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.
Geoheritage in the Shallow Submarine Slopes of an Oceanic Volcanic Edifice: A New Option for Diving Geotourism
Volcanic oceanic islands are large buildings that grow from the ocean floor up to their highest peaks above sea level. It is estimated that only a small part of the volcanic edifices emerge above sea level, leaving almost 90% of the volcanic structure submerged. The geology of this submerged area is mainly known from indirect geophysical studies, general and detail mapping, bathymetry, and some drill holes and different types of dredges and humanned–unhumanned submersibles. However, this information is quite poor for geoheritage studies since it does not allow a geological classification of the environment, their genesis and geoheritage value. Hence, direct observation in inner platform and coastal zones has become essential to identify submerged geological structures, rocks, sediments, pyroclastic deposits and morphologies that could be considered as part of a geoheritage inventory. In fact, underwater there are unique and representative geological elements, which in many cases are visited by divers who do not know their significance and value, since their main objective is to observe the fauna and submarine scenery. Therefore, the identification and enhancement of underwater shallow geological heritage is crucial for the development of one of the emerging resources, underwater and diving geotourism. This study contributes to the knowledge of the shallow submarine geology of Lanzarote and Chinijo Islands UNESCO Global Geopark and highlights the existence of fifteen geosites suitable for the implementation of sustainable submarine geotourism.
Sediment transport model of the southeastern Mediterranean coast
Abstract The relationship between: (a) the gradual change of the shoreline orientation in the southeastern Mediterranean from east—west to north—south, (b) the longest fetch direction of the Mediterranean (east—west), and (c) the dominant source of sediments being the Nile Delta to the west, provides a unique opportunity for construction of a model of the longshore sediment transport patterns. The input for this model consisted of: (a) two depth grids totaling 33,795 depths, and (b) nine selected wave conditions. The nine selected wave conditions were based on an analysis of the existing wave observer data, fetch considerations and storm records. The input conditions were waves from the northwest and west with wave periods of 5, 9 and 11 sec, southwest waves of limited fetch with wave periods of 5 and 9 sec, and 13-sec waves from 282.5° azimuth, potentially the largest fetch (2,400 km) direction. The 13-sec waves are both the longest waves theoretically possible and also the longest waves observed. The results show that the rate of longshore transport is larger for short-period (5 sec) than for long-period (9, 11 sec) waves, for all wave approach directions, given the same input wave heights. This is because of the larger shoreline angles of the short-period waves, due to lesser wave refraction. The results of these computations also illustrate the presence of four distinct zones of longshore sediment transport (from southwest to northeast): 1. (1) Western Zone (El Arish to Rafah), where all wave approach directions cause transport to the northeast, and therefore net transport equals gross transport. 2. (2) Central Zone (Rafah to Haifa), which is characterized by converging longshore transport nodal points that shift along the coast in response to changes in wave direction and to a lesser extent, wave period (i.e., north of the nodal point longshore transport is directed to the south, and south of the nodal point transport is directed to the north). For waves from 282.5°, the nodal point is at Netanya and for 315° at Rafah, the southern border of the central zone. 3. (3) Haifa Bay, a 20-km shoreline segment having significantly lower wave energy than the other coastal zones for all wave conditions except 5-sec waves from the northwest which cause southern transport. Even for southwest 9-sec waves, the sediment transport in this area is essentially zero due to wave refraction, and this area may be considered a sediment sink. 4. (4) Northern Zone (Akko to Rosh Haniqra) which is subject to intense wave refraction over the nearshore Akhziv Canyon, resulting in great variably of local longshore transport for most wave conditions. This model of longshore sediment transport of the southeastern Mediterranean coast explains many observed shoreline phenomena. For example, the lack of quartz sediment north of Akko, derived from the Nile River and Kurkar cliffs to the south, appears to be due to Haifa Bay which acts as a sediment sink for northward moving sand. The large differences in sediment transport between the Bardawil Lagoon (Western Zone) and Gaza (Central Zone), as evidenced by the differing sand accumulations on the southern sides of coastal constructions in these two zones, is attributed to the increasing importance of waves from the northwest in causing southwestern transport along the coast northeast of Rafah. The lack of strong indicators of transport direction (such as sediment accumulations differentially on one side of the structures) along the coast of Tel-Aviv and to the north is due to the continuously changing directions of longshore transport with changing wave conditions in the Central Zone, and to intense refraction in the Northern Zone.