Main Eruption Research Articles

Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland

The active rift zones in Iceland provide unique insight into the geodynamic processes of divergent plate boundaries. The geodynamics of Iceland are studied intensively, particularly, by geophysical methods sensitive to active and/or visible structures such as earthquake seismic and Synthetic Aperture Radar observations or aerial photographs. However, older and less active structures, that may exert a strong control on the presently active geodynamics, are often buried beneath recent volcanic or sedimentary deposits and are—due to their passive mode—overseen by the typical geophysical investigations. Aeromagnetic surveys provide spatial information about subsurface magnetization contrasts relating to both active and inactive structures. However, the aeromagnetic data in Iceland were collected in the 1970-80s and are relevant only to large-scale regional rift studies. With the availability of reliable drones and light-weight atomic scalar sensors, high-quality drone magnetic surveys can provide an unprecedented spatial resolution of both active and passive structures of rift systems as compared to conventional airborne surveys. Here, we present the results of a drone-towed magnetic scalar field and scalar gradiometry study of the north-northeast trending Bárðarbunga spreading center to the north of the Vatnajökull ice cap, Iceland. Our results provide new information about the structural complexity of rift zones with evidence of densely-spaced, conjugate and oblique faults throughout the area. Evidence is shown of a hitherto unknown and prominent east-northeast trending fault structure that coincides with the northern tip of the main eruption edifice of the 1797 and 2014-15 Holuhraun volcanic events. We suggest that this pre-existing structure controlled the locus of vertical magma migration during the two Holuhraun events.

Subsurface delineation of Sukadana Basalt Province based on gravity method, Lampung, Indonesia

Research subject. The geological profile of Sukadana Basalt Province as a large basalt outcrop in the back arc of Sumatra remains to be unclear. This also concerns the geological structures and their relationship with the Sundaland regional geology. Aim. To reveal the type and pattern of geological structures that controlled the Sukadana Basalt Province (SBP) to the surface, the distribution of Sukadana Basalt on subsurface and its relationship with Sundaland regional tectonics. Materials and Methods. A reprocessed bouguer anomaly map of Tanjungkarang quadrangle 1991 was used. Results. We found that the main eruption was located in the center of SBP. The forward modeling data show the thickness of SBP to reach 3,200 m. There are two Northwest-Southeast striking normal faults and one fissure controlling the development of SBP. These fractures served as the primary conduit for magma to ascend from the mantle to the Earth’s surface. We also found North-South striking normal faults and West-East dextral strike-slip fault that formed at Early Oligocene and indirectly supported the magma ascend to the surface. Conclusions. The North-South striking normal faults were correlated with the Sundaland oroclinal bending. These faults developed through the extrados zone, a large pull-apart area that caused the continental lithosphere to become thinner. Meanwhile, Quaternary-Northwest-Southeast striking fractures are correlated with the development of the Great Sumatra Fault. The formation of Northwest-Southeast striking fractures was affected by the Great Sumatra Fault movement, and the thinning of the back-arc crust affected by multi-extensional structures was implicated in the ascend of SBP’s magma to the surface.

An Investigation on the Ionospheric Response to the Volcanic Explosion at Hunga Ha'apai in 2021

AbstractThe Hunga Ha'apai volcano eruption (20.536°S, 175.382°W in Tonga), which started intermittently around December 2021 and most violently erupted on 15 January 2022, is considered to be the largest volcanic outbreak in recent decades. In this research, we derived the ionospheric total electron content (TEC) over Sanya (18.400°N, 109.600°E), Wuhan (30.530°N, 114.610°E), and Mohe (53.500°N, 122.370°E), from the Global Navigation Satellite System observations. Then we investigated the coupling between the volcano eruption and ionosphere through the TEC variations. The TEC anomaly decayed from about 10 days before main eruption of the Hunga Ha'apai volcano, and showed obvious fluctuations during the eruption phase. The TEC anomaly propagated periodically, with its autocorrelation‐analyzed period of about 16.5 hr during the intermittent outbreak and about 8 hr during the main outbreak phase. Its independently derived wavelet‐analyzed periods are about 9.4 hr during the intermittent outbreak and about 9.4 and 18.8 hr during the main outbreak phase. The propagation is mainly expressed in low frequencies, with energy concentrated in the range of 0–10−3 Hz. This study highlights that the preeruption activities may play an important role in the coupling between the volcanic eruption and ionosphere disturbances.

SO 2 emissions during the 2021 eruption of La Soufrière, St Vincent, revealed with back-trajectory analysis of TROPOMI imagery

Abstract Determining SO 2 emission time-series from explosive eruptions can provide important insights into the driving magmatic processes, however accurate measurements are difficult to collect. Satellite-based platforms provide SO 2 imagery, however translating this to the altitude- and time-resolved emission history required to unravel volcanic processes is a major challenge. This means SO 2 emission time-series are rarely quantified for major eruptions, producing a gap in our understanding of explosive volcanism. Here, we combine SO 2 imagery collected by the TROPOspheric Monitoring Instrument (TROPOMI) with PlumeTraj, a back-trajectory analysis toolkit, to reconstruct the SO 2 emission prior to, and during, the explosive eruption of La Soufrière volcano, St Vincent, in April 2021. Precursory SO 2 emissions were quantified the day before the eruption, with emission rates in agreement with ground-based measurements. We estimate initial magma sulfur contents by comparing the measured SO 2 emissions with erupted magma volumes, finding that the initial explosion was sulfur poor (730 ppm S) compared to the main eruption phase (up to 3400 ppm S). This suggests that the initial explosion cleared old, previously degassed magma resident in the shallow plumbing system, followed by the eruption of the main, mostly un-degassed magma source.

Eruptive history of the last-1300-years activity of Kelud volcano, Indonesia: Inferences from stratigraphy, chronology, sedimentology, componentry, and geochemistry

Kelud is considered one of the deadliest volcanoes in Indonesia due to its proximity to three cities in East Java (Malang, Kediri, and Blitar) and violent eruptions over the last century. Regardless of the frequently witnessed eruptions, the volcanic stratigraphy for the historical ages has been poorly understood. Here, we provide the first documentation of volcanic stratigraphy for the last 1300 years of activity at Kelud. Componentry and 14C data are coupled with detailed field observations to develop a comprehensive stratigraphy and characterize the main eruption types. The volcanic succession can be subdivided into ten bed-sets composed of pyroclastic density current (PDC) and tephra fallout deposits. A total of twelve fallouts and ten individual PDC units were identified between ∼1.3 and 0.1 cal. ka B.P. One of these units may be attributed to the 1481C.E. eruption. The fallout layers are generally thin, derived from short-sustained eruption columns. By contrast, PDC deposits are massive to stratified, suggesting variable particle concentrations typically resulting from low-column collapses. This complex stratigraphy suggests that Kelud is capable of producing a wide spectrum of eruptions with an increasing eruptive frequency over time and shorter dormancy periods than those between witnessed eruptions (from once /∼100 years to once/∼10 years). This stratigraphic framework, which documents extended records from the oldest witnessed eruption in Kelud (1000C.E.), sheds new insights into Kelud's activity during historical time. Since the products share similar characteristics with those from the most recent activities at Kelud (e.g., 1990, 2007–2008, and 2014), similar eruptions may also occur in the future.

Analysis of Volcanic Development Model and Main Controlling Factors of Oil Distribution in the Third Member of Shahejie Formation in Zaoyuan Oilfield

In order to clarify the influence in the volcanic mode and structure on the oil reservoirs, the volcanic reservoir characteristics, volcanic eruption pattern, and volcanic eruption period of the third member of the Shahejie formation in the Dagang Oilfield Zao35 fault block are studied by combining logging, 3D seismic, and production data, and to provide geological basis for the subsequent development of volcanic reservoirs. The results show that the volcanic body of the Zao35 fault block is jointly controlled by the fissure-centered eruption mode, and there are three strings of bead-shaped eruption centers as well as a fault overflow channel. Based on the seismic response characteristics, the volcanic rocks can be divided into three main eruption cycles. Moreover, combined with the relatively stable mudstone interlayer encountered by the single well, it can be further divided into eight volcanic eruption periods. There are three different lava units in the overflow facies of each stage, namely thick layer dense basalt, basalt with pores developed at the top and dense at the bottom, and basalt with pores developed at the top and dense in the middle. Influenced by the volcanic development model, the oil is mainly distributed in the volcanic reservoir on the slope belt between the central eruption and the fracture eruption. Affected by volcanic eruption periods, the pore basalt at the top and bottom of each period controls the distribution of the oil reserves. Therefore, the thick layer stomatal basalt located between the two eruption modes is the key target of the next development.

High-Precision Characterization of Seismicity from the 2022 Hunga Tonga-Hunga Ha'apai Volcanic Eruption

AbstractThe earthquake swarm accompanying the January 2022 Hunga Tonga-Hunga Ha'apai (HTHH) volcanic eruption includes a large number of posteruptive moderate-magnitude seismic events and presents a unique opportunity to use remote monitoring methods to characterize and compare seismic activity with other historical caldera-forming eruptions. We compute improved epicentroid locations, magnitudes, and regional moment tensors of seismic events from this earthquake swarm using regional to teleseismic surface-wave cross correlation and waveform modeling. Precise relative locations of 91 seismic events derived from 59,047 intermediate-period Rayleigh- and Love-wave cross-correlation measurements collapse into a small area surrounding the volcano and exhibit a southeastern time-dependent migration. Regional moment tensors and observed waveforms indicate that these events have a similar mechanism and exhibit a strong positive compensated linear vector dipole component. Precise relative magnitudes agree with regional moment tensor moment magnitude (Mw) estimates while also showing that event sizes and frequency increase during the days after the eruption followed by a period of several weeks of less frequent seismicity of a similar size. The combined information from visual observation and early geologic models indicate that the observed seismicity may be the result of a complex series of events that occurred after the explosive eruption on 15 January, possibly involving rapid resupply of the magma chamber shortly after the eruption and additional faulting and instability in the following weeks. In addition, we identify and characterize an Mw 4.5 event five days before the paroxysmal explosion on 15 January, indicating that additional seismic events preceding the main eruption could have been identified with improved local monitoring. Our analysis of the HTHH eruption sequence demonstrates the value of potentially utilizing teleseismic surface-wave cross correlation and waveform modeling methods to assist in the detailed analysis of remote volcanic eruption sequences.

Late Permian High-Ti and Low-Ti Basalts in the Songpan–Ganzi Terrane: Continental Breakup of the Western Margin of the South China Block

Although the Emeishan Large Igneous Province (ELIP) has been thoroughly researched, the role of the ELIP in the tectonics of the Songpan–Ganzi extensional basin in the eastern Tibetan Plateau has long been argued without any corroborated and robust evidence. We have investigated the basalt succession of the Dashibao Formation along Xindianzi and Xuecheng sections in the southeast margin of the Songpan–Ganzi Terrane (SGT). New SIMS zircon U-Pb ages and geochemical features of the Dashibao Formation are reported in this paper. Zircons of basalt sample XDZ02-1 yielded a weighted mean age of 259.1 ± 1.66 Ma, which is in alignment with the period when the main eruption of the ELIP occurred. Zircons from two tuff samples XDZ05-1 and XC05-2, overlying the basalt succession, were dated at 251.8 ± 1.57 Ma and 251.5 ± 0.27 Ma, respectively. These new dating results revealed a ~10 Ma eruption for the Dashibao basalts. The Dashibao basalts are geochemically classified into alkaline basalts (Group 1) and tholeiitic basalts (Group 2), which are a part of the Emeishan basalt. We thus propose that the Dashibao basalts erupted in a continental rift setting, located at the margin of the ELIP. The temporal and spatial coincidence of the Dashibao basalt, ELIP, and continental rifting in the western margin of the South China Block suggest that the continental breakup is a response to the Permian mantle plume that triggered the separation of the SGT in the eastern Tibetan Plateau.

The Hunga Tonga–Hunga Ha’apai Eruption of 15 January 2022: Observations on the International Monitoring System (IMS) Hydroacoustic Stations and Synergy with Seismic and Infrasound Sensors

AbstractExamination of the International Monitoring System (IMS) hydroacoustic data recorded during the 15 January 2022 eruption of the Hunga Tonga–Hunga Ha’apai (HTHH) volcano shows that the in-water hydroacoustic sensors recorded a long-duration (40 min) activity starting before and ending after the paroxysmal HTHH eruption at about 4:15 UTC. The main eruption at 4:15 UTC simultaneously generated low-frequency [0.001–0.05] Hz seismic body waves and large infrasound waves in the atmosphere, as well as a tsunami. The peak-to-peak pressure observed at the closest IMS station, IS22, 1850 km away from the source, was 340 Pa, dwarfing the largest previously observed record for the signal from the Chelyabinsk meteor. The infrasound waves included a Lamb wave containing periods at least up to 2000 s. The Lamb wave and tsunami are well recorded on infrasound and near-shore seismometers. The air wave generated a precursor tsunami ahead of the main tsunami, but we do not observe it on the hydroacoustic IMS network. The dispersive tail of the main tsunami is observed on four in-water hydroacoustic hydrophone stations, one of them as far as 16,120 km away in the Atlantic Ocean.

SN 2019zrk, a bright SN 2009ip analog with a precursor

We present photometric and spectroscopic observations of the Type IIn supernova SN 2019zrk (also known as ZTF 20aacbyec). The SN shows a > 100 day precursor, with a slow rise, followed by a rapid rise toM ≈ −19.2 in therandgbands. The post-peak light-curve decline is well fit with an exponential decay with a timescale of ∼39 days, but it shows prominent undulations, with an amplitude of ∼1 mag. Both the light curve and spectra are dominated by an interaction with a dense circumstellar medium (CSM), probably from previous mass ejections. The spectra evolve from a scattering-dominated Type IIn spectrum to a spectrum with strong P-Cygni absorptions. The expansion velocity is high, ∼16 000 km s−1, even in the last spectra. The last spectrum ∼110 days after the main eruption reveals no evidence for advanced nucleosynthesis. From analysis of the spectra and light curves, we estimate the mass-loss rate to be ∼4 × 10−2 M⊙yr−1for a CSM velocity of 100 km s−1, and a CSM mass of 1 M⊙. We find strong similarities for both the precursor, general light curve, and spectral evolution with SN 2009ip and similar SNe, although SN 2019zrk displays a brighter peak magnitude. Different scenarios for the nature of the 09ip-class of SNe, based on pulsational pair instability eruptions, wave heating, and mergers, are discussed.

Satellite Detection of a Massive Phytoplankton Bloom Following the 2022 Submarine Eruption of the Hunga Tonga‐Hunga Haʻapai Volcano

AbstractThe largest submarine volcanic eruption of this century led to a dramatic phytoplankton bloom north of the island of Tongatapu, in the Kingdom of Tonga. In the absence of shipboard observations, we reconstructed the dynamics of this event by using a suite of satellite observations. Two independent bio‐optical approaches confirmed that the phytoplankton bloom was a robust observation and not an optical artifact due to volcanogenic material. Furthermore, the timing, size, and position of the phytoplankton bloom suggest that plankton growth was primarily stimulated by nutrients released from volcanic ash rather than by nutrients upwelled through submarine volcanic activity. The appearance of a large region with high chlorophyll a concentrations <48 hr after the largest eruptive phase indicates a fast ecosystem response to nutrient fertilization. However, net phytoplankton growth probably initiated before the main eruption, when weaker volcanism had already fertilized the ocean.

Pitted-Ground Volcanoes on Mercury

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

Monitoring magma migration at Mt. Etna using the Seismic Amplitude Ratio Analysis method

The Seismic Amplitude Ratio Analysis method (SARA) was applied to data recorded six days before the May 13, 2008 eruption of Mt. Etna to test its potential as a forecasting attribute. By using this method, the magma migration path, as well as the seismic migration, can be determined with the amplitude of continuous data recorded at least at one pair of stations from a seismic network near the eruption site. Due to the sudden changes in the seismic amplitude ratio calculated for each pair of stations, the seismic migration trend, as well as the magma path at depths, were detected before the main eruption. The start and end times of the seismic swarms were also determined. The standard practice to achieve similar results is to use volcanic tremors, which must be pre-selected thus reducing efficiency and increasing the time needed. By using the whole seismic signal, the method provides a simpler semi-automated alternative, especially for a seismic event or places where it is not possible to record tremors continuously. This simple method is useful to reduce uncertainties relative to hazardous magma propagation during volcanic unrest, as it helps improve the accuracy of locating seismic swarms and determining the direction of magma movement at depth before the eruption. We also analyzed the amplitude ratio trend using Mann-Kendall and Sen's estimator test. The results of these tests confirmed a positive and increasing trend from the day before the eruption in most pairs of stations.

Analysis of the 2020 Taal Volcano tephra fall deposits from crowdsourced information and field data

After 43 years of dormancy, Taal Volcano violently erupted in January 2020 forming a towering eruption plume. The fall deposits covered an area of 8605 km2, which includes Metro Manila of the National Capital Region of the Philippines. The tephra fall caused damage to crops, traffic congestion, roof collapse, and changes in air quality in the affected areas. In a tropical region where heavy rains are frequent, immediate collection of data is crucial in order to preserve the tephra fall deposit record, which is readily washed away by surface water runoff and prevailing winds. Crowdsourcing, field surveys, and laboratory analysis of the tephra fall deposits were conducted to document and characterize the tephra fall deposits of the 2020 Taal Volcano eruption and their impacts. Results show that the tephra fall deposit thins downwind exponentially with a thickness half distance of about 1.40 km and 9.49 km for the proximal and distal exponential segments, respectively. The total calculated volume of erupted fallout deposit is 0.057 km3, 0.042 km3, or 0.090 km3 using the exponential, power-law, and Weibull models, respectively, and all translate to a VEI of 3. However, using a probabilistic approach (Weibull method) with 90% confidence interval, the volume estimate is as high as 0.097 km3. With the addition of the base surge deposits amounting to 0.019 km3, the volume translates to a VEI of 4, consistent with the classification for the observed height and umbrella radius of the 2020 main eruption plume. VEI 4 is also consistent with the calculated median eruption plume height of 17.8 km and sub-plinian classification based on combined analysis of isopleth and isopach data. Phreatomagmatic activity originated from a vent located in Taal Volcano’s Main Crater Lake (MCL), which contained 42 million m3 of water. This eruptive style is further supported by the characteristics of the ash grain components of the distal 12 January 2020 tephra fall deposits, consisting dominantly of andesitic vitric fragments (83–90%). Other components of the fall deposits are lithic (7–11%) and crystal (less than 6%) grains. Further textural and geochemical analysis of these tephra fall deposits contributes to better understand the volcanic processes that occurred at Taal Volcano, one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) because of its destructive nature and proximity to densely populated areas. The crowdsourcing initiative provided a significant portion of the data used for this study while at the same time educating and empowering the community to build resilience.

Estimates on the Frequency of Volcanic Eruptions on Venus

AbstractVenus hosts many thousands of volcanic landforms, including individual edifices, volcanotectonic structures, and vast expanses of effusively emplaced plains lavas. Numerous lines of circumstantial evidence together suggest that the planet is volcanically active today. Although previous studies have calculated volcanic eruptive fluxes on the basis of the volumes of lava needed to bury craters of various diameters on Venus, no estimates of the frequency of volcanic eruptions on the planet yet exist. In this study, we analyzed records for eruptive events on Earth between 1 January 1980 and 21 January 2021 for which data on duration and eruption intensity were available, and classified those events by tectonic setting. We then extrapolated those results to Venus by a simple scaling factor. We estimate that as many as 120 discrete eruptions, from individual volcanic edifices and of any duration and intensity, may occur on Venus per Earth year. Further, within any given 60‐day window—a nominal timeframe over which an aerial platform capable of detecting volcanic activity might operate in the middle Venus atmosphere—we expect about four new eruptions to begin, with that number rising to almost eight when both new events and those ending within 100 days of the main eruption are included, or to as many as 20 when considering activity that lasts for 1,000 days. Several complementary techniques exist with which to search for volcanic eruptions at Venus, either from orbit, within the atmosphere, or on the surface, that can be used to test the estimates we make here.

Multi-Wavelength Observations of a Failed Filament Eruption and Associated Hovered Coronal Mass Ejection

Failed filament eruption remains mysterious on its initiation, magnetic environment, and erupting and failing mechanisms. We present multi-wavelength observations of a failed filament eruption and its associated hovered coronal mass ejection (hovered-CME) from limb observations of the Ahead of Solar Terrestrial Relations Observatory. On-disk observations from Solar Dynamics Observatory show the expansion of the anchored leg of an S-shaped filament during the pre-eruption phase. The main eruption starts as a sudden ejection of the erupted leg, which is followed by the appearance of EUV brightening in the S-shaped magnetic field. The brightening is spatio-temporal accompanied with hard X-ray emission enhancement, and cancellation of opposite magnetic polarities, which imply possible reconnection. After reaching the maximum displacement, the erupted material drains back to the Sun along the remaining anchored leg. The non-linear force free magnetic field extrapolation shows an S-shaped magnetic field, formed by two magnetic structures, with a strong enveloped magnetic field. The decay index at the possible apex of the filament is 0.8–1.2. Observations indicate that the failed filament eruption is triggered by tether cutting reconnection and is possibly confined by the upper magnetic field. The hovered-CME, resulting from the failed filament eruption and recording as a coronal mass ejection (CME), may cause the overestimation of the CME count.

The geology of the late-Cretaceous Salpeterkop volcano near Sutherland: A geomorphologic benchmark

The Salpeterkop volcano is spatially part of the Sutherland Suite of alkaline rocks in the Northern Cape. It is one of the best preserved volcanoes in South Africa with part of the tuff ring still intact, remnants of the ejecta mantle outside the crater still preserved, and is host to epiclastic rocks, including ash and lapillistone and water lain sediments, inside the crater. New dates from apatites and phlogopites from Salpeterkop suggest an age close to 70 Ma. This Upper Cretaceous age is supported by the silicified wood found within the epiclastic sediments. Its relationship to the alkaline rocks in this cluster is not entirely clear but field evidence suggests that initial olivine melilitites and ultramafic bodies were followed by the main eruption that produced Salpeterkop. Clear igneous components in the associated breccias and pyroclastics are rare but indicate that this volcano was linked to an alkaline (trachytic) intrusion driven by phreatic magmatism. This is further highlighted by the presence of (nepheline?) syenite xenoliths in some carbonatite breccias and dykes that are part of the later carbonatites with its associated hydrothermal alteration products. Although the carbonatites are largely late-stage, there is evidence of earlier carbonatite activity from a precursor carbonatite dyke that has off-set an olivine melilitite dyke. Relatively unaltered pyroclastics, associated with two vents, northeast and northwest of the crater respectively, represent the final phase of this volcanic centre. Finally, the preservation of the Salpeterkop crater and its associated volcaniclastics highlights the change of intense landscape denudation, that ensued from Gondwana break-up to the end of the Cretaceous, to a period of drastically reduced erosion rates during the Cenozoic Era.

Carbon reservoir perturbations induced by Deccan volcanism: Stable isotope and biomolecular perspectives from shallow marine environment in Eastern India.

The Deccan Traps in Western India is hypothesized to have caused significant fluctuations in climatic condition and organic matter (OM) productivity across the Cretaceous-Paleogene Boundary (K/PgB). The periodic release of large amounts of volatiles into the atmosphere is thought to drive these changes. Yet, direct impact of volcanism on the carbon cycle and ecosystem remains relatively unconstrained. For the first time, we attempt to trace changes in both marine and terrestrial carbon reservoirs from pre- and intervolcanic sedimentary units (infra- and inter-trappeans respectively) from Rajahmundry, ~1500km SE of main eruption sites in Western India. Molecular level characterization of OM and stable isotope composition of carbonates (δ13 Ccarb ), bulk OM (δ13 Corg ), and n-alkane (δ13 Calk and δDalk ) have been analysed to provide a chemo-stratigraphic framework. In Rajahmundry, high CO2 concentration estimated from infra-trappean carbonate nodule is synchronous with the onset of the Deccan Traps and the Late Maastrichtian warming episode. Impact of the warming event is reflected in Rajahmundry from a major shift in the terrestrial ecosystem. Marine OM production also seems to have been low throughout the infra-trappean. A steady decrease in δ13 Ccarb values, increase in mortality rates and dwarfism in invertebrates immediately below the first volcanic units in Rajahmundry suggest stressed conditions from eruption in the western part of India ~40-60kyrs prior to K/PgB. A significant increase in heterotrophic activity is observed after the volcanic deposits in Rajahmundry that seems to have controlled the marine carbon reservoir for a maximum of ~200kyrs after the boundary. Advent of pteridophytes, increase in carbon content and positive shifts in δ13 Ccarb and δ13 Calk values in the upper inter-trappean units mark the onset of recovery in terrestrial and marine environments. Overall, our results suggest significant perturbations in the carbon reservoir as a consequence of the Deccan eruption.

Back-arc tectonic tempos: Records from Jurassic–Cretaceous basins in the eastern North China Craton

Magmatic and structural tempos have been recognized in continental magmatic arcs, such as Cordilleran and Andean arcs. However, it remains unclear whether similar tempos or episodicity occur in back-arc settings, knowledge of which would be crucial for understanding back-arc geodynamics. The western Liaoning (WL) region in eastern China contains well-preserved basins of Jurassic–Cretaceous age and provides an opportunity to investigate back-arc tectonic processes. We present stratigraphic, structural, and geochronological data from the WL region to constrain tectonic evolution during the Jurassic–Cretaceous. The results show four stages of rifting or extension during 190–168, 167–137, 136–97, and 96–70 Ma, indicating a duration of 20–40 Myr for each extensional stage. Aside from a magmatic lull at 96–70 Ma, volcanism was associated with each of the three earlier extensional stages. Each main period of volcanism had a duration of 10–20 Myr, with the main eruption events occurring on an average cycle of ~25 Myr. The Jurassic–Cretaceous extension and rifting were interrupted by three compressional events at 168–167, 137–136, and 97–96 Ma, as evidenced by angular unconformities, basin inversion, and structural shortening. Each episode of compression lasted for ~1 Myr, on a 30–40 Myr cycle. The results indicate tempos in both back-arc stress state and magmatism. The back-arc tectonic evolution was characterized by frequent alternation of long-lived extensional and short-lived compressional events, and the back-arc magmatism in all cases occurred in an extensional setting. The back-arc tectonic tempos can be explained by a slab-driven model involving control by alternating phases of slab rollback and retreat on back-arc stress states and magmatism.

Origin and Properties of Hydrothermal Tremor at Lone Star Geyser, Yellowstone National Park, USA

AbstractGeysers are rare geologic features that intermittently discharge liquid water and steam driven by heating and decompression boiling. The cause of variability in eruptive styles and the associated seismic signals are not well understood. Data collected from five broadband seismometers at Lone Star Geyser, Yellowstone National Park are used to determine the properties, location, and temporal patterns of hydrothermal tremor. The tremor is harmonic at some stages of the eruption cycle and is caused by near‐periodic repetition of discrete seismic events. Using the polarization of ground motion, we identify the location of tremor sources throughout several eruption cycles. During preplay episodes (smaller eruptions preceding the more vigorous major eruption), tremor occurs at depths of 7–10 m and is laterally offset from the geyser's cone by ~5 m. At the onset of the main eruption, tremor sources migrate laterally and become shallower. As the eruption progresses, tremor sources migrate along the same path but in the opposite direction, ending where preplay tremor originates. The upward and then downward migration of tremor sources during eruptions are consistent with warming of the conduit followed by evacuation of water during the main eruption. We identify systematic relations among the two types of preplays, discharge, and the main eruption. A point‐source moment tensor fit to low‐frequency waveforms of an individual tremor event using half‐space velocity models indicates average VS ≳ 0.8 km/s, source depths ~4–20 m, and moment tensors with primarily positive isotropic and compensated linear vector dipole moments.