Lava Discharge Research Articles

A comparison of field- and satellite-derived thermal flux at Piton de la Fournaise: implications for the calculation of lava discharge rate

We present thermal measurements made by high spatial resolution ground-based (a hand-held thermal camera) and low spatial resolution space-based (MODIS) instruments for a lava flow field active during the last phase of the May–July 2003 eruption at Piton de la Fournaise (La Reunion). Multiple oblique ground-based thermal images were merged to provide full coverage of the flow-field. These were then corrected for path length attenuation and orthorectified, allowing the at-surface radiance emitted by the flow-field to be estimated. Comparison with the radiance recorded by the MODIS sensors during the eruption reveals that, for clear-sky conditions and moderate-to-low viewing angles (satellite zenith <40°), the satellite measurements represent ∼90% of the at-surface radiance, and thus represent valuable data for quantifying volcanic thermal anomalies. Nevertheless, extreme viewing geometries and the presence of clouds strongly affect the radiance reaching the sensor and affected data from 94% of the overpasses. Ground-based thermal data were used to investigate an empirical relationship between the radiant heat flux and lava discharge rate during the emplacement of pahoehoe flows. While the average radiation temperature for flow surface that were 6–24 h old ranged between 500 K and 625 K, the ratio between radiative heat flux and Time-Averaged lava Discharge Rate (TADR) ranged between 1.5 × 108 J m−3 and 3.5 × 108 J m−3. This relationship was used to estimate TADR values from optimal MODIS data and produced results in line with those obtained from GPS surveys (Coppola et al. 2005). Our results underscore the importance of ground-based thermal analysis for the interpretation of satellite measurements, particularly in terms of calculating discharge rate trends.

The evolution of the Sciara del Fuoco subaerial slope during the 2007 Stromboli eruption: Relation between deformation processes and effusive activity

Focusing on the Island of Stromboli, this research investigates whether airborne remote sensing systems, such as those based on digital photogrammetry and laser scanner sensors, can be adopted to monitor slope deformation and lava emplacement processes in active volcanic areas. Thanks to the capability of extracting accurate topographic data and working on flexible time schedules, these methods can be used to constrain the regular and more frequent measurements derived from satellite observations. This work is dedicated to the monitoring of Stromboli's volcanic edifice which is beneficial when obtaining quantitative data on the geometry of deformation features and the displaced (failures and landslides) and emplaced (lava flows) volumes. In particular, we focus on the capability of extracting average effusion rates from volume measurements that can be used to validate or integrate satellite-derived estimates. Since 2001, a number of airborne remote sensing surveys, namely Digital Photogrammetry (DP) and Airborne Laser Scanning (ALS), have been carried out on Stromboli's volcano to obtain high resolution Digital Elevation Models (DEM) and orthophotos with sub-meter spatial resolution and a time schedule suitable for monitoring the morphological evolution of the surface during the quiescent phases. During the last two effusive eruptions (2002–2003 and 2007) the surface modifications, created on the Sciara del Fuoco slope and on the crater area as a consequence of effusive activity, were quantified and monitored using the same methodologies. This work, which is based on the results obtained from the multi-temporal quantitative analysis of the data collected from 2001 to 2007, mainly focuses on the 2007 eruption but also accounts for analogies and differences regarding the 2002–2003 event. The 2007 eruption on the Sciara del Fuoco slope from 27 February until 2 April, produced a compound lava field including a lava delta on the shoreline, discharging most of the lava into the sea. The comparison of the 2007 DEMs with a pre-eruption surface (2006 LIDAR survey) allowed for the evaluation of the total lava volume that accumulated on the subaerial slope while two syn-eruption DEMs were used to calculate the average effusion rates during the eruption. Since the evolution of a lava field produced during an eruption can be seen as a proxy for the magma intrusion mechanism, hypotheses are formulated on the connection between the lava discharge and the instabilities suffered by the slope.

Lava discharge rate and effusive pattern at Piton de la Fournaise from MODIS data

We analysed the effusive activity of 15 eruptions of Piton de la Fournaise by using the data acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) during 2003–2007 period. Thermal anomalies were detected by adjusting the values of the Normalised Thermal Index (NTI) threshold [Wright, R.L., Flynn, H., Garbeil, A.J.L., Harris Pilger, E., 2002. Automated volcanic eruption detection using MODIS. Remote Sens. Environ. 82: 135–155.] in accord to the seasonal and topographic variations of the background temperature at Piton de la Fournaise. Each satellite overpass, has been classified according to the presence of clouds and the satellite viewing geometry. The analyzed data indicate that at Piton de la Fournaise only 10% of MODIS overpasses occurred in optimal conditions (clear sky and satellite zenith < 40°). However this classification allowed us to use the 4 μm radiance to estimate time average of lava discharge rates (TADR) for most of the analysed eruptions. These data has been used to compare the inferred effusive pattern with the real time seismic amplitude data (RSAM) recorded during the same events. We found that summit eruptions, characterised by a lower discharge rate (< 2 m 3s − 1 ), induce a separation of the gas phase which translate into a decoupling between TADR and RSAM. This regime coupled with the low magma ascent rate and the typical steady effusion of these eruptions imply a very low pressurization of the shallower reservoir which is consistent with a direct overflow of the magma supplied from depth. Conversely, the distal eruptions show a TADR linearly correlated with the RSAM thus indicating a more homogeneous degassing regime and the absence of gas accumulation process within the shallow reservoir. The high initial TADR (> 20 m 3 s − 1 ) and the following vanishing phase indicate that distal eruptions are triggered when a critical overpressure is reached (>5 MPa). This last seems to be increased during the whole analysed period up to the onset of the April 2007 which led to the collaps of the Dolomieu crater. Finally we propose that the recent activity of PdF may result from a persistent loading of the shallow reservoir with a magma supply rate which increased from 1135 kg s − 1 to 4310 kg s − 1 during the period between 2003 and 2007.

Lava flow simulations using discharge rates from thermal infrared satellite imagery during the 2006 Etna eruption

Techniques capable of measuring lava discharge rates during an eruption are important for hazard prediction, warning, and mitigation. To this end, we developed an automated system that uses thermal infrared satellite MODIS data to estimate time-averaged discharge rate. MODIS-derived time-varying discharge rates were used to drive lava flow simulations calculated using the MAGFLOW cellular automata model, allowing us to simulate the discharge rate-dependent spread of lava as a function of time. During the July 2006 eruption of Mount Etna (Sicily, Italy), discharge rates were estimated at regular intervals (i.e., up to 2 times/day) using the MODIS data. The eruption lasted 10 days and produced a ~3-km-long lava flow field. Time-averaged discharge rates extracted from 13 MODIS images were utilized to produce a detailed chronology of lava flow emplacement, demonstrating how infrared satellite data can be used to drive numerical simulations of lava flow paths during an ongoing eruptive event. The good agreement between simulated and mapped flow areas indicates that model-based inundation predictions, driven by time-varying discharge rate data, provide an excellent means for assessing the hazard posed by ongoing effusive eruptions.

Pāhoehoe flow cooling, discharge, and coverage rates from thermal image chronometry

Theoretically‐ and empirically‐derived cooling rates for active pāhoehoe lava flows show that surface cooling is controlled by conductive heat loss through a crust that is thickening with the square root of time. The model is based on a linear relationship that links log(time) with surface cooling. This predictable cooling behavior can be used assess the age of recently emplaced sheet flows from their surface temperatures. Using a single thermal image, or image mosaic, this allows quantification of the variation in areal coverage rates and lava discharge rates over 48 hour periods prior to image capture. For pāhoehoe sheet flow at Kīlauea (Hawai`i) this gives coverage rates of 1–5 m2/min at discharge rates of 0.01–0.05 m3/s, increasing to ∼40 m2/min at 0.4–0.5 m3/s. Our thermal chronometry approach represents a quick and easy method of tracking flow advance over a three‐day period using a single, thermal snap‐shot.

The November 2002 eruption at Piton de la Fournaise volcano, La Réunion Island: ground deformation, seismicity, and pit crater collapse

An eruption on the eastern flank of Piton de la Fournaise volcano started on 16 November, 2002 after 10 months of quiescence. After a relatively constant level of activity during the first 13 days of the eruption, lava discharge, volcanic tremor and seismicity increased from 29 November to 3 December. Lava effusion suddenly ceased on 3 December while shallow earthquakes beneath the Dolomieu summit crater were still recorded at a rate of about one per minute. This unusual activity continued and increased in intensity over the next three weeks, ending with the formation of a pit crater within Dolomieu. Based on ground deformation, measured by rapid-static and continuous GPS and an extensometer, seismic data, and lava effusion patterns, the eruptive period is divided into five stages: 1) slow summit inflation and sporadic seismicity; 2) rapid summit inflation and a short seismic crisis; 3) rapid flank inflation, onset of summit deflation, sporadic seismicity, accompanied by stable effusion; 4) flank inflation, coupled with summit deflation, intense seismicity, and increased lava effusion; and finally 5) little deflation, intense shallow seismicity, and the end of lava effusion. We propose a model in which the pre-intrusive inflation of Stage 1 in the months preceding the eruption was caused by a magma body located near sea level. The magma reservoir was the source of an intrusion rising under the summit during Stage 2. In Stage 3, the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano, causing lava effusion. Pressure decrease in the magmatic plumbing system followed, resulting in upward migration of a collapse front, forming a subterranean column of debris by faulting and stoping. This caused intense shallow seismicity, increase in discharge of lava and volcanic tremor at the lateral vent in Stage 4 and, eventually the formation of a pit crater in Stage 5.

Seismicity of an andesitic volcano during block-lava effusion: Volcán de Colima, México, November 1998–January 1999

The block-lava effusion at Volcan de Colima, Mexico began on November 20, 1998, after 12 months of seismic activity, and ended about 80 days later. Three types of seismic events were observed during the lava effusion. Volcano—tectonic earthquakes occurred mainly at the very beginning and after the termination of lava effusion. Explosion earthquakes occurred frequently during the period of the maximum rate in lava effusion. The remainder of the seismic signals were associated with pyroclastic flows and rockfalls from the lava dome. These latter signals increased sharply in number at the onset of lava effusion. The rate of occurrence remained high when the lava discharge rate decreased but gradually decreased after the termination of lava effusion. Maximum daily durations of seismic signals are proportional to the daily volumetric output of lava, indicating the dependence of the number of pyroclastic flows on the rate of lava output. A log-log plot of seismic signal duration vs. number of events with this duration displays a linear relationship. The short-period seismic signals can be divided into three categories based on duration: short events with durations less than 100 s; intermediate events with durations between 100 and 250 s; and long events with durations longer than 250 s. We infer that long events correspond to pyroclastic flows with mean deposit volume ∼2×105 m3, and intermediate events represent pyroclastic flows with mean deposit volume ∼1×103 m3.

Global positioning system measurements of ground deformation caused by magma intrusion and lava discharge: the 1990–1995 eruption at Unzendake volcano, Kyushu, Japan

Global positioning system (GPS) measurements made around Unzendake volcano, Kyushu, Japan, since January 1991 have detected ground deformation caused by magma intrusion and lava discharge. In the intermittent phreatic and phreatomagmatic eruption stage, the ground was inflating. After growth of the lava dome and following frequent pyroclastic flows at Unzendake volcano, the ground began deflating. These ground deformations are explained by the inflation and deflation of a Mogi's source model (a point source model) located about 6 km west of the active crater at a depth of 11 km, at an aseismic region. The observed horizontal displacement vectors pointed radially away from the estimated pressure source during inflation and pointed to the pressure source during deflation. The horizontal displacements at the reference GPS station calculated from contraction of the estimated pressure source coincide well with the actual horizontal displacements observed from other GPS baseline systems. These observations validate our estimates for the pressure source. Based on the relation between the deformation volume of the ground surface and the discharged volume of the lava, it is estimated that during the eruption there was magma supply from the deeper portion as well as magma discharge at the crater. Magma is estimated to be supplied to the reservoir at an average rate of 1.1×10 5 m 3/day; magma intrusion began in December 1989 at the latest and continued for 1.9×10 3 days.

Implications of longeval lava lakes for geomorphological and plutonic processes at Erta 'Ale volcano, Afar

Erta 'Ale volcano, sited within the Afar Triangle of Ethiopia, is one of the least visited of perennially active, subaerial volcanoes. Satellite images recorded over the past thirty years illustrate the sustained activity of the volcano and complement the few brief periods of field observation. We consider that Erta 'Ale's lava lakes have probably persisted for ≥ 90 years, placing them among the longest-lived yet recorded. Despite sustained surface heat fluxes of 100–400 MW, the net surface growth rate integrated over the interval 1968–1995 was only ≈ 10 kg s −1. We speculate that this minimal lava discharge cannot be used to infer a low magma supply rate to the volcano, since heat losses from die lava lakes inhibit eruption by increasing magma density. This implies growth of the underlying crust by formation of dikes and sills containing cumulates, accommodated, and possibly promoted, by regional extension and intrusion loading. Open vent degassing and rift kinematics are clearly reflected in Erta 'Ale's morphology which is characterised by very gentle (< 3 °) slopes and a summit caldera.

Cellular automata for simulating lava flows: A method and examples of the Etnean eruptions

Abstract This paper presents a bidimensional cellular model for simulating lava flows and its application to the simulation of the 1986–87 and 1991–92 Etnean eruptions. Lava flow is viewed as a dynamic system based on local interactions with discrete time and space, where space is represented by square cells. Each cell is characterized by specific values (the state) of the following selected physical parameters: altitude, lava thickness, lava temperature and lava outflows toward the neighbouring cells. Lava rheology is considered indirectly through its effect on lava thickness. The boundary values constraining a simulation are those describing underlying topography, lava discharge rate, eruption temperature, solidus temperature and rheology. The Cellular Automata model has been tested against growth data for Etna's 1986–87 and 1991–92 flow fields. Even though the data set is heterogeneous, the model and real flow field show strikingly similar growth patterns. The close similarity highlights the flexibility of the Cellular Automata approach; as a matter of fact it should be noted that the cell dimension can be chosen in order to define the approximation, to which the simulation must be developed and topography can be easily updated on account of solidification thanks to the discrete specification for space and time, thus allowing the simulation of multiple flows. first deals with the reduction of the dimension of the cells from 10 m to 5 m. This scale is better adapted to the study of medium and small events. The second is linked to the evolution of the transition algorithm so as to modify certain types of behaviour, such as tunneling, not easy to simulate in the current form.

Volcanism and sedimentation in part of a Late Archaean rift: the Hartbeesfontein basin, Transvaal, South Africa

AbstractThe Hartbeesfontein basin is one basin within the Late Archaean rift system of South Africa. This rift system has been recently compared to the Basin and Range province in western North America and may therefore be an ensialic extensional back‐arc basin. Structurally, the Hartbeesfontein basin is a half‐graben structure bounded to the south‐east by a major, normal, listric fault and to the north‐east and south‐west by strike‐slip (transfer?) fault zones. It is infilled by over 2000 m of diamictites, shales, lavas and chemical sediments. Initial basin formation appears to be accompanied by phreatomagmatic volcanic activity caused by the interaction between basic tholeiitic magmas rising along fractures and groundwater. Volcaniclastic debris from these eruptions was incorporated into laharic debris flows and deposited on basin marginal alluvial fans. At the same time a deep, permanent lake formed within the basin in which silts and muds accumulated. Major fissure eruptions of basic, tholeiitic lavas followed, their eruptive centres being apparently located along the strike‐slip (transfer?) fault /ones. Initially, these fissure eruptions had high rates of magma discharge accompanied by intense fire fountaining that resulted in the rapid accumulation of aa type flows. Later lava discharge rates decreased and more quiescent pahoehoe type flows were erupted. Localized centres of acid volcanism within the basic lava pile were located along the south‐western strike‐slip fault zone. These acid volcanic rocks are interpreted as co‐ignimbrite lag breccias and pyroclastic flow deposits and tuffs produced by the repeated formation and collapse of Plinian eruption columns. Towards the top of the basic lava pile, two breaks in volcanism permitted the formation of dolomitic playa lakes. Sedimentation in these lakes was terminated by further basic lava flows. At the top of the basin fill sequence is a thick, bedded chert interpreted as a magadiitic, alkaline playa lake fed by silica‐rich hot springs located along the south‐eastern edge of the basin. Quartzites and conglomerates deposited by braided rivers unconformably overlie the basin‐fill sequence and probably represent a through flowing river system signifying termination of the Hartbeesfontein basin as a separate basin. The Hartbeesfontein basin and its fill demonstrate that a close relationship exists between fissure volcanism, sedimentation and basin evolution and that the strike‐slip, transfer faults acted as the loci of volcanic activity.

The settling of olivine in Kilauean magma as shown by lavas of the 1959 eruption

Compositions of lavas of the 1959 Kilauea eruption in Kilauea Iki crater characterize the first stage of fractional crystallization of tholeiitic magma with unusual precision and completeness. Gravitative settling of olivine (Fa (sub 12.5) ) produces a series of lava types ranging from picrite-basalt to olivine-poor basalt. Variation of lava temperature with olivine content suggests zoning of the subterranean magma body into a cooler, olivine-depleted upper part and a hotter, olivine-enriched lower part. The most picritic lavas were erupted during periods of high rates of lava discharge; unusually strong magma currents may have mobilized the sludge of sedimented olivines at the bottom of the magma chamber to produce picritic magma.