Volcanic Caves Research Articles

Вертикальні провалені отвори до вулканічних печер на поверхні Марса

Studies of Mars have indicated the presence of caves of volcanic and possibly glacial origin on its surface. During volcanic eruptions, flows of lava flow out. As they cool, they are covered with a hard crust and form lava tubes. After the eruption is over, the lava flows out of the tubes at the lowest point and leaves the cavity. Therefore, lava caves are located on the slopes of volcanoes close to the surface. Sometimes their upper part collapses. A large part of the surface of Mars is covered with volcanic craters and mountain ranges. Dark, rounded spots were found in photographs of one of the volcanic plateaus of Tharsis. Their study showed that they are entrances to volcanic caves. The relative youth of these formations is indicated by the sharp edges of these dips. Lava tubes on Mars appear as straight chains of collapses with flat bottoms and nearly vertical slopes. Such objects should become the object of research by future settlers.

The High-Altitude Volcanic Caves of Mount Etna (Eastern Sicily): A Relevant Refuge for Some Ptero-Bryophyte Communities

A phytosociological analysis of the plant communities in high-altitude volcanic caves of Mount Etna (Sicily), based on literature data and unpublished relevés, is presented. A total of 147 phytosociological relevés were processed and analyzed using classification and ordination methods. Classification of the relevés, supported by ordination, showed two main vegetation groups: the first one includes communities of the Pohlion crudae alliance, and the other includes the vegetation from the Pohlio crudae–Asplenion septentrionalis alliance. Furthermore, two new communities, Pohlio crudae–Cystopteridetum dickieanae subass. amphidietosum mougeotii and Pohlio crudae–Cystopteridetum dickieanae subass. polystichetosum lonchitis, are proposed for Etna. The high-altitude caves can be considered a refuge for these ptero-bryophytic rare communities.

STATUS SURVEY OF THE CAVE SCORPION <i>Chaerilus chubluk</i> IN A VOLCANIC CAVE, KRONG NO DISTRICT, DAK NONG PROVINCE

Status survey of the cave scorpion, Chaerilus chubluk Lourenço, Tran & Pham, 2020 was carried out in a volcanic cave, in Krong No district, Dak Nong province in 2022 and 2023. A total of 43 individuals were recorded, 25 individuals were recorded in the year 2022 and 18 individuals were recorded in the year 2023. This species is only known from Co Cave which is now strongly threatened by human impact. Based on the current area of occupancy (AOO) and extent of occurrence (EOO) of Chaerilus chubluk, associated with its recent regression in both AOO and number of individuals, this species is tentatively classified as critically endangered by IUCN. The research results are presented for the first time, as scientific data for the conservation of this scorpion and integrated into the IUCN database.

Guidelines for Managing Radon Hazards in Tourist Volcanic Caves in Spain.

Tourist volcanic caves are in high demand for ecotourism and geotourism lovers, as well as by sun and beach tourists as a complementary activity during their holidays. There are six tourist volcanic caves in the Canary Islands, all of them managed by the local administration of the island. The managers of these caves must ensure the safety of visitors and workers, who are exposed to natural hazards, such as radon, inherent to the environment in which the activity takes place. The methodology for analyzing natural radon radiation is based on the latest studies published by experts in this field and on previous experiences in tourist caves. This article proposes a protocol for the correct management of radon in tourist caves in the Canary Islands, adapted to current regulations, to mitigate effects on the health of visitors and workers.

Microbiological exploration of the Cueva del Viento lava tube system in Tenerife, Canary Islands.

Cueva del Viento, located in the Canary Islands, Spain, is the Earth's sixth-longest lava tube, spanning 18,500 m, and was formed approximately 27,000 years ago. This complex volcanic cave system is characterized by a unique geomorphology, featuring an intricate network of galleries. Despite its geological significance, the geomicrobiology of Cueva del Viento remains largely unexplored. This study employed a combination of culture-dependent techniques and metabarcoding data analysis to gain a comprehensive understanding of the cave's microbial diversity. The 16S rRNA gene metabarcoding approach revealed that the coloured microbial mats (yellow, red and white) coating the cave walls are dominated by the phyla Actinomycetota, Pseudomonadota and Acidobacteriota. Of particular interest is the high relative abundance of the genus Crossiella, which is involved in urease-mediated biomineralization processes, along with the presence of genera associated with nitrogen cycling, such as Nitrospira. Culture-dependent techniques provided insights into the morphological characteristics of the isolated species and their potential metabolic activities, particularly for the strains Streptomyces spp., Paenarthrobacter sp. and Pseudomonas spp. Our findings underscore the potential of Cueva del Viento as an ideal environment for studying microbial diversity and for the isolation and characterization of novel bacterial species of biotechnological interest.

The geomicrobiology of limestone, sulfuric acid speleogenetic, and volcanic caves: basic concepts and future perspectives.

Caves are ubiquitous subterranean voids, accounting for a still largely unexplored surface of the Earth underground. Due to the absence of sunlight and physical segregation, caves are naturally colonized by microorganisms that have developed distinctive capabilities to thrive under extreme conditions of darkness and oligotrophy. Here, the microbiomes colonizing three frequently studied cave types, i.e., limestone, sulfuric acid speleogenetic (SAS), and lava tubes among volcanic caves, have comparatively been reviewed. Geological configurations, nutrient availability, and energy flows in caves are key ecological drivers shaping cave microbiomes through photic, twilight, transient, and deep cave zones. Chemoheterotrophic microbial communities, whose sustenance depends on nutrients supplied from outside, are prevalent in limestone and volcanic caves, while elevated inorganic chemical energy is available in SAS caves, enabling primary production through chemolithoautotrophy. The 16S rRNA-based metataxonomic profiles of cave microbiomes were retrieved from previous studies employing the Illumina platform for sequencing the prokaryotic V3-V4 hypervariable region to compare the microbial community structures from different cave systems and environmental samples. Limestone caves and lava tubes are colonized by largely overlapping bacterial phyla, with the prevalence of Pseudomonadota and Actinomycetota, whereas the co-dominance of Pseudomonadota and Campylobacterota members characterizes SAS caves. Most of the metataxonomic profiling data have so far been collected from the twilight and transient zones, while deep cave zones remain elusive, deserving further exploration. Integrative approaches for future geomicrobiology studies are suggested to gain comprehensive insights into the different cave types and zones. This review also poses novel research questions for unveiling the metabolic and genomic capabilities of cave microorganisms, paving the way for their potential biotechnological applications.

Mountain caves of the central region of Veracruz: A vertebrate biodiversity reservoir in a Neotropical hotspot.

The mountain region of central Veracruz, Mexico hosts a large system of karst and volcanic caves that are unexplored. In particular, the vertebrates that inhabit these subterranean ecosystems are unknown. This study evaluated the diversity of mammals, birds, reptiles, amphibians, and fish in three environments (euphotic, disphotic, and aphotic) of 16 caves of different geological origin (12 karst caves and 4 volcanic caves) distributed along an altitudinal gradient (300-2400 m a.s.l.). We found a richness of 242 vertebrate species (184 birds, 30 mammals, 15 reptiles, 12 amphibians, and 1 fish) and an abundance of a total of 11,323 individuals (4,969 mammals, 6,483 birds, 36 reptiles, 27 amphibians, and 5 fish). The richness of all vertebrate classes was higher in karst than in volcanic caves. Vertebrate diversity was also higher at mid-altitudes between 600-899 m a.s.l. Diversity varied between environments, where bird and reptile richness was higher in the euphotic environment, while mammal and amphibian diversity was higher in the aphotic environment. The similarity in the composition of vertebrate species does not depend on the distance between karstic and volcanic caves. Volcanic and karst caves shared on average up to 70% and 55% of vertebrate species, which indicates that only 30% and 45% of species, respectively, is different in each cave type. Given the vulnerability and fragility of these subterranean ecosystems, as well as the important diversity that they contain, we recommend including the caves of the central region of Veracruz in the conservation agenda of local governments and communities. Community-based conservation can help ensure the presence of vertebrate species in the caves of this region.

DARK SOIL PITS AND GRAVES IN VOLCANIC CAVE C6.1, KRONG NO, DAK NONG PROVINCE: DOCUMENTATION AND DISCUSSION

Dark soil pits and graves are critical documents discovered in volcanic cave C6.1. As a result of the investigation and excavation of cave C6.1 conducted in 2017, 2018, and 2019, we have discovered vestiges of nine dark soil pits and seven relatively intact graves, together with teeth and other human remains scattered in the cultural layer. This is an important source of information on the racial composition of the prehistoric inhabitants of the Central Highlands during the Neolithic period, as well as the paleoenvironment, environmental adaptations, and flora and fauna that prehistoric inhabitants exploited for their livelihoods. This article introduces documents and reconstructs the socioeconomic picture of the prehistoric inhabitants of cave C6.1. It also contributes scientific documents for the general conservation and promotion of heritage to develop sustainable cultural tourism in Dak Nong Province.

Archeology of the Volcanic Caves in Krong No: Historical - Cultural Significance

This article introduces the results of excavation and research on the cultural remains of prehistoric people in the volcanic caves at Krong No, Dak Nong (Vietnam). The sediments in the caves have preserved a standard stratigraphy of the prehistoric culture of the ancient people who lived there, allowing an assessment of the tools, burial characteristics, and vestiges of animals and plants. The absolute dating system (14C) has revealed continuous human habitation in the caves from 7,000 to 4,000 BP. In addition, the archeological evidence from the volcanic caves at Krong No provides important information about the past environment, evolutionary history and diversity of nature, adaptation of people to changes in the environment, and their spiritual culture (from burial documents). Clear findings on the characteristics of the ancient fauna and flora are not commonly found in the archeological evidence of the Central Highlands volcanic region of Vietnam and Southeast Asia.

New terrestrial cyanobacteria from the Azores Islands: description of Venetifunis gen. nov. and new species of Albertania, Kovacikia and Pegethrix

ABSTRACT The taxonomy of cyanobacteria has advanced quickly with the use of molecular methods in combination with well-defined morphological and ecological characters. Using this approach, many taxonomical changes have occurred in the Synechococcales and Oscillatoriales, with the description of new families, genera and species. Here we present the study of four cyanobacterial strains from the Bank of Algae and Cyanobacteria of the Azores (BACA) culture collection, all isolated from the Azores Archipelago. The strains were genetically characterized through the amplification of the 16S rRNA gene and 16S-23S rRNA internal transcribed spacer (ITS) region, as well as morphologically by light and transmission electron microscopy. One of the strains presented a high genetic divergence from known genera of Synechococcales and was described as Venetifunis florensis gen. & sp. nov. (Trichocoleusaceae, Cyanobacteria). The remaining three strains were found to be new species of the genera Albertania, Kovacikia and Pegethrix. Venetifunis florensis was isolated from the shores of Lake Rasa in Flores Island, Kovacikia atmophytica sp. nov. is a new species mainly distinguished genetically from other Kovacikia species from Terceira Island. Albertania obscura sp. nov. was isolated from inside a volcanic cave in Terceira Island and is distinct both morphologically and genetically from the already described species. Pegethrix atlantica sp. nov. is a new morphologically and genetically different species isolated from São Miguel Island. The description of these new taxa increases the biogeographic knowledge of the four mentioned cyanobacterial genera to remote oceanic islands and new terrestrial habitats.

Research for the classification of volcanic caves in the Central Highlands

Volcanic caves in Central Highlands have been discovered since 2007. This is a volcanic cave system with the largest scale, length and uniqueness in Southeast Asia. The discovery has opened up many new research directions (specialised, interdisciplinary earth science and life science), with many scientific and technological projects at different levels... Since the volcanic cave system in the Central Highlands was discovered, there have not had any publications on the taxonomy of Vietnamese volcanic caves. In the practice of studying volcanic caves, there are many methodologies to classify caves depending on the purpose and requirements of use, such as origin, formation mechanism, distribution characteristics, morphology, or a mixture of the above classifications. In this study, the authors classified the Central Highlands volcanic caves according to the mixture of the above classifications and other uses, such as scientific caves, mass caves, prehistoric caves, adventure cave, etc.

First Insights into the Bacterial Diversity of Mount Etna Volcanic Caves.

While microbial communities in limestone caves across the world are relatively understood, knowledge of the microbial composition in lava tubes is lagging behind. These caves are found in volcanic regions worldwide and are typically lined with multicolored microbial mats on their walls and ceilings. The Mount Etna (Sicily, S-Italy) represents one of the most active volcanos in the world. Due to its outstanding biodiversity and geological features, it was declared Natural Heritage of Humanity by the UNESCO in 2013. Despite the presence of more than 200 basaltic lava tubes, the microbial diversity of these hypogean systems has never been investigated so far. Here, we investigated bacterial communities in four lava tubes of Mount Etna volcano. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features. We documented an abundant presence of microbial cells with different morphotypes including rod-shaped, filamentous, and coccoidal cells with surface appendages, resembling actinobacteria reported in other lava tubes across the world. Based on 16S rRNA gene analysis, the colored microbial mats collected were mostly composed of bacteria belonging to the phyla Actinomycetota, Pseudomonadota, Acidobacteriota, Chloroflexota, and Cyanobacteria. At the genus level, the analysis revealed a dominance of the genus Crossiella, which is actively involved in biomineralization processes, followed by Pseudomonas, Bacillus, Chujaibacter, and Sphingomonas. The presence of these taxa is associated with the carbon, nitrogen, and ammonia cycles, and some are possibly related to the anthropic disturbance of these caves. This study provides the first insight into the microbial diversity of the Etna volcano lava tubes, and expands on previous research on microbiology of volcanic caves across the world.

Radon Dynamics and Effective Dose Estimation in a Touristic Volcanic Cave: La Cueva del Viento, Tenerife (Canary Islands, Spain).

La Cueva del Viento is a volcanic lava tube located in Tenerife Island (Canary Islands, Spain). Its touristic section, 180m long, receives more than 28,200 visitants each year. According to the European and Spanish legislation, a radon monitoring program is required to minimize the radon exposition of workers, tourists, and cavers. In this work, we studied the radon concentration dynamics in the touristic section of the cave for ca. 1year, using both passive and active radon detectors. Pluviometry and external air temperature played an important role in the seasonal and daily variations of indoor radon concentrations. Daily fluctuations during the dry season were analyzed using time series (Box-Jenkins methodology) and frequency analysis (Fourier and Wavelet transforms) methods. The experimental radon time-series was well-fitted using a seasonal autoregressive integrated moving average model: Seasonal Auto-Regressive Integrated Moving Average (2,0,1) (2,1,0)24, and its value, in a short-time window (ca. 1week) was conveniently forecasted. Finally, this work revealed that the annual effective doses received, during the observation period (1year), by the touristic guides and visitors was ca. 2mSv/yr and 4μSv/hr, respectively. We concluded that the touristic exploitation of La Cueva del Viento is safe for both tourists and guides. However, based on our results, La Cueva del Viento had to be classified as a "Monitoring zone" and a regular monitoring program should be implemented.

Stability Analysis of the Volcanic Cave El Mirador (Galápagos Islands, Ecuador) Combining Numerical, Empirical and Remote Techniques

El Mirador de los Túneles is a tube-shaped volcanic cave with a sinuous structure in the Galápagos Islands formed due to cooled near-surface lava flows. Since this natural formation is considered a tourist site, a large number of people frequent it daily; however, its safety conditions have not yet been defined by a comprehensive geotechnical study. In this research, a stability analysis was carried out by combining both empirical methodologies based on geomechanical classifications using Barton’s Q Index and the recently created Cave Geomechanical Index (CGI), and numerical modeling through the finite element method. In addition, three-dimensional modelling was performed using the remote photogrammetric technique Structure from Motion (SfM) to create the numerical calculation sections and dimensions of the different critical parts of the cave. The results of the analysis showed that there is evidence of instability and subsidence along the tunnel. Furthermore, the geotechnical parameters obtained from the different methods complemented each other, resulting in more realistic engineering representation of the subsurface environment. Finally, a graph showing the two empirical methodologies Barton’s Q Index and CGI, with the addition of the Factors of Safety (FoS) obtained from the modeling is presented.

History and significance of tropical cave biology

“Nothing could possibly live there!” They said. Indeed, until recently, few specialized cave-adapted animals were known from volcanic, tropical, or oceanic island caves, and plausible theories had been put forward to explain their absence. But assume nothing in science! One must illuminate, explore, and survey habitats before declaring them barren. Our understanding of cave biology changed dramatically about 50 years ago following the serendipitous discovery of cave-adapted insects and other terrestrial arthropods in lava caves on the young oceanic islands of the Galapagos and Hawai‘i. The discovery and subsequent studies on the evolutionary ecology of cave animals have revealed a remarkable hidden fauna and created new sub-disciplines within biospeleology. Biological surveys of caves in other regions have confirmed the results developed in Hawai‘i. We now predict that, rather than being relicts trapped in caves by changing climate, animals actively colonized caves and adapted to exploit food resources wherever there were suitable subterranean voids. The physical environment in caves can be determined with great precision because the habitat is buffered by rock. Furthermore, the bizarre adaptations displayed by obligate cave animals are similar across many taxonomic groups. These two characteristics make caves nearly ideal natural laboratories for studying evolution and ecology. However, to the untrained researcher, caves can appear hostile and dangerous, and in fact, fieldwork in caves requires a unique marriage of athletic ability and science. In other words, it is exciting! Join me on a virtual tour of exploration, discovery, and research in caves during the past half-century.

Organic geochemistry and mineralogy suggest anthropogenic impact in speleothem chemistry from volcanic show caves of the Galapagos

SummaryThe network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A, and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres, and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, and cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.

Diversity Analysis and Genome Mining of Microbial 16S rRNA Gene and Metagenomic Data for the Discovery of Novel Antibiotics

There is an urgent need for new antimicrobials due to constantly advancing antimicrobial resistance. Here, we worked with environmental samples from diverse habitats including different savannah and forest soils, volcanic caves, and termite mounds and assessed their microbial communities for the potential of biosynthesis of secondary metabolites. We analysed and compared microbial composition by applying the QIIME2 pipeline to 16S rRNA gene data. We focused on the abundance of Actinobacteria and Streptomyces as they are important producers of antimicrobials. Out of the samples analysed, the highest abundance of Actinobacteria was found in termite mound and volcanic cave samples. Moreover, the termite mound samples also had the highest abundance of Streptomyces. When comparing microbial composition, soil samples and termite mound samples each formed their own clusters, but volcanic cave samples appeared more dispersed. We assessed the antimicrobial potential of a subset of samples by analysing metagenomic data to predict biosynthetic gene clusters (BGCs) using antiSMASH5.2.0, which resulted in over 800 hits per sample. This number was narrowed down by evaluating identified BGCs based on antimicrobial potential, completeness, size, presence/absence of regulatory and transport-related genes, and dissimilarity with known BGCs. This resulted in an average of 20 BGCs per sample. These BGCs will be subjected to further sequence-based analyses before attempting heterologous expression. Following successful expression, antimicrobial potential will be assessed by screening for growth inhibition of multidrug resistant E.coli strains and the ESKAPE pathogens.

Geochemical interactions among water, minerals, microbes, and organic matter in formation of speleothems in volcanic (lava tube) caves

Volcanic (lava tube) caves at Lava Beds National Monument (N. CA, USA) provide a valuable terrestrial analog for volcanic caves on Mars and the Moon. Terrestrial volcanic caves host a diverse microbial life, liquid water, and a variety of secondary mineral deposits (speleothems) with diverse morphologies and chemical compositions. Speleothems may preserve records of past and present microbial life and signatures of paleoenvironmental changes in terrestrial volcanic caves. Distinguishing between speleothems via chemical processes and microbially-mediated processes in terrestrial volcanic caves will provide valuable insights for future exploration of martian volcanic caves. To elucidate the formation of speleothems, we studied the chemical makeup (inorganic and organic) of cave waters in seven volcanic caves of variable ages, temperature, moisture content, light intensity, and frequency of human visitation. Cave water was characterized by stable isotopic composition (δ18O and δ2H), concentrations of major and trace elements, cations, anions, and characteristics of dissolved organic matter (DOM). A forward reaction model (PHREEQC) was used to test possible pathways for secondary mineral precipitation that formed these speleothems. The source of cave water was primarily regional meteoric precipitation that entered the caves through cave openings or through the cave overburden and fractured basalt walls as indicated by cave floor puddle water line δ2H = 8.32*δ18O + 9.55 parallel to the global meteoric water line (GMWL, δ2H = 8.3*δ18O + 10). A line formed by cave ceiling drip water δ2H = 3.39*δ18O – 44.77 intersecting the GMWL indicated that the water may be undergoing evaporation within the caves. Silicate weathering was found to be a primary process resulting in cave water enriched in Si (22 ± 7 mg/L), and contained trace levels of Al, Fe, Zn, Li, Sr, Cu, B, V, Ba, Cr and Mn. Geochemical calculations indicated that cave waters were undersaturated with respect to both amorphous silica (SiO2am) and calcite (CaCO3) which were the major components of speleothems observed within the caves. Results of a forward reaction model showed that evaporation of cave waters could lower the solubility of SiO2am and CaCO3 by increasing their saturation and ultimately precipitate these two secondary minerals forming the speleothems. The cave water DOM was characterized by high concentrations of dissolved organic carbon (DOC, 12 ± 8 mg/L) with a molar C/N ratio ranging from 2 to 22. The DOM was found to be aromatic (SUVA254, 1.2–2.9 L/mg.m), terrestrially derived and humic-like (humification index, 7–26) and contained molecules of 100 Da and 5000 Da approximate molecular weight (AMU). Our results indicated that the terrestrially derived carbonaceous organic matter transported into the caves was not utilized for heterotrophic microbial metabolisms as DOC was accumulated over dissolved inorganic carbon (DIC). Both findings suggest that with minimal heterotrophy, chemo-litho-autotrophy may be important pathways that cycle the elements within these volcanic caves with low light conditions. Together, this study proposes a potential pathway of speleothem precipitation through the interaction of water, dissolved mineral constituents, and microbial life where dissolved ions are concentrated in cave drip water through cyclic condensation-vaporization processes. This work is part of a multi-disciplinary project Biologic Resource Analog in Low Light Environments (BRAILLE) funded by the NASA PSTAR Program (NNH16ZDA001N), which focuses on studying volcanic caves as terrestrial analogs for the Moon and Mars.

THE ON-SITE VOLCANIC CAVE CONSERVATION MUSEUM AT THE DAK NONG UNESCOGLOBAL GEOPARK

The Krong No volcanic caves at the Dak Nong UNESCO Global Geopark (Dak Nong UGGp) were discovered in 2007. Between 2017 and the present, they were comprehensively studied and evaluated for heritage value from the perspectives of geology, biology and cultural studies. These primitive, endogenic caves are characterized by rich and diverse interior formations, representing seven types of geological heritage as classified by the UNESCO and its GILGES classification system. The applicable types are A (Paleontology), B (Geomorphology), C (Paleo-Environment), D (Rock), E (Stratigraphy), F (Minerals), and I (Tectonics). The cave system’s wildlife is highly diverse and includes a number of newly discovered species endemic to Krong No. Thanks to research and excavation work, many types of archaeological artifacts have been discovered in the Krong No volcanic caves, including relics of residence, a tool-making site, burial artifacts, a makeshift hunting camp, and some artifacts possibly expressive of religious ritual. All of these are unique, valuable and rare. The various types of heritage discovered in the Krong No volcanic caves constitute the premise of an on-site conservation museum, established to promote heritage of value, teaching and scholarship, as well as community education and recreation. This article introduces a new direction for further research, related to the development of an on-site conservation museum of the volcanic cave heritage in the context of sustainable socio-economic development.

A Comparison of Primers in 16S rRNA Gene Surveys of Bacteria and Archaea from Volcanic Caves

The construction of amplified 16S rRNA gene libraries has been a major methodology for bacterial/archaeal environmental community profiling for decades. Over the years, a variety of alternative primer sets targeting different portions of the rRNA gene have been used. Gradually a widespread collaborative effort, supported by the Earth Microbiome Project (EMP) and other community initiatives, has settled on primers targeting the V4 region (515F/806R) of the 16S rRNA gene, which amplifies both Archaea and Bacteria. Understudied volcanic cave ecosystems possess a high proportion of unclassified bacterial and archaeal lineages, highlighting the selection of optimal primers for community analysis in this environment. Therefore, we investigated the coverage of EMP and alternative archaea-specific (519F/1017R) and bacteria-specific (27F/515R) primers, using microbial and mineral deposits from two volcanic caves. In silico and sequencing analyses showed that the two bacterial primers captured similar amounts and types of Bacteria, while significant differences in the type and abundance of taxa detected between the EMP primers and archaea-specific primers were noted. Our results validate the use of V4 EMP primers for Bacteria in this cave ecosystem, but strongly suggest that Archaea diversity is better captured with the archaea-specific primer in the cave deposits studied.