Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks... more Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hy...
<p>GPS data suggest that the NW South America corner forms a semi-rigid and... more <p>GPS data suggest that the NW South America corner forms a semi-rigid and distinct tectonic block (Northern Andean Block) drifting at 0.6 cm/yr NE-ward along regional dextral strike-slip faults that bound an oceanic terrane accreted in Late Cretaceous times to western Ecuador and Colombia. This is consistent with an average 0.76 cm/yr Quaternary slip rate obtained from field investigation along the main strike-slip faults. Nevertheless, pure thrust tectonics characterize the external (eastern) Northern Andes deformation front from Ecuador to Colombia. Thus, the relevance of strike-slip versus thrust tectonics during Cenozoic times and their relation with oceanic terrane accretion are unclear. </p><p>The incertitude on the magnitude of a hypothetical Cenozoic strike-slip deformation is reflected by the variable interpretations of the tectonic regime that generated the Ecuadorian Interandean Valley. This tectonic depression, blanketing the eastern side of the Cordillera Occidental, has been variably considered as due to extensional, thrust, or strike-slip tectonics.</p><p>Paleomagnetism may represent an important tool to unravel the Cenozoic tectonic history of the Northern Andean Block, as peculiar patterns of vertical axis rotations arise from strike-slip and thrust tectonics.</p><p>Here we report on the paleomagnetism of 31 mid-upper Eocene to upper Miocene mainly volcanic sites from the Cordilleras Occidental and Real of southern Ecuador. Eleven sites show that the western Cordillera Occidental underwent a 24°±10° clockwise (CW) rotation with respect to South America after late Miocene, while no rotation occurred further east. We relate the regional CW rotation to the emplacement of the Cordillera Occidental nappe onto the continental sediments of the Interandean Valley. As rotation and continental sedimentation onset ages are similar, we interpret such tectonic depression as a narrow flexural basin formed ahead of the advancing nappe front.</p><p>Previous authors find a post-Cretaceous 28°±9° CW rotation of the Coastal forearc that is statistically indistinguishable from the 24°±10° Neogene CW rotation documented by us in the Cordillera Occidental and Interandean Valley, implying that the whole W Ecuador Andean chain was detached and rotated over a mid-crustal detachment during the last 10 Ma. Eocene-Miocene paleomagnetic inclination values are systematically consistent with those expected for South America, thus excluding latitudinal terrane drift. Our results show that thrust tectonics prevailed over strike-slip displacement in the southern Ecuadorian Andes during the late Cenozoic.</p><p>Finally, we note that the orogenic reentrant-salient sequence of the Nazca trench / Andean chain from northern Chile to Ecuador mimics closely the margin of the Archean–Paleoproterozoic Amazonian Craton and other minor cratons of South America. Considering our results on a continental scale and in combination with previous paleomagnetic data from the Andean belt we infer that the stiff crust of the Amazonian Craton behaved as a foreland indenter, hampered inland deformation propagation, and caused the formation of what we call the “Ecuadorian Orocline”, arisen by opposite-sign nappe rotations around the Craton apex.</p>
Bulletin of the Seismological Society of America, 2018
Starting on the day after the mainshock, we mapped in the field and compiled all the available ob... more Starting on the day after the mainshock, we mapped in the field and compiled all the available observations on earthquake environmental effects (EEEs) caused by the Mw 7.8 subduction earthquake that hit the coastal region of Ecuador on 16 April 2016 (the Pedernales earthquake). These effects include: (a) permanent ground deformation, (b) open cracks, (c) liquefaction, (d) landslides, and (e) tsunami waves. We use these observations to evaluate the macroseismic field of the Environmental Seismic Intensity (ESI\u201007) scale and compare our results with published macroseismic data collected using traditional damage\u2010based intensity scales. We found systematic difference in the assessed earthquake intensity and in the intensity attenuation with distance. A comparison of our dataset with the macroseismic data of six instrumental large\u2010subduction earthquakes that occurred between Ecuador and Chile suggests that, for the Pedernales earthquake, the ESI\u201007 works better in the near field, whereas damage\u2010based scales are more reliable in the far field. Therefore, we generate a single integrated intensity dataset for the Pedernales earthquake, including data measured with the European Macroseismic Scale 1998 (EMS\u201098), the modified Mercalli (MM) scale, and the ESI\u201007 scale. This new integrated macroseismic field provides reliable and comparable information on the seismogenic source, suggesting that a similar approach could be successfully applied to refine the source model of past subduction earthquakes in Ecuador and elsewhere
Journal of Volcanology and Geothermal Research, 2016
Abstract Preceded by 14 days of intense seismic activity, a new eruption started on the south fla... more Abstract Preceded by 14 days of intense seismic activity, a new eruption started on the south flank of Mt. Etna, Sicily (Italy) early in the morning of 11 March 1669 opening up a series of NS eruptive fissures. The eruption is one of the most destructive flank eruptions of Etna in historical times; it lasted until 11 July, and was characterized by simultaneous explosive and effusive activity during the first three months, while only lava flow output in the last month. The activity built up the large composite cone of the “Monti Rossi” at the lower end of the eruptive fissures, and caused severe damage to the nearby inhabited areas. The prolonged effusive activity generated lava flows for > 15 km, which destroyed several villages and the western part of the town of Catania before reaching the coastline and entering the sea. In this paper, we examine the tephro-stratigraphy of the products of the explosive activity. An in-depth analysis of historical accounts was used to define the chronology of the main eruptive phases (precursors, explosive activity and initial effusive phenomena). The geology of the cone and of the fallout deposits were defined through a field survey over a distance of 5 km from the Monti Rossi. Textural (grain-size, morphological, componentry), density and petrological analyses of tephra samples provided a sedimentological, physical and geochemical characterization of erupted products. Integrating ground and historical data enabled defining the evolution of the cone, identifying and correlating four main cone-forming units. By tracing the dispersal map of the main distal tephra beds (the finer ash being dispersed mainly to the NE as far as Calabria and to the south of Sicily and the 10-cm isopach of the total deposit covering an area up to 53 km2), we estimated a total tephra fallout volume, including the Monti Rossi cone, of about 6.6 × 107 m3 (about 3.2 × 107 m3 DRE). The 1669 event can be considered an archetype of the most hazardous expected eruption on the densely populated flanks of Etna. Reconstructing the eruptive chronology and styles of the 1669 eruption therefore, represents the basic data to assess volcanic hazard from eventual similar flank events in the future.
Proceedings of the 17th LACCEI International Multi-Conference for Engineering, Education, and Technology: “Industry, Innovation, and Infrastructure for Sustainable Cities and Communities”, 2019
The 3D point clouds obtained from the low-cost, remote, and precise SfM (Structure from Motion) t... more The 3D point clouds obtained from the low-cost, remote, and precise SfM (Structure from Motion) technique allow the extraction and acquisition of discontinuities and their characteristics both manually, with the compass and virtual ruler of the Cloud Compare software, and automatically with the DSE (Discontinuity Set Extractor) program, which is faster, more accurate, and safe. Some control plans have been used, which basically consist of identifying one or several fractures and taking measurements on them manually and remotely. The difference between both types of measurements is around 5°, which we believe is reasonable since it is within the precision and repeatability of measurements with a geologist’s compass. This work analyzes the stability of six slopes (five excavated and one natural) by applying five different analysis methodologies based on the rock mass classification system (SMR, RHRSmod, and Qslope), kinematic analysis, and analytical analysis (limit equilibrium). Thei...
Geological lineaments are linear or curvilinear surfaces that are considered a superficial expres... more Geological lineaments are linear or curvilinear surfaces that are considered a superficial expression of discontinuities on the earth’s surface. The extraction of lineaments from remotely sensed satellite data is one of the most frequently used applications of remote sensing in geology. This study focuses on the semi-automatic extraction of lineaments in the Girón–Santa Isabel basin using a Topographic Position Index (TPI). The lineaments were extracted in the PCI Geomatics 2016 software and analyzed in the ArcGIS and Rockworks software. Statistical and density map analyses of the lineaments were performed; then, these results were interpreted to obtain the geological lineaments. Finally, a bibliographic verification was carried out, and structures such as faults and folds were defined. The total number of geological lineaments was 76, and 71 of them were defined as faults, the longest with a length of 33 km. It was determined that the preferential orientation of the lineaments is N...
El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápago... more El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical para...
Latin American journal of sedimentology and basin analysis, 2019
The coastal sector of Ecuador, on the area comprised between Salango and Jama (Manabi Province), ... more The coastal sector of Ecuador, on the area comprised between Salango and Jama (Manabi Province), is characterized by the presence of whitish to grey, centimeters to meters thick ash deposits associated to secondary rain-triggered lahars. The ash deposits, outcropping far to 160 km from the nearest volcanic vents, varied from parallel stratified fine rich ash to a massive lithic-rich fine-rich ash to a massive lithic breccia tuff and a faintly stratified lapilli-rich tuff debris flows. Sharp contacts, very fine ash laminated layers and sand and silt layers interbedded with volcanic ash beds confirmed that multiple lahar events affected the area related with secondary remobilization of the fall ash deposits. Rain events generated the multiple pulses both in short time and after large periods. The presence of human remains confirmed also that this kind of events strongly affected the ancient populations (Mantena) present on the coastal sector of Ecuador. This study confirms that the co...
The cavities or lava tubes in the Galapagos Islands were formed by the differential cooling of th... more The cavities or lava tubes in the Galapagos Islands were formed by the differential cooling of the basaltic flow of the volcanoes surrounding these islands. In this article, a stability analysis was carried out to determine the degree of safety of different lava tubes using three methods: two empirical ones based on geomechanical classifications and one strain–strain (Hoek–Brown failure criterion). The methodology used consisted of the following phases: (i) compilation of information based on existing geomechanical mapping; (ii) geomechanical classification of the rock mass using Barton’s Q index and rock mass rating; (iii) steady state qualification using the geotechnical index of cavities (GCI); (iv) numerical modeling applying the Hoek–Brown criterion; (v) comparison of methodology and discussion of the results. The data obtained indicate that the methodologies used to evaluate the stability of the lava tubes have high reliability since they allowed the characterization of the di...
Few moderate-to-strong earthquakes associated with active and capable geological faults have been... more Few moderate-to-strong earthquakes associated with active and capable geological faults have been documented for the southern coastal region of Ecuador. The seismic record of Ecuador initiates with the Guayaquil earthquake in 1787 (Mw 6.5), followed by the 1943 (Mw 6.2), and the most recent one in 1980 (Mw 6.1). The available data is insufficient to evaluate the seismic hazards associated with faults capable of generating seismic events of magnitude Mw≥6.0 in the region. Also, earthquakes of minor magnitudes can be disregarded as they do not induce significant ground coseismic effects. In this context, this study presents a catalog of geological faults, delineating 40 segments of capable and active faults on the sea floor of the Gulf of Guayaquil and inland segments of Guayas, Santa Elena, and El Oro provinces. This methodological approach estimates a variety of seismicity levels ranging between Mw 6.2 and Mw 7.2, with rock peak ground accelerations between 0.24 g and 0.41 g. These ...
In areas characterized by many volcanoes, identifying the source of a deposit may not be trivial.... more In areas characterized by many volcanoes, identifying the source of a deposit may not be trivial. This becomes much more complicated when looking for the source of a debris avalanche deposit (DAD), the common products of catastrophic volcanic edifice collapses. To overcome this problem, in this work a methodology is proposed based on the integration of texture features and areal distribution of the deposit, comparison between the petrog-raphy of the coarser clasts within the DAD and of the proximal products, grain-size analysis, and the volumetric estimations of the deposit and the volume missing from the volcanic edifice. This methodology has been tested to a DAD occurred near the city of Ibarra (Imbabura Province; Northern Ecuador), having a controversial source. Two main volcanic edifice are located in proximity of the DAD, the Cubilche volcano (3826 m.a.s.l.), located immediately south of and east of the colossal dormant Imbabura volcano. The former displays a sharp horseshoe-shaped scar towards the north and inside this post-collapse edifice, that we name old Cubilche volcano (OCV), is located the young Cubilche volcano (YCV) that refilled a portion of the collapse scar and partially covered the southern flank of the OCV. Detailed knowledge of Cubilche volcano is critical because of its close proximity and interspersed activity with Imbabura volcano. In fact, Imbabura most recent edifice was built over the northwestern slope of the OCV and partially covered it. Recent studies linked the studied DAD to both Imbabura volcano as a product of its northern sector collapse, as well as neighboring Cubilche volcano. Our data points to Cubilche as the most likely source for this DAD. A perspective view of the shaded relief image of the present day OCV shows that the morphology of the volcano is well-preserved on its southern, eastern, and western flanks. This allows us to reconstruct the morphology of the OCV previous to the collapse through interpolation of elevation and altitude data of preserved flanks. A DEM of the present day topography was used for extrapolating the morphology. Using similar methodology, the post collapse base of the amphitheater was reconstructed by removing the relief of the present day YCV. The reconstructed topography of the OCV shows that it could have been a symmetric cone, reaching a maximum elevation of ~4100 m.a.s.l. with a lack volume of ~3.5 km 3. Based on this scenario, the deposit originated from the OCV main collapse should have a volume N3–3.5 km 3 in accordance to the volume calculated for the studied DAD.
Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks... more Wide areas of the Southern sector of Ecuador are characterized by Cretaceous mafic volcanic rocks, pervasively altered by a propylitic mineralogical assemblage with epidote, chlorite, and quartz with minor titanite, illite and prehnite. These propylitically altered rocks host significant gold mineralization in veins, deeply exploited in the last decades. Porphyry Au-Cu deposits also occur in the area. This work focuses on the study of this propylitic alteration to assess the genetic conditions and the relation with the distance from the porphyry system, through the chemical composition of the secondary minerals (particularly trace elements in epidote and chlorite) and fluid inclusion data. The aim is to improve knowledge of the trace element geochemistry of secondary minerals in propylitic alteration and their relationship to the causative porphyry systems. The results of this work indicate that alteration affecting the rocks of the Pallatanga Fm. can be related to the propylitic hy...
<p>GPS data suggest that the NW South America corner forms a semi-rigid and... more <p>GPS data suggest that the NW South America corner forms a semi-rigid and distinct tectonic block (Northern Andean Block) drifting at 0.6 cm/yr NE-ward along regional dextral strike-slip faults that bound an oceanic terrane accreted in Late Cretaceous times to western Ecuador and Colombia. This is consistent with an average 0.76 cm/yr Quaternary slip rate obtained from field investigation along the main strike-slip faults. Nevertheless, pure thrust tectonics characterize the external (eastern) Northern Andes deformation front from Ecuador to Colombia. Thus, the relevance of strike-slip versus thrust tectonics during Cenozoic times and their relation with oceanic terrane accretion are unclear. </p><p>The incertitude on the magnitude of a hypothetical Cenozoic strike-slip deformation is reflected by the variable interpretations of the tectonic regime that generated the Ecuadorian Interandean Valley. This tectonic depression, blanketing the eastern side of the Cordillera Occidental, has been variably considered as due to extensional, thrust, or strike-slip tectonics.</p><p>Paleomagnetism may represent an important tool to unravel the Cenozoic tectonic history of the Northern Andean Block, as peculiar patterns of vertical axis rotations arise from strike-slip and thrust tectonics.</p><p>Here we report on the paleomagnetism of 31 mid-upper Eocene to upper Miocene mainly volcanic sites from the Cordilleras Occidental and Real of southern Ecuador. Eleven sites show that the western Cordillera Occidental underwent a 24°±10° clockwise (CW) rotation with respect to South America after late Miocene, while no rotation occurred further east. We relate the regional CW rotation to the emplacement of the Cordillera Occidental nappe onto the continental sediments of the Interandean Valley. As rotation and continental sedimentation onset ages are similar, we interpret such tectonic depression as a narrow flexural basin formed ahead of the advancing nappe front.</p><p>Previous authors find a post-Cretaceous 28°±9° CW rotation of the Coastal forearc that is statistically indistinguishable from the 24°±10° Neogene CW rotation documented by us in the Cordillera Occidental and Interandean Valley, implying that the whole W Ecuador Andean chain was detached and rotated over a mid-crustal detachment during the last 10 Ma. Eocene-Miocene paleomagnetic inclination values are systematically consistent with those expected for South America, thus excluding latitudinal terrane drift. Our results show that thrust tectonics prevailed over strike-slip displacement in the southern Ecuadorian Andes during the late Cenozoic.</p><p>Finally, we note that the orogenic reentrant-salient sequence of the Nazca trench / Andean chain from northern Chile to Ecuador mimics closely the margin of the Archean–Paleoproterozoic Amazonian Craton and other minor cratons of South America. Considering our results on a continental scale and in combination with previous paleomagnetic data from the Andean belt we infer that the stiff crust of the Amazonian Craton behaved as a foreland indenter, hampered inland deformation propagation, and caused the formation of what we call the “Ecuadorian Orocline”, arisen by opposite-sign nappe rotations around the Craton apex.</p>
Bulletin of the Seismological Society of America, 2018
Starting on the day after the mainshock, we mapped in the field and compiled all the available ob... more Starting on the day after the mainshock, we mapped in the field and compiled all the available observations on earthquake environmental effects (EEEs) caused by the Mw 7.8 subduction earthquake that hit the coastal region of Ecuador on 16 April 2016 (the Pedernales earthquake). These effects include: (a) permanent ground deformation, (b) open cracks, (c) liquefaction, (d) landslides, and (e) tsunami waves. We use these observations to evaluate the macroseismic field of the Environmental Seismic Intensity (ESI\u201007) scale and compare our results with published macroseismic data collected using traditional damage\u2010based intensity scales. We found systematic difference in the assessed earthquake intensity and in the intensity attenuation with distance. A comparison of our dataset with the macroseismic data of six instrumental large\u2010subduction earthquakes that occurred between Ecuador and Chile suggests that, for the Pedernales earthquake, the ESI\u201007 works better in the near field, whereas damage\u2010based scales are more reliable in the far field. Therefore, we generate a single integrated intensity dataset for the Pedernales earthquake, including data measured with the European Macroseismic Scale 1998 (EMS\u201098), the modified Mercalli (MM) scale, and the ESI\u201007 scale. This new integrated macroseismic field provides reliable and comparable information on the seismogenic source, suggesting that a similar approach could be successfully applied to refine the source model of past subduction earthquakes in Ecuador and elsewhere
Journal of Volcanology and Geothermal Research, 2016
Abstract Preceded by 14 days of intense seismic activity, a new eruption started on the south fla... more Abstract Preceded by 14 days of intense seismic activity, a new eruption started on the south flank of Mt. Etna, Sicily (Italy) early in the morning of 11 March 1669 opening up a series of NS eruptive fissures. The eruption is one of the most destructive flank eruptions of Etna in historical times; it lasted until 11 July, and was characterized by simultaneous explosive and effusive activity during the first three months, while only lava flow output in the last month. The activity built up the large composite cone of the “Monti Rossi” at the lower end of the eruptive fissures, and caused severe damage to the nearby inhabited areas. The prolonged effusive activity generated lava flows for > 15 km, which destroyed several villages and the western part of the town of Catania before reaching the coastline and entering the sea. In this paper, we examine the tephro-stratigraphy of the products of the explosive activity. An in-depth analysis of historical accounts was used to define the chronology of the main eruptive phases (precursors, explosive activity and initial effusive phenomena). The geology of the cone and of the fallout deposits were defined through a field survey over a distance of 5 km from the Monti Rossi. Textural (grain-size, morphological, componentry), density and petrological analyses of tephra samples provided a sedimentological, physical and geochemical characterization of erupted products. Integrating ground and historical data enabled defining the evolution of the cone, identifying and correlating four main cone-forming units. By tracing the dispersal map of the main distal tephra beds (the finer ash being dispersed mainly to the NE as far as Calabria and to the south of Sicily and the 10-cm isopach of the total deposit covering an area up to 53 km2), we estimated a total tephra fallout volume, including the Monti Rossi cone, of about 6.6 × 107 m3 (about 3.2 × 107 m3 DRE). The 1669 event can be considered an archetype of the most hazardous expected eruption on the densely populated flanks of Etna. Reconstructing the eruptive chronology and styles of the 1669 eruption therefore, represents the basic data to assess volcanic hazard from eventual similar flank events in the future.
Proceedings of the 17th LACCEI International Multi-Conference for Engineering, Education, and Technology: “Industry, Innovation, and Infrastructure for Sustainable Cities and Communities”, 2019
The 3D point clouds obtained from the low-cost, remote, and precise SfM (Structure from Motion) t... more The 3D point clouds obtained from the low-cost, remote, and precise SfM (Structure from Motion) technique allow the extraction and acquisition of discontinuities and their characteristics both manually, with the compass and virtual ruler of the Cloud Compare software, and automatically with the DSE (Discontinuity Set Extractor) program, which is faster, more accurate, and safe. Some control plans have been used, which basically consist of identifying one or several fractures and taking measurements on them manually and remotely. The difference between both types of measurements is around 5°, which we believe is reasonable since it is within the precision and repeatability of measurements with a geologist’s compass. This work analyzes the stability of six slopes (five excavated and one natural) by applying five different analysis methodologies based on the rock mass classification system (SMR, RHRSmod, and Qslope), kinematic analysis, and analytical analysis (limit equilibrium). Thei...
Geological lineaments are linear or curvilinear surfaces that are considered a superficial expres... more Geological lineaments are linear or curvilinear surfaces that are considered a superficial expression of discontinuities on the earth’s surface. The extraction of lineaments from remotely sensed satellite data is one of the most frequently used applications of remote sensing in geology. This study focuses on the semi-automatic extraction of lineaments in the Girón–Santa Isabel basin using a Topographic Position Index (TPI). The lineaments were extracted in the PCI Geomatics 2016 software and analyzed in the ArcGIS and Rockworks software. Statistical and density map analyses of the lineaments were performed; then, these results were interpreted to obtain the geological lineaments. Finally, a bibliographic verification was carried out, and structures such as faults and folds were defined. The total number of geological lineaments was 76, and 71 of them were defined as faults, the longest with a length of 33 km. It was determined that the preferential orientation of the lineaments is N...
El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápago... more El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical para...
Latin American journal of sedimentology and basin analysis, 2019
The coastal sector of Ecuador, on the area comprised between Salango and Jama (Manabi Province), ... more The coastal sector of Ecuador, on the area comprised between Salango and Jama (Manabi Province), is characterized by the presence of whitish to grey, centimeters to meters thick ash deposits associated to secondary rain-triggered lahars. The ash deposits, outcropping far to 160 km from the nearest volcanic vents, varied from parallel stratified fine rich ash to a massive lithic-rich fine-rich ash to a massive lithic breccia tuff and a faintly stratified lapilli-rich tuff debris flows. Sharp contacts, very fine ash laminated layers and sand and silt layers interbedded with volcanic ash beds confirmed that multiple lahar events affected the area related with secondary remobilization of the fall ash deposits. Rain events generated the multiple pulses both in short time and after large periods. The presence of human remains confirmed also that this kind of events strongly affected the ancient populations (Mantena) present on the coastal sector of Ecuador. This study confirms that the co...
The cavities or lava tubes in the Galapagos Islands were formed by the differential cooling of th... more The cavities or lava tubes in the Galapagos Islands were formed by the differential cooling of the basaltic flow of the volcanoes surrounding these islands. In this article, a stability analysis was carried out to determine the degree of safety of different lava tubes using three methods: two empirical ones based on geomechanical classifications and one strain–strain (Hoek–Brown failure criterion). The methodology used consisted of the following phases: (i) compilation of information based on existing geomechanical mapping; (ii) geomechanical classification of the rock mass using Barton’s Q index and rock mass rating; (iii) steady state qualification using the geotechnical index of cavities (GCI); (iv) numerical modeling applying the Hoek–Brown criterion; (v) comparison of methodology and discussion of the results. The data obtained indicate that the methodologies used to evaluate the stability of the lava tubes have high reliability since they allowed the characterization of the di...
Few moderate-to-strong earthquakes associated with active and capable geological faults have been... more Few moderate-to-strong earthquakes associated with active and capable geological faults have been documented for the southern coastal region of Ecuador. The seismic record of Ecuador initiates with the Guayaquil earthquake in 1787 (Mw 6.5), followed by the 1943 (Mw 6.2), and the most recent one in 1980 (Mw 6.1). The available data is insufficient to evaluate the seismic hazards associated with faults capable of generating seismic events of magnitude Mw≥6.0 in the region. Also, earthquakes of minor magnitudes can be disregarded as they do not induce significant ground coseismic effects. In this context, this study presents a catalog of geological faults, delineating 40 segments of capable and active faults on the sea floor of the Gulf of Guayaquil and inland segments of Guayas, Santa Elena, and El Oro provinces. This methodological approach estimates a variety of seismicity levels ranging between Mw 6.2 and Mw 7.2, with rock peak ground accelerations between 0.24 g and 0.41 g. These ...
In areas characterized by many volcanoes, identifying the source of a deposit may not be trivial.... more In areas characterized by many volcanoes, identifying the source of a deposit may not be trivial. This becomes much more complicated when looking for the source of a debris avalanche deposit (DAD), the common products of catastrophic volcanic edifice collapses. To overcome this problem, in this work a methodology is proposed based on the integration of texture features and areal distribution of the deposit, comparison between the petrog-raphy of the coarser clasts within the DAD and of the proximal products, grain-size analysis, and the volumetric estimations of the deposit and the volume missing from the volcanic edifice. This methodology has been tested to a DAD occurred near the city of Ibarra (Imbabura Province; Northern Ecuador), having a controversial source. Two main volcanic edifice are located in proximity of the DAD, the Cubilche volcano (3826 m.a.s.l.), located immediately south of and east of the colossal dormant Imbabura volcano. The former displays a sharp horseshoe-shaped scar towards the north and inside this post-collapse edifice, that we name old Cubilche volcano (OCV), is located the young Cubilche volcano (YCV) that refilled a portion of the collapse scar and partially covered the southern flank of the OCV. Detailed knowledge of Cubilche volcano is critical because of its close proximity and interspersed activity with Imbabura volcano. In fact, Imbabura most recent edifice was built over the northwestern slope of the OCV and partially covered it. Recent studies linked the studied DAD to both Imbabura volcano as a product of its northern sector collapse, as well as neighboring Cubilche volcano. Our data points to Cubilche as the most likely source for this DAD. A perspective view of the shaded relief image of the present day OCV shows that the morphology of the volcano is well-preserved on its southern, eastern, and western flanks. This allows us to reconstruct the morphology of the OCV previous to the collapse through interpolation of elevation and altitude data of preserved flanks. A DEM of the present day topography was used for extrapolating the morphology. Using similar methodology, the post collapse base of the amphitheater was reconstructed by removing the relief of the present day YCV. The reconstructed topography of the OCV shows that it could have been a symmetric cone, reaching a maximum elevation of ~4100 m.a.s.l. with a lack volume of ~3.5 km 3. Based on this scenario, the deposit originated from the OCV main collapse should have a volume N3–3.5 km 3 in accordance to the volume calculated for the studied DAD.
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Papers by Maurizio Mulas