Lava Effusion Research Articles

Re-assessing volcanic hazard maps for improving volcanic risk communication: application to Stromboli Island, Italy

Please click here to download the map associated with this article. Hazard and risk maps are tools for both mitigating against risk and informing and preparing the general public. Recent studies have highlighted that volcanic hazard and risk maps used during emergencies can be difficult to interpret. Our research focuses on evaluating and improving the efficacy of currently available maps of Stromboli volcano on Stromboli island (Italy) for the communication of volcanic hazard and risk information. Stromboli is an active volcano characterised by persistent explosive activity, sporadic lava effusions and landslides on the volcanos northwestern flank, which sometimes generates tsunamis, most recently in 2002. This study used semi-structured interviews conducted with local legislators, administrators and ‘enforcers’ to understand their perceptions of available risk information; to evaluate the respondents mental spatial maps; and to determine the most important components in encouraging risk-reducing behaviour in a hazardous situation. Respondents were asked to evaluate a contour map, an aerial photograph, a digital elevation model (DEM) and an innovative 3D tsunami risk map. These results enabled the development of different volcanic risk maps for use by ‘experts’ and ‘tourists’ using a contour map and a DEM (Scale 1:12.500). A 3D map focused on the tsunami risk (Scale 1:6.500) area was also produced.

Reply to comment by Ferlito et al. on “Complex magma dynamics at Mount Etna revealed by seismic, thermal and volcanological data”

Reply to comment by Ferlito et al. on “Complex magma dynamics at Mount Etna revealed by seismic, thermal and volcanological data”

Compositional evolution of magma from Parícutin Volcano, Mexico: The tephra record

The birth of Parícutin Volcano, Mexico, in 1943 provides an unprecedented opportunity to document the development of a monogenetic cinder cone and its associated lava flows and tephra blanket. Three ‘type’ sections provide a complete tephra record for the eruption, which is placed in a temporal framework by comparing both bulk tephra and olivine phenocryst compositions to dated samples of lava and tephra. Our data support the hypothesis of Luhr (2001) that the first four months of activity were fed by a magma batch (Phase 1) that was distinct from the magma that supplied the subsequent eight years of activity. We further suggest that the earliest erupted (vanguard) magma records evidence of temporary residence at shallow levels prior to eruption, suggesting early development of a dike and sill complex beneath the vent. Depletion of this early batch led to diminished eruptive activity in June and July of 1943, while arrival of the second magma batch (Phase 2) reinvigorated activity in late July. Phase 2 fed explosive activity from mid-1943 through 1946, although most of the tephra was deposited by the end of 1945. Phase 3 of the eruption began in mid-1947 with rapid evolution of magma compositions from basaltic andesite to andesite and dominance of lava effusion. The combined physical and chemical characteristics of the erupted material present a new interpretation of the physical conditions that led to compositional evolution of the magma. We believe that syn-eruptive assimilation of wall rock in a shallow complex of dikes and sills is more likely than pre-eruptive assimilation within a large magma chamber, as previously assumed. We further suggest that waning rates of magma supply from the deep feeder system allowed evolved, shallowly stored magma to enter the conduit in 1947, thus triggering the rapid observed change in the erupted magma composition. This physical model predicts that assimilation should be observable in other monogenetic eruptions, particularly those with low pressure melt inclusions and with eruption durations of months to years.

Degassing, crystallization and eruption dynamics at Stromboli: trace element and lithium isotopic evidence from 2003 ashes

During its 1800-year-long persistent activity the Stromboli volcano has erupted a highly porphyritic (HP) volatile-poor scoriaceous magma and a low porphyritic (LP) volatile-rich pumiceous magma. The HP magma is erupted during normal Strombolian explosions and lava effusions, while the LP one is related to more energetic paroxysms. During the March–April 2003 explosive activity, Stromboli ejected two typologies of juvenile glassy ashes, namely highly vesicular LP shards and volatile-poor HP shards. Their textural and in situ chemical characteristics are used to unravel mutual relationships between HP and LP magmas, as well as magma dynamics within the shallow plumbing system. The mantle-normalized trace element patterns of both ash types show the typical arc-lava pattern; however, HP glasses possess incompatible element concentrations higher than LP glasses, along with Sr and Eu negative anomalies. HP shards are generally characterized by higher Li contents (to ~20 ppm) and lower δ7Li values (+1.2 to −3.8‰) with respect to LP shards (Li contents of 7–14 ppm and δ7Li ranging between +4.6 and +0.9‰). Fractional crystallization models based on major and trace element compositions, combined with a degassing model based on open-system Rayleigh distillation and on the assumption that melt/fluidDLi > 1, show that abundant (~30%) plagioclase precipitation and variable degrees of degassing can lead the more primitive LP magma to evolve toward a differentiated (isotopically lighter) HP magma ponding in the upper conduit and undergoing slow continuous degassing-induced crystallization. This study also evidences that in March 2003 Stromboli volcano poured out a small early volume of LP magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending LP magma erupted during the April 5 paroxysm. The different ascent rates and cooling rates of the two LP magma batches (i.e., pre- and post-paroxysm) resulted in small, but detectable, differences in their chemical signatures. Finally, this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of Li isotopes as tracers of degassing processes within the shallow plumbing system.

Controls on the explosivity of scoria cone eruptions: Magma segregation at conduit junctions

Violent strombolian (transitional) eruptions are common in mafic arc settings and are characterized by simultaneous explosive activity from scoria cone vents and lava effusion from lateral vents. This dual activity requires magma from the feeder conduit to split into vertical and lateral branches somewhere near the base of the scoria cone. Additionally, if the flow is separated, gas and liquid (+ crystals) components of the magma may be partitioned unevenly between the two branches. Because flow separation requires bubbles to move independently of the liquid over time scales of magma ascent separation is promoted by low magma viscosities and by high magma H 2O content (i.e. sufficiently deep bubble nucleation to allow organization of the gas and liquid phases during magma ascent). Numerical modeling shows that magma and gas distribution between vertical and horizontal branches of a T-junction is controlled by the mass flow rate and the geometry of the system, as well as by magma viscosity. Specifically, we find that mass eruption rates (MERs) between 10 3 and 10 5 kg/s allow the gas phase to concentrate within the central conduit, significantly increasing explosivity of the eruption. Lower MERs produce either strombolian or effusive eruption styles, while MER > 10 5 kg/s prohibit both gas segregation and lateral magma transport, creating explosive eruptions that are not accompanied by effusive activity. These bracketing MER constraints on eruptive transitions are consistent with field observations from recent eruptions of hydrous mafic magmas.

Patterns in open vent, strombolian behavior at Fuego volcano, Guatemala, 2005–2007

Fuego volcano, Guatemala is a high (3,800 m) composite volcano that erupts gas-rich, high-Al basalt, often explosively. It spends many years in an essentially open vent condition, but this activity has not been extensively observed or recorded until now. The volcano towers above a region with several tens of thousands of people, so that patterns in its activity might have hazard mitigation applications. We conducted 2 years of continuous observations at Fuego (2005–2007) during which time the activity consisted of minor explosions, persistent degassing, paroxysmal eruptions, and lava flows. Radiant heat output from MODIS correlates well with observed changes in eruptive behavior, particularly during abrupt changes from passive lava effusion to paroxysmal eruptions. A short-period seismometer and two low-frequency microphones installed during the final 6 months of the study period recorded persistent volcanic tremor (1–3 Hz) and a variety of explosive eruptions. The remarkable correlation between seismic tremor, thermal output, and daily observational data defines a pattern of repeating eruptive behavior: 1) passive lava effusion and subordinate strombolian explosions, followed by 2) paroxysmal eruptions that produced sustained eruptive columns, long, rapidly emplaced lava flows, and block and ash flows, and finally 3) periods of discrete degassing explosions with no lava effusion. This study demonstrates the utility of low-cost observations and ground-based and satellite-based remote sensing for identifying changes in volcanic activity in remote regions of underdeveloped countries.

Variations in eruptive style and depositional processes associated with explosive, phonolitic composition, caldera-forming eruptions: The 151 ka Sutri eruption, Vico Caldera, central Italy

Vico Volcano in central Italy, experienced a complex eruptive history (419–95 ka). The Vico volcanic edifice was constructed by voluminous (50 km 3) leucitite composition effusive lava flows and minor explosive activity over a 50 ka period (305–258 ka). The summit of the edifice was destroyed during the Sutri eruption (151 ka) that resulted in the formation of the 8 km caldera depression. A revised stratigraphy for the eruptive products produced by the Sutri eruption (Sutri Formation) is proposed, based on extensive field observations, detailed stratigraphic logging and petrographic analysis; the Sutri A unit consists of a fallout deposit of limited dispersal; the Sutri B unit consists of a small volume, variably welded pumice-rich ignimbrite; the Sutri C unit is a lithic and spatter clast-rich co-ignimbrite lag-flow breccia; the Sutri D unit is a fines-depleted pumice-rich ignimbrite; Sutri (E1–E3) subunits consist of spatter clast-rich ignimbrite; Sutri E4 (sbx) is a spatter clast-rich co-ignimbrite lag-flow breccia; the Sutri E4 (lsbx) subunit is a lithic, pumice and spatter clast-rich co-ignimbrite lag-flow breccia; the climactic Sutri E5 unit is a variably zeolitised spatter and pumice-rich ignimbrite (with lithic-rich base; Sutri E4 flsbx) to the west). The reconstruction of the Sutri eruption leading up to and including formation of the Vico Caldera based on the new stratigraphy of the Sutri Formation, consists of three distinct phases: Phase 1—Initial Plinian activity produced a fallout deposit (Sutri A) deposited to the south, followed by partial eruption column collapse that generated a pyroclastic flow directed to the south/southeast (Sutri B). Vent widening in response to vent-wall rock instabilities and increased magma discharge rate overloaded the eruption column with dense, lithic debris resulting in southward collapse and deposition of a thick co-ignimbrite lag breccia in the deflation zone (Sutri C). A change in clast supply at vent from lithic clast-dominated to pumice clast-dominated produced a fines-depleted ignimbrite, Sutri D (plbx) prior to cessation of activity in the south. Phase 2—Shortly following the initial Plinian phase or partially overlapping, decompression of the magma chamber in response to partial magma chamber roof block collapse promoted explosive fragmentation of magma at the base of the conduit (as pumice) and led to the opening of a new vent in the north. Sustained mixing of highly vesiculated, grey pumice clasts and dense, poorly vesiculated, black spatter clasts occurred both in the conduit and in the eruption column and subsequent column collapse produced a small volume pyroclastic flow directed to the north, dominated by dense, black spatter clasts (Sutri E1–E3). Phase 3—Sustained eruptive activity continued in the north and increased magma discharge rate likely then resulted in great instability of the magma chamber roof and surrounding wall rocks of the progressively draining magma chamber. The eruption column collapsed radially depositing vast quantities of lithic clasts, spatter clasts and some pumice clasts into the deflation zone as co-ignimbrite lag-flow breccias (Sutri E4 sbx, lsbx), signalling the onset of caldera collapse. Eruption column collapse also produced a radially distributed, pyroclastic flow that deposited a moderate volume ignimbrite (Sutri E5) with a lithic-rich base (Sutri E4 flsbx) at proximal localities in the west. Final caldera collapse occurred shortly following emplacement of Sutri E5 presumably in response to evacuation of the magma chamber and final collapse of the magma chamber roof. We infer from the eruption dynamics that progressive collapse of the magma chamber roof occurred culminating in final climactic and post-eruptive caldera collapse.

A late-Ordovician phreatomagmatic complex in marine soft-substrate environment: The Crozon volcanic system, Armorican Massif (France)

The mafic lavas and the diabases of Crozon (Armorican Massif, France), belong to an anorogenic Ordovician volcanic complex, emplaced on a rifted passive margin in North Gondwana. Magma passed through syn-volcanic soft sedimentary substrate, which is today mostly composed of alternating sandstones and mudstones, from Llanvirn to Ashgill in age. Field observations together with microscopic studies and geochemical analyses of magmatic rocks lead us to propose a model of volcano formation which combines hydromagmatic processes, peperitic intrusions, a shallow submarine tephra settling, eruption-fed turbidity currents, and a pillow lava effusion. The Crozon outcrops can be used to reconstruct a complete cross-section from the root of the volcanic complex to the lavas and breccias emplaced on the sea floor. The sites expose: (i) a hypabyssal breccia containing mud chunks and coarse-grained diabase clasts with amoeboidal fine-grained magmatic material; (ii) bulbous peperitic sills and pillow-like lobes bearing a great quantity of sediment-derived enclaves of fluidal morphology; (iii) volcaniclastic breccias containing near-spherical magmatic clasts that resulted from the complete fragmentation of sills in the ductile regime; (iv) a rhythmic peperitic breccia interpreted as the product of mingling between thin lava flows and soft calcareous sediment. The Crozon volcanic form, resulting from explosive interaction with subsurface/surface water, was probably a subaqueous collapsed tuff cone. This upper part of the system is synchronous with an Ashgill carbonate sedimentation, which overlies an Ordovician siliciclastic succession deposited in shelf environments.

Assumptions in the evaluation of lava effusion rates from heat radiation

The availability of high‐resolution thermal imagery of active lava flows has stimulated the use of radiance maps for the evaluation of lava effusion rates. This is made possible by simple formulae relating the lava flow rate to the energy radiated per unit time from the planimetric surface of the flow. Such formulae are based on a specific flow model and, consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of the formulae is not consistent with the model. The reason why they provide reasonable, although very rough, values for effusion rates appears to be that the actual radiated energy is controlled by a feature (the nonuniform temperature of flow surface) which is not accounted for by the model and which counterbalances the effect of inconsistent use of the formulae.

The Cerro Morado Andesites: Volcanic history and eruptive styles of a mafic volcanic field from northern Puna, Argentina

The Upper Miocene Cerro Morado Andesites constitutes a mafic volcanic field (∼100 km 2) composed of andesite to basaltic andesite rocks that crop out ∼75 km to the east from the current arc, in the northern Puna of Argentina. The volcanic field comprises lavas and scoria cones resulting from three different eruptive phases developed without long interruptions between each other. Lavas and pyroclastic rocks are thought to be sourced from the same vents, located where orogen-parallel north-south faults crosscut transverse structures. The first eruptive phase involved the effusion of extensive andesitic flows, and minor Hawaiian-style fountaining which formed subordinate clastogenic lavas. The second phase represents the eruption of slightly less evolved andesite lavas and pyroclastic deposits, only distributed to the north and central sectors of the volcanic field. The third phase represents the discharge of basaltic andesite magmas which occurred as both pyroclastic eruptions and lava effusion from scattered vents distributed throughout the entire volcanic field. The interpreted facies model for scoria cones fits well with products of typical Strombolian-type activity, with minor fountaining episodes to the final stages of eruptions. Petrographic and chemical features suggest that the andesitic units (SiO 2 > 57%) evolved by crystal fractionation. In contrast, characteristics of basaltic andesite rocks are inconsistent with residence in upper-crustal chambers, suggesting that batches of magmas with different origins or evolutive histories arrived at the surface and erupted coevally. Based on the eruptive styles and lack of volcanic quiescence gaps between eruptions, the Cerro Morado Andesites can be classified as a mafic volcanic field constructed from the concurrent activity of several small, probably short-lived, monogenetic centers.

Significance of widespread low effusion rate eruptions over the past two million years for delivery of magma to the overlapping spreading centers at 9°N East Pacific Rise

Ever since the discovery that the mid-ocean ridge axis deepens at most axial discontinuities, there has been vigorous debate about whether ridge axis depth and shape reflect magma supply. Here we report evidence, from one of the most thoroughly studied ridge discontinuities on a fast-spreading mid-ocean ridge, that volcanic eruption effusion rates have been low relative to nearby segment centers throughout its two million year history. This pattern of low volcanic effusion rates is inferred from the fields of constructional volcanic mounds on the seafloor which are much more abundant in the off-axis discordant zone of the East Pacific Rise (EPR) 9°N Overlapping Spreading Centers (OSC) than on typical EPR seafloor. Detailed seafloor mapping in 2007 shows that these mound fields consist of concentrations of large pillow mounds that formed within the current OSC basin and ridge tips, rather than off-axis. Pillow lava, erupted at approximately an order of magnitude lower effusion rate than lobate or sheet flows, primarily builds mounds on the seafloor. Crustal thickness, a proxy for long-term magma supply, does not decrease in spite of the decreased lava effusion rates implied by widespread pillow eruptions. To resolve the problem of achieving the same magma emplacement rate with lower effusion rates, without violating our observations by requiring drastically increased eruption frequency or unreasonably long eruption durations, we propose that eruptions occur across the entire OSC basin. The current configuration of mid-crustal melt sills within the OSC as resolved by multichannel seismic reflection surveys have neither the correct location nor appropriate size to deliver magma to these eruptive vents in the OSC basin via vertically propagating dikes. Instead, we propose that magma delivery to eruptions occurs via laterally propagating dikes from robust mid-crustal melt sills outside of the overlap zone.

Magma dynamics during the 2007 Stromboli eruption (Aeolian Islands, Italy): Mineralogical, geochemical and isotopic data

After the 6 month-long effusive event of 2002-2003, a new lava effusion occurred at Stromboli between 27 February and 2 April 2007. Despite the different durations, approximately the same volume of magma was emitted in both eruptions, in the order of 10 7 m 3. A paroxysmal eruption occurred at the summit craters in both the 2002–2003 and 2007 episodes, during which a significant amount of low porphyritic (LP), volatile-rich magma was erupted. In both cases, the paroxysm did not interrupt the lava emission. Here, we present compositional data, including texture, mineralogy, chemistry and Sr and Nd isotope ratios of bulk-rock, groundmass and separated minerals of lavas erupted in 2007, together with chemistry and Sr and Nd isotope composition of the pumices emitted during the 15 March paroxysm. As a whole, the lavas have the same texture and chemistry that characterize the highly porphyritic (HP) products usually erupted at Stromboli during normal Strombolian activity and effusive events. Compared to the previous HP products, the 2007 lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest increase of the magma supply rate of the volcano. Compositional variations during the entire duration of the event are very modest. Glass chemistry changes in lavas erupted in the second half of March can be explained by the minor mixing between the volatile-rich LP magma rising through the shallow magmatic system during the 15 March paroxysm and the degassed residing HP magma. A first conclusion of this study is that there is no compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the effusive activity, as also suggested for the 2002–2003 event. The activity of Stromboli is controlled by a steady state feeding system in which refilling, mixing, degassing and crystallization at shallow level continuously operate, with modest oscillations in the magma supply rate. Switching between normal Strombolian and effusive activity is related to periods of relatively more vigorous refilling of the shallow system, leading to progressive pressure increase in the upper conduits associated with only minor compositional variations in the erupted products.

Ground deformation and seismicity related to the propagation and drainage of the dyke feeding system during the 2007 effusive eruption at Stromboli volcano (Italy)

The 2007 effusive eruption of Stromboli volcano produced a ground deformation detected by two high-resolution borehole tiltmeters installed at an elevation > 500 masl and at a distance of < 800 m from the active vents. Ground inflation was recorded about 12 h before the eruption onset as a consequence of magma ascent within the shallow feeding conduit. Tilt vectors converging towards the summit area indicate a confined or vertically elongated source. The increased magma input rate led to a well alimented lava flow, which was detected as a major tilt deflation during the 6 days following the eruption onset. Unlike during the inflation, the ground deformation that accompanied the lava effusion, is not consistent with a confined source close to the summit area, but rather suggests a process of deflation of the volcanic structure along a dyke-shaped structure striking 40°N. The tilt data presented in this paper represent a great opportunity to investigate the mechanism of magma effusion and the response of the feeding system to the increased magma flux. High value of seismic tremor amplitude and surface fracturing is the evidence of the increased magma input rate, which led to the SW-NE propagation of the dike, acting as a linear source of deflation when the system was rapidly drained by the sustained lava emission. A secondary inflation process, acting during the tilt decay, was clearly recorded in the afternoon on February 27 2007, representing the evidence of the magma intrusion, that led to the opening of an effusive vent at 400 m elevation.

Depth profiles of venusian sinuous rilles and valley networks

More than 200 venusian channels and valleys have been mapped based on analyses of Magellan SAR images. Sinuous rilles are the most abundant channels among six types of venusian channels, and they are widely distributed on Venus. Morphological characteristics of venusian sinuous rilles include sinuous narrowing reaches, source depressions, and length of several 10s to a few 100s of km. This type of channels is known to exist on the Moon and possibly on Mars. Valley networks on Venus often occur in the vicinity of or in connection to sinuous rilles. Cross-sectional morphologies of sinuous rilles and valley networks are of special importance in discussing their formation processes both qualitatively and quantitatively. We reconstructed cross-sectional profiles of 6 sinuous rilles and 2 valley networks using a new radar clinometric method. Reconstructed cross-sections revealed that floors of the channels and valleys are clearly lower than the surrounding plains. This finding implies that the sinuous rilles and the valley networks have erosional origins. Longitudinal depth profiles of the sinuous rilles show distinct decreasing trends toward the termini. Such decreasing trends of depths are qualitatively in agreement with theoretical models and laboratory experiments of thermal erosion. In order to verify this assertion quantitatively, we conduct simple 1-dimensional model calculations under the assumption that both channel-forming lavas and ground substrate are tholeiitic basalt. For initial lava thicknesses in the range 2–6 m, the model calculations yield good matches to the depth profiles. Estimated duration of lava effusion ranges from several months to a few years. These numerical results support thermal erosion of the sinuous rilles but do not necessarily exclude contributions from mechanical erosion processes. Valley networks seem to have formed under a strong structural control in comparison to sinuous rilles. The valleys vary widely in characteristics of the depth profile and flow directions relative to surface slopes. Therefore valley networks appear to have originated from diverse formation mechanisms.

The emplacement of an obsidian dyke through thin ice: Hrafntinnuhryggur, Krafla Iceland

An eruption along a 2.5 km-long rhyolitic dyke at Krafla volcano, northern Iceland during the last glacial period formed a ridge of obsidian (Hrafntinnuhryggur). The ridge rises up to 80 m above the surrounding land and is composed of a number of small-volume lava bodies with minor fragmental material. The total volume is < 0.05 km 3. The lava bodies are flow- or dome-like in morphology and many display columnar-jointed sides typical of magma–ice interaction, quench-fragmented lower margins indicative of interaction with meltwater and pumiceous upper surfaces typical of subaerial obsidian flows. The fragmental material compromises poorly-sorted perlitic quench hyaloclastites and poorly-exposed pumiceous tuffs. Lava bodies on the western ridge flanks are columnar jointed and extensively hydrothermally altered. At the southern end of the ridge the feeder dyke is exposed at an elevation ∼ 95 m beneath the ridge crest and flares upwards into a lava body. Using the distribution of lithofacies, we interpret that the eruption melted through ice only 35–55 m thick, which is likely to have been dominated by firn. Hrafntinnuhryggur is therefore the first documented example of a rhyolitic fissure eruption beneath thin ice/firn. The eruption breached the ice, leading to subaerial but ice/firn-contact lava effusion, and only minor explosive activity occurred. The ridge appears to have been well-drained during the eruption, aided by the high permeability of the thin ice/firn, which appears not to have greatly affected the eruption mechanisms. We estimate that the eruption lasted between 2 and 20 months and would not have generated a significant jökulhlaup (< 70 m 3 s − 1 ).

Frequent eruptions of Mount Rainier over the last ∼2,600 years

Field, geochronologic, and geochemical evidence from proximal fine-grained tephras, and from limited exposures of Holocene lava flows and a small pyroclastic flow document ten–12 eruptions of Mount Rainier over the last 2,600 years, contrasting with previously published evidence for only 11–12 eruptions of the volcano for all of the Holocene. Except for the pumiceous subplinian C event of 2,200 cal year BP, the late-Holocene eruptions were weakly explosive, involving lava effusions and at least two block-and-ash pyroclastic flows. Eruptions were clustered from ∼2,600 to ∼2,200 cal year BP, an interval referred to as the Summerland eruptive period that includes the youngest lava effusion from the volcano. Thin, fine-grained tephras are the only known primary volcanic products from eruptions near 1,500 and 1,000 cal year BP, but these and earlier eruptions were penecontemporaneous with far-traveled lahars, probably created from newly erupted materials melting snow and glacial ice. The most recent magmatic eruption of Mount Rainier, documented geochemically, was the 1,000 cal year BP event. Products from a proposed eruption of Mount Rainier between AD 1820 and 1854 (X tephra of Mullineaux (US Geol Surv Bull 1326:1–83, 1974)) are redeposited C tephra, probably transported onto young moraines by snow avalanches, and do not record a nineteenth century eruption. We found no conclusive evidence for an eruption associated with the clay-rich Electron Mudflow of ∼500 cal year BP, and though rare, non-eruptive collapse of unstable edifice flanks remains as a potential hazard from Mount Rainier.

Radiant flux from Earth's subaerially erupting volcanoes

During the past decade an average of 60 volcanoes erupted each year, around 20 of which were erupting on any given day. Some of these, such as Erta Ale in Ethiopia, are persistently active, whereas others, such as Bezymianny in Russia, erupt more sporadically. Satellite remote sensing offers a convenient way to monitor changes in the thermal budgets of these volcanoes from space. Using data acquired by the National Aeronautics and Space Administration (NASA) Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, we show how the amount of heat radiated into the Earth's atmosphere by 65 active volcanoes has varied between 26 February 2000 and 31 December 2006. We find that the radiant volcanic heat flux into the atmosphere occurs at a relatively steady‐state baseline level, superimposed on which are large thermal emission ‘spikes’. These anomalous emission events are associated with the emplacement of basaltic ‘a’a lava flows at volcanoes such as Mount Etna, Italy, and Nyamuragira, in the Democratic Republic of Congo. We also demonstrate how these data can be used to estimate lava effusion rates during effusive eruptions, and magma flux rates at persistently active volcanoes that host active lava lakes.

Spaceborne Monitoring 2000–2005 of the Pu'u `O'o-Kupaianaha (Hawaii) Eruption by Synergetic Merge of Multispectral Payloads ASTER and MODIS

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The spaceborne thermal monitoring of the great eruption of Pu'u `O'o-Kupaianaha in Hawaii (1987 to present) was attempted, integrating high-resolution SWIR–TIR and low-resolution MIR–TIR observations. Data acquired by multispectral payloads ASTER and MODIS onboard spacecraft Terra, and MODIS onboard Aqua, were processed behind real time by the use of computing routines “MyVOL” and “MyMOD” based on assessed theory and designed for real-time operations. The process was tested against the 2000–2005 eruptive history, both in geometry and volume dynamics of the lava flow. Here, instant lava effusion rates obtained from approximately 1800 cloud-free (over a total <formula formulatype="inline"><tex>$≫$</tex></formula> 3000) day-/nighttime MODIS scenes and 12 cloud-free (over a total of 30) nighttime ASTER scenes are compared with each other and with volcanological ground truth composed of gas <formula formulatype="inline"><tex>$(\hbox{SO}_{2})$</tex></formula>- and electromagnetic potential (very low frequency)-derived eruption rates. Remote-sensed eruption rates are consistent with ground truth from approximately 1 <formula formulatype="inline"><tex>$\hbox{m}^{3}/\hbox{s}$</tex> </formula> up to the peak effusion rates of 1.2–1.3 million <formula formulatype="inline"><tex>$\hbox{m}^{3}/ \hbox{day}$</tex></formula> observed in 2005. </para>

Using infrared satellite data to drive a thermo‐rheological/stochastic lava flow emplacement model: A method for near‐real‐time volcanic hazard assessment

We combine two flow simulation models to provide a computationally efficient means of predicting the final dimensions of active lava flows. By using a stochastic approach to predict all the downhill paths that a lava flow could possibly follow and a thermo–rheological model to terminate these paths once the predicted cooling–limited length for the flow has been attained, this approach allows for rapid assessment of the area likely to be inundated by lava. The 1991–1993 eruption of Mount Etna is used as a case study. Lava effusion rate exerts a strong control on the maximum length a lava flow can attain, and we demonstrate how the model can be driven by time–varying effusion rates, obtained from infrared satellite data. As such data are obtained in near–real–time, this approach allows flow simulations to be updated in a timely manner, in response to changing eruption conditions.

Record of complex scoria cone eruptive activity at Red Mountain, Arizona, USA, and implications for monogenetic mafic volcanoes

Scoria cone eruptions are generally modeled as a simple succession from explosive eruption to form the cone to passive effusion of lava, generally from the base of the cone. Sector collapse of scoria cones, wherein parts of the cone are rafted on a lava flow, is increasingly recognized as common, but the reasons that a cone may not be rebuilt are poorly understood. Red Mountain volcano is a Pleistocene scoria cone in the San Francisco Volcanic Field of northern Arizona, USA. The cone lies along the trace of a major steeply dipping normal fault that originated during Proterozoic tectonism and was reactivated in Tertiary time. The earliest phase of eruption at Red Mountain was typical “Strombolian”, forming a cone that was followed by or possibly synchronous with lava effusion, toward the west from the base of the cone. Rafting then ensued as the west side of the cone collapsed; approximately 15% of the cone is preserved in mounds as much as 30 m high. Rafting was extensive enough to remove most of the cone over the vent area, which effectively reduced the pressure cap on the magma conduit. Resultant low fountaining fed clastogenic lava flows and minor scoria fallback. Clastogenic flows traveled as far as 4 km and now form a cliff 30–40 m high at the edge of the lava platform. Although several possibilities explain the change in vent dynamics and eruptive style, we favor the interpretation that an increase in magma-rise rate caused collapse of the cone. The abrupt removal of 300 m of material over the vent removed a conduit “cork” and low fountaining began. Magma that had erupted effusively suddenly became explosive. This aspect of scoria cone rafting at Red Mountain is broadly similar to sector collapse followed by explosive eruption in larger systems. A steep-walled, 150-m-high amphitheatre on the northeast side of Red Mountain exposes weakly to strongly altered scoria cemented by calcite, iron, and zeolites. We suggest that vapor-phase alteration was responsible for sealing fine-grained ash beds in the cone, and a pressurized system developed. Residual heat from a dike that was emplaced as part of the magmatic activity provided heat that drove groundwater along the regional fault up into the cone. Eventually the overpressurized system exploded in a phreatic eruption that created the amphitheatre, which has subsequently been enlarged by water and wind erosion. The combined sequence of events at Red Mountain illustrates some of the complexities in monogenetic scoria cone eruptions that have received little attention to date.