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The coexistence of monogenetic and polygenetic volcanoes is a common phenomenon in volcanic areas. However, the genetic relationship between monogenetic and polygenetic systems and the factors controlling their distinct eruptive styles are not well understood. In active volcanic areas, analysing the clustering and vent alignment of monogenetic volcanoes, as well as examining the geomorphology and relative ages of scoria cones, offers quantitative insights into magma supply rates, volcano type distribution, and volcanic development trends. Our study presents geomorphological and spatio-temporal analyses of the co -existing monogenetic volcanoes in the Longgang Volcanic Field (LVF) and those associated with a polygenetic volcano (Tianchi) in the Changbaishan Volcanic Area, China. The distance between the two volcanic areas is around 150 km. Monogenetic vents in the LVF exhibit greater density compared to the dispersed system associated with Tianchi. The LVF vents also show better alignment, particularly in the direction of pre-existing basement faults (NE-SW, NW-SE and EW). By using scoria cone morphometric parameters and features, we estimated the relative ages and erupted volumes of monogenetic volcanoes in the LVF and the Tianchi area. We classified the cones of the two volcanic systems into five eruptive periods and found that, despite similar magma sources and output rates over approximately 870 kyr, differing numbers of scoria cones across age classes suggest that Tianchi's magma system influences its associated monogenetic volcanic plumbing. Furthermore, the continuous rise in output rates of monogenetic volcanoes in the Tianchi area highlights the increasing magma supply sustaining Tianchi volcano. Together, these interpretations are consistent with the two systems being controlled by different factors: the Tianchi monogenetic volcanic system is more controlled by magmatism, whereas the LVF is more strongly controlled by local tectonic structures, alongside an increasing magma supply causing the formation of progressively larger individual volcanoes. In volcanic areas, analysing monogenetic volcanoes' spatial-temporal distribution, volumes and recurrence rate provides a framework to evaluate magma supply rates and tectonic associations, which are key to the development of different volcano types. • In the CVA, changes in scoria cones' crater morphological parameters are sensitive to their relative age. • LVF volcanism is more controlled by tectonism, whereas Tianchi's distributed vents are more controlled by magmatism. • Analysing spatial-temporal data of monogenetic volcanoes can assess transitions between volcanic types within an area. • The increasing rate of magma output in the LVF indicates the potential for future, larger volcanic events. [ABSTRACT FROM AUTHOR]

Estimating eruption volumes of volcanoes is crucial for studying the development and evolution of volcanoes and assessing volcanic hazards. Volume estimates for polygenetic volcanoes are well-explored but individual monogenetic volcanoes have received less attention. This could be attributed to the lower perceived hazards resulting from their smaller size and rare eruptive occurrences within volcanic fields. However, accurately determining the volume of individual monogenetic volcanoes is significant for understanding volcanic field development and evolution. Estimates of individual monogenetic eruptions may be challenging due to overlapping lava flows from different vents within a volcanic field or underestimation resulting from the breaching of small-volume scoria cones. This study aims to evaluate the relationship between the morphometric parameters of scoria cones and the volumes of associated lava flows using the globally free Advanced Land Observing Satellite (ALOS) World 3D 30 m (AW3D30) DEM, the US National Elevation Dataset (NED) 10 m DEM, and related satellite images and terrain maps. The results show that the diameter of the scoria cone base (Wco) correlates best with the associated lava flow volume, and Wco is the parameter least affected by later onlapping lava flows. Numerous factors influence the volumes of monogenetic volcanic eruptions. The regional tectonic environment, such as tectonic setting and crust thickness, has been found to control Wco and hence the volume of monogenetic volcanoes. Subduction zones and thicker crust settings are characterized by the most voluminous monogenetic volcanoes. These environments facilitate the accumulation of magma, supporting larger volcanic eruptions. Magma density also correlates with monogenetic eruption volume. Lower density magma is more likely to erupt and form larger monogenetic volcanoes. Furthermore, pre-existing crustal weaknesses such as fault systems are the main factors affecting magma movement in monogenetic shallow plumbing systems and facilitate magma ascent to the surface. Local stresses appear to have a lesser influence on eruptive volumes. Magma source shape has minor influence on monogenetic eruption volumes. Evaluation of all these parameters will provide more robust estimates of potential eruption volumes, hence informing volcanic field hazards assessment. • The diameter of scoria cone base is the best measure of the volume of associated lava flow. • Regional tectonic settings are the main factor affecting the size of monogenetic volcanoes. • Subduction environment and thicker crust are associated with larger monogenetic volcanoes. • Pre-existing fault systems with extensional/strike-slip regime are more favorable for magma to migrate to the surface. • Magma density controls the resulting eruptive volume of monogenetic volcanoes. [ABSTRACT FROM AUTHOR]

The Auckland intraplate volcanic province consists of four small fields of basaltic monogenetic volcanoes. Each of these was active for a period of ~1 Myr and during the last 3 Myr the locus of magmatic activity migrated northward in discrete ~50 km steps. The most recent of these volcano fields is the Auckland Volcanic Field (AVF) in which individual eruptions have produced discrete magma batches within the composition range nephelinite to sub-alkaline basalt. This range of compositions is explained by partial melting involving variable melt/solid ratios together with modal heterogeneity in their mantle source. Eruptions in the field have been irregularly spaced during its 200 kyr life with repose periods varying between ≤0.1 and 13 kyr. Although most of Auckland's volcanoes represent a single period of eruption, paired eruption sequences in which smaller more alkaline magma batches have been followed by more voluminous less alkalic magmas have also occurred. A significant flare-up in activity at about 30 kyr produced compositionally discrete eruptions from at least five spatially separate locations all within a temporal interval of as little as 100 years. An interpretation of these data is that each event (volcano) in the AVF represents a discrete batch of magma extracted from an source with the capacity of producing a compositional variety of magma. Such a source forms when upwelling mantle undergoes adiabatic rise and exists as a metastable entity at the asthenosphere-lithosphere boundary for prolonged periods (105–106 years) during which time it is tapped to create individual magma batches. The shorter term magma extraction events that produced individual volcanoes in the AVF are suggested to be the result of crustal scale tectonic events. The behaviour of these four spatially separate monogenetic volcanic systems at temporal intervals of <106 years is likely linked to the long term tectonic evolution of the Pacific-Australian Plate boundary beneath the New Zealand region. • In northern New Zealand systematic spatial and temporal migration of small-scale intraplate basaltic volcanic systems is linked to evolution of the adjacent convergent margin. • Patterns of eruptions ons in the youngest of the fields indicates the presence of a long term partially melted mantle source tapped by far field tectonism. • These observations lead to a model in which batches separate from convecting mantle to provide static relatively long-lived magma sources producing volcanic fields. [ABSTRACT FROM AUTHOR]

The 6 August 2012 Te Maari eruption produced violent and widespread “cold” Pyroclastic Density Currents (PDCs) following unroofing of the pressurized hydrothermal system. Despite an erupted volume of only ~ 5 × 10 5 m 3 , and lacking any juvenile component, the 340,000 m 3 of PDCs spread over an area of 6.1 km 2 and had mobilities that were on the order of volcanic blasts or blast-like PDCs. This great mobility was due to strong lateral focussing of explosion energy, producing jets with initial velocities > 100 m/s. We present a type-stratigraphy for these hydrothermal-derived low-temperature PDCs that show a tripartite deposit sequence. Each of the deposit units dominates respectively three outward-gradational sedimentary facies, reflecting transitions in the propagating PDC transport and depositional mechanisms. The largest PDCs, directed west and east of the Upper Te Maari area were generated from outer-cone breccias and tuffs that were mostly highly hydrothermally altered. Landsliding and the geometry of the hydrothermal area led to the directed jetting. Initial particle-laden jets laid sheets, grading into lobes of proximal massive sand to gravel-rich facies dominated by unit A and extending up to 1 km from the vents. As the jets were collapsing, a vertically and longitudinally stratified PDC developed within the first few hundred metres from source. Exponential thinning and coarse-tail grading-dominated fining with radial distance of massive unit A resulted from fast deposition and progressive depletion of the most concentrated flow region behind the PDC head. Markedly slower tractional sedimentation from the passing PDC body and tail deposited the highly stratified and ripple-bedded fine-coarse ash of unit B. This formed distinctive dune fields of the medial dune-bedded ash-rich facies. Upwards in depositional sequences the waning of the current can be seen, by replacement of higher-energy bedforms to progressively lower ones. Downstream progressive waning and further depletion are characterised by the development of the distal wavy to planar-bedded ash-rich facies. This is increasingly dominated by the uppermost deposition unit C of laminated fine-med ash deposited by gently turbulent, dilute phoenix clouds. These high energy PDCs, sourced from flank hydrothermal systems should be regarded as a serious threat in any multihazard assessment of a stratovolcano, even though they may not be one of the major magmatic vent sites. In addition, further detailed studies of these hydrothermal jetting events and their deposits should be pursued in order to better understand large-volume volcanic blasts, which appear to be a larger scale sibling phenomenon. [ABSTRACT FROM AUTHOR]

The weak geophysical precursors of the 6 August 2012 Te Maari eruption of Mt. Tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed, hot hydrothermal system. Strong magmatic signals in pre- and post-eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption. Here we examine the volcanic ash produced during the August eruption with the aim of determining whether juvenile magma was erupted or not. The widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results. The Te Maari ash sorting and trend towards a unimodal grain-size distribution increase with distance along the dispersal axis. Proximal to intermediate sites showing polymodal grain-size distributions can be related to the re-fragmentation of different pre-existing lithologies, overlapped erupted pulses and transport mechanisms, and to particle aggregation. Between 69 and 100 vol.% of particles coarser than 3 ϕ and 45–75 vol.% of grains finer than 3 ϕ were sourced from the pre-existing, commonly hydrothermally altered, vent-area lavas and pyroclasts. Free crystals (pyroxene > plagioclase > magnetite > pyrite) make up 0–23 vol.% of particles coarser than 3 ϕ, and 22–41 vol.% of grains finer than 3 ϕ. Brown to black fragments of fresh glass are a small (1–15 vol.%), but notable, component. Under SEM, these blocky, glassy particles are poorly vesicular, and irregularly shaped, some with fluidal or bubble-wall surfaces, and others with fragmented stepped surfaces and fine adhering ash. In thin section, they contain variable amounts of microlites within an isotropic groundmass. The range in silica content of the microprobe-analysed glass is very wide (56–77 wt.%) and cannot be correlated to any specific particle textural type. These chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts; both their diversity, and their match with vent country rocks, argue strongly against a “juvenile” origin for the glassy fragments. We conclude that rising magma provided only heat and gas into the overlying, sealed vapour-dominated hydrothermal system. A landslide from this area led to a rapid decompression and ash was produced by top-down hydrothermal explosions. Careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations, as well as to the context of their source vent, in order to be confident that new magma has reached the surface. [ABSTRACT FROM AUTHOR]