Unprecedented pressure increase in deep magma reservoir triggered by lava‐dome collapse
B. VoightA. T. LindeI. Selwyn SacksG. S. MattioliR. S. J. SparksDerek ElsworthD. HidayatP. E. MalinE. ShalevChristina WidiwijayantiS. R. YoungV. BassA. B. ClarkeP. N. DunkleyW. JohnstonN. McWhorterJürgen NeubergP. Williams
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The collapse of the Soufrière Hills Volcano lava dome on Montserrat in July 2003 is the largest such event worldwide in the historical record. Here we report on borehole dilatometer data recording a remarkable and unprecedented rapid (∼600s) pressurisation of a magma chamber, triggered by this surface collapse. The chamber expansion is indicated by an expansive offset at the near dilatometer sites coupled with contraction at the far site. By analyzing the strain data and using added constraints from experimental petrology and long‐term edifice deformation from GPS geodesy, we prefer a source centered at approximately 6 km depth below the crater for an oblate spheroid with overpressure increase of order 1 MPa and average radius ∼1 km. Pressurisation is attributed to growth of 1–3% of gas bubbles in supersaturated magma, triggered by the dynamics of surface unloading. Recent simulations demonstrate that pressure recovery from bubble growth can exceed initial pressure drop by nearly an order of magnitude.Keywords:
Lava dome
Overpressure
Magma chamber
Dome (geology)
The structures and textures preserved in lava domes reflect underlying magmatic and eruptive processes, and may provide evidence of how eruptions initiate and evolve. This study explores the remarkable cycles in lava extrusion style produced between 1922 and 2012 at the Santiaguito lava dome complex, Guatemala. By combining an examination of eruptive lava morphologies and textures with a review of historical records, we aim to constrain the processes responsible for the range of erupted lava type and morphologies. The Santiaguito lava dome complex is divided into four domes (El Caliente, La Mitad, El Monje, El Brujo), containing a range of proximal structures (e.g. spines) from which a series of structurally contrasting lava flows originate. Vesicular lava flows (with a'a like, yet non-brecciated flow top) have the highest porosity with interconnected spheroidal pores and may transition into blocky lava flows. Blocky lava flows are high volume and texturally variable with dense zones of small tubular aligned pore networks and more porous zones of spheroidal shaped pores. Spines are dense and low volume and contain small skeletal shaped pores, and subvertical zones of sigmoidal pores. We attribute the observed differences in pore shapes to reflect shallow inflation, deflation, flattening or shearing of the pore fraction. Effusion rate and duration of the eruption define the amount of time available for heating or cooling, degassing and outgassing prior to and during extrusion, driving changes in pore textures and lava type. Our new textural data when reviewed with all the other published data allows cyclic models to be developed. The cyclic eruption models are influenced by viscosity changes resulting from (1) initial magmatic composition and temperature, and (2) effusion rate which in turn affects degassing, outgassing and cooling time in the conduit. Each lava type presents a unique set of hazards and understanding the morphologies and dome progression is useful in hazard forecasting.
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Abstract Merapi volcano has a well-known eruption type, namely Merapi type, in which an extruded lava dome collapses and is accompanied by pyroclastic density current (PDC). This type of eruption makes morphological monitoring of the lava dome crucial in the hazard mitigation process. After the VEI 4 eruption in 2010, a new lava dome of Merapi appeared on top of the 2010 lava dome in August 2018 and continuously grew. In November 2019, the lava dome started to collapse outward the crater area. We reported the lava dome morphological monitoring using a UAV (Unmanned Aerial Vehicle) photogrammetry conducted from August 2018 to February 2019. This UAV monitoring provides processed aerial photo data in Digital Terrain Model (DTM) and orthophoto with low operating costs and short data acquisition time. The lava domes erupted from the same eruptive canter within this period and grew evenly in all directions. The 2018-2019 Merapi lava dome has basal ratio of 0.183 to 0.290 with height of 11 to 41 m, respectively. Volume changed from 33,623 m 3 in August 2018 to 658,075 m 3 in February 2019, suggesting growth rate at ~3,500 m 3 /day. The lava base filled the crater base area (0.21 km 2 ) and started to collapse outward in November 2019.
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SUMMARY Lava domes form when highly viscous magmas erupt on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma. Here, we develop a 2-D axisymmetric model of magma extrusion on the surface and lava dome evolution and analyse the dome morphology using a finite-volume method implemented in Ansys Fluent software. The magma/lava viscosity depends on the volume fraction of crystals and temperature. We show that the morphology of domes is influenced by two parameters: the characteristic time of crystal content growth (CCGT) and the discharge rate (DR). At smaller values of the CCGTs, that is, at rapid lava crystallization, obelisk-shaped structures develop at low DRs and pancake-shaped structures at high DRs; at longer CCGTs, lava domes feature lobe- to pancake-shaped structures. A thick carapace of about 70 per cent crystal content evolves at smaller CCGTs. We demonstrate that cooling does not play the essential role during a lava dome emplacement, because the thermal thickness of the evolving carapace remains small in comparison with the dome's height. A transition from the endogenic to exogenic regime of the lava dome growth occurs after a rapid increase in the DR. A strain-rate-dependent lava viscosity leads to a more confined dome, but the influence of this viscosity on the dome morphology is not well pronounced. The model results can be used in assessments of the rates of magma extrusion, the lava viscosity and the morphology of active lava domes..
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Mount Sinabung, North Sumatra, Indonesia, erupted for the first time in 2010 and reactivated again in 2013. The eruption started with a phreatic phase, changed to phreatomagmatic, and then andesite lava appeared at the summit crater in late December 2013. Lava effusion continued and has been associated with partial to complete collapses of the lava complex, which successively generated pyroclastic density currents (PDCs). The lava complex grew first as a lava dome and then developed into a lava flow (lava extension stage). It extended up to about 3 km in horizontal runout distance by late 2014. When the front of the lava complex moved onto the middle and lower slope of the volcano, PDC events were initially replaced by simple rock falls. Inflation of the upper part of the lava complex began in mid-2014 when the movement of the lava flow front stagnated. The inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex, generating PDC events with long travel distances. From mid-September 2014, new lobes repeatedly appeared near the summit and collapsed. Cyclic vulcanian events began in August 2015 when hybrid events peaked, and continued > 1.5 years (vulcanian stage). These events sometimes triggered PDCs, whose deposits contained vesiculated lava fragments. The distribution of PDC deposits, which extended over time, mostly overlapped in areal extent with that of the 9th–10th century eruption. Eruption volumes were estimated based on measurements with a laser distance meter during 6 periods, digital surface model (DSM) analysis of satellite images during one period, and the cumulative number of seismically detected PDC events, assuming a constant volume of each PDC event. The total volume of eruption products reached about 0.16 km3 DRE as of the end of 2015. The lava discharge rate was largest during the initial stage (> 7 m3/s) and decreased exponentially over time. The discharge rate during the vulcanian stage was ≪ 1 m3/s. The trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a GPS measurement. The chemical composition of lava slightly evolved with time. Cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses.
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The third episode of lava dome growth at Soufrière Hills Volcano began 1 August 2005 and ended 20 April 2007. Volumes of the dome and talus produced were measured using a photo‐based method with a calibrated camera for increased accuracy. The total dense rock equivalent (DRE) volume of extruded andesite magma (306 ± 51 Mm 3 ) was similar within error to that produced in the earlier episodes but the average extrusion rate was 5.6 ± 0.9 m 3 s −1 (DRE), higher than the previous episodes. Extrusion rates varied in a pulsatory manner from <0.5 m 3 s −1 to ∼20 m 3 s −1 . On 18 May 2006, the lava dome had reached a volume of 85 Mm 3 DRE and it was removed in its entirety during a massive dome collapse on 20 May 2006. Extrusion began again almost immediately and built a dome of 170 Mm 3 DRE with a summit height 1047 m above sea level by 4 April 2007. There were few moderate‐sized dome collapses (1–10 Mm 3 ) during this extrusive episode in contrast to the first episode of dome growth in 1995–8 when they were numerous. The first and third episodes of dome growth showed a similar pattern of low (<0.5 m 3 s −1 ) but increasing magma flux during the early stages, with steady high flux after extrusion of ∼25 Mm 3 .
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: Lava flow and lava dome growth are two main manifestations of effusive volcanic eruptions. Less-viscous lava tends to flow long distances depending on slope topography, heat exchange with the surroundings, eruption rate, and the erupted magma rheology. When magma is highly viscous, its eruption on the surface results in a lava dome formation, and an occasional collapse of the dome may lead to a pyroclastic flow. In this chapter, we consider two models of lava dynamics: a lava flow model to determine the internal thermal state of the flow from its surface thermal observations, and a lava dome growth model to determine magma viscosity from the observed lava dome morphological shape. Both models belong to a set of inverse problems. In the first model, the lava thermal conditions at the surface (at the interface between lava and the air) are known from observations, but its internal thermal state is unknown. A variational (adjoint) assimilation method is used to propagate the temperature and heat flow inferred from surface measurements into the interior of the lava flow. In the second model, the lava dome viscosity is estimated based on a comparison between the observed and simulated morphological shapes of lava dome shapes using computer vision techniques.
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Usu volcano has erupted eight times since 1663. The last four eruptions took place in the 20th century, and were monitored using standard instruments. Only the 1944 eruption produced a lava dome with a mound. However, growth of the lava dome and the mound beneath have not been discussed quantitatively because direct data of the dome formation were not obtained. During the early period of the 1944 eruption, T. Minakami repeated precise levels along the road traversing the eastern foot of Usu volcano which had grown to a part of the new dome (Showa-shinzan). The surveying period covered the stages of precursory upheaval, mound upheaval, explosions, and finally, lava dome extrusion. Though the surveying route grazed the upheaving mound, the results of the precise levels prove to be extremely useful in deriving a pseudo growth curve for the mound and the lava dome. The growth curves afford us important information on ground upheavals and lava dome extrusions. Such knowledge can not be obtained by model experiments or theoretical simulations.
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Imaging growing lava domes has remained a great challenge in volcanology due to their inaccessibility and the severe hazard of collapse or explosion. Changes in surface movement, temperature, or lava viscosity are considered crucial data for hazard assessments at active lava domes and thus valuable study targets. Here, we present results from a series of repeated survey flights with both optical and thermal cameras at the Caliente lava dome, part of the Santiaguito complex at Santa Maria volcano, Guatemala, using an Unoccupied Aircraft System (UAS) to create topography data and orthophotos of the lava dome. This enabled us to track pixel-offsets and delineate the 2D displacement field, strain components, extrusion rate, and apparent lava viscosity. We find that the lava dome displays motions on two separate timescales, (i) slow radial expansion and growth of the dome and (ii) a narrow and fast-moving lava extrusion. Both processes also produced distinctive fracture sets detectable with surface motion, and high strain zones associated with thermal anomalies. Our results highlight that motion patterns at lava domes control the structural and thermal architecture, and different timescales should be considered to better characterize surface motions during dome growth to improve the assessment of volcanic hazards.
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