Cent. Eur. J. Geosci. • 5(2) • 2013 • 254-271 DOI: 10.2478/s13533-012-0125-8

Central European Journal of Geosciences

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

Research Article

Mohammed R. Moufti1, Károly Németh1;2∗, Nabil El-Masry1 and Atef Qaddah1

1 Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80200, Jeddah, 21589, Saudi Arabia 2 Institute of Agriculture and Environment, Massey University, Private Bag 11222, Palmerston North, New Zealand

Received 30 March 2013; accepted 26 May 2013

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. Keywords: maar, tuff ring • phreatomagmatic • crater • scoria • pahoehoe • tumuli • geopark • geosite © Versita sp. z o.o.

1. Introduction Earth [1–3]. Such projects not only ensure that future generations can visit protected and preserved volcanic heritage sites, but also direct the focus of scientific research towards understanding the geological Geoconservation and geoeducation projects are value of these areas, particularly as they relate to increasingly popular in many volcanic fields on volcanic hazard education. One of the first steps in the protection and promotion of volcanic geoheritage ∗E-mail: [email protected] is to establish a comprehensive database of potential

254 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

geosites that can later be grouped and promoted in is conducting intensive research on understanding the various scientific and educational programs under the extensive intracontinental volcanic fields in western Saudi umbrella of regional and global geoparks [1, 4–9]. It is Arabia. In the first phase of the project volcanological clear that research on geoheritage sites that highlights and associated geophysical research was focused on the their regional and global value is an emerging area Al Madinah Volcanic Field (part of the Rahat Volcanic that is gaining greater respect from general end-users, Field), due to the fact that the youngest volcanic educators and researchers [10]. To identify and record the eruption in the Kingdom of Saudi Arabia took place geological heritage of geosites and/or geomorphosites about 20 km from the holy city of Al Madinah in 1256 is a complex process that is based not only on the pure AD [14–17] (Figure 1). Research on understanding the scientific value of the site but also its regional importance eruptive mechanisms of volcanoes forming the Al Madinah in terms of understanding the region’s geological Volcanic Field also highlighted the need to define the and geomorphological evolution. Some workers have geological heritage values of these volcanoes in order highlighted the fact that this process is fundamentally to provide the impetus for this site to be developed driven by 1) the experts’ categorisation of the diversity of as a volcanic geopark and the information necessary to a geosite and geomorphosite and 2) the preconceptions create associated geoconservation, geohazard education and prevailing ideas of the local population concerning and geotourism programs [18]. the geodiversity and geoconservation value of the The Al Wahbah crater is a prominent volcanic landform specific site [11]. To define appropriately a geosite’s and part of an older volcanic field, the Kishb Volcanic or geomorphosite’s geological value requires both the Field, just south of the Al Madinah Volcanic Field geological and geomorphological expertise of scientists (part of the greater Rahat Volcanic Field). There is as well as a general understanding of the importance of new interest in understanding its formation, due to the each site in the eyes of the local communities [11]. This growing public awareness that volcanoes that formed means that to successfully initiate a geoconservation, due to violent explosive eruptions, either by magma and geoeducation, and geotourism project requires not just water interaction (phreatomagmatism) or magmatic gas promotion of the scientific value of the respective sites, expansion, are hazardous. While Kishb Volcanic Field but also a survey of the local community’s views on the and Al Wahbah crater are older than the younger part of selected sites. the Al Madinah Volcanic Field, they are still fairly young and, therefore, can provide clues to understand the full Al Wahbah crater in the Kishb Volcanic Field in western spectrum of volcanic hazards that might be associated with Saudi Arabia (Figure 1), with its dramatic landscape future volcanism along the western Saudi Arabian volcanic as a huge "hole-in-the-ground", has acted as a magnet fields. Near Al Wahbah crater, other well-exposed, but to visitors long before any unofficial or official plans more remote, explosion craters are known. It seems that were initiated to define and categorize its geological these explosion craters were formed by a combination heritage value. Al Wahbah crater has also played an of phreatomagmatic and magmatic explosive eruptions important role in the life of local Bedouin communities, and; therefore, they can act as excellent demonstration who utilized its sheltered location for terraced agriculture sites to show the variability of eruption styles that form in its upper crater wall (Figure 2A). Tourists started small-volume (monogenetic) volcanoes. In this respect Al visiting Al Wahbah crater long before it was "discovered" Wahbah crater is a key volcanic feature that can help by tourist authorities who built the local access road define one of the most potentially hazardous volcanic to its crater rim very recently. The region was the phenomena facing Saudi Arabia. Al Wahbah crater’s subject of geological mapping in the late 1980s which volcanic heritage and its exceptional landscape value has culminated in the production of geological maps, as (including its aesthetic value) provide the justification for well as scientific reports on the volcanic evolution and identifying it as a locally and internationally significant volcanic stratigraphy, of the Harrat Kishb (harrat means geosite that deserves future protection. black lava fields in ) [12]. Al Wahbah crater later on appeared in a scientific report that highlighted its touristic potential without presenting the information in a way that allowed for it to be used to promote its geoheritage 2. Harrat Kishb value [13]. Currently, an ongoing international research project between the King Abdulaziz University (KAU), Harrat Kishb (also referred to as Kishb Volcanic Field Jeddah, Kingdom of Saudi Arabai and the University of - KVF) is a monogenetic volcanic field spread over an Auckland (AU) in New Zealand (aligned with Massey area of 6000 km2 [12]. Based on a limited number University (MU) in New Zealand), funded by KAU, of mostly K-Ar age determinations, the field has been

255 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

Figure 1. A) Cenozoic volcanic fields in eastern Saudi Arabia form a broad zone of volcanic fields. In the northern part of is the location where the last volcanic eruption in the Kingdom of Saudi Arabia took place in 1256 AD. A star marks the location of Al Wahbah crater. B) An overview map of Harrat Kishb from a Google Earth image. Two additional tuff rings (TR1 and TR2) are also significant volcanic craters. An additional volcano Aslaj (As) is a spectacular location of mantle xenoliths and could also be included as a significant geotope in the development of a geopark in the region. C) Google Earth image of the Al Wahbah maar crater (22◦54’4.18” N; 41◦8’23.30” E) shows its ”hole-in-the-ground” morphology. Please note the how the young lava flow in its northern side was diverted by the tephra ring.

active since 2 Ma and its youngest volcanic landforms typical bimodal volcanic field that consists of volcanoes are inferred to be as young as 4.5-2 ka [12]. The formed by eruption of alkaline olivine basalt-basanitic Harrat Kishb is one of the extensive volcanic fields that magma, with minor hawaiite/olivine transitional basalts form a belt from Syria to , parallel with and and phonolitic magma [12]. The alkaline basaltic to about 150-250 km inland from, the Red Sea coastline basanitic suits commonly host mantle nodules, primarily (Figure 1). Harrat Kishb has been determined to be a peridotite lherzolite in composition [12, 19–22]. The

256 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

Figure 2. A) Al Wahbah crater hosts vegetation as a result of its sheltered nature. The microclimate, as well as some ground-water inflow through the porous pre-maar lava foot and top breccias, meant that the crater has been a site for local agriculture in the past and a refuge for local wildlife, making Al Wahbah not only geologically but also biologically a special location. B) Typical scoria cones aligned in the northern margin of the Harrat Kishb C) Lava surface features on top of a pahoehoe lava flow diverted by the Al Wahbah tephra ring. Arrow points to the location of the Al Wahbah crater.

extensive basaltic lava flow sheets are inferred to be unconfined pahoehoe to transitional pahoehoe-to-aa lava primitive, but not primary, melt; their origin was inferred fields (Figure 2B). The sizes of the scoria cones are to be controlled mainly by various degrees of partial similar to other scoria cones worldwide, with landform melting [12]. Fractional crystallisation was concluded features such as partial flank collapse, partial rehealing to be an important process in the production of more or lava spatter collar-preserved erosional features that evolved composition melts [12]. While field evidence shows are common elsewhere [24–26]. The lava flow fields that mixing between differently sourced melts was limited, host spectacular lava surface textures (Figure 2C), such some locations showed that shallow level mixing of distinct as slabby/rubbly pahoehoe [27], shelly pahoehoe [28] melts did take place and formed transitional, mostly or transitional pahoehoe-to-aa lava textures [29] with lava spatter dominated, successions with tephriphonolitic tumuli [30, 31], and inflation and deflation features [28] compositions [12]. The volcanic landforms of the Harrat or extensive lava tubes. Lava tubes are exceptional Kishb are diverse and many of their volcanoes follow features of the Harrat Kishb and significant geosites, strong alignments, suggesting some sort of structural they have been systematically studied and recorded to control on the volcanism [12, 23]. The main volcano in a comprehensive database [32–34]. Based on these types of the Harrat Kishb are scoria cones and lava new volcanological studies, the geoheritage value of spatter cones, many of them associated with extensive the volcanism that formed the Harrat Kishb has now

257 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

started to be identified and recorded. This short note cone gradually transforms to scoriaceous lapilli, ash beds, provides some fundamental geological basis to justify the and their reworked units, as expected along the marginal significance, as well as the unique geological value, of zone of any scoria cone [36]. The facies architecture of the the Al Wahbah crater and also provides a first order half-sectioned scoria cone suggests that it was formed due approach to design a scientifically-based geoconservation, to Strombolian-style explosive eruptions and intermittent geoeducation and geotourism program that can be aligned lava fountaining, based on the abundance of lava spatter with other similar projects proposed in the volcanic fields in the host scoriaceous deposits [36, 37]. Along the crater of Western Saudi Arabia. wall localized lava spatter deposits overly lava flows, indicating that prior to crater formation Hawaiian lava fountaining occurred along the vents that likely followed 3. Al Wahbah Crater Geotope a fissure alignment of roughly NW-SE. Recently obtained Ar/Ar geochronology has also confirmed that the pre-maar scoria cone (1.147 +/-0.004 Ma) is slightly younger than Geotopes are complex geological features that represent the underlying lava flow sheets (1.261 +/- 0.021 Ma - numerous individual geosites, which together define an 1,178 +/- 0.007 Ma) [38]. This new geochronology gives interrelated and geologically diverse entity [2, 7, 35]. the formation of Al Wahbah maar the minimum age of Geotopes are often considered to be analogous to biotops, 1.147 +/- 0.004 Ma and clearly separates it from the expressing the complex nature of the naturalphenomena uppermost pre-maar lava flow emplacement period [38]. they represent. In volcanic regions, a volcano or volcanic While the chronological order of events seems to be cone can be defined as a geotope, based on the fact that it correct, the geological evidence demonstrates that the is not just a single volcanic landscape element but also a uppermost part of the pre-maar lava flow units is in close geological site that hosts a great variety of volcanic rock genetic relationship with the pre-maar scoria cone. Lava units formed through a series of volcanic eruption episodes surface textures, lava protrusions into the basal tuff ring and diverse volcanic processes. Al Wahbah crater itself tephra, as well as gradual transition from lava flows to fulfils the above mentioned criteria, with its well defined lava spatter units and clastogenic lava flows, suggest crater zone and associated tephra ring. The age of Al that the uppermost pre-maar lava flows and the pre- Wahbah is undefined, but judging by its geomorphology maar scoria cones are genetically closely related and and its stratigraphic relationship to older scoria cones and likely formed in a relatively short period in the same lava fields, as well as to the young lava fields banking over eruptive episode. Similar gradual time continuum can its tuff ring, it is of Quaternary age [12]. Maar craters be established between the scoria cone and the tuff ring are relatively rare features in the arid Arabian landscape formation, suggesting that at least the upper volcanic and with their "hole-in-the-ground" morphology they differ sequence, which includes the uppermost pre-maar lava strikingly from other volcanic landforms in the region, flows, the pre-maar scoria cone, and the capping tuff ring, adding significant and unique landscape value to the must have formed in the same eruptive episodes. Since volcanic fields of Arabia (Figure 3). Such extra landscape the recently published Ar/Ar data did not define clearly value has been argued to be an important parameter the samples’ exact locations, it is difficult to establish to consider in the process of identifying regionally and more refined stratigraphy. In addition, it cannot be internationally significant geosites and geotopes [6, 7]. Al excluded that the basal pre-maar lava flows represent a Wahbah is not only aesthetically unique but its volcanic complex lava flow stratigraphy, including lava sheets that geology is special. A half sectioned pre-maar scoria cone are clearly part of a pre-maar landscape and lava flows in its NW crater wall exposes interesting volcanic facies associated with the early evolution of the pre-maar scoria architecture between pre-maar scoria cone-building rock cone, as evidenced from field data. units and tuff ring successions associated directly with the formation and growth of the maar crater (Figure 4). The Proterozoic diorite basement is covered by at least The half sectioned scoria cone consists of alternating two basanitic lava sheets (each of them are columnar scoriaceous lapilli and bomb-bearing beds (each dm- jointed and at least 5 m in thickness) exposed ubiquitously scale thick and laterally consistent) rich in degassed bed- in the crater wall forming the immediate underlying rocks flattened lava spatter. An increase in welding towards the below the half-sectioned scoria cone (Figure 3). These centre of the scoria cone is evident in the units that are lava flows are fairly uniform in thickness, with a slight agglutinated, as well as locally rheomorphic. The base decrease from the location of the half-sectioned scoria of the scoria cone is difficult to access, but it is clear cone toward the SE. At least two major lava flows can that it is sitting over a series of pre-scoria-cone lava be distinguished that are separated by a discontinuous sheets. The distal section of the half-sectioned scoria lava foot and top breccia horizons. The topmost part

258 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

of the pre-maar lava flows consists of complex lava flow explosive eruptions that culminated in maar crater and sheets that thicken toward the pre-maar scoria cone. The tuff ring formation. A similar eruption scenario has upper lava surface of these lava flows has a pahoehoe been proposed for other maar volcanoes, such as the lava flow surface texture and suggests low viscosity flow, Crater Elegante in Sonora, Mexico [49] or several maar as recorded in some inflation features. The half-sectioned craters in the Calatrava Volcanic Field in Spain [50]. A pre-maar lava spatter/scoria cone demonstrates that the drop in the magma discharge rate is inferred to cause crater formation post-dates the initial lava shield and cone magma withdrawal below the regional ground-water table, formation (Figure3 & Figure4). allowing direct entry of ground-water in to the hot interior of the shallow plumbing system of the volcanic complex The tephra ring of Al Wahbah crater consists of about and triggering phreatomagmatic explosions that formed 20-m thick pyroclastic successions, which seem to be numerous base surges. Country rock excavation and the thicker in the NW area of the tephra ring and cover mechanical destabilisation of the basement and pre-maar the outer margin of the half-sectioned scoria cone volcanic edifices eventually led to crater floor subsidence. (Figure5). The tephra ring succession comprises a series At Al Wahbah this resulted in a large and deep maar, of dune- and cross-bedded lapilli tuff and tuff interbedded creating a very special volcanic landscape. The flat- with up to few dm-thick pyroclastic breccia horizons floored crater hosts an ephemeral lake that is filled with commonly rich in ballistically transported accidental lithic shallow saline water after occasional heavy rain fall that blocks derived from underlying lava flow units, lava can diminish quickly leaving behind salt pans and aeolian spatter successions, and fragments from the basement silt bars (Figure6). The large crater also acts as a diorites (Figure5). The entire succession is rich in "humidity trap" providing refuge for living creatures from exotic rock fragments from underlying country rocks the scorching sun, making Al Wahbah the host of a unique (Figure5). At the microscopic level, the rocks contain ecosystem. The crater rim has some advanced erosional relatively small proportions (about 20 vol % by visual features, indicating about 200 metres of retreat of the estimate) of moderately palagonitized, yellow, blocky and original tephra ring rim. Overall Al Wahbah is more low-to-moderately vesicular sideromelane glass shards, than "just" a geosite, and it is best defined as a geotope indicating that these pyroclasts formed due to sudden with numerous individual geosites. The promotion of chilling consistent with a magma-water interaction Al Wahbah maar as a geotope is part of an extensive driven phreatomagmatic explosive fragmentation [39–42]. project that has started recently to build a repository of Bedform characteristics of the tephra ring succession are volcanic geotopes and geosites in the Kingdom of Saudi typical for base surge dominated deposition, which is Arabia for geoconservation, geoeducation and geotourism characteristic for lateral moving low particle concentration purposes [14, 18]. pyroclastic density currents regardless of the cause of the explosive fragmentation and turbulent current expansion [40, 43–46]. The textural evidence to support sudden chilling of magma and its brittle fragmentation 4. Other unique volcanic explosion from the tuff ring-forming pyroclastic succession suggest, craters at Harrat Kishb however, that the tuff ring deposits around Al Wahbah crater are a direct result of phreatomagmatic explosive Al Wahbah is not the only large and broad volcanic crater eruptions similar to other maar volcanoes elsewhere [47]. in the Harrat Kishb. In the southern region of the volcanic There is no clear evidence to support a significant time field there are large volcanic craters. These locations are break between the pre-maar cone-building eruptions and difficult to access, only 4WD desert tracks can take the the tuff ring-forming base surge-dominated successions visitors to these sites. The geology of these volcanoes (Figure5), suggesting that the pre-maar scoria cone, at is fairly unknown, and only some preliminary information least the uppermost pre-scoria cone lava flow, and the is available based on reconnaissance visits to these tuff ring formation is in a time-continuum within the same locations. There are at least two large craters about 25 km eruptive episode. In this respect Al Wahbah’s eruption is to the east of Al Wahbah which hold exceptional landscape unique and differs from a usual maar formation of initial values (Figure1). These locations could be promoted as magma-water interaction-driven explosions near surface gateways to other interesting volcanoes in the interior of followed by gradual explosion locus deepening as a result the volcanic field, such as phonolitic lava domes, phonolite of gradual exhaustion of ground-water sources [48]. Al lava fields, and complex basaltic shield volcanoes with Wahbah seems to have followed an opposite eruption multiple lava pit craters. The two large craters to the evolution, starting with an initial lava shield and cone- east of Al Wahbah (referred to here as TR1 and TR2) are building phase that was intervened by phreatomagmatic well preserved constructional volcanic landforms, making

259 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

Figure 3. The Al Wahbah crater forms a typical ”hole-in-the-ground” volcanic landform and is one of the largest maar craters in the Arabian Peninsula. Star represents one of the locations where the maar tephra ring pyroclastic succession is exposed, which is accessible and could form part of a study path. Arrow points to the half-sectioned scoria cone. Dashed line in the left side of the half-sectioned scoria cone marks the base of the tephra ring deposits, while the black line shows the contact between the basal lava flows and the basement rocks.

Figure 4. Half-section of a scoria cone cut by the Al Wahbah maar crater wall in the NW side of the crater (the inner crater unconformity of the scoria cone is marked by a dashed line). An arrow points to a remnant of a thin tephra ring deposit that covered the pre-existing scoria cone flank. Dotted line marks the contact between the pre-maar scoria cone and the tephra ring deposit. A continuous line marks the contact between the pre-maar lava flows and the basement rocks.

them different from the Al Wahbah crater. TR1 and TR2 demonstrate an alternative way to form broad craters. are elongated craters sitting on a constructional volcanic TR1’s elongated crater is surrounded by a tephra ring edifice (Figure7), while Al Wahbah is clearly a "hole-in- that is composed of accidental lithic-rich lapilli tuff beds the-ground" landform, cutting deep into the pre-eruptive with dune-bedded textures indicating their pyroclastic stratigraphy (and therefore defined as a maar sensu stricto surge origin [47]. The common presence of accretionary following Lorenz’s definition from 1986). The TR1 volcano lapilli, vesicular tuff and the abundance of accidental is best defined as a broad tuff ring, with the crater lithics in this succession indicate that the eruption was outline indicating multiple crater-forming events. TR2 likely controlled by phreatomagmatic explosive events. in the south has a more symmetric crater. TR1 can be The central part of the crater rim is covered by lava accessed more easily than TR2 through an approximately spatter deposits, indicating some late stage lava spatter 30 minute ascent to its crater rim from which the elongated events through lava fountaining. The crater of TR1 hosts a crater can be examined. Therefore, TR1 is suggested complex, but small and intact, scoria cone, suggesting that to be defined as another significant geotope that can after the formation of the crater subsequent Strombolian

260 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

Figure 5. Typical base surge-dominated pyroclastic succession forming the tephra ring around the Al Wahbah maar (picture was taken from the location marked with a star on Figure 2). Note the dune-bedded base surge succession in the right hand side of the image.

Figure 6. Ephemeral lake in the Al Wahbah crater after heavy rain fall. The lake can quickly (matter of hours) evaporate leaving behind white salt pans. The image was taken from near the top of the half-sectioned scoria cone. Note the broad erosional surface (arrows) opened up on the pre-maar basement by stripping off the tephra ring deposits in the NE side of the crater (tr marks the tephra rim).

and Hawaiian style eruptions took place and formed an ash-plain, can provide a graphic example to the general intra-crater volcano in this location (Figure 7A). TR1, public to demonstrate the power and landscape modifying therefore, represents a different, but dominantly explosive, force of an explosive volcanic eruption (Figure 7B). In eruption history in comparison to Al Wahbah’s eruption this respect, TR2 is also suggested to be included in history. In addition, TR1 offers spectacular scenery, as the design of a geoeducational program based on the well as a perfect 360 degrees view to the SE sector of the volcanic features of the Harrat Kishb that could form the Harrat Kishb, justifying its assignment as a significant basis for the future establishment of a geopark in this geotope in the field. TR2, on the other hand, has no volcanic region. In the northern part of the Harrat Kishb intra-crater scoria cones and its surrounding landscape is (Figure 1), another volcanic cone is suggested to be listed covered by its eruptive products, which are under current a significant geosite with its complex geotope nature. This volcanological investigation. However, the extension of cone, called as Aslaj, is considered to be one of the main its eruptive products, which form a broad light-coloured locations of great abundance of mantle derived xenolith

261 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

Figure 7. A) The elongated crater of the TR1 cone hosts fresh black scoria cones, making the crater an exceptionally unique volcanic landscape with high aesthetic value. B) TR2 is a constructional volcanic edifice with a relatively simple, but deep crater. The surroundings of the TR2 volcano are covered by light colour ash and lapilli creating a perfect landscape to demonstrate the effect of tephra dispersal from explosive volcanic eruptions that makes this location a perfect educational site.

nodules in Western Saudi Arabia [19, 20, 51]. In this simple way. Main values has been determined along location, large (up to 50 cm across) mantle nodules can three group of variables: 1) Scientific/Educational Value be found in lapilli tuff and tuff successions, as well as in (VSE), 2) Scenic/Aesthetic Value (VSA) and 3) Protection lava flows initiated from this volcano. The fairly remote (VPr) [52]. The VSE can be further divided into Rarity, and only 4WD guided tours are recommended to visit it, Representativeness, Knowledge on geoscientific issues, and, therefore, this location would fulfil expectations for and Level of interpretation. The VSA variables have adventure tourism. been divided into Viewpoints, Surface, Surrounding landscape and nature, and Environmental fitting of sites. The VPr has been defined to consist of Current 5. Evaluation of the proposed condition, Protection level, Vulnerability, and Suitable geosites/geotopes number of visitors [52]. While this evaluation scheme contains some subjective elements, these can be reduced and/or smoothed through the use of a scale to measure Recent studies have shown that evaluating the each parameter as 0, 0.25, 0.5, 0.75 and 1 [52]. This geoheritage value of a geosite/geotope can be a evaluation scheme refers to the proposed geosite’s main complicated procedure. The most difficult issue is geoheritage values only. A high score on this scale is reducing the subjectivity of the measuring scale, as well considered to be a requirement to propose that a geosite as establishing a realistic and balanced scale along be identified as a high geoheritage value site. To refine which individual geosites/geotopes can be compared. the scale, inclusion of mainly infrastructural parameters On the other hand, any evaluation method should be (e.g. accessibility), defined as additional values, has relatively simple to perform and cover major aspects been proposed [52]. The additional values have been or variables which may influence the overall value grouped into 1) Functional values (VFn) and 2) Touristic of a single geosite/geotope. Here we have chosen values (Vtr) [52]. Functional values have been measured to apply a recently developed evaluation method, along Accessibility, Additional natural values, Additional defined as a "preliminary geosite assessment model" or anthropogenic values, Vicinity of emissive centers (e.g. GAM [52]. This method was developed on the basis main cities), Vicinity to main roads (or rail network), and of distinguishing Main Values from Additional Values Additional functional values [52]. The touristic values that can be measured relatively objectively and in a

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have been evaluated by estimating the Promotion, Annual additional scientific work at an international level would number of organised visits, Vicinity to a visitor center, be essential to enforce the status of these sites and Interpretative panels, Annual number of visitors, Tourism promote their listing as significant geoheritage value infrastructure, Tour guide services, Hostelry services, and geosites. In the case of Al Wahbah, targeted tourism Restaurant services [52]. The additional elements were marketing, including freely available information leaflets, graded in a similar way as the main elements, ranking sign-posting, information boards, or establishment of a each band to 0, 0.25, 0.5, 0.75 and 1. After evaluating local information booth, could dramatically enhance the each element, a discrimination diagram was created geoheritage and geotouristic value of the site. where the total score of the main elements was plotted against the total score of the additional element [52, 53]. The resulting score matrix can be grouped into a 12 element field from Z11, Z12, Z13 to ::: Z33 (Figure 8) 6. Conclusion by gradually increasing the main and additional element scores [52]. Naturally, geosites/geotopes with high main and additional element values (plot to the Z33 field) are The southern part of the Harrat Kishb hosts three the ideal places with high geoheritage values and are volcanoes unique among the volcanoes forming commonly listed as the main geoheritage sites of official the western Saudi Arabian Miocene to Recent regional and global geoparks [53]. intracontinental volcanic fields, which are dominated by scoria cones and extensive lava fields. These three A preliminary study has applied this method successfully volcanoes together demonstrate unique explosive volcanic to compare geosites of protected areas and highlight eruptions that are considered to be among the most main areas where development is needed to achieve hazardous volcanic events in the western Saudi Arabian more effective nature conservation and/or geotourism [53]. volcanic fields. The uniqueness of Al Wahbah crater, Here we applied the GAM method to four proposed besides its exceptional landscape aesthetic values, is that geosites/geotopes from the Harrat Kishb. In the this volcano is one of the largest maar craters formed evaluation we have treated the two tuff rings (TR1 and by explosive phreatomagmatic interaction of rising mafic TR2) as a single site, due to the limited information magma and ground-water. Although Al Wahbah is an available on them and their similar remote characteristics isolated and distant location, it is well connected by high (Table 1 & Table 2). In this study we have included quality highways to the major motorway and highway a fourth location (Aslaj cone). We created a table on network of the Kingdom of Saudi Arabia, making this the main elements and another one on the additional location a potential gateway point for the geopark that elements and ranked each location (Table 1 & Table 2). is under consideration to be established. The unique In the main elements’ score table, we have provided a physical arrangement of two major volcanic craters short explanation to the reason to give the specific scores, situated on a constructional volcanic edifice can be used while with the additional elements such explanation as justification for developing a geoconservation and was not necessary due to the clarity of the scales geoeducation project on the Harrat Kishb that eventually used (Table 1). Following the aforementioned step, the would lead to the official establishment of a geopark. total score of the main elements were plotted against The dominance of explosive-style volcanism among the additional elements (Figure 8). On this scale the these three volcanic features, whether it was caused by Al Wahbah crater fell in the Z32 field, which means phreatomagmatic explosive eruption or purely magmatic that Al Wahbah has a very high value on its main volatile driven explosive processes (or a combination of elements but additional element scores are moderate both), suggests that these types of eruptiven processes (Figure 8). In this respect Al Wahbah is similar to (which are unique in the western Saudi Arabian volcanic many geosites and geotopes that are already listed in fields) should be the backbone of the geoeducational accepted geopark / geoheritage sites (Figure 8). The concept of the proposed geopark. The Harrat Kishb, other volcanic geosties measured here from Harrat Kishb in addition, hosts other more remote volcanoes that showed lower geoheritage values, especially on the carry individual geoheritage values, such as the Aslaj additional element scale, suggesting that to successfully volcano in the remote northern part of the volcanic promote these sites as significant geosites or geotopes field, which is a major mantle xenolith location. This some fundamental investment is required to elevate them study validates the notion that a geopark in the Harrat to protection status, e.g., making them accessible through Kishb has unique natural features that will attract local improved infrastructure and providing extra information and international visitors, and the geopark concept has for visitors . In addition, at the TR1 and TR2 locations numerous well-thought out concepts ready to be utilised.

263 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

Table 1. Main Values (applying Vujicićˇ et al. method [52]) of geosites/geotopes of Harrat Kishb.

Geosites/Geotops Al Wahbah TR1/TR2 Aslaj I. Scientific/Educational values (VSE) 1. Rarity Common=0 Regional=0.25 0.5-Broad tuff rings with or without intra-crater scoria cones, unique in Harrat Kishb, but probably not so unique globally International=0.75 0.75-One of the largest maar 0.75-a unique location for in the Arabian Peninsula and abundant mantle-derived nodules, probably on Earth globally significant but not the only one The only occurrence=1 2. Representativeness None=0 Low=0.25 Moderate=0.5 High=0.75 0.75-representative for those few large tuff rings known from Harrat Kishb, similar volcanoes are known elsewhere Utmost=1 1-probably the most spectacular 1-the most representative mantle well-exposed maar crater in the nodule occurrence in the Harrat Arabian Peninsual and on Earth, Kishb and among the top spots on a perfect representation for maar Earth craters 3. Knowledge on geo-scientific issues None=0 0 no scientific literature other than few paragraph references in various reports Local publications=0.25 Regional publications=0.5 National 0.75-only mentioned briefly in publications=0.75 international literature, detailed international scientific work is missing, however, national literature treats it as a well- known place International 1-location mentioned in top publications=1 peer reviewed geochemistry international papers 4. Level of interpretation None=0 Moderate level of processes but hard to explain to non experts=0.25 Good example of processes but hard to explain to non experts=0.5 Moderate level of 0.75-some effort needed to 0.75-some effort needed to processes but easy to explain eruption history, some explain eruption history, some explain to common Earth Science background Earth Science background visitor=0.75 essential to understand the story essential to understand the story Good example of 1-perfect site to explain maar processes and easy to crater formation due to perfect explain to common exposures along the crater wall, visitor=1 globally unique scenario 264 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

(continued) II Scenic/Aesthetic values (VSA) 1. Viewpoints (each must present a particular angle of view and be situated less than 1 km from the site) None=0 One=0.25 2 to 3=0.5 4 to 6=0.75 More than 6=1 1-lava flow surface textures, 1-contrasting types of volcanoes, 1-blast deposits, pit craters, intra exposed basement rock textures, arid landscape, ash plains, scoria crater lava flows, lava spatter, scoria cone inner structure, maar cone morphology, lava spatter, scoria cone alignment, ash plain, lake deposits, aeolian processes, intra-crater lava flows etc. arid climate erosion etc. unique tuff ring pyroclastic successions, arid erosional processes etc. 2. Surface (each considered in quantitative relation to other) Small=0 SM=0.25 Medium=0.5 ML=0.75 Large=1 1-area is large 100s of metres 1-area is large 100s of metres 1-area is large 100s of metres scale scale scale 3. Surrounding landscape and nature Minimum = 0 Low=0.25 Medium-0.5 High=0.75 0.75-view is attractive to the surrounding but not special to other locations in the field Utmost=1 1-amazing views to the 1-amazing views to a row of scoria surrounding areas especially cones aligned north to south, to the distant phonolitic lava probably the best view flows and lava domes, probably the best view points 4. Environmental fitting of sites Unfitting=0 UN=0.25 Neutral=0.5 NF=0.75 Fitting=1 1-perfect representation of the 1-perfect representation of the 1-perfect representation of the location location location III Protection (VPr) 1. Current condition Totally damaged (as a result of human activities)=0 Highly damaged (as a result of natural processes)=0.25 Medium damaged (with essential geomorphologic features preserved) = 0.5 Slightly damaged=0.75 0.75-some local rubish damped at main view point No damage=1 1-untouched 1-untouched 2. Protection level None=0 0-no formal protection 0-no formal protection Local=0.25 Reginal=0.5 0.5-some regional protection and some formal national protection initiatives National=0.75 265 International=1 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

(continued) 3. Vulnerability Irreversible (with possibility of total loss)=0 High (could be easily damaged)=0.25 Medium (could be damaged by natural processes or human activities)=0.5 Low (could be damaged 0.75-visitor driven damage 0.75-crater of TR1 can be 0.75-potential collectors of only by human probable if the number of visitors accesses by 4WD car, that could mantle xenliths could leave activities)=0.75 increase, especially in the crater damage the intact nature of the impact on outcrop faces infill, due to walking through crater floor, TR2 has no such sand bars, salt pans problem None=1 4. Suitable number of visitors zero=0 0 to 10=0.25 10 to 20=0.5 20 to 50=0.75 More than 50=1 1-the open places can hold more 1-the open places can hold more 1-the open places can hold more than 50 visitors in any time than 50 visitors in any time than 50 visitors in any time Total (VSE+VSA+VPr) 10.25 8.75 10.25

Figure 8. Discrimination diagram of CAM scores plotting main against additional values of the evaluated geosites (after Petrovic et al. [53]). The diagram shows various geosites from an already listed UNESCO Geopark (Papuk Geopark, Croatia) while another one (Fruška Gora, Serbia) has applied for the same status. Plotting Al Wahbah, TR1/TR2 and Aslaj on the same diagram shows clearly that Al Wahbah scored highly on the main values, and even its score on the additional values are similar to sites that have already been selected to be a part of a geopark. Al Wahbah’s scores suggest that a focused attempt to develop information leaflets, boards or internet resources accompanied by tour guide education could significantly elevate the additional value scores and put Al Wahbah among the high geoheritage value sites globally.

266 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

Table 2. Additional Values (applying Vujicićˇ et al. method [52]) of geosites/geotops of Harrat Kishb.

Geosites/Geotopes Al Wahbah TR1/2 Aslaj I Functional values (VFn) 1. Accessibility Inaccessible=0 Low (on foot with special equipment and expert guide tours)=0.25 Medium (by bicycle and other means of man-powered transport)=0.5 High (by car)*=0.75 0.75 0.75 0.75 Utmost (by bus)=1 2. Additional natural values None=0 One=0.25 2 to 3=0.5 0.5-special habitat in craters, nearby phonolitic lava flows and domes 4 to 6=0.75 0.75-special habitat in pit craters, various lava surface textures, desert erosional features, box valleys More than 6=1 1-special ecosystem in crater, water inflow from crater wall, various erosional features, rock falls and fans, nearby scoria cones, variety of lava surface textures 3. Additional anthropogenic values None=0 0 0 One=0.25 0.25-plantation in crater wall 2 to 3=0.5 4 to 6=0.75 More than 6=1 4. Vicinity of emissive centres More than 100 km=0 0 0 100 to 50 km=0.25 0.25 50 to 25 km=0.5 25 to 5 km=0.75 Less than 5 km=1 5. Vicinity of important road network None=0 Local=0.25 0.25 Regional=0.5 0.5 National=0.75 0.75 International=1 6. Additional functional values None=0 Low=0.25 Medium=0.5 0.5-good network of 4WD 0.5-good network of 4WD roads, but local knowledge is roads, but local knowledge is needed needed High=0.75 0.75-good infrastructure to access nearly any points on crater wall, established but difficult walking path to the crater floor Utmost=1

267 Geoheritage values of one of the largest maar craters in the Arabian Peninsula: the Al Wahbah Crater and other volcanoes

(continued) II Touristic values (VTr) 1. Promotion None=0 0 0 Local=0.25 Regional =0.5 0.5 National =0.75 International=1 2. Annual number of organised visits ** None=0 0 Less than 12 per year=0.25 0.25 12 to 24 per year=0.5 24 to 48 per year=0.75 0.75 More than 48 per year=1 3. Vicinity of visitors centre More than 50 km= 0 0 0 0 50 to 20 km=0.25 20 to 5 km=0.5 5 to 1 km=0.75 Less than 1 km=1 4. Interpretative panels (characteristics of text and graphics, material quality, size, fitting to surroundings, etc.) None=0 0 0 0 Low quality=0.25 Medium quality=0.5 High quality=0.75 Utmost quality=1 5. Annual number of visitors ** None=0 0 0 Low (less than 5000)=0.25 0.25 Medium (5001 to 10.000)=0.5 High (10.001 to 100.000=0.75 Utmost (more than 100.000)=1 6. Tourism infrastructure (pedestrian pathways, resting places, garbage cans, toilets, wellsprings etc.) None=0 0 0 Low=0.25 Medium=0.5 0.5 High=0.75 Utmost=1 7. Tour guide service (expertise level, knowledge of foreign language(s), interpretative skills, etc) None=0 0 0 Low=0.25 0.25 Medium=0.5 High=0.75 Utmost=1 8. Hostelry service More than 50 km=0 0 0 0 25-50 km=0.25 10-25 km = 0.5 5-10 km=0.75 Less than 5 km=1 9. Restaurant service More than 25 km=0 0 0 0 10-25 km=0.25 10-5 km=0.5 1-5 km=0.75 Less than 1 km=1 Total VFn + VTr 6 2.25 2.5 * please note that TR1/TR2 and Aslaj can only accessed by 4WD car, ** Estimated value

268 M. R. Moufti, K. Németh, N. El-Masry and A. Qaddah

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