Assessment of the values of abiotic nature is a widely pursued goal worldwide to provide an objectively determined spatial distribution of such elements [1
]. Many researchers are concentrating on understanding and describing geodiversity of the environment, because this knowledge underlies biodiversity and humanity’s connection to the Earth itself. Biodiversity is underlain by an abiotic foundation. This foundation is continuously evolving and shaped by human societies towards their convenience and needs. Meanwhile, humanity uses abiotic nature as it does flora and fauna, but with a higher rate of alteration and through the provision of needs. This significance of geodiversity for humanity has been accurately described by Grey who questions “Geodiversity and geoconservation: what, why, and how?” [8
], stating unliving nature is not just a location providing needs for survival (economic and functional values), but also providing a range of “supernatural” (non-material) values such as cultural and aesthetic benefits. This demonstrates the significance of geodiversity for understanding the evolution of the environment.
The latest research in this topic shows that geodiversity includes a range of elements such as: geology, geomorphology, climate, hydrology, human and biological footprints, and tectonic processes. In addition, soils, as an element of abiotic nature, are also considered as transit zones where geodiversity adjoins biodiversity [9
]. Geological and geomorphological elements should be viewed as two main parameters underlying geodiversity as foundational elements of the abiotic environment. Other elements are the results of weathering and/or erosion processes or altered rock material [4
]. Even though hydrology is considered a process, it should be studied as another main parameter of geodiversity. However, this assessment of geodiversity concentrates on geosite recognition for the utilization of its role within the geosystem services (e.g., geotourism) rather than providing a complete geodiversity model. The methodology utilizes two core parameters, geology (quality) and geomorphology (form), which can be evaluated to identify the most valuable locations.
A geosite is defined as a location with significant information preserved within associated geological formations [4
]. The identification of such locations is a key goal of qualitative–quantitative geodiversity assessments, because areas of research contain many different types of information, which may be mostly unreadable from the surface during observation. To find these places of significance, accurate observational research of the defined area must be undertaken on all levels, beginning with the literature, and mapping observations with direct on-site field observations of potential sites. However, significant technological innovations and developments can assist the assessment. For example, digital mapping provides tools to collect and calculate all available spatial data and highlight locations requiring further observation and research, reducing the areas of field observation to some specific places. Gathering and analyzing these data can thus demonstrate the significance of a site within the context of Earth’s history, and inform plans to preserve and manage sites in order to spread knowledge of geodiversity and provide opportunities for communities to engage with the geological stories of their land [11
]. In conclusion, in assessments of geodiversity, digital technology can be utilized to define, assess, and subsequently manage potential geosites in a more objective, efficient, and faster way.
The type of assessment of geodiversity is a significant consideration when utilizing GIS (geographical information systems), because digital calculations require data, being highly dependent on the methodology and aim of research. A qualitative–quantitative method of geodiversity assessment [4
], requiring a relatively low amount of information, utilizing a standard geological map and SRTM (Shuttle Reader Topography Mission) model [14
], can be used to highlight the most significant places of research. However, its accuracy depends on the quality of the data and evaluation system. Utilizing this methodology and data from previous research on Western Samoa (Southwest Pacific) [4
], this assessment further applies improvements in evaluation systems, and demonstrates an issue with previous grid scaling systems in comparison with a non-grid methodology [2
Scaling is one of the main issues in any kind of assessment [15
]. This article demonstrates qualitative–quantitative assessments, aiming to highlight the most valuable geosites on Western Samoa. Hence, the places of interest must be as accurate as possible, where a non-grid methodology can be utilized. Unlike a grid method, this does not divide the area of research on similar cell regions (rectangles or hexagons), but create more natural shapes based on elements and their value-input in modeling. Non-grid methodology utilizes the sum of values of two main elements of geodiversity (geology and geomorphology), which together creates a global value of studied region, but can also be improved with local elements (specific sites with cultural, archeological, volcanological, and/or other values). The accuracy of assessment using this scaling method depends only on the quality of data; grid deviation of the territory is not required. We chose Western Samoa, located in the Southwest Pacific (Figure 1
) as a suitable region for comparisons of grid and non-grid types of assessments of geodiversity, as well as providing opportunities to build on previous research on this territory.
Qualitative–quantitative assessment of geodiversity is an important methodology for highlighting abiotic aspects of sites with the potential for demonstrating information and processes relating to Earth’s evolution. However, the scale of assessment is one of the most significant parameters, directly influencing the accuracy of results Therefore, we consider this an important area for further research; here, we demonstrate contrasting accuracy and the utility of grid and non-grid methods of scaling.
The results of our assessment of geodiversity were the sum of all defined elements in Western Samoa, valued on a scale from 1 to 7 points for each element and 1 point assigned for eruptive centers. The calculation was applied to the same model, contrasting two different methodologies: grid and non-grid. The grid method (Figure 6
) utilized cells with a size of 2.5 km per side, an appropriate distance for further observation of chosen sites, because this scale is acceptable for justification on the field. In contrast, the non-grid (Figure 7
) methodology utilized borders of assessed elements as areas of deviation from some shapes, where each shape contained information from all layers (geomorphological, geological, volcanic heritage, and eruptive centers). To compare the methods, two models were created, with a sum of evaluated points (Table 1
) (7 for each element, and 1 for eruptive centers), which were then divided into six categories with their point values ranging from 0 to 22. Additionally, all categories contained their area of spreading.
3.1. Geodiversity Results Based on Grid Scaling Methods
The grid model (Figure 6
) is presented for the whole area of research, except the ocean, and contained 586 cells, dividing the whole territory into regions containing cells with the same sum of arithmetic averages of all elements. In our results, 0–3/22 points were unclassified, because these geodiversity values are very low to be considered for further assessment; moreover, this was only 0.07% of the whole research territory. This area of the northeastern part of Upolu Island mainly contains alluvial sediments, which are also classified as the most common type of rock present on the Earth’s surface. Thus, 4–6/22 is still considered a relatively low value for geodiversity, with no areas of this value present on our model. Salani volcanism represented 20% of our research territory with a value of 7–9/22, in the central–western part of Savai’i Island and mostly in the southeastern part of Upolu Island. The middle value of geodiversity, 10–12/22, mostly represented Mulifanua and Lefaga volcanics, and less so Salani and Fagaloa volcanics. These areas were considered to contain important additional information justifying further observation. Their area of spread was the largest (nearly 50%), mostly occurring in the western part of Savai’i Island and some areas closer to the east coast. On Upolu Island, they are situated in the western and central parts of the island. Finally, 13–15/22 was the highest value for geodiversity occurring in our study area. These were the areas that should be subject to further observation and assessment as potential geosites for Western Samoa. Areas with the highest values covered 30.52% of our total study area. These high-value areas were mostly found in the central, northern, and eastern regions of Savai’i Island, closer to coastal areas, and on Upolu in an area from the north to the south in the central part of the island. These areas were mostly formed by Puapua and Aopo volcanics. The places with the absolute highest values for geodiversity (16–18/22 and 19–22/22) were found in this model. Therefore, our grid method of assessment provided an area of 1016.8 km2
with protentional geosites, which should be observed for further assessment and inventory.
3.2. Geodiversity Results Based on Non-Grid Scaling Methods
Using the non-grid methodology, we obtained slightly different results compared with the grid model. The non-grid model (Figure 7
) was based on areas with the same range of value points as the grid-based version; however, for scale we used a natural shape border, which resulted in 23,453 discreet regions. The regions were based on summarizing layers of geodiversity elements adapted specifically for the Western Samoa region. Layers and their associated range of points were geology (1–7 points); geomorphology (1–7 points); volcanic heritage (1–7 points); and eruptive centers (+1 point). Hence, the highest absolute value was 22, which was not present in this territory. In this model, the unclassified value range 0–3/22 (0.08%) was defined as a larger area compared with the grid model and is formed by alluvium (Holocene) in the northwestern part of Upolu Island, which we consider unnecessary for further research in a geoheritage context. The value 4–6/22 did not occur in the grid model, and in this non-grid model it was not considered influential because it occurred only in a small area (0.02%) contiguous with the lower unclassified values. Areas with the next value 7–9/22 of geodiversity (still considered low) are slightly higher in this model (20.3%) compared with the grid model. Both models include the same locations and rock formations in these areas, but some sites contain higher values influenced by geomorphology and eruptive centers. The middle value (10–12/22 points) of geodiversity is the most common range for Western Samoa for both models, but a slightly smaller area of spread (47.53%) on this non-grid model. The smaller area is described by more an accurate scale of regions with same value, especially in the western part of Upolu Island, where some locations with higher values are present, because of the presence of eruptive centers. The high value 13–15/22 is larger in area (31.64%) in this non-grid model, and mostly includes the same locations as the grid model. This value also appears more specifically throughout the territory of Western Samoa in areas of middle value with eruptive centers and/or steeper slopes. These areas, together with regions with the highest present value of geodiversity (16–18/22), should be marked for further research, observations, and assessment. The highest range had a small area of spread (0.42%) and was mostly concentrated locally on areas with a high value occurring closer to eruptive centers and featuring steeper slopes. The absence of these areas in the grid model is notable.
4.1. Grid and Non-Grid Methods of Scaling for Geodiversity Assessments
The main goal of our research was a comparison of two different scales applied to methods for assessments of geodiversity of Western Samoa. We observed slight differences in accuracy, but the overall locations and area of spread were similar. We considered the non-grid model to be better able to highlight locations with potential for classification as geosites. These locations often exhibited eruptive centers demonstrating geological and geomorphological processes. Additionally, they highlight an area most likely to feature surface outcrops of representative rock types which can be further described through detailed field observations. In contrast, we consider the grid assessment method to be more suitable for estimating the geodiversity of large territorial areas, rather than islands. Grid assessments can easily define larger areas (e.g., multiple cell size) to be considered for future geoconservation initiatives and potential geopark establishments. In contrast, non-grid assessments are more suited to estimating geodiversity values in small areas, with the goal of highlighting of potential geosites. Grid models can be used prior to non-grid models, especially in large territories, to identify optimum places for future studies. However, the drawback can be in the loss of some small geological objects such as vents that are hidden inside a grid cell, which are unlikely to have enough influence on the final mark of the grid.
4.2. Alternative Geomorphological Models and Their Issues for Geodiversity Assessments
Based on our research to date, we note the need for refinements in assessing the geomorphological factors in our overall assessment of geodiversity. Geodiversity estimates should be driven by geological, volcanological, and hydrological elements as a proxy for potential geodiversity values in the geomorphological context. Currently, we suggest using slope degree as the main factor informing assigned values, but also considering geomorphon, topographical position index (TPI), roughness, curvatures, slope aspect, and raggedness as parameters sensitive to surface complexities. However, these parameters are still hard to evaluate because they do not show a direct association with geological formations, which makes them hard to include in assessments. Moreover, most of them are based on slope steepness and some additional parameters of calculation for specific purpose. For example, TPI utilizing slope angle and elevation dividing slopes on different parts and creating number of landforms such as valleys and ranges, which looks very good on a map but currently not showing any important information, which can lead us to see locations with possible geosites. In the current state, they are unlikely be used for qualitative–quantitative assessments of geodiversity. Naturally, this geomorphological layer of assessment is necessary for areas with no volcanism; however, we note that it can also be applied as an additional layer when assessing the value of geological and volcanological heritage, and other elements of geodiversity. Therefore, values assigned to geological elements can be considered import for distinguishing individual geosites compared with others, and this can be further emphasized by considering geomorphological elements.
4.3. Issues with the Territory of Western Samoa
Western Samoa Islands were chosen for this assessment as a challenge. This territory contains low value from a geomorphological perspective, and high value from a geological perspective, but this is evenly spread throughout the whole region, giving everything the same importance. Moreover, geological, and tectonic information of the islands is limited because it shows young volcanism without specific structural elements, but with a high number of vents diagonally spread throughout the islands of Western Samoa [25
]. As a result, the assessment of Western Samoa with additional values of volcanic heritage specifically tailored to this territory shows that its geodiversity has fallen in value and is considered to be average. Even though Savaii Island has a large territory, which marks it as high value, it is unsuitable for study, because it is better to concentrate on the large number of small spots with the highest values. These locations are mostly concentrated on places with eruptive centers. Additionally, coastal areas must be considered as a good location, especially cliff sites. As a result, these conditions, with a relatively pure geodiversity, tropical climate, and a small human population are perfect for a high distribution of tropical forests, creating high biodiversity of the region [28
]. Hydrology, one of the elements of geodiversity, was not included in this assessment because its evaluation remains unsolved; there are some possible ways of assessing the weathering power, accumulating alluvial sediments, and/or type of water (stream, lake, marshland, etc.). Additionally, hydrological information of Western Samoa is also limited, similarly to the geological data. However, from DEMs, the territory probably supports a large number of small streams with a short fluvial network, especially in the central part of Savaii Island and central–northern part of Upolu. Here, waterfalls are one of the most important hydrological features which can be included into assessments because they carry high geotouristic values, but they cannot be extracted directly from DEMs or other model, only input into assessments after observation or extracted from topographical maps. Meanwhile, in Western Samoa, waterfalls are commonly linked to the places of geological boundary (e.g., lava flow contacts), which decreases their importance for qualitative–quantitative type of assessment. In conclusion, Western Samoa is a place with opportunity to study geoeducation from a geodiversity perspective, but information is still limited and further observations are required.
4.4. Aims for Future Research
The non-grid type of assessment with four elements of geodiversity and subject to a 7-point evaluation system is currently is our most developed qualitative–quantitative methodology. However, further research is proposed that would provide a more holistic overview by including elements such as archeological sites and soils. Additionally, biological factors and the human footprint must be considered in any overall assessment of geodiversity, enabling a comparison of geodiversity and biodiversity to inform and direct further research on omnidiversity [34
Both the grid and non-grid scaling methods presented in our study of geodiversity assessment methods display similar results on a global perspective. However, at a local scale, the non-grid methodology displays more complete and spatially refined results, providing exact locations with specific values based on the evaluation system. Hence, on a global perspective and/or for large territories, grid systems work well enough, whereas non-grid systems are more applicable for local scales. It is better to recommend grid systems for the assessment of geoparks, whereas non-grid systems should be used highlight specifical geosites.
To date, improvements in assessments of geodiversity demonstrate a need for further development of associated concepts. Results from our evaluation system demonstrate the high volcanic heritage value of eruptive centers as well as their influence on geodiversity values overall, applicable at a highly localized scale of assessment. Other values should be subject to the same studies and assessments as volcanic heritage, where geology and geomorphology situate the geodiversity in a global context, and additional elements such as archeology, cultural history, hydrology, and soils should be included and calculated for the local perspective and uniqueness, and to provide a more holistic overview of geoheritage.