Nabil El-Masry

Identifying multiple eruption phases from a compound tephra blanket: an example of the AD1256 Al-Madinah eruption, Saudi Arabia

It has been drawn to our attention that the simple calculation of volume from the naïve isopachs (Fig. 2) by means of the Pyleogram contains an error (a factor of pi). The actual volume thus calculated should be 0.0077 km. This error is not propagated into the remainder of the analysis, where volumes were calculated via direct numerical integration from the contours imputed from our model (Fig. 12). These are far more extensive than those in Fig. 2, particularly in the West, East and especially South directions. Hence the volume calculated for these is approximately a factor of 3 larger.

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.

Geosite of a steep lava spatter cone of the 1256 AD, Al Madinah eruption, Kingdom of Saudi Arabia

UNESCO promotes geoconservation through various programs intended to establish an inventory of geologically and geomorphologically significant features worldwide that can serve as an important database to understand the Earth’s global geoheritage. An ultimate goal of such projects globally is to establish geoparks that represent an integrated network of knowledge transfer opportunities, based on a specific array of geological and geomorphological sites able to graphically demonstrate how the Earth works to the general public. In these complex geoconservation and geoeducational programs, the identification of significant geological and geomorphological features is very important. These are commonly referred to as ‘geosites’ or ‘geomorphosites’, depending on whether the feature or processes the site demonstrates is more geological or geomorphological, respectively. The Kingdom of Saudi Arabia is an extraordinary place due to its arid climate and therefore perfect exposures of rock formations. The Kingdom is also home to extensive volcanic fields, named “harrats” in Arabic, referring particularly to the black, basaltic lava fields that dominate the desert landscape. Current efforts to increase awareness of the importance of these volcanic fields in the geological landscape of Arabia culminated in the first proposal to incorporate the superbly exposed volcanic features into an integrated geoconservation and geoeducation program that will hopefully lead to the development of a geopark named, “The Harrat Al Madinah Volcanic Geopark” [1]. Here we describe one of the extraordinary features of the proposed Harrat Al Madinah Volcanic Geopark, namely a steep lava spatter cone formed during a historical eruption in 1256 AD.

Geology and geochemistry of Late Quaternary volcanism in northern Harrat Rahat, Kingdom of Saudi Arabia: implications for eruption dynamics, regional stratigraphy and magma evolution

Abstract Harrat Rahat (<10 Ma) is one of the largest volcanic fields on western Arabia. In the north of the field, some of the youngest volcanic centres evolved through either point-like, complex or multiple aligned vents (i.e. along fissures), and have pyroclastic cones, lapilli fall deposits and/or lava flows associated with them. The products reflect dominantly Hawaiian eruptions, and only one centre experienced phreatomagmatism. Results from new 3He surface-exposure dating provide constraints on stratigraphy of the youngest (<0.3 Ma) products. The rocks are compositionally alkali-basalt and hawaiite, with intra-plate basalt (prevalent mantle (PREMA)) affinity. Each eruption displays a distinct whole-rock composition in an overall linear trend. We suggest that the magma source for each centre is similar, and that composition of the products is different due to different degrees of fractionation. In a single eruption, the magma that reaches the surface first is the least evolved, with the most evolved magma erupting last. We also found that the most primitive magmas erupt less explosively. We think that the degree of magma evolution might correlate with ascent times, assuming that the more evolved magma spent more time en route. We suggest that magma ascent time is likely to be longer than that of other more primitive intra-plate basalts. Supplementary material: Whole-rock chemistry results, mineral chemistry results and fractional crystallization modeling data are available at https://doi.org/10.6084/m9.figshare.c.3488988

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.