Quantitative volcanic susceptibility analysis of Lanzarote and Chinijo Islands based on kernel density estimation via a linear diffusion process
Risk management stakeholders in high-populated volcanic islands should be provided with the latest high-quality volcanic information. We present here the first volcanic susceptibility map of Lanzarote and Chinijo Islands and their submarine flanks based on updated chronostratigraphical and volcano structural data, as well as on the geomorphological analysis of the bathymetric data of the submarine flanks. The role of the structural elements in the volcanic susceptibility analysis has been reviewed: vents have been considered since they indicate where previous eruptions took place; eruptive fissures provide information about the stress field as they are the superficial expression of the dyke conduit; eroded dykes have been discarded since they are single non-feeder dykes intruded in deep parts of Miocene-Pliocene volcanic edifices; main faults have been taken into account only in those cases where they could modified the superficial movement of magma. The application of kernel density estimation via a linear diffusion process for the volcanic susceptibility assessment has been applied successfully to Lanzarote and could be applied to other fissure volcanic fields worldwide since the results provide information about the probable area where an eruption could take place but also about the main direction of the probable volcanic fissures.
Spatio-temporal hazard assessment of a monogenetic volcanic field, near México City
Abstract An eruption in the Younger Chichinautzin Monogenetic Field (YCMF) represents a major volcanic hazard to Mexico City, one of the most important cultural and financial centres in Latin America where >20 million people live. The birth of a new volcano in this field could severely impact the economic and social activity of the country. To identify where and when the next eruption in the YCMF could occur, the temporal and spatial distribution of past events were analyzed, assuming that future activity will follow a similar tendency. We reconstructed ages for the non-dated monogenetic volcanoes based on cone morphometric analyses correlated with published radiometric dates (R2 = 0.901). A Grid Probability Analysis (GPA) was applied for the first time in a monogenetic volcanic field to calculate the spatio-temporal probability of a new volcano forming. The field was divided into 96 cells of 5 × 5 km, which is the maximum observed distance between volcanoes. The recurrence rate and probability of a new volcano forming was then calculated for each cell using the estimated ages and a spatio-temporal probability map was constructed for the field. There are at least three areas with higher probability, concentrated in the central and northwestern parts of the study area. These areas are close to the volcanoes with the most recent eruptions and an eruption in these zones could seriously impact Mexico City and nearby areas as did Xitle and Chichinautzin volcanoes ~2000 years ago.
Magnetic imaging of the feeding system of oceanic volcanic islands: El Hierro (Canary Islands)
SUMMARY El Hierro is the youngest of the Canary Islands, a volcanic archipelago in the central Atlantic, near the African coast. The subaerial part of the island shows the characteristic shape of three convergent ridges that has been interpreted as a triple-arm rift system. At least four giant landslides formed wide, horseshoe embayments that separate these ridges. Recent studies based on high-resolution bathymetry, however, showed that the submarine rift structure is much more complex. We analysed an aeromagnetic anomaly data set acquired in 1993 by the Spanish National Geographic Institute in order to obtain a structural model of the island from a magnetic point of view. A digital elevation model of the volcanic edifice was divided into a mesh of prismatic cells, each of them with a top corresponding to the topographic height (or bathymetric depth in the marine area) and a bottom at a constant depth of 4000 m below sea level. A three-dimensional (3-D) inversion algorithm and forward modelling along representative profiles provided us with a magnetization distribution containing valuable information about the inner structure of the island. The magnetic model cast new light on the rift structure of El Hierro. In particular, high magnetization values have been mainly interpreted as intrusive complexes on which rift zones are rooted. Their location confirms the hypothesis of a complex rift structure in the marine area. The inverse magnetization that characterizes the NE submarine rift area implies that this part of the volcanic edifice formed during the Matuyama and, therefore, predates the NW submarine rift zone, which is normally magnetized. The N‐S rift zone extending southwards from the island seems to be shifted to the west with respect to the bathymetric high in this area. This result suggests that the original rift zone was located in the area where the highest magnetizations presently occur so that the present morphology may reflect the westward collapse of the original ridge. In addition, very low magnetizations characterize the areas affected by giant landslides, indicating that magnetic anomalies can provide important constraints on the distribution of these catastrophic events.