosive eruption at Volcán de Colima: Pyroclastic density currents with exceptional runouts and volume

http://dx.doi.org/10.1016/j.jvolgeores.2015.11.022Reporte preliminar acerca de una de las últimas etapas eruptivas de Volcán de Colima, análisis realizado a partir de técnicas de percepción remotaOn July 10–11, 2015 an eruption occurred at Colima volcano produced 10.5 km long pyroclastic density currents (PDCs) along the Montegrande, and 6.5 km long along the San Antonio ravines. The summit dome was destroyed and a new crater excavated and breached to the south. This new breach connects to a narrow channel that descends along Colima's southern flank and was used by a subsequent lava flow. The Montegrande PDCs represent the longest and hottest flow of this type recorded during the past 30 years but are still smaller in comparison to the 15-km long PDCs produced during the 1913 Plinian eruption. Data obtained from field reconnaissance, lahar monitoring stations, and satellite imagery suggest that at least six PDCs occurred. The two largest PDCs (H/L 0.2) were able to surmount topographic barriers or bends. Based on field reconnaissance and digital elevation models extracted from SPOT satellite imageries we estimate a minimum volume for the valley-pond and distal fan deposits of 4.5 × 106 m3. After one week, the deposits were still hot with burning trees on the surface and millimeter-sized holes from which fumes were emanating. The juvenile components of the deposits consist of gray dense blocks and vesicular dark-gray blocks and bombs with bread-crust textures and cooling joints. The mineral association of these rocks consists of plagioclase + clinopyroxene + orthopyroxene + FeTi-oxides ± olivine and resorbed hornblende in a dark glassy matrix that corresponds to an andesitic composition.CONACY

A normalized difference lahar index based on Terra/Aster and Spot 5 images: an application at Colima Volcano, Mexico

For the evaluation of recent lahar deposits, we propose a Normalized Difference Lahar Index (NDLI) based on the analysis of eigenvectors of Principal Components Analysis (PCA) applied to Terra/Aster and Spot 5 multispectral images of the Colima Volcano. As a result, the normalization of bands 3 and 4 of both sensors produces the best results for the spectral enhancement of lahar deposits with respect to the rest of the components in the image. Such normalization is the basis for the NDLI. For the validation of results in this case of study, fieldwork was carried out based on ground control points (GCP) on the hillsides of Colima Volcano. Likewise, to corroborate the validity of the NDLI, we performed enhancements and segmentations of lahar deposits using a Variant of Principal Component Analysis (VPCA) and a region growth algorithm. These enhancements and segmentations were compared with results from the NDLI. The application of the NDLI allows the identification of new deposit units and new alluvial fan forms from recurrent lahar deposits, principally on Montegrande and San Antonio ravines on the south flank of the volcano. The application of remote sensing techniques, as the introduction of the NDLI, is a useful tool for the identification of lahar deposits associated to recent volcanic activity

Spatio-temporal land-use changes in the Colima-Villa de Álvarez metropolitan area, and their relationship to floodings

Demographic growth and consequent land-use changes are consid - ered one of the main factors causing inundations in many cities in de - veloping countries. During the last decade, the city of Colima, Mexico, has suffered from an increase in flooding events. These episodes mostly occurred during tropical rainstorms associated to hurricanes (such as Jova in 2011, Manuel in 2013, and Patricia in 2015, all with average accumulated rainfall of 200 mm in 24 h), as well as during short- duration, high-intensity rainfall events at the beginning of the rainy season. To define the mechanisms leading to the increased occurrence of floodings, a space-time analysis of land-use changes, coupled with the characterization of natural and urban soils, are presented here for the Colima metropolitan area. Three land-use categories were created: native land (N1), urban land (N4), and cultivated land (N5). Each of these categories has subcategories depending on vegetative cover and/ or level of urbanization. SPOT imagery acquired in 2005, 2009, and 2015 was classified to analyze the spatial and temporal changes in land use. Thirty-two soil samples representative of different land uses were analyzed to obtain their physical and chemical properties such as granulometry, bulk and particle densities, porosity, and organic matter content. Hydraulic conductivity tests were performed in situ using a drip-infiltrometer device. The temporal and spatial analysis of SPOT images revealed that most changes in land use correspond to urban area and cultivated land, the former showing an increase and the latter a drastic decrease, especially towards the northern part of the city, where urban growth is evident for the 20052009 period. Analyzed soils from cultivated land have the highest permeability, and engineered soils correspond to the least permeable soils in the area; consequently, replacement of agriculture with housing has significant impacts on the rainfall-runoff process. These results indicate that as more permeable land area is substituted by disturbed urban soils, the infiltration capability will be reduced, leading to increasing flooding frequency in the Colima-Villa de Álvarez metropolitan area. To prevent and reduce the disruptive im - pact of inundation in the Colima metropolitan area, it is recommended to have adequate management of land-use change and to conserve the permeable areas around the city. In addition, it is necessary to revise the hydraulic infrastructure of the existing urban areas and to properly define the most suitable locations for future ones. Avoiding develop - ment in flood-prone areas through planning and zoning ordinances may reduce loss of life and damage to property