Magma Supply Rate Research Articles

Constraints from melt inclusions on depths of magma residence at intermediate magma supply along the Galápagos Spreading Center

Shallow, seismically imaged melt lenses are a ubiquitous feature of mid-ocean ridges with high magma supply; melt lenses deepen and become less continuous along axis as the rate of magma supply decreases. Despite compelling petrologic evidence for evolution of magma within the crust prior to eruption at lower magma supply, melt lenses are rarely detected along ridge segments with rates of magma supply less than 0.3×106 m3/yr/km, and the depths of sub-axial magma reservoirs are therefore poorly known. We use ion microprobe measurements of H2O and CO2 concentrations of olivine-hosted melt inclusions to calculate vapor saturation pressures that constrain crystallization depths at two locations along the Galápagos Spreading Center (94.2°W and 95°W). These sites were chosen to examine crystallization pressures in the presence (94.2°W) and absence (95°W) of a seismically imaged melt lens. At 95°W, where magma supply is too low to sustain a seismically resolvable melt lens, samples were selected from each of the three most recent eruptive units, allowing us to document temporal variations in vapor saturation pressures and the depth of magma residence at this location. Clusters in melt inclusion entrapment depths for these eruptions range from 3.0 to 3.4 km below the seafloor, indicating that magmas at 95°W resided at a narrow range of mid-crustal depths prior to eruption, generally consistent with the global trend of increasing melt lens depth with decreasing rate of magma supply. A discrepancy between seismic data and the peak in melt inclusion entrapment depths at 94.2°W may reflect temporal variability of magmatic systems at this location. This study demonstrates the potential for using measurements of the concentrations of H2O and CO2 in olivine-hosted melt inclusions to determine the depths of crustal magmatic systems that feed mid-ocean ridge eruptions, even in locations where seismic studies have not detected melt lenses.

Transient explosions at open-vent volcanoes: The case of Stromboli (Italy)

Stromboli is a persistently active, open-vent basaltic volcano whose activity is controlled by the balance between magma supply, outgassing, and eruptive rates, and is characterized by low-intensity, regular Strombolian explosions. However, two types of large, transient, violent explosive eruptions suddenly occur with no clear precursory activity. These explosions, called “major” and “paroxysmal” depending on size, cover a large variability in intensity and mag- nitude, but are all marked by short duration. Paroxysms have significantly larger intensities (>106 kg/s) than major explosions (104 kg/s) and fundamental differences in the characteris- tics (composition, crystallinity, vesicularity) of the erupted tephra, suggesting that different sources feed these two eruption types. Paroxysms are generated by the explosive fragmen- tation of low-porphyricity (LP) magma mingled with high-porphyricity resident magma in the shallow reservoir, whereas major eruptions are likely associated with destabilization of the lower portion of the shallow magmatic system, continuously hybridized by the arrival of LP magma. In general, the intensity of these explosions is related to the amount of the LP magma erupted (>107 kg in paroxysms and 104–105 kg in major explosions), suggesting that the magma plays a major role in the fragmentation mechanism. Despite its primary impor- tance in the hazards of Stromboli, the total amount of magma erupted in these events in the past 10 years is less than 1% of the total mass erupted by the volcano.

The role of crystallinity and viscosity in the formation of submarine lava flow morphology

Submarine lava flow morphology is commonly used to estimate relative flow velocity, but the effects of crystallinity and viscosity are rarely considered. We use digital petrography and quantitative textural analysis techniques to determine the crystallinity of submarine basaltic lava flows, using a set of samples from previously mapped lava flow fields at the hotspot-affected Galapagos Spreading Center. Crystallinity measurements were incorporated into predictive models of suspension rheology to characterize lava flow consistency and rheology. Petrologic data were integrated to estimate bulk lava viscosity. We compared the crystallinity and viscosity of each sample with its flow morphology to determine their respective roles in submarine lava emplacement dynamics. We find no correlation between crystallinity, bulk viscosity, and lava morphology, implying that flow advance rate is the primary control on submarine lava morphology. However, we show systematic variations in crystal size and shape distribution among pillows, lobates, and sheets, suggesting that these parameters are important indicators of eruption processes. Finally, we compared the characteristics of lavas from two different sampling sites with contrasting long-term magma supply rates. Differences between lavas from each study site illustrate the significant effect of magma supply on the physical properties of the oceanic upper crust.

Time‐averaged discharge rate of subaerial lava at Kīlauea Volcano, Hawai‘i, measured from TanDEM‐X interferometry: Implications for magma supply and storage during 2011–2013

AbstractDifferencing digital elevation models (DEMs) derived from TerraSAR add‐on for Digital Elevation Measurements (TanDEM‐X) synthetic aperture radar imagery provides a measurement of elevation change over time. On the East Rift Zone (EZR) of Kīlauea Volcano, Hawai‘i, the effusion of lava causes changes in topography. When these elevation changes are summed over the area of an active lava flow, it is possible to quantify the volume of lava emplaced at the surface during the time spanned by the TanDEM‐X data—a parameter that can be difficult to measure across the entirety of an ~100 km2 lava flow field using ground‐based techniques or optical remote sensing data. Based on the differences between multiple TanDEM‐X‐derived DEMs collected days to weeks apart, the mean dense‐rock equivalent time‐averaged discharge rate of lava at Kīlauea between mid‐2011 and mid‐2013 was approximately 2 m3/s, which is about half the long‐term average rate over the course of Kīlauea's 1983–present ERZ eruption. This result implies that there was an increase in the proportion of lava stored versus erupted, a decrease in the rate of magma supply to the volcano, or some combination of both during this time period. In addition to constraining the time‐averaged discharge rate of lava and the rates of magma supply and storage, topographic change maps derived from space‐based TanDEM‐X data provide insights into the four‐dimensional evolution of Kīlauea's ERZ lava flow field. TanDEM‐X data are a valuable complement to other space‐, air‐, and ground‐based observations of eruptive activity at Kīlauea and offer great promise at locations around the world for aiding with monitoring not just volcanic eruptions but any hazardous activity that results in surface change, including landslides, floods, earthquakes, and other natural and anthropogenic processes.

Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i

Research Article| July 01, 2014 Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i Donald A. Swanson; Donald A. Swanson 1U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718, USA Search for other works by this author on: GSW Google Scholar Timothy R. Rose; Timothy R. Rose 2Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA Search for other works by this author on: GSW Google Scholar Adonara E. Mucek; Adonara E. Mucek 3Department of Geology and Geophysics, SOEST (School of Ocean and Earth Science and Technology), University of Hawai‘i, Honolulu, Hawai‘i 96822, USA Search for other works by this author on: GSW Google Scholar Michael O. Garcia; Michael O. Garcia 3Department of Geology and Geophysics, SOEST (School of Ocean and Earth Science and Technology), University of Hawai‘i, Honolulu, Hawai‘i 96822, USA Search for other works by this author on: GSW Google Scholar Richard S. Fiske; Richard S. Fiske 2Department of Mineral Sciences, Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013, USA Search for other works by this author on: GSW Google Scholar Larry G. Mastin Larry G. Mastin 4U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington 98683, USA Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (7): 631–634. https://doi.org/10.1130/G35701.1 Article history received: 21 Mar 2014 rev-recd: 10 May 2014 accepted: 13 May 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Donald A. Swanson, Timothy R. Rose, Adonara E. Mucek, Michael O. Garcia, Richard S. Fiske, Larry G. Mastin; Cycles of explosive and effusive eruptions at Kīlauea Volcano, Hawai‘i. Geology 2014;; 42 (7): 631–634. doi: https://doi.org/10.1130/G35701.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The subaerial eruptive activity at Kīlauea Volcano (Hawai‘i) for the past 2500 yr can be divided into 3 dominantly effusive and 2 dominantly explosive periods, each lasting several centuries. The prevailing style of eruption for 60% of this time was explosive, manifested by repeated phreatic and phreatomagmatic activity in a deep summit caldera. During dominantly explosive periods, the magma supply rate to the shallow storage volume beneath the summit dropped to only a few percent of that during mainly effusive periods. The frequency and duration of explosive activity are contrary to the popular impression that Kīlauea is almost unceasingly effusive. Explosive activity apparently correlates with the presence of a caldera intersecting the water table. The decrease in magma supply rate may result in caldera collapse, because erupted or intruded magma is not replaced. Glasses with unusually high MgO, TiO2, and K2O compositions occur only in explosive tephra (and one related lava flow) and are consistent with disruption of the shallow reservoir complex during caldera formation. Kīlauea is a complex, modulated system in which melting rate, supply rate, conduit stability (in both mantle and crust), reservoir geometry, water table, and many other factors interact with one another. The hazards associated with explosive activity at Kīlauea’s summit would have major impact on local society if a future dominantly explosive period were to last several centuries. The association of lowered magma supply, caldera formation, and explosive activity might characterize other basaltic volcanoes, but has not been recognized. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Supra-subduction zone tectonic setting of the Muslim Bagh Ophiolite, northwestern Pakistan: Insights from geochemistry and petrology

The geology of the Muslim Bagh area comprises the Indian passive continental margin and suture zone, which is overlain by the Muslim Bagh Ophiolite, Bagh Complex and a Flysch Zone of marine–fluvial successions. The Muslim Bagh Ophiolite has a nearly-complete ophiolite stratigraphy. The mantle sequence of foliated peridotite is mainly harzburgite with minor dunite and contains podiform chromite deposits that grade upwards into transition zone dunite. The mantle rocks (harzburgite/dunite) resulted from large degrees of partial melting of lherzolite and have also been affected by melt–peridotite reaction. The Muslim Bagh crustal section has a cyclic succession of ultramafic–mafic cumulate with dunite at the base, that grades into wehrlite/pyroxenite with gabbros (olivine gabbro, norite and hornblende gabbro) at the top. The sheeted dykes are immature in nature and are rooted in crustal gabbros. The dykes are mainly metamorphosed dolerites, with minor intrusions of plagiogranites. The configuration of the crustal section indicates that the crustal rocks were formed over variable time periods, in pulses, by a low magma supply rate. The whole rock geochemistry of the gabbros, sheeted dykes and the mafic dyke swarm suggests that they formed in a supra-subduction zone tectonic setting in Neo-Tethys during the Late Cretaceous. The dykes of the mafic swarm crosscut both the ophiolite and the metamorphic sole rocks and have a less-marked subduction signature than the other mafic rocks. These dykes were possibly emplaced off-axis and can be interpreted to have been generated in the spinel peridotite stability zone i.e., < 50–60 km, and to have risen through a slab window. The Bagh Complex is an assemblage of Triassic–Cretaceous igneous and sedimentary rocks, containing tholeiitic, N-MORB-like basalts and alkali basalts with OIB-type signatures. Nb–Ta depletion in both basalt types suggests possible contamination from continental fragments incorporated into the opening Tethyan oceanic basin during break-up of Gondwana. The lithologies and ages of the Bagh Complex imply that these rocks formed in an area extending from the continental margin over the Neo-Tethyan ocean floor. The Bagh Complex was then juxtaposed with the Muslim Bagh Ophiolite in the final stage of tectonic emplacement.

Eruption style at Kīlauea Volcano in Hawai‘i linked to primary melt composition

Explosive eruptions at basaltic volcanoes have been linked to gas segregation from magmas at shallow depths in the crust. The composition of primary melts formed at greater depths was thought to have little influence on eruptive style. Ocean island basaltic volcanoes are the product of melting of a geochemically heterogeneous mantle plume and are expected to give rise to heterogeneous primary melts. This range in primary melt composition, particularly with respect to the volatile components, will profoundly influence magma buoyancy, storage and eruption style. Here we analyse the geochemistry of a suite of melt inclusions from 25 historical eruptions at the ocean island volcano of Kīlauea, Hawai‘i, over the past 600 years. We find that more explosive styles of eruption at Kīlauea Volcano are associated statistically with more geochemically enriched primary melts that have higher volatile concentrations. These enriched melts ascend faster and retain their primary nature, undergoing little interaction with the magma reservoir at the volcano’s summit. We conclude that the eruption style and magma-supply rate at Kīlauea are fundamentally linked to the geochemistry of the primary melts formed deep below the volcano. Magmas might therefore be predisposed towards explosivity right at the point of formation in their mantle source region. The explosive style of volcanic eruptions has been linked to gas separation from magmas in the shallow crust. Geochemical analysis of magmas erupted over the past 600 years at Kīlauea Volcano, Hawai‘i, now reveal a link between eruption style and the geochemistry of magmas formed at greater depths, implying that some magmas are predisposed towards explosivity.

Origin of two types of rhyolites in the Tarim Large Igneous Province: Consequences of incubation and melting of a mantle plume

Abstract The Early Permian Tarim Large Igneous Province (LIP) in northwestern China contains a large area of silicic volcanics (~ 48,000 km 2 ) which are spatially and temporally associated with mafic–ultramafic rocks. In order to understand the behavior of crust above a mantle plume, selected rhyolitic samples are investigated in terms of U–Pb zircon dating, geochemical and isotopic analyses. The Tarim rhyolites have high A/CNK ratios (= molar Al 2 O 3 /CaO + Na 2 O + K 2 O), Fe # , Ga/Al ratios, concentrations of high field strength elements (HFSEs) such as Zr and Nb, and rare earth elements (REEs), along with high zircon saturation temperatures (872–940 °C), typical of aluminous A-type granitoids. Two contrasting rock types have been recognized. The low Nb–Ta type rhyolites are mainly associated with the first phase of the Tarim flood basalt magmatism at ~ 290 Ma. They are characterized by negative Nb–Ta anomalies, low e Nd (t) and e Hf (t) values, and high 87 Sr/ 86 Sr(t) and δ 18 O zircon values, consistent with a derivation from continental crustal source. The high Nb–Ta type rhyolites and their plutonic equivalents are associated with the second episode of Tarim magmatism (283–272 Ma). They are characterized by small negative to positive Nb–Ta anomalies, oceanic island basalt (OIB)-like trace element ratios, low 87 Sr/ 86 Sr(t) and high e Nd (t) and e Hf (t) values. These high Nb–Ta rhyolites are best interpreted as hybrid products of crystal fractionation of mafic magmas, coupled with crustal assimilation. The temporal and compositional evolution of the Tarim rhyolites reflects various extents of thermal and mass exchange between mantle-derived basaltic magma and crustal material above a mantle plume. When the plume head rises to the base of the Tarim craton, it first melts enriched components in the lithospheric mantle (~ 290 Ma), part of which may have ponded near the crust–mantle boundary and induced crustal anatexis leading to the formation of the low Nb–Ta type rhyolites. At ~ 280 Ma, large magma chambers and plumbing systems were formed due to increasing magma supply rate during decompression melting of the mantle plume. This led to the formation of a mafic–ultramafic and felsic association of which the high Nb–Ta type rhyolites are a part.

New insights into the magmatic plumbing system of the South Australian Quaternary Basalt province from 3D seismic and geochemical data

Recent seismic reflection studies of large-volume, anorogenic basaltic provinces at passive continental margins have challenged the traditional viewpoint that erupted magmas predominantly ascend through the lithosphere via dykes that exploit high-angle faults. However, such seismic-based methods are yet to be applied to identify the magmatic plumbing systems of low-volume basaltic provinces, such as the Cretaceous–Cenozoic Newer Volcanic Province (NVP) in southeastern Australia (total volume <20 000 km3). The South Australian Quaternary Basalt (SAQB) represents the most recent phase of activity both within the NVP and on the Australian continent. This province is located within the Otway Basin, and a large amount of seismic data from gas exploration is available for this region. Consequently, the SAQB represents a superb natural laboratory in which geochemical and seismic data can be combined in order to study the magmatic plumbing system of a low-volume continental basalt province and discriminate between the competing hypotheses for magma transport through the Earth's crust. Geochemical analyses and thermodynamic modelling suggests that the magma that fed the SAQB was generated by adiabatic decompressional melting of a secondary mantle plume. These models imply that melt segregation took place at successively lower pressures from about ∼4000 to 3000 MPa during the ca 1 Ma SAQB eruptive history that culminated in the Northern Group, Mt Schank and Mt Gambier eruptions. During ascent, the magma underwent 34–41% fractional crystallisation and cooled ∼200 °C, while residing in the crust for a time period on the order of days to weeks. Interpretation of a 3D seismic survey that overlaps with the northeastern part of the SAQB reveals a saucer-shaped sill with an unusual morphology, exhibiting a series of vertical concentric steps towards its outer rim. This sill appears to be fed by magma that intruded along steep normal faults from a feeder dyke that is hosted by the regional, NW–SE-trending Hungerford-Kalangadoo Fault. Our results suggest that the melt that fed the SAQB rose through the crust via dykes and high-angle normal faults, with less evidence for significant horizontal transport of magma than observed in large-volume basaltic provinces in sedimentary basins at rifted continental margins, possibly highlighting a correlation between the extent, volume and magma supply rate within a basaltic province and the nature of magma ascent.

The 2011–2012 summit activity of Mount Etna: Birth, growth and products of the new SE crater

Between January 2011 and April 2012, the Southeast Crater (SEC) on Mount Etna was the site of 25 episodes of lava fountaining, which led to the construction of a new pyroclastic cone on the eastern flank of the SEC. During these episodes lava overflows reached 4.3km in length with an area of 3.19km2 and a volume of 28×106m3. The new cone, informally called New Southeast Crater (NSEC), grew over a pre-existing subsidence depression (pit crater), which had been formed in 2007–2009. The evolution of the NSEC cone was documented from its start by repeated GPS surveys carried out both from a distance and on the cone itself, and by the acquisition of comparison photographs. These surveys reveal that after the cessation of the lava fountains in April 2012, the highest point of the NSEC stood 190m above the pre-cone surface, while the cone volume was about 19×106m3, representing 38% of the total (bulk) volume of the volcanic products including pyroclastic fallout erupted in 2011–2012, which is 50×106m3 (about 33×106m3 dense-rock equivalent). Growth of the new cone took place exclusively during the paroxysmal phases of the lava fountaining episodes, which were nearly always rather brief (on the average 2h). Overall, the paroxysmal phases of all 25 episodes represent 51h of lava fountaining activity — the time needed to build the cone. This is the fastest documented growth of a newborn volcanic cone both in terms of volume and height. Mean effusion rates during the lava fountaining episodes on 20 August 2011 (E11), as well as 12 and 24 April 2012 (E24 and E25) exceeded 500m3/s (with maximum rates of 980m3/s during E11) and thus they are among the highest effusion rates ever recorded at Etna. The composition of the erupted products varies in time, reflecting different rates of magma supply into the shallow feeding system, but without notable effects on the eruptive phenomenology. This implies that the dynamics leading to the episodic lava fountaining was largely, though not entirely, controlled by the repeated formation and collapse of a foam layer in the uppermost portion of the magmatic reservoir of the NSEC.

Edifice strength and magma transfer modulation at Piton de la Fournaise volcano

AbstractFrom 2003 to 2007, eruptive activity at Piton de la Fournaise was shown to follow cycles, comprising many summit/proximal eruptions and finishing by a distal eruption. GPS measurements evidenced striking asymmetric deformation between its western and eastern flanks. Horizontal displacements recorded during interdistal periods showed a characteristic amplitude at the top of the eastern flank. Displacements recorded at the base of the summit cone showed a bimodal distribution, with low amplitudes during interdistal periods and large ones during distal eruptions. To account for displacement asymmetry, characteristic amplitude, and large flank displacement, we modeled the volcanic edifice using a Drücker‐Prager elastoplastic rheology. Friction angles of 15° and &gt;30° were needed to model the displacements respectively during distal eruptions and interdistal periods; this change shows that strain weakening occurred during distal events. Large plastic displacement that occurred in the eastern flank during distal eruptions relaxed the horizontal elastic stress accumulated during interdistal periods; it triggered summit deflation, horizontal magma transfer, and distal flank eruption and reset the eruptive cycle. Our elastoplastic models also show that simple source geometries may induce large eastern flank displacements that would be explained by a complex geometry in a linear elastic edifice. Magma supply is often thought to control volcano's eruptive activity, with surface deformation reflecting changes in magma supply rate, the volcano's response being linear. Our results bring some evidences that on Piton de la Fournaise time‐space discretization of magma transfer may be the result of the edifice's nonlinear response, rather than changes in magma supply.

Magma storage and migration associated with the 2011–2012 El Hierro eruption: Implications for crustal magmatic systems at oceanic island volcanoes

Starting in July 2011, anomalous seismicity was observed at El Hierro Island, a young oceanic island volcano. On 12 October 2011, the process led to the beginning of a submarine NW‐SE fissural eruption at ~15 km from the initial earthquake loci, indicative of significant lateral magma migration. Here we conduct a multifrequency, multisensor interferometric analysis of spaceborne radar images acquired using three different satellite systems (RADARSAT‐2, ENVISAT, and COSMO‐SkyMed (Constellation of Small Satellites for Mediterranean Basin Observation)). The data fully captures both the pre‐eruptive and coeruptive phases. Elastic modeling of the ground deformation is employed to constrain the dynamics associated with the magmatic activity. This study represents the first geodetically constrained active magmatic plumbing system model for any of the Canary Islands volcanoes, and one of the few examples of submarine volcanic activity to date. Geodetic results reveal two spatially distinct shallow (crustal) magma reservoirs, a deeper central source (9.5 ± 4.0 km), and a shallower magma reservoir at the flank of the southern rift (4.5 ± 2.0 km). The deeper source was recharged, explaining the relatively long basaltic eruption, contributing to the observed island‐wide uplift processes, and validating proposed active magma underplating. The shallowest source may be an incipient reservoir that facilitates fractional crystallization as observed at other Canary Islands. Data from this eruption supports a relationship between the depth of the shallow crustal magmatic systems and the long‐term magma supply rate and oceanic lithospheric age. Such a relationship implies that a factor controlling the existence/depth of shallow (crustal) magmatic systems in oceanic island volcanoes is the lithosphere thermomechanical behavior.

Characteristics of magma‐driven hydrothermal systems at oceanic spreading centers

AbstractWe use one‐ and two‐limb single‐pass models to de termine vent field characteristics such as mass flow rate Q, bulk permeability in the discharge zone kd, thickness of the conductive boundary layer at the base of the system δ, magma replenishment rate, and residence time in the discharge zone. Data on vent temperature, vent field area, heat output, and the surface area and depth of the subaxial magma chamber (AMC) constrain the models. The results give Q ~ 100 kg/s, kd ~ 10−13 m2, and δ ~ 10 m, essentially independent of spreading rate, and detailed characteristics of the AMC. In addition, we find no correlation between heat output at individual vent fields and spreading rate or depth to the AMC. We conclude that high‐temperature hydrothermal systems are driven by local magma supply rates in excess of that needed for steady state crustal production and that crustal permeability enables hydrothermal circulation to tap magmatic heat regardless of AMC depth. Using data on partitioning of heat flow between focused and diffuse flow, we find that 80–90% of the hydrothermal heat output is derived from high‐temperature fluid, even though much of the heat output discharges as low‐temperature fluid. In some cases, diffuse flow fluids may exhibit considerable conductive cooling or heating. By assuming conservative mixing of diffuse flow fluids at East Pacific Rise 9°50′N, we find that most transport of metals such as Fe and Mn occurs in diffuse flow and that CO2, H2, and CH4 are taken up by microbial activity.

Extrusion cycles during dome-building eruptions

We identify and quantify controls on the timescales and magnitudes of cyclic (periodic) volcanic eruptions using the numerical model DOMEFLOW (de’ Michieli Vitturi et al., 2010) which was developed by the authors for magma systems of intermediate composition. DOMEFLOW treats the magma mixture as a liquid continuum with dispersed gas bubbles and crystals in thermodynamic equilibrium with the melt and assumes a modified Poiseuille form of the viscous term for fully developed laminar flow in a conduit of cylindrical cross-section. During ascent, magma pressure decreases and water vapor exsolves and partially degasses from the melt as the melt simultaneously crystallizes, causing changes in mixture density and viscosity. Two mechanisms previously proposed to cause periodic eruption behavior have been implemented in the model and their corresponding timescales explored. The first applies a stick–slip model in which motion of a shallow solid plug is resisted by static/dynamic friction, as described in Iverson et al. (2006). For a constant magma supply rate at depth, this mechanism yields cyclic extrusion with timescales of seconds to tens of seconds with values generally depending on assumed friction coefficients. The second mechanism does not consider friction but treats the plug as a high-viscosity Newtonian fluid. During viscous resistance, pressure beneath the degassed plug can increase sufficiently to overcome dome overburden, plug weight, and viscous forces, and ultimately drive the plug from the conduit. In this second model cycle periods are on the order of hours, and decrease with increasing magma supply rate until a threshold is reached, at which point periodicity disappears and extrusion rate becomes steady (vanishingly short periods). Magma volatile content for fixed chamber pressure has little effect on cycle timescales, but increasing volatile content increases mass flow rate and cycle magnitude as defined by the difference between maximum and minimum extrusion rates. Increasing mass flow rate also increases the magnitude of predicted deformation cycles. Both models have been applied to dome-building eruptions using conditions appropriate for the Soufrière Hills volcano, Montserrat. Results suggest that the modeled stick–slip mechanism cannot explain the cycles of extrusion and explosion well-documented at Montserrat (timescales of hours). However, a subset of the simulations for the viscous plug model are consistent with the Montserrat data and therefore demonstrate the feasibility of this second formulation.

Controls on magmatic cycles and development of rift topography of the Manda Hararo segment (Afar, Ethiopia): Insights from cosmogenic 3He investigation of landscape evolution

Crustal extension at mature continental rifts and oceanic ridges occurs by a combination of normal faulting and magma injection, which interact to create rift morphology. Quantifying the relative roles of faulting and melt intrusion in accommodating extension at magmatic rifts remains difficult and requires studies at sufficient spatial and temporal scales to resolve the interaction between these processes. In this study we provide new chronological constraints based on cosmogenic exposure dating for the ∼100kyr topographic evolution of a young and active magmatic rift segment in Afar, Ethiopia. We combine structural investigations, field mapping, geochemical analysis and cosmogenic 3He exposure dating of lava surfaces in order to investigate the interplay between volcanic activity and fault growth in the northern part of the axial depression, where the rift segment intersects a large stratovolcano. Our results allow us to determine the roles of the various magma reservoirs feeding this rift system and their interactions during accretion over the past 100kyr. New age data for key lava units allow several magmatic cycles to be distinguished. Each cycle lasts 20–40ka resulting in periods of high and low magma supply rate. The variations in magma supply rate at the segment extremity strongly affect the development of the rift depression, with the availability of melt controlling the morphological impact of faulting. Melts from different magma reservoirs feeding the segment are chemically distinct and geochemical analysis of lavas from the rift floor allows their respective contributions to maintaining magmatic accretion to be estimated. We propose that melts from the magma reservoir at the northern end of the segment contribute around one-third of the length of this portion of the segment, whereas the mid-segment reservoir is responsible for the remaining two-thirds of the segment accretion.

Forecasting catastrophic stratovolcano collapse: A model based on Mount Taranaki, New Zealand

Research Article| November 01, 2012 Forecasting catastrophic stratovolcano collapse: A model based on Mount Taranaki, New Zealand Anke V. Zernack; Anke V. Zernack 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Shane J. Cronin; Shane J. Cronin 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Mark S. Bebbington; Mark S. Bebbington 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Richard C. Price; Richard C. Price 2Faculty of Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand Search for other works by this author on: GSW Google Scholar Ian E.M. Smith; Ian E.M. Smith 3School of Environment, University of Auckland, Private Bag 92 019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar Robert B. Stewart; Robert B. Stewart 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Jonathan N. Procter Jonathan N. Procter 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Search for other works by this author on: GSW Google Scholar Author and Article Information Anke V. Zernack 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Shane J. Cronin 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Mark S. Bebbington 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Richard C. Price 2Faculty of Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand Ian E.M. Smith 3School of Environment, University of Auckland, Private Bag 92 019, Auckland, New Zealand Robert B. Stewart 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Jonathan N. Procter 1INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand Publisher: Geological Society of America Received: 05 Feb 2012 Revision Received: 26 Apr 2012 Accepted: 27 Apr 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (11): 983–986. https://doi.org/10.1130/G33277.1 Article history Received: 05 Feb 2012 Revision Received: 26 Apr 2012 Accepted: 27 Apr 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Anke V. Zernack, Shane J. Cronin, Mark S. Bebbington, Richard C. Price, Ian E.M. Smith, Robert B. Stewart, Jonathan N. Procter; Forecasting catastrophic stratovolcano collapse: A model based on Mount Taranaki, New Zealand. Geology 2012;; 40 (11): 983–986. doi: https://doi.org/10.1130/G33277.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Regular large-scale edifice collapse and regrowth is a common pattern during the long lifespans of andesitic stratovolcanoes worldwide. The >130 k.y. history of Mount Taranaki, New Zealand, is punctuated by at least 14 catastrophic collapses, producing debris avalanche deposits of 1 to >7.5 km3. The largest of these sudden events removed as much as one-third of the present-day equivalent cone. The resulting deposits show similar sedimentary and geomorphic features, suggesting similar proto-edifice characteristics, failure trigger mechanisms, and runout path conditions. Each collapse was followed by sustained renewed volcanism and cone regrowth, although there are no matching stepwise geochemical changes in the magma erupted; instead a stable, slowly evolving magmatic system has prevailed. Last Glacial climatic variations are also uncorrelated with the timing or magnitudes of edifice collapse. We demonstrate here that, if the magmatic composition erupted from stratovolcanoes is constant and basement geology conditions are stable, large-scale edifice collapse and the generation of catastrophic debris avalanches will be governed by the magma supply rate. Using a mass balance approach, a volume-frequency model can be applied to forecasting both the probable timing and volume of future edifice failure of such stratovolcanoes. In the Mount Taranaki case, the maximum potential size of a present collapse is estimated to be 7.9 km3, while the maximum interval before the next collapse is <16.2 k.y. The current annual collapse probability is ∼0.00018, with the most likely collapse being a small one (<2 km3). You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pulsatory andesite lava flow at Bagana Volcano

Using a time series of TerraSAR‐X spaceborne radar images we have measured the pulsatory motion of an andesite lava flow over a 14‐month period at Bagana Volcano, Papua New Guinea. Between October 2010 and December 2011, lava flowed continuously down the western flank of the volcano forming a 3 km‐long blocky lava flow with a channel, levees, overflows and branches. We captured four successive pulses of lava advancing down the channel system, the first such behavior of an andesite flow to be recorded using radar. Each pulse had a volume of the order of 107 m3 emplaced over many weeks. The average extrusion rate estimated from the radar data was 0.92 ± 0.35 m3 s−1, and varied between 0.3 and 1.8 m3 s−1, with higher rates occurring earlier in each pulse. This, together with observations of sulphur dioxide emissions, explosions and incandescence suggest a variable supply rate of magma through Bagana's conduit as the most likely source of the pulsatory behavior.

Conduit degassing and thermal controls on eruption styles at Mount St. Helens

The explosivity of silicic eruptions depends on the interplay between magma rheology, exsolution kinetics, and degassing. Magma degassing is governed by the competing effects of vertical transport within the conduit and the lateral flux of gas out of the conduit (Diller et al., 2006; Jaupart and Allegre, 1991). We combine a simplified treatment of these degassing processes with thermodynamic modeling to examine the conditions present at Mount St. Helens during the spine extruding eruption from 2004 to 2008. We find that two parameters are primarily responsible for controlling the eruptive style: the magma chamber temperature, and a dimensionless parameter that gauges the efficiency of lateral degassing. Together, these parameters determine whether and where magma can solidify at depth to form a dense solid plug that is gradually extruded as a volcanic spine. We show that the small (50oC) decrease in magma chamber temperature between eruptive activity in the 1980s and that of 2004–2008, combined with a modest increase in degassing efficiency associated with lower volumetric flux, can explain the observed change in erupted material from viscous lava flows to solidified spines. More generally, we suggest that similar threshold behavior may explain observed abrupt transitions in effusive eruptive styles at other intermediate composition volcanoes. Finally, we extrapolate our results to suggest that the increase in degassing efficiency accompanying decreasing magma supply rates may have caused the transition from explosive to effusive activity in late 1980.

Komatiite Magmas and Sulfide Nickel Deposits: A Comparison of Variably Endowed Archean Terranes

Komatiites are found in most Archean granite-greenstone terranes, but sulfide Ni mineralization associated with these rocks has a very biased distribution. The global endowment of sulfides Ni in Archean komatiites is overwhelmingly dominated by the Kalgoorlie terrane of the Eastern Goldfields Superterrane in the Yilgarn Craton. The question of whether the Kalgoorlie terrane komatiites possess any exceptional attributes which could explain this bias is addressed through an exhaustive compilation of geochemical data from this terrane and a number of others: the southeastern Youanmi terrane of the Yilgarn Craton; the eastern terranes of the Eastern Goldfields superterrane (Kurnalpi, Burtville and others); and the Abitibi greenstone belt of the Superior province. High MgO komatiite magmas, with MgO in the 25 to 30% range, are found in all the terranes sampled, but the proportion of these compositions appears to be higher in the Kalgoorlie terrane, and the abundance of strongly adcumulate olivine cumulates is much higher. Crustal contamination is apparently more extensive and advanced in the Kalgoorlie terrane than in all the others, but there is no systematic difference in the lithophile trace element (LILE) characteristics and degree of source depletion evident in the most primitive magmas from all the terranes. Consideration of variable-valency transition metals V and Cr indicates there are no systematic variations in oxidation state between the terranes and komatiites uniformly evolved close to the quartz-fayalite-magnetite buffer. Platinum-group element (PGE) variations imply that komatiites in all the terranes were emplaced sulfide undersaturated and were derived from sources with remarkably similar PGE contents. There is no evidence that the Kalgoorlie terrane magmas were in any way exceptional. The Forrestania and Lake Johnston Belts of the Youanmi terrane include the only known examples of Al-depleted komatiites hosting significant Ni sulfide resources, and they are also the only komatiites of this type that form adcumulate dunite bodies. The presence of adcumulate dunites, formed by high magma fluxes in central conduits, is the common feature between these belts and the Kalgoorlie terrane. Coupled with evidence for higher degrees of contamination in the Kalgoorlie terrane, and the availability of accessible crustal S sources, it appears that magma flux, rather than primitive magma composition, is the critical factor, and that craton-scale deep lithospheric structure is the ultimate control on the rate of magma supply between mantle source and crustal emplacement site. The Kalgoorlie terrane komatiites were emplaced at exceptionally high rates, giving rise to well-developed long-lived magma conduits, either lava tubes or subvolcanic channelized sills, which are interpreted to be the essential condition for forming large deposits.

Effects of variable magma supply on mid‐ocean ridge eruptions: Constraints from mapped lava flow fields along the Galápagos Spreading Center

Mapping and sampling of 18 eruptive units in two study areas along the Galápagos Spreading Center (GSC) provide insight into how magma supply affects mid‐ocean ridge (MOR) volcanic eruptions. The two study areas have similar spreading rates (53 versus 55 mm/yr), but differ by 30% in the time‐averaged rate of magma supply (0.3 × 106 versus 0.4 × 106 m3/yr/km). Detailed geologic maps of each study area incorporate observations of flow contacts and sediment thickness, in addition to sample petrology, geomagnetic paleointensity, and inferences from high‐resolution bathymetry data. At the lower‐magma‐supply study area, eruptions typically produce irregularly shaped clusters of pillow mounds with total eruptive volumes ranging from 0.09 to 1.3 km3. At the higher‐magma‐supply study area, lava morphologies characteristic of higher effusion rates are more common, eruptions typically occur along elongated fissures, and eruptive volumes are an order of magnitude smaller (0.002–0.13 km3). At this site, glass MgO contents (2.7–8.4 wt. %) and corresponding liquidus temperatures are lower on average, and more variable, than those at the lower‐magma‐supply study area (6.2–9.1 wt. % MgO). The differences in eruptive volume, lava temperature, morphology, and inferred eruption rates observed between the two areas along the GSC are similar to those that have previously been related to variable spreading rates on the global MOR system. Importantly, the documentation of multiple sequences of eruptions at each study area, representing hundreds to thousands of years, provides constraints on the variability in eruptive style at a given magma supply and spreading rate.