Atef A. Qaddah

Volcanic Geotopes and Their Geosites Preserved in an Arid Climate Related to Landscape and Climate Changes Since the Neogene in Northern Saudi Arabia: Harrat Hutaymah (Hai’il Region)

Maars and tuff rings are some of the most common volcanic landforms on Earth. They are inferred to be the product of the explosive interaction between rising magma (mostly basaltic) and various groundwater sources or surface water bodies. Maar and tuff ring volcanoes are commonly associated with extensive scoria cone fields that are fed by dispersed volcanic vents, providing access to the surface for magma over a long period of time (thousands to millions of years’ timescale). The presence of maar and tuff ring volcanoes, therefore, is an important signifier of the availability of water from sub-surface and/or surface water sources. As environmental conditions change over time, the groundwater table, as well as surface water availability, can change dramatically and this is likely be reflected in the type of volcanoes formed on the surface. Such changes are the most graphic and visible in volcanic fields that are today located in arid environments, where the presence of young volcanoes formed through interactions with water demonstrates how the environment can change over geological timescales. Therefore, these areas have high geoeducational values and can contribute to our understanding of how external (water sources controlled by climatic factors) and internal (magmatic) forces can shape the style of volcanism of a volcanic field. Harrat Hutaymah is one of the excellent locations where there is great abundance of maars and tuff rings. They are located in an area dominated today by various types of deserts. Harrat Hutaymah, therefore, demonstrates the global geological changes that can affect the style of volcanism and hence the resulting volcanic landscape. The richness of the region in archaeological sites and early settlements indicates the importance of this region for the early evolution of civilizations in the Middle East, which is likely to have been enhanced and/or modified by similar environmental changes over a much smaller timescale. Harrat Hutaymah provides a firm basis to demonstrate global changes through its volcanic heritage that are easily accessible and well exposed.

Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes (Harrat Kishb, Saudi Arabia)

Al Wahbah Crater is one of the largest and deepest Quaternary maar craters in the Arabian Peninsula. It is NW-SE-elongated, ∼2.3 km wide, ∼250 m deep and surrounded by an irregular near-perpendicular crater wall cut deeply into the Proterozoic diorite basement. Very few scientific studies have been conducted on this unique site, especially in respect to understanding the associated volcanic eruption processes. Al Wahbah and adjacent large explosion craters are currently a research subject in an international project, Volcanic Risk in Saudi Arabia (VORiSA). The focus of VORiSA is to characterise the volcanic hazards and eruption mechanisms of the vast volcanic fields in Western Saudi Arabia, while also defining the unique volcanic features of this region for use in future geoconservation, geoeducation and geotourism projects. Al Wahbah is inferred to be a maar crater that formed due to an explosive interaction of magma and water. The crater is surrounded by a tephra ring that consists predominantly of base surge deposits accumulated over a pre-maar scoria cone and underlying multiple lava flow units. The tephra ring acted as an obstacle against younger lava flows that were diverted along the margin of the tephra ring creating unique lava flow surface textures that recorded inflation and deflation processes along the margin of the post-maar lava flow. Al Wahbah is a unique geological feature that is not only a dramatic landform but also a site that can promote our understanding of complex phreatomagmatic monogenetic volcanism. The complex geological features perfectly preserved at Al Wahbah makes this site as an excellent geotope and a potential centre of geoeducation programs that could lead to the establishment of a geopark in the broader area at the Kishb Volcanic Field.

GIS-based site-suitability modeling for seismic stations

Spatial planners and geographers are interested in decision problems that are based on geographically defined alternatives. These alternatives are evaluated with respect to their spatial arrangement. A geographic information system-based methodology in conjunction with the multi-criteria decision analysis (MCDA) was used to evaluate alternative site suitability to identify priority sites for seismic stations setting up. Comprehensive analyses were conducted in order to identify the best location for seismic stations based on given criteria. By considering the environmental objectives and the economical feasibility, the criteria were developed in the GIS environment then individual satisfaction degrees for each alternative location are calculated using weighted overlay tool. By selecting appropriate weights, the MCDA provides effective tools for seismic station site suitability that may serve to improve the performance and capabilities of seismic networks. Several alternative comparisons were carried out to evaluate the confidence in the model and helped in the priority areas refinements.The application of this method in Harrat Al-Madinah volcanic field, Saudi Arabia, provided a suitability map for the area. Five selective sites were proposed and found to coincide with accessible areas appropriate for seismic station installation in the northeastern, central and southern parts of the region. A seismic noise survey was carried out additionally in different places within the area and indicated that the proposed areas exhibit high signal-to-noise ratios with respect to the low-priority areas. GIS-MCDA was used to model the suitability map for seismic stations setting up.Analyses were conducted in Harrat Rahat volcanic field for new seismic stations.Alternatives comparisons are carried out to evaluate the confidence in the model.The proposed sites exhibited low-PSD values of ambient noise.

Magnetic and gravity data analysis of Rahat Volcanic Field, El-Madinah city, Saudi Arabia

Abstract The Rahat volcanic field represents one of the widely distributed Cenozoic volcanic fields across the western regions of the Arabian Peninsula. Its human significance stems from the fact that its northern fringes, where the historical eruption of 1256 A.D. took place, are very close to the holy city of Al-Madinah Al-Monawarah. In the present work, we analyzed aeromagnetic data from the northern part of Rahat volcanic field as well as carried out a ground gravity survey. A joint interpretation and inversion of gravity and magnetic data were used to estimate the thickness of the lava flows, delineate the subsurface structures of the study area, and estimate the depth to basement using various geophysical methods, such as Tilt Derivative, Euler Deconvolution and 2D modeling inversion. Results indicated that the thickness of the lava flows in the study area ranges between 100 m (above Sea Level) at the eastern and western boundaries of Rahat Volcanic field and getting deeper at the middle as 300–500 m. It also showed that, major structural trend is in the NW direction (Red Sea trend) with some minor trends in EW direction.