Nabil El-Masry

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

Granitoid rocks of Um Qeisum–El-Regeita area include quartz diorite, granodiorite, quartz monzonite, hornblende biotite granite, quartz syenite, and biotite granite. These rocks are chemically classified as subalkaline, I-type granitoids. Granodiorite and quartz monzonite are metaluminous to peraluminous have trace element characteristics of subduction-related, volcanic-arc granites (VAG). Biotite granites show, however, some characteristics of within-plate granites (WPG). Parameters calculated using zirconium saturation thermometer and Al-in-hornblende barometer, indicate that the minimum temperature attained during crystallization of the granitoid rocks ranged between 778 and 819°C, whereas the Crystallization pressure for quartz monzonite ranged between 0.71 and 1.61 kbar, i.e. corresponds to depths between 2.30 to 5.32 kilometer. Biotite, muscovite, and hornblende in the granodiorites and quartz monzonite were analyzed by electron microprobe spectrometry. The obtained results in...

ABSTRACT Harrat Rahat represents one of the widely distributed Cenozoic volcanic fields across the western regions of the Arabian Peninsula. Its 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 the aeromagnetic data of the northern part of Harrat Rahat volcanic field including the location of historical eruption. We also carried out ground gravity survey to integrate with the aeromagnetic data to estimate the thickness of the lava flow and to delineate the subsurface structures of the study area using various geophysical methods, such as Tilt Derivative, Source Edge Detection, and Analytic signal. Results indicated that the thickness of the lava flow in the study area ranges between 0 m at the borders of the Harrat to about 750 m at its center with average depth of 270 m. They also showed that the area is dominated by a NNW-trending set of faults. The isopach map of the area markedly revealed a NW-trending graben (~30 km long) parallel to the main trend of the Red Sea rift.

The dominant volcanism in the Harrat Rahat is the effusion of large basaltic lava flows. This often means that tephra falls are an overlooked component of the hazard assessment for this area. In the periodically windy environment of the Harrat Rahat that also suffers rare flash floods, distal tephra deposits are generally not well preserved. Their absence is deceiving, especially considering the presence of large scoria cones (such as several that are known as Jabal al Maalsa), which attest to large-scale tephra producing eruptions in the field. Distinctive widespread tephra fall deposits are best described and studied around the AD1256 chain of craters. This eruption apparently took place over at least 52 days and involved several periods of tephra fall with local eye-witnesses recording high plumes (Camp et al., 1987). This study concentrates on the eruption mechanisms and distribution of the AD1256 tephras in order to provide quantitative limits on this hazard for the Harrat Rahat.

Harrat Rahat is a volcanic field located in the centre of an aligned series of such fields parallel to the Red Sea, on the western margin of the Arabian Peninsula. Harrat Rahat is one of the biggest volcanic fields (Camp and Roobol, 1989) and comprises more than 950 volcanoes (Runge et al.; 2013, this volume) associated with extensive lava flow fields (Camp and Roobol, 1989). Its geological history spans from 10 Ma until historical times, with the last three eruptions occurring in 641, 1256 and 1293 AD (Camp et al., 1987; Camp and Roobol, 1989; Ambraseys et al., 2005). Compositionally, Harrat Rahat has erupted lavas from basaltic to trachytic composition, including hawaiites, mugearites and benmorites (Moufti et al., 2012). In northern Harrat Rahat, the most recent eruptions have been predominately effusive with the exception of the 641 AD eruption which started with phreatomagmatic activity (Moufti et al., 2013a). Erupted composition has been predominately basaltic, with some compo...

Western Saudi Arabia is tectonically considered as a region of low seismic activity. However, historical and instrumental records reflect some potentiality of earthquake and volcanic activities for the global importance of Al-Madinah City and surrounding areas, it was important to investigate the current state of ground motion affecting this region in light of the historical eruption of AD 1256 and the seismic swarm of 1999 in Harrat Rahat and the seismic swarm of 2009 in Harrat Ash Shaqa (Lunayyir), which forced the evacuation of more than 40,000 of the inhabitants of Al-Ays Town and its surroundings, some 220 km to the northwest of Al-Madinah City. This study is an attempt to develop peak ground velocity (PGV) and acceleration (PGA) maps for western Arabia using four different empirical ground motion relations. We integrated a large dataset merging the current seismicity that has occurred in the western Arabia with those of historical earthquakes and volcanic activities. This study shows that the maximum PGA and PGV values are found in the Gulf of Aqaba with average values of 310 cm/s 2 and 52 cm/s, respectively. The Red Sea rift zone comes next with average PGA values between 150 and 230 cm/s 2 and PGV values of 24–41 cm/s. Al-Madinah City exhibits an average value of 22 cm/s 2 and 6 cm/s, for PGA and PGV, respectively.

A gravity survey was undertaken to cover the King Abdulaziz University’s campus (~ 8 km2) as a pilot project funded from Deanship of Scientific Research (DSR). In the current study, 408 gravity stations were collected using the Scintrex CG5 gravimeter and a DGPS system, covering the whole university’ campus. The aim of this survey is to produce the first microgravity map for the King Abdulaziz University campus and image the subsurface conditions which help in the future constructions. Gravity surveys are carried out for 16 days, nights, and weekends when the campus has less traffic noise. Data were processed using conventional gravity data reduction technique, and then microgravity map for the campus was generated. Data were subject to geophysical filters such as edged detection (e.g., horizontal gradient) and depth estimation (e.g., Euler deconvolution, and 3D inversion) to image the subsurface conditions. Results indicate that bedrock relief surface is located at about 150 m. Some cracks/fractures were traced/detected underneath the surface in various directions. The results also indicate that the university campus is located on high-density rock zones, giving more stability to buildings.

The peculiar environment of Sharm El-Sheikh area, upon which its tourism industry is based, is undoubtedly threatened by different sources of pollution that are directly related to the rapid growth of the city, the influx of millions of tourists every year, and to the increased maritime activities in the Gulf of Aqaba and the Red Sea. The 1999’s oil spillage in Sharm El-Maya Bay represented an extreme example of one of these threats. Although the spillage itself was promptly contained, only few studies were conducted to investigate the source of the pollution and its spatial and temporal variations. The present study, therefore, aimed to determine the extent of the pollution, its spatial variation, and its source. Three different types of samples were collected and analyzed for petroleum hydrocarbons. They included sediment samples from the headland, and samples of seabed sediments and seawater from the subtidal zone. Total hydrocarbons were determined using conventional gravimetric...

ABSTRACT In this study we introduce the results of the seismic waveform analysis of the data recorded by the Vorisa seismic network in the period 2012-2013. The Vorisa seismic network consists of 8 borehole stations and 5 surface stations deployed in Harrat Al-Madinah area. The borehole stations are installed 120m deep and consist of 3-component 2Hz velocity sensors and Reftek acquisition system (DAS 130), Data are stored in binary Passcal format with 250 samples/sec. The surface stations, installed in appropriate accessible areas, are Taurus instruments with compact trillium 120 sec sensors and store data in miniSEED format with the same sampling rate. After the comprehensive analysis of the data recorded by this network we have triggered a number of events. About 350 local events (including earthquakes and blasts, M>-1.0), ~200 regional events (M>5.1), and more than 180 teleseismic events (M>6.0) are detected in the period 4/2012-7/2013. Although the borehole stations are not of broadband type, the teleseismic data is particularly investigated to cover the shortage of local earthquakes detected in this area. The validity of the teleseismic arrival time data is confirmed by a comparison with the surface stations data which are of broadband types. This data is used jointly with the local data in seismic tomography study (Abdelwahed et al., 2013, this volume). In this study, the earthquakes occurred in and around Harrat Rahat are investigated through integrated studies of source parameters and focal mechanism studies. It is found that the swarm area critically consists of significant partial melting material which is clearly observed in the recorded waveforms. Outside the swarm area, no significant seismicity or activities are found. Most of the local events recorded are mainly occurred in the swarm area accompanied with a small number of small magnitude (M<1.5) earthquakes inside the area. The resulted source parameters and focal mechanisms estimated in this study reveals that the swarm area events have a strike slip fault mechanism trending N-W direction which is consistent with the major trend of the Harrat Rahat volcanic field.

ABSTRACT Erratum to: Bull Volcanol (2015) 77: 6DOI 10.1007/s00445-014-0890-yIt 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 km3. 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.

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 for...

ABSTRACT 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.

ABSTRACT A “lava morphotype” refers to the recognizable and distinctive characteristics of the surface morphology of a lava flow after solidification, used in a similar way to a sedimentary facies. This classification method is explored on an example volcanic field in the Kingdom of Saudi Arabia, where copious lava outpourings may represent an important transition between monogenetic and flood basalt fields. Here, young and well-preserved mafic lava fields display a wide range of surface morphologies. We focussed on four post-4500 yrs. BP lava flow fields in northern Harrat Rahat (<10 Ma) and propose a framework for describing systematic changes in morphotypes down-flow. The morphotypes give insight into intrinsic and extrinsic parameters of emplacement, rheology and dominant flow behavior, as well as the occurrence and character of other lava structures. The Harrat Rahat lava flow fields studied extend up to 23 km from the source, and vary between 1–2 m and 12 m in thickness. Areas of the lava flow fields are between ∼32 and ∼61 km2, with individual flow field volumes estimated between ∼0.085 and ∼0.29 km3. They exhibit Shelly-, Slabby-, and Rubbly-pahoehoe, Platy-, Cauliflower-, and Rubbly-a’a, and Blocky morphotypes. Morphotypes reflect the intrinsic parameters of: composition, temperature, crystallinity and volatile-content/vesicularity; along with external influences, such as: emission mechanism, effusion rate, topography and slope control of flow velocity. One morphotype can transition to another in individual flow-units or lobes and they may dominate zones. Not all morphotypes were found in a single lava flow field. Pahoehoe morphotypes are related to the simple mechanical disaggregation of the crust, whereas a’a morphotypes are related to the transitional emergence and subsequent transitional disappearance of clinker. Blocky morphotypes result from fracturing and auto-brecciation. A’a morphotypes (i.e. platy-, cauliflower-, rubbly-a’a) dominate the lava flow field surfaces in northern Harrat Rahat, which suggests that core-dominated flows were predominant during flow movement. Lava structures are well-developed and well-preserved and some may be related to some morphotypes. Down-flow changes exhibit key illustrative and easy recognizable features in the lava flow fields and might provide insights into real-time monitoring of future flows in this region.

ABSTRACT 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 theMiddle 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.

The ring dyke structure of Saint Catherine is a part of the Late Precambrian alkaline batholithic phase in South Sinai. It is distinguished into two geomorphic elements: the ring dyke wall which, forms a steeply dipping elliptical intrusion commonly known as Catherina ring dyke, and the ring dyke roof, which occurs as isolated remnants of a saucer-shaped subvolcanic intrusion erroneously identified as Catherina Volcanics. The ring dyke wall and its roof, if viewed together, would form an upright cylindriform intrusion that once sealed-off a down-faulted central block of older country rocks and, in a latter time, was intruded by a pluton of fluorite-bearing biotite granite known as Catherina pluton. The emplacement of the ring dyke was preceeded by the formation of arched fractures below a collapsed caldera after a period of intense volcanicity. An isolated central block was then moved along steeply dipping funnel-shaped fractures. The fractures were passively filled with a syenitic ...

Jabal Laiq Late-Precambrian Ring Dike represents a subsurface cauldron subsidence intrusion composed of anorogenic A-type granite. It is composed of two geomorphic elements, namely, the roof and the wall. A flat-lying remnant of a saucer-shaped intrusion, less than 0.6 km2 in areal extent, distinguishes the very peak of Jabal Laiq. It is composed of a hornblende-granite and overlies a country rock comprising tonalite, epiclastics, pyroclastics, and subvolcanics. It represents the only preserved remnant of the “ring dike roof” or “the cauldron subsidence intrusion” recognized so far. The second geomorphic element occurs as a faulted steep tabular intrusion of a pyroxene-bearing hornblende-granite representing “the ring dike wall”, or shortly “the ring dike”. It is cut and displaced by NW-SE, NE-SW, and N-S orienting steeply dipping strike-slip faults. Left-lateral separations recorded along these faults indicate that different segments of “the ring dike wall” are dislocated by distan...

The peculiar environment of Sharm El-Sheikh area, upon which its tourism industry is based, is undoubtedly threatened by different sources of pollution that are directly related to the rapid growth of the city, the influx of millions of tourists every year, and to the increased maritime activities in the Gulf of Aqaba and the Red Sea. The 1999’s oil spillage in Sharm El-Maya Bay represented an extreme example of one of these threats. Although the spillage itself was promptly contained, only few studies were conducted to investigate the source of the pollution and its spatial and temporal variations. The present study, therefore, aimed to determine the extent of the pollution, its spatial variation, and its source. Three different types of samples were collected and analyzed for petroleum hydrocarbons. They included sediment samples from the headland, and samples of seabed sediments and seawater from the subtidal zone. Total hydrocarbons were determined using conventional gravimetric...

The study of the magmatic microgranular enclaves (MMEs) as relics of mafic magmas gives important information on the origin of parent magmas and their evolution. In the study area, MMEs are either concentrated at the margins of the I-type granodiorite ...

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 3 He 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.