Volcanic Terrain Research Articles

Volcanic evolution through geomorphological mapping: A case study of Cerro Bravo volcano (Colombia)

Geomorphological mapping is essential for identifying landforms, determining erosion, and reconstructing the morphological evolution over time. The relative chronology between features can be established, supporting the study of the potential hazard and associated risks in volcanic terrains. Geomorphological analysis, performed on a 12.5 m ALOS PALSAR DEM, along with field-work and new K–Ar geochronological data, help to clarify the overall evolution of the Cerro Bravo volcano. The observed north-south arrangement of the craters, the stratigraphic relationships, and the new K–Ar ages reveal that the volcanic activity migrated towards the north, with the younger activity concentrated north of the volcanic area. This evolution, which occurred from the Middle Pleistocene to the Holocene, is evidenced by four consecutive semicircular crater-like structures associated with four building stages. Effusive and explosive activity was observed in all recorded volcanic activity stages, indicating a consistent volcanological behavior of this volcano over time, characterized by a bimodal effusive-explosive eruption style. The effusive activity involved lava domes and lava flows, while the explosive activity included dome collapses and Plinian eruptions. This morphological study can help assess the geological risk and potential hazards of inaccessible areas.

Quantitative assessment of aqueous sulfate contributions from Fe3+- and O2-driven oxidation pathways of hydrothermal sulfur using oxygen isotopes

Sulfate (SO42−) has been found in elevated concentrations in modern hydrothermal settings on Earth and linked to coupled ferric iron (Fe3+)- and molecular oxygen (O2)-driven oxidations of hydrothermal H2S and secondary sulfur (S) deposits enriched in elemental S and sulfide minerals. However, the relative proportions of SO42− from these two oxidation mechanisms in surface acidic hydrothermal systems are unclear. To address this uncertainty, we determined the aqueous SO42− contributions via Fe3+- and O2-driven oxidation pathways in acidic hot springs and mudpots of Iceland (Námafjall, Krýsuvík) and the United States (Valles Caldera, Lassen, Yellowstone). Approximately 40 water and 11 fumarole sediment samples were collected for oxygen isotope analyses (δ18O). The oxidation processes appear to be accompanied by large variation of the δ18O of SO42− (−8.8 to +5.5 ‰) similar to the δ18O of hot spring and mudpot water (−15.5 to +6.3 ‰), which is greatly controlled by inflow of meteoric water (e.g., runoff, groundwater) and surface evaporation. In the studied sites, the Fe3+-driven oxidation of hydrothermal elemental S and sulfide minerals appears to be an important source of SO42−, contributing ∼55 to 100% of SO42− when compared to contributions from O2-driven oxidation. Additionally, the distinctive high δ18O values of SO42− (up to +13.7 ‰) accompanied direct oxidation of H2S and/or hydrothermal S minerals by atmospheric O2 in dry (fumarolic) environments. This, in turn, is in agreement with previously determined O isotope fractionations (εsulfate-atm.oxygen ∼ 9.8 ‰) for low-temperature sulfide oxidation in the presence of O2. Our new quantitative measures of oxidation pathways signify the importance of Fe3+-driven oxidation of hydrothermal S to SO42− in the surface volcanic settings, which have significant implications for understanding widespread occurrences of SO42− found on the Fe-rich volcanic terrains of Mars.

The arc-scale spatial distribution of volcano erosion implies coupled magmatism and regional climate in the Cascades arc, United States

The morphology and distribution of volcanic edifices in volcanic terrains encodes the structure and evolution of underlying magma transport as well as surface processes that shape landforms. How magmatic construction and erosion interact on long timescales to sculpt these landscapes, however, remains poorly resolved. In the Cascades arc, distributed volcanic edifices mirror long-wavelength topography associated with underlying crustal magmatism and define the regional drainage divide. The resulting strong along- and across-arc modern precipitation gradients and extensive glaciation provide a natural laboratory for climate-volcano interactions. Here, we use 1,658 volcanic edifice boundaries to quantify volcano morphology at the arc-scale, and reconstruct primary edifice volumes to create first-order estimations of Cascades erosion throughout the Quaternary. Across-arc asymmetry in eroded volumes, mirroring similarly asymmetric spatial distribution of volcanism, suggests a coupling between magmatism and climate in which construction of topography enhances erosion by orographic precipitation and glaciers on million-year timescales. We demonstrate with a coupled landscape evolution and crustal stress model that mountain building associated with magmatism and subsequent orographically-induced erosion can redistribute surface loads and direct subsequent time-averaged magma ascent. This two-way coupling can thus contribute to Myr-scale spatial migration of volcanism observed in the Cascades and other arcs globally.

A “cool-water”, non-tropical, mixed volcaniclastic–carbonate ramp from the Early Cretaceous of southern Chile (45°40’S)

The Aysén-Río Mayo Basin was a back-arc/marginal basin developed in southwestern South America (43°–47°S) between the Tithonian–Aptian. Its sedimentary fill corresponds to the Coyhaique Group, which represents a transgressive–regressive succession. Six lithofacies and five microfacies were defined for three outcrops exposed south of Coyhaique (45°40’S). The outcrops have a mixed calcareous–volcaniclastic composition and were assigned to the early transgressive Toqui Formation, i.e., lowermost part of the Coyhaique Group. These mixed rocks comprise bioclastic–volcaniclastic conglomerate, gravelly allochemic sandstone, and gravelly–sandy allochem limestone. Bedding is sharp to amalgamated, sometimes rippled, depicting a wave- and storm-influenced, mixed inner- to mid-ramp. The ramp developed over a Valanginian, active volcanic terrain (Foitzick Volcanic Complex), source of the volcaniclastic sediments. Limestones are rich in reworked bioclasts, and controlled by calcitic organisms including gryphaeid oysters, non-geniculate red algae, and echinoid fragments, defining a heterozoan association (“maerl”-like sediments); less frequent are ahermatypic corals, serpulids, and carbonized wood. Based on their inferred paleolatitude (south of 45°–50°S), fossil assemblage (heterozoan), and kind of carbonate platform (ramp-type), these calcareous rocks of the Toqui Formation depict a “cool-water” (sensu lato), non-tropical setting. The fossil assemblage includes oysters (Aetostreon spp.), and abundant calcareous red algae attributed to Archamphiroa jurassica Steinmann (1930), a taxon previously known from the upper Tithonian Cotidiano Formation of Argentina. A. jurassica is here reported for the first time for the Lower Cretaceous of Chile, suggesting a broader upper Tithonian—Valanginian-Hauterivian? range for the species. The facies model presented here contrasts with the depositional environments depicted for correlative reefal rocks in Argentina (Tres Lagunas Formation), which reflect a “warm-water” setting. In the Aysén-Río Mayo Basin, the influence of sea-water key physical variables in the carbonate sedimentation, as well as the position and hydraulic regime of the carbonate platforms within the basin, and their interaction with the volcanism are still unclear.

Pliocene volcanic terrain of the South Caucasus as a missing link in Eurasian palaeobiogeography: Dating and palaeoenvironments of vertebrate assemblages of the Jradzor locality, Armenia

Cenozoic faunal exchanges between Europe, Asia, Africa and America played a key role in shaping modern-day Eurasian ecosystems with dispersal pathways controlled by the dynamics of natural palaeogeographic barriers (e.g., deserts, isthmuses, large water bodies, etc.). The South Caucasus is a mountainous region between Asia and Europe, which served as an important dispersal route during the late Cenozoic for the intercontinental exchanges of diverse terrestrial vertebrates. The Pliocene geology of this region is dominated by volcanic and volcaniclastic deposits that are generally not favourable for fossil preservation. However, a few rich fossil vertebrate faunas do occur although they lack comprehensive palaeoenvironmental and age constraints. In this paper, we present an integrated study of the stratigraphy and palaeontology of the Jradzor section located in the Gegham volcanic province of Armenia, to improve knowledge of late Cenozoic dispersal pathways. The 57-m-thick succession comprises 19 fossiliferous horizons with at least 48 identified vertebrate taxa (excluding birds). The palaeoenvironmental reconstruction suggests that the succession was deposited within a short-lived dammed lake that was subject to pyroclastic density flows, and later evolved into soil catenas. Taphonomic observations indicate that pyroclastic flows caused a high mortality of small-size vertebrates in most fossiliferous horizons, while a catastrophic lahar buried the large vertebrate fauna. Multiproxy dating places the studied section between 4.3 and ∼ 3.03 Ma and the mammalian fauna correlates to the MN15. Comparison with similar age localities from across the region shows that Jradzor comprises the most continuous Pliocene succession with the highest number of fossil taxa and fills the MN15 interregional gap. The rich fossil vertebrate faunas have Asian and primarily European affinities. Findings show that the South Caucasus was a significant dispersal route for terrestrial vertebrates between Europe, Asia and Africa, and is of crucial importance for understanding Eurasian palaeogeography.

Geotechnical aspects of drilling and excavation of volcanic terrain for groundwater exploitation

Heterogeneity of volcanic materials that constitute the Canary Islands (Spain) means that mining work in water galleries excavated on these islands, drilling into the terrain for many kilometres, is very challenging. They are composed of materials that vary significantly in terms of cohesion, ranging from very consolidated to loose and highly unstable. Water galleries have been key in the development of the Canary Islands, in order to obtain drinking water from the aquifer. Generally, aquifers are located in mountainous areas with difficult access, which complicates the drilling work. This article analyses the main geotechnical problems encountered in the construction of subterranean water galleries in the Canary Islands, as well as possible solutions to these problems, so that these can be applied to similar territories. As a general conclusion, the instabilities inherent in volcanic materials affect this type of work, and it is necessary to take specific measures for each type of geotechnical risk, as proposed in this article.

Mineralogy of explosive and effusive volcanic edifices in the Marius Hills Volcanic Complex

The Marius Hills Volcanic Complex exhibits the highest concentration of extrusive volcanic landforms on the Moon, in the form of both domes and cones. The interpretive advancements made in this investigation result from improved spectral resolution and analysis techniques. Moon Mineralogy Mapper (M3) spectral analysis shows that the rounded landforms in MHVC exhibit spectra consistent with glass, confirming a cinder cone with an explosive volcanic origin. The presence of scoria-like glass-rich pyroclasts that should be distinct from the glass beads collected during Apollo. This research provides evidence that spectroscopy can identify volcanic landforms when visible images of the morphology are inconclusive, which is essential for future exploration of volcanic terrains. The likely concurrent eruption of the domes and cones with the differences in the mineralogy of the resulting edifices (e.g., presence of glass) add supporting evidence to the hypothesis that extrinsic properties (e.g., ascent rate), not changes in magma composition (e.g., amount of volatiles), led to the different volcanic morphologies. Combining the morphology and the spectral data, we hypothesize that the magma evolution of the region was long-lived and with distinct early edifice-forming and later mare-forming episodes. The long-lived volcanism recorded in multiple volcanic units within close proximity in MHVC would be ideal for future exploration and eventual sample return.

Comparison of two landslide hazard zonation methods in the volcanic terrain of Temanggung Regency, Central Java, Indonesia

Landslides are a recurring phenomenon that disrupts the natural environment and causes yearly property damage, economic losses, and fatalities. The damage is expected to increase due to deforestation rates, population growth, agriculture, slope-building infrastructure expansion, and global climate change. This study assesses the susceptibility to landslides through Weight of Evidence (WoE) and Frequency Ratio (FR) methods in the Temanggung Regency, Central Java Province, Indonesia, that located on the slopes of two active volcanoes. Initially, a landslide record and the input parameters of the landslide controlling factors were prepared from field surveys, remote sensing data, and secondary data and processed by a geographic information system (GIS). Six landslide parameters in thematic layer maps were selected to develop landslide susceptibility: slope, lithology type, geological structure density, land cover, and rainfall. According to the WoE and FR models, a landslide susceptibility zoning map was classified into four landslide-prone zones from low to very high. Finally, the success and predictive rate curves method confirmed the landslide susceptibility maps to check the model accuracy. The results showed that the landslide susceptibility map using the WoE method had better accuracy than the FR method, with a success rate of 78.48% and a prediction rate of 81.1%. In comparison, the FR method was 74.53% for the success rate and 78.48% for the prediction rate. These landslide susceptibility maps can be used as a guideline to develop land-use planning and landslide disaster mitigation.

Scoria Field: Volcanic Imaginaries of Tamaki Makaurau

How might a volcanic material imaginary — particularly of the basalt scoria volcanic field that underlies Tāmaki Makaurau / Auckland in Aotearoa New Zealand — provide ways for people to see themselves collectively? Our surroundings shape a sense of identity, and spatial interactions organize our experience in the city. ’Scoria Field’ is a spatial design research inquiry into place-making; investigating the potential for material experiences of a volcanic landscape to produce public space along the coast of Takapuna, on Tāmaki’s North Shore. Through imaginative engagement with volcanic rock, this research explores abstract and tangible ways to unfold a narrative of matter. Through a practice of drawing and artisanal material explorations, the research engages with geographical, cultural, and social aspects of scoria and the volcanic landscape of Tāmaki Makaurau. The project culminates with a proposal to refurbish an existing car park as a public space that offers a new way for people to see each other collectively by engaging with their volcanic terrain.

A Case Study: Groundwater Level Forecasting of the Gyorae Area in Actual Practice on Jeju Island Using Deep-Learning Technique

As a significant portion of the available water resources in volcanic terrains such as Jeju Island are dependent on groundwater, reliable groundwater level forecasting is one of the important tasks for efficient water resource management. This study aims to propose deep-learning-based methods for groundwater level forecasting that can be utilized in actual management works and to assess their applicability. The study suggests practical forecasting methodologies through the Gyorae area of Jeju Island, where the groundwater level is highly volatile and unpredictable. To this end, the groundwater level data of the JH Gyorae-1 point and a total of 12 kinds of daily hydro-meteorological data from 2012 to 2021 were collected. Subsequently, five factors (i.e., mean wind speed, sun hours, evaporation, minimum temperature, and daily precipitation) were selected as hydro-meteorological data for groundwater level forecasting through cross-wavelet analysis between the collected hydro-meteorological data and groundwater level data. The study simulated the groundwater level of the JH Gyorae-1 point using the long short-term memory (LSTM) model, a representative deep-learning technique, with the selected data to show that the methodology is adequately applicable. In addition, for its better utilization in actual practice, the study suggests and analyzes (i) a derivatives-based groundwater level learning model which is defined as derivatives-based learning to forecast derivatives (gradients) of the groundwater level, not the target groundwater time series itself, and (ⅱ) an ensemble forecasting methodology in which groundwater level forecasting is performed repetitively with short time intervals.

Pliocene Volcanic Terrain of the South Caucasus: The Missing Link in Eurasian Palaeobiogeography

Pliocene Volcanic Terrain of the South Caucasus: The Missing Link in Eurasian Palaeobiogeography

Geophysical data provide three dimensional insights into porphyry copper systems in the Silverton caldera, Colorado, USA

The Silverton caldera in southwest Colorado, USA hosts polymetallic veins and pervasively altered rocks indicative of porphyry copper systems. Nearly a kilometer of erosion has exposed multiple levels of the hydrothermal systems from shallow lithocaps down to quartz-sericite-pyrite veins. New airborne electromagnetic and magnetic survey data are integrated with previous alteration mapping and porphyry models to show the subsurface geophysical response of shallow to deep levels of the porphyry system. Qualitative map views show lateral changes in the magnetization and resistivity of the hydrothermally altered rocks. The volcanic terrain exhibits high magnetization and high amplitude anomalies map near-surface plutonic rocks associated with porphyry systems. Magnetic susceptibility measurements on outcrops of hydrothermally altered rocks indicate magnetite content decreases upward and outward from the source intrusions where magnetic anomaly lows are observed over the lithocaps. The resistivity maps highlight hydrothermal alteration as resistivity lows with exception being rocks having propylitic alteration. Quantitative resistivity models show low resistivity zones with an apparent thickness around 50–150 m beneath quartz-sericite-pyrite veins interpreted to be the result of supergene processes that may continue today, and the calculated magnetic source depths occur near the top of this zone. The resistivity models also show rocks having propylitic, silicic, and quartz-alunite-pyrophyllite assemblages exhibit high resistivity with depth, and argillic alteration assemblages had high resistivity due to high quartz content. This integrated approach presented in a three-dimensional environment provides guidance when exploring for porphyry copper systems in less exposed terrains.

Geodiversity influences limnological conditions and freshwater ostracode species distributions across broad spatial scales in the northern Neotropics

Abstract. Geodiversity is recognized as one of the most important drivers of ecosystem characteristics and biodiversity globally. However, in the northern Neotropics, the contribution of highly diverse landscapes, environmental conditions, and geological history in structuring large-scale patterns of aquatic environments and aquatic species associations remains poorly understood. We evaluated the relationships among geodiversity, limnological conditions, and freshwater ostracodes from southern Mexico to Nicaragua. A cluster analysis (CA), based on geological, geochemical, mineralogical, and water-column physical and chemical characteristics of 76 aquatic ecosystems (karst, volcanic, tectonic) revealed two main limnological regions: (1) karst plateaus of the Yucatán Peninsula and northern Guatemala, and (2) volcanic terrains of the Guatemalan highlands, mid-elevation sites in El Salvador and Honduras, and the Nicaraguan lowlands. In addition, seven subregions were recognized, demonstrating a high heterogeneity of aquatic environments. Principal component analysis (PCA) identified water chemistry (ionic composition) and mineralogy as most influential for aquatic ecosystem classification. Multi-parametric analyses, based on biological data, revealed that ostracode species associations represent disjunct faunas. Five species associations, distributed according to limnological regions, were recognized. Structural equation modeling (SEM) revealed that geodiversity explains limnological patterns of the study area. Limnology further explained species composition, but not species richness. The influence of conductivity and elevation were individually evaluated in SEM and were statistically significant for ostracode species composition, though not for species richness. We conclude that geodiversity has a central influence on the limnological conditions of aquatic systems, which in turn influence ostracode species composition in lakes of the northern Neotropical region.

Volcanically-derived deposits and sequences: a unified terminological scheme for application in modern and ancient environments

Abstract The genesis of particles and their transport mechanisms are the two fundamental factors driving the accumulation of sediments associated with volcanism or derived from volcanic sources. These factors are therefore the most important criteria on which to base a useful classification of sediments in such environments. However, the relative significance of the nature of particles v. the transporting mechanism forming a deposit varies in existing terminological schemes: those schemes applied where volcanological contextual information is available tend to give precedence to the transportation process; whereas sedimentological schemes examining ancient deposits tend to focus principally on the nature of particles. Here, we provide an outline of the challenges in classifying volcanically derived sediments and put forward a scheme that aims to bridge current terminological differences and accommodate variable levels of uncertainty. This work defines three endmembers ( primary volcaniclastic , secondary volcaniclastic , volcanic epiclastic ) that correspond to (a) deposits whose particles are produced, transported and emplaced directly by volcanic mechanisms; (b) deposits whose particles are produced directly by volcanic events but transported and accumulated by non-volcanic mechanisms, either in continuum with the events or after interim storage; (c) deposits whose particles are produced by weathering/erosion of volcanic terrains and transportation of derived material by non-volcanic mechanisms. When the complex combination of genetic and transportation processes accumulating volcaniclastic sequences is not clear, but a strong relationship between an eruptive event and the studied volcaniclastic deposit can still be demonstrated, a further category ( volcanogenic ) has been introduced.

Microbial Response to Increased Temperatures Within a Lava-Induced Hydrothermal System in Iceland: An Analogue for the Habitability of Volcanic Terrains on Mars.

Fossil hydrothermal systems on Mars are important exploration targets because they may have once been habitable and could still preserve evidence of microbial life. We investigated microbial communities within an active lava-induced hydrothermal system associated with the 2014-2015 eruption of Holuhraun in Iceland as a Mars analogue. In 2016, the microbial composition in the lava-heated water differed substantially from that of the glacial river and spring water sources that fed into the system. Several taxonomic and metabolic groups were confined to the water emerging from the lava and some showed the highest sequence similarities to subsurface ecosystems, including to the predicted thermophilic and deeply branching Candidatus Acetothermum autotrophicum. Measurements show that the communities were affected by temperature and other environmental factors. In particular, comparing glacial river water incubated in situ (5.7°C, control) with glacial water incubated within a lava-heated stream (17.5°C, warm) showed that microbial abundance, richness, and diversity increased in the warm treatment compared with the control, with the predicted major metabolism shifting from lithotrophy toward organotrophy and possibly phototrophy. In addition, thermophilic bacteria isolated from the lava-heated water and a nearby acidic hydrothermal system included the known endospore-formers Geobacillus stearothermophilus and Paenibacillus cisolokensis as well as a potentially novel taxon within the order Hyphomicrobiales. Similar lava-water interactions on Mars could therefore have generated habitable environments for microbial communities.

Consolidated Chemical Provinces on Mars: Implications for Geologic Interpretations

AbstractChemical provinces were defined on Mars a decade ago using orbital nuclear spectroscopy of K, Th, Fe, Si, Ca, Cl, and H2O. However, past multivariate analyses yielded three sets of provinces, suggesting methodologic variability. Province‐stability to the inclusion of Al and S is also unknown, presenting additional uncertainties for geologic insight. Here we consolidate key multivariate methods to define the first cross‐validated provinces. In southern highlands, the highly incompatible K and Th show non‐uniform distribution with higher values in mid Noachian and Hesperian than late Noachian – early Hesperian volcanic terrains. Silica‐ and Al‐depletion trends from Noachian to Amazonian indicate highly differentiated mantle with variable degree of melting. Late Hesperian lowlands are highly depleted in Al and enriched in K and Th, consistent with volcanic resurfacing from a low‐degree partially melted, garnet‐rich mantle. Furthermore, older volatile‐rich regions such as Medusae Fossae Formation exhibit igneous geochemistry, consistent with water‐limited isochemical weathering throughout Mars's history.

Vanadium for Green Energy: Increasing Demand but With Health Implications in Volcanic Terrains.

The transition to a clean energy future may require a very substantial increase in resources of vanadium. This trend brings into focus the potential health issues related to vanadium in the environment. Most vanadium enters the Earth's crust through volcanic rocks; hence, vanadium levels in groundwaters in volcanic aquifers are higher than in other aquifers and can exceed local guidance limits. The biggest accumulation of volcanogenic sediment on the planet is downwind of the Andes and makes up much of Argentina. Consequently, groundwaters in Argentina have the highest vanadium contents and constitute a global vanadium anomaly. The high vanadium contents have given rise to health concerns. Vanadium could be extracted during remediation of domestic and other groundwater, and although the resultant resource is limited, it would be gained using low‐energy technology.

Remote Sensing Survey of Altiplano-Puna Volcanic Complex Rocks and Minerals for Planetary Analog Use

The Altiplano-Puna Volcanic Complex (APVC) of the Central Andes is an arid region with extensive volcanism, possessing various geological features comparable to those of other solar system objects. The unique features of the APVC, e.g., hydrothermal fields and evaporite salars, have been used as planetary analogs before, but the complexity of the APVC presents a wealth of opportunities for more analog studies that have not been exploited previously. Motivated by the potential of using the APVC as an analog of the volcanic terrains of solar system objects, we mapped the mineralogy and silica content of the APVC up to ~100,000 km2 in northern Chile based on a combination of remote sensing data resembling those of the Moon and Mars. The band ratio indices of Landsat 8 Operational Land Imager multispectral images and mineral classifications based on spectral hourglass approach using Earth Observing-1 Hyperion hyperspectral images (both in the visible to shortwave infrared wavelengths) were used to map iron-bearing and alteration minerals. We also used Hyperion imagery to detect feldspar spectral signatures and demonstrated that feldspar minerals can be detected on non-anorthosites, which may influence interpretations of feldspar spectral signatures on Mars. From the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Emissivity Dataset, we derived the silica percentage of non-evaporite rocks within errors of approximately 2–3 wt.% SiO2 for those in the 60–70 wt.% range (about 8 wt.% errors for the 50–60 wt.% range). Based on an integrated assessment of the three datasets, we highlighted three regions of particular interest worthy of further field investigation. We also evaluated the benefits and limitations of all three remote sensing methods for mapping key minerals and capturing rock diversity, based on available samples and existing geological maps.

Modeling spatial landslide susceptibility in volcanic terrains through continuous neighborhood spatial analysis and multiple logistic regression in La Ciénega watershed, Nevado de Toluca, Mexico

Modeling spatial landslide susceptibility in volcanic terrains through continuous neighborhood spatial analysis and multiple logistic regression in La Ciénega watershed, Nevado de Toluca, Mexico

Phosphorus limitation in low nitrogen lakes in New Zealand

ABSTRACT Lakes on volcanic soils of the North Island of New Zealand, compared to north temperate lakes, have low total nitrogen:total phosphorus (TN:TP) ratios, low dissolved inorganic nitrogen concentrations during summer stratification, and have positive chlorophyll a responses to N additions more frequently than to P in nutrient enrichment bioassays. This response has resulted, in some cases, to the imposition of N loading caps on some lake catchments, in contrast to nutrient management in north temperate lakes focused more on P management. To explore this possible difference in limiting nutrients, a suite of nutrient status indicators based on measurement of ambient seston stoichiometry and metabolic activity, which have been widely used in north temperate lakes, were applied to 8 lakes on volcanic terrain with previously reported N limitation. These nutrient status measurements were previously calibrated to inform whether in situ phytoplankton are growth-rate limited and, if so, which nutrient is limiting growth rate. In austral summer 2015, all 8 lakes showed indications of P limitation, and P limitation was more extreme, pervasive, and persistent (among samplings) than N limitation. Indications of N limitation were not observed without contemporaneous evidence of P limitation, but P limitation was frequently observed without evidence of N limitation. One lake, Rotorua, was not strongly nutrient limited, and phytoplankton were likely growing at or near optimum growth rates. In this study the commonly used TN:TP ratio was a poor predictor of which nutrient was potentially limiting in situ phytoplankton.