Lava Flow Field Research Articles

Satellite and Ground Remote Sensing Techniques to Trace the Hidden Growth of a Lava Flow Field: The 2014–2015 Effusive Eruption at Fogo Volcano (Cape Verde)

Fogo volcano erupted in 2014–2015 producing an extensive lava flow field in the summit caldera that destroyed two villages, Portela and Bangaeira. The eruption started with powerful explosive activity, lava fountains, and a substantial ash column accompanying the opening of an eruptive fissure. Lava flows spreading from the base of the eruptive fissure produced three arterial lava flows. By a week after the start of the eruption, a master lava tube had already developed within the eruptive fissure and along the arterial flow. In this paper, we analyze the emplacement processes based on observations carried out directly on the lava flow field, remote sensing measurements carried out with a thermal camera, SO2 fluxes, and satellite images, to unravel the key factors leading to the development of lava tubes. These were responsible for the rapid expansion of lava for the ~7.9 km length of the flow field, as well as the destruction of the Portela and Bangaeira villages. The key factors leading to the development of tubes were the low topography and the steady magma supply rate along the arterial lava flow. Comparing time-averaged discharge rates (TADR) obtained from satellite and Supply Rate (SR) derived from SO2 flux data, we estimate the amount and timing of the lava flow field endogenous growth, with the aim of developing a tool that could be used for hazard assessment and risk mitigation at this and other volcanoes.

The Volume of Lava Erupted During the 2014 to 2015 Eruption at Holuhraun, Iceland: A Comparison Between Satellite‐ and Ground‐Based Measurements

AbstractThe 31 August 2014 to 27 February 2015 eruption at Holuhraun created the largest lava flow field in Iceland since the 1783–1784 Laki eruption. Emplacement of a basaltic flow field of this magnitude onto an effectively flat surface (<0.1°) is a rare occurrence. Lava discharge rate, a fundamental variable that controls flow field emplacement, allows us to estimate the total volume of lava erupted when integrated over time. Thus, discharge rate data are important for volcano monitoring and lava flow modeling. Here we compare discharge rates estimated using data from National Aeronautics and Space Administration's MODerate Resolution Imaging Spectroradiometer (MODIS) and the method of Harris et al. (1997a, https://doi.org/10.1029/96JB03388; 1997b, https://doi.org/10.1007/s004450050174; 2007, https://doi.org/10.1007/s00445‐007‐0120‐y), with estimates of discharge rates derived from comparing intermittent ground‐based measurements of flow field volume. The time‐averaged discharge rates (TADR) reveal a pulsed increase in the first few days of the eruption. Although the trends of the satellite‐ and ground‐based discharge rates are similar, the ground‐based estimates are systematically higher than the satellite‐derived estimates (about 2 to 3 times higher) in the first 30 days of the eruption, and relatively close (within 30%) for the next 20 days. Conversely, during the final 130 days, the satellite‐based estimates are systematically higher than the ground‐based estimates (about 2 times higher). This difference likely arises from the assumption of the lava flow surface temperature used in the space‐based calculation, which may not be entirely representative of this uniquely large and intense basaltic eruption. However, the satellite‐based technique yields a total erupted volume of about 1.21 km3 in good agreement with the 1.2 km3 (84 km2) derived from field observations and mapping.

The effect of inflation on the morphology-derived rheological parameters of lava flows and its implications for interpreting remote sensing data - A case study on the 2014/2015 eruption at Holuhraun, Iceland

Morphology-derived lava flow rheology is a frequently used tool in volcanology and planetary science to determine rheological parameters and deduce the composition of lavas on terrestrial planets and their moons. These calculations are usually based on physical equations incorporating 1) lava flow driving forces: gravity, slope and flow-rate and 2) morphological data such as lava flow geometry: flow-width, -height or shape of the flow outline. All available methods assume that no geometrical changes occur after emplacement and that the measured flow geometry reflects the lava's apparent viscosity and/or yield strength during emplacement. It is however well-established from terrestrial examples that lava flows may inflate significantly after the cessation of flow advance. This inflation affects, in turn, the width-to-height ratio upon which the rheological estimates are based and thus must result in uncertainties in the determination of flow rheology, as the flow height is one of the key parameters in the morphology-based deduction of flow properties. Previous studies have recognized this issue but, to date, no assessment of the magnitude of this error has been presented. This is likely due to a lack of digital elevation models (DEMs) at sufficiently high spatial and temporal resolution.The 2014/15 Holuhraun eruption in central Iceland represents one of the best monitored large volume (1.5 km3) lava flow fields (85 km2) to date. An abundance of scientific field and remote sensing data were collected during its emplacement. Moreover, inflation plays a key role in the emplacement dynamics of the late stage of the lava field. Here, we use a time series of high resolution DEMs acquired by the TanDEM-X satellite mission prior, during and after the eruption to evaluate the error associated with the most common methods of deriving lava flow rheology from morphological parameters used in planetary science.We can distinguish two dominant processes as sources of error in the determination of lava flow rheology from morphology 1) wholesale inflation of lava channels and 2) post halting inflation of individual lava toes. These result in a 2.4- to 17 - fold overestimation of apparent viscosity and a 0.7- to 2.4 - fold overestimation of yield strength. When applied in planetary sciences, this overestimation in rheological parameters translates directly to an overestimation of the respective lavas silica content. We conclude that, although qualitatively informative, morphological analysis is insufficient to discern lava rheology and composition. Instead, in-situ analysis together with high resolution remote sensing data is needed to properly constrain the compositions involved in planetary volcanism.

Extensive young silicic volcanism produces large deep submarine lava flows in the NE Lau Basin

New field observations reveal that extensive (up to ~ 402 km2) aphyric, glassy dacite lavas were erupted at multiple sites in the recent past in the NE Lau basin, located about 200 km southwest of Samoa. This discovery of volumetrically significant and widespread submarine dacite lava flows extends the domain for siliceous effusive volcanism into the deep seafloor. Although several lava flow fields were discovered on the flank of a large silicic seamount, Niuatahi, two of the largest lava fields and several smaller ones (“northern lava flow fields”) were found well north of the seamount. The most distal portion of the northernmost of these fields is 60 km north of the center of Niuatahi caldera. We estimate that lava flow lengths from probable eruptive vents to the distal ends of flows range from a few km to more than 10 km. Camera tows on the shallower, near-vent areas show complex lava morphology that includes anastomosing tube-like pillow flows and ropey surfaces, endogenous domes and/or ridges, some with “crease-like” extrusion ridges, and inflated lobes with extrusion structures. A 2 × 1.5 km, 30-m deep depression could be an eruption center for one of the lava flow fields. The Lau lava flow fields appear to have erupted at presumptive high effusion rates and possibly reduced viscosity induced by presumptive high magmatic water content and/or a high eruption temperature, consistent with both erupted composition (~ 66% SiO2) and glassy low crystallinity groundmass textures. The large areal extent (236 km2) and relatively small range of compositional variation (σ = 0.60 for wt% Si02%) within the northern lava flow fields imply the existence of large, eruptible batches of differentiated melt in the upper mantle or lower crust of the NE Lau basin. At this site, the volcanism could be controlled by deep crustal fractures caused by the long-term extension in this rear-arc region. Submarine dacite flows exhibiting similar morphology have been described in ancient sequences from the Archaean through the Miocene and in small batches on present-day seafloor spreading centers. This study shows that extensive siliceous lavas can erupt on the modern seafloor under the right conditions.

Using scoria cones, lava lakes and tephra islands to understand the evolution of basaltic fissure eruptions

Basaltic fissure eruptions are the most common eruption type on Earth. They are characterised by linear lava fountains that construct pyroclastic cones and expansive lava flow fields. The histories of these eruptions can be notoriously difficult to interpret due to the geochemical homogeneity of the tephra, and due to the fact that many of the early deposits become buried during later stages of the eruption. Furthermore, observing the construction of the pyroclastic cones is inherently difficult and dangerous due to the presence of active lava fountains. However, glacial outbursts in the north of Iceland have dissected the products of a Holocene fissure eruption. Examination of the pyroclastic cones, tephra deposits and a solidified lava lake along the fissure has allowed us to elucidate the complex eruptive processes that occur during these eruptions.

UAV-based remote sensing surveys of lava flow fields: a case study from Etna’s 1974 channel-fed lava flows

During an eruption, time scales of topographic change are fast and involve vertical and planimetric evolution of millimeters to meters as the event progresses. Repeat production of high spatial resolution terrain models of lava flow fields over time scales of a few hours is thus a high-value capability in tracking the buildup of the deposit. Among the wide range of terrestrial and aerial methods available to collect such topographic data, the use of an unmanned aerial vehicle (UAV) as an acquisition platform, together with structure from motion (SfM) photogrammetry, has become especially useful. This approach allows high-frequency production of centimeter-scale terrain models over kilometer-scale areas, including dangerous and inaccessible zones, with low cost and minimal hazard to personnel. This study presents the application of such an integrated UAV-SfM method to generate a high spatial resolution digital terrain model and orthomosaic of Mount Etna’s January–February 1974 lava flow field. The SfM method, applied to images acquired using a UAV platform, enabled the extraction of a very high spatial resolution (20 cm) digital elevation model and the generation of a 3-cm orthomosaic covering an area of 1.35 km2. This spatial resolution enabled us to analyze the morphology of sub-meter-scale features, such as folds, blocks, and cracks, over kilometer-scale areas. The 3-cm orthomosaic allowed us to further push the analysis to centimeter-scale grain size distribution of the lava surface. Using these data, we define three types of crust structure and relate them to positions within a channel-fed ʻaʻā flow system. These crust structures are (i) flow parallel shear lines, (ii) raft zones, and (iii) folded zones. Flow parallel shear lines are found at the channel edges, and are 2-m-wide and 0.25-m-deep zones running along the levee base and in which cracking is intense. They result from intense shearing between the moving channel lava and the static levee lava. In zones where initial levees are just beginning to form, these subtle features are the only marker that delimits the moving lava from the stagnant marginal lava. Rafts generally form as the system changes from a stable to a transitional channel regime. Over this 170-m-long zone, the channel broadens from 8 to 70 m and rafts are characterized by topographically higher and poorly cracked areas, surrounded by lower, heavily cracked areas. We interpret the rafts as forming due to breakup of crust zones, previously moving in a coherent manner in the narrow proximal channel reach. Folded zones involve arcuate, cross-flow ridges with their apexes pointing down-flow, where ridges have relatively small clasts and depressions are of coarser-grained breccia. Our folds have wavelengths of 10 m and amplitudes of 1 m; are found towards the flow front, down-flow of the raft zones; and are associated with piling up of lava behind a static or slowly moving flow front. The very high spatial resolution topographic data available from UAV-SfM allow us to resolve surfaces where roughness has a vertical and horizontal scale of variation that is less than 1 m. This is the case over pāhoehoe and ʻaʻā flow surfaces, and thus allows us to explore those new structures that are only apparent in the sub-metric data. Moreover, during future eruptions, the possibility to acquire such information in near-real time will allow a prompt analysis of developing lava flow fields and structures therein, such as developing lava channel systems, so as to contribute to timely hazard assessment, modeling, and projections.

New Insights for Detecting and Deriving Thermal Properties of Lava Flow Using Infrared Satellite during 2014–2015 Effusive Eruption at Holuhraun, Iceland

A new lava field was formed at Holuhraun in the Icelandic Highlands, north of Vatnajökull glacier, in 2014–2015. It was the largest effusive eruption in Iceland for 230 years, with an estimated lava bulk volume of ~1.44 km3 covering an area of ~84 km2. Satellite-based remote sensing is commonly used as preliminary assessment of large scale eruptions since it is relatively efficient for collecting and processing the data. Landsat-8 infrared datasets were used in this study, and we used dual-band technique to determine the subpixel temperature (Th) of the lava. We developed a new spectral index called the thermal eruption index (TEI) based on the shortwave infrared (SWIR) and thermal infrared (TIR) bands allowing us to differentiate thermal domain within the lava flow field. Lava surface roughness effects are accounted by using the Hurst coefficient (H) for deriving the radiant flux ( Φ rad ) and the crust thickness (Δh). Here, we compare the results derived from satellite images with field measurements. The result from 2 December 2014 shows that a temperature estimate (1096 °C; occupying area of 3.05 m2) from a lava breakout has a close correspondence with a thermal camera measurement (1047 °C; occupying area of 4.52 m2). We also found that the crust thickness estimate in the lava channel during 6 September 2014 (~3.4–7.7 m) compares closely with the lava height measurement from the field (~2.6–6.6 m); meanwhile, the total radiant flux peak is underestimated (~8 GW) compared to other studies (~25 GW), although the trend shows good agreement with both field observation and other studies. This study provides new insights for monitoring future effusive eruption using infrared satellite images.

Extended SO2 outgassing from the 2014\u20132015 Holuhraun lava flow field, Iceland

The 2014–2015 Holuhraun eruption was the largest fissure eruption in Iceland in the last 200 years. This flood basalt eruption produced ~ 1.6 km3 of lava, forming a lava flow field covering an area of ~ 84 km2. Over the 6-month course of the eruption, ~ 11 Mt of SO2 were released from the eruptive vents as well as from the cooling lava flow field. This work examines the post-eruption SO2 flux emitted by the Holuhraun lava flow field, providing the first study of the extent and relative importance of the outgassing of a lava flow field after emplacement. We use data from a scanning differential optical absorption spectroscopy (DOAS) instrument installed at the eruption site to monitor the flux of SO2. In this study, we propose a new method to estimate the SO2 emissions from the lava flow field, based on the characteristic shape of the scanned column density distribution of a homogenous source close to the ground. Post-eruption outgassing of the lava flow field continued for at least 3 months after the end of the eruption, with SO2 flux between < 1 and 9 kg/s. The lava flow field post-eruption emissions were not a significant contributor to the total SO2 released during the eruption; however, the lava flow field was still an important polluter and caused high concentrations of SO2 at ground level after lava effusion ceased.

Tracking morphological changes and slope instability using spaceborne and ground-based SAR data

Stromboli (Aeolian Archipelago, Italy) is an active volcano that is frequently affected by moderate to large mass wasting, which has occasionally triggered tsunamis. With the aim of understanding the relationship between the geomorphologic evolution and slope instability of Stromboli, remote sensing information from space-born Synthetic Aperture Radar (SAR) change detection and interferometry (InSAR) () and Ground Based InSAR (GBInSAR) was compared with field observations and morphological analyses.Ground reflectivity and SqueeSAR™ (an InSAR algorithm for surface deformation monitoring) displacement measurements from X-band COSMO-SkyMed satellites (CSK) were analysed together with displacement measurements from a permanent-sited, Ku-band GBInSAR system.Remote sensing results were compared with a preliminary morphological analysis of the Sciara del Fuoco (SdF) steep volcanic flank, which was carried out using a high-resolution Digital Elevation Model (DEM). Finally, field observations, supported by infrared thermographic surveys (IRT), allowed the interpretation and validation of remote sensing data. The analysis of the entire dataset (collected between January 2010 and December 2014) covers a period characterized by a low intensity of Strombolian activity. This period was punctuated by the occurrence of lava overflows, occurring from the crater terrace evolving downslope toward SdF, and flank eruptions, such as the 2014 event.The amplitude of the CSK images collected between February 22nd, 2010, and December 18th, 2014, highlights that during periods characterized by low-intensity Strombolian activity, the production of materials ejected from the crater terrace towards the SdF is generally low, and erosion is the prevailing process mainly affecting the central sector of the SdF. CSK-SqueeSAR™ and GBInSAR data allowed the identification of low displacements in the SdF, except for high displacement rates (up to 1.5mm/h) that were measured following both lava delta formation after the 2007 eruption and the lava overflows of 2010 and 2011. After the emplacement of the 2014 lava field, high displacements in the central and northern portions of the SdF were recorded by the GBInSAR device, whereas the spaceborne data were unable to detect these rapid movements. A comparison between IRT images and GBInSAR-derived displacement maps acquired during the same time interval revealed that the observed displacements along the SdF were related to the crumbling of newly emplaced 2014 lava and of its external breccia. Detected slope instability after the 2014 flank eruption was related to lava accumulation on the SdF and to the difference in the material underlying the 2014 lava flow: i) lava flows and breccia layers related to the 2002–03 and 2007 lava flow fields in the northern SdF sector and ii) loose volcaniclastic deposits in the central part of the SdF. This work emphasizes the importance of smart integration of spaceborne, SAR-derived hazard information with permanent-sited, operational monitoring by GBInSAR devices to detect areas impacted by mass wasting and volcanic activity.

Compositional and volumetric development of a monogenetic lava flow field: The historical case of Paricutin (Michoacán, Mexico)

Paricutin volcano is the youngest and most studied monogenetic volcano in the Michoacán-Guanajuato volcanic field (Mexico), with an excellent historical record of its nine years (February 1943 to March 1952) of eruptive activity. This eruption offered a unique opportunity to observe the birth of a new volcano and document its entire eruption. Geologists surveyed all of the eruptive phases in progress, providing maps depicting the volcano's sequential growth. We have combined all of those previous results and present a new methodological approach, which utilizes state of the art GIS mapping tools to outline and identify the 23 different eruptive phases as originally defined by Luhr and Simkin (1993). Using these detailed lava flow distribution maps, the volume of each of the flows was estimated with the aid of pre- and post-eruption digital elevation models. Our procedure yielded a total lava flow volume ranging between 1.59 and 1.68km3 DRE, which is larger than previous estimates based on simpler methods. In addition, compositional data allowed us to estimate magma effusion rates and to determine variations in the relative proportions of the different magma compositions issued during the eruption. These results represent the first comprehensive documentation of the combined chemical, temporal, and volumetric evolution of the Paricutin lava field and provide key constraints for petrological interpretations of the nature of the magmatic plumbing system that fed the eruption.

The role of unsteady effusion rates on inflation in long-lived lava flow fields

The emission of volcanic gases and particles can have global and lasting environmental effects, but their timing, tempo, and duration can be problematic to quantify for ancient eruptions where real-time measurements are absent. Lava flows, for example, may be long-lasting, and their impact is controlled by the rate, tempo, and vigor of effusion. These factors are currently difficult to derive from the geologic record but can have large implications for the atmospheric impact of an eruption. We conducted a set of analogue experiments on lava flow inflation aiming at connecting lava morphologies preserved in the rock record to eruption tempo and dynamics through pulsating effusion rates. Inflation, a process where molten material is injected beneath the crust of an active lava flow and lifts it upwards, is a common phenomenon in basaltic volcanic systems. This mechanism requires three components: a) a coherent, insulating crust; b) a wide-spread molten core; and c) pressure built up beneath the crust from a sustained supply of molten material. Inflation can result in a lava flow growing tens of meters thick, even in flow fields that expand hundreds of square kilometers. It has been documented that rapid effusion rates tend to create channels and tubes, isolating the active part of the flow from the stagnant part, while slow effusion rates may cause crust to form quickly and seize up, forcing lava to overtop the crust. However, the conditions that allow for inflation of large flow fields have not previously been evaluated in terms of effusion rate. By using PEG 600 wax and a programmable pump, we observe how, by pulsating effusion rate, inflation occurs even in very low viscosity basaltic eruptions. We show that observations from inflating Hawaiian lava flows correlate well with experimental data and indicate that instantaneous effusion rates may have been 3 times higher than average effusion rates during the emplacement of the 23 January 1988 flow at Kīlauea (Hawai‘i). The identification of a causal relationship between pulsating effusion rates and inflation may have implications for eruption tempo in the largest inflated flows: flood basalts.

Geoheritage Values of a Mature Monogenetic Volcanic Field in Intra-continental Settings: Harrat Khaybar, Kingdom of Saudi Arabia

Harrat Khaybar is one of the most extensive of about 15 volcanic fields located in the western margin of the Arabian Peninsula. Most of these fields are located in the Kingdom of Saudi Arabia about 100–150 km inland from the Red Sea. The volcanic area is located near the culturally and religiously important city of Al Madinah. The field hosts monogenetic volcanoes such as scoria cones, tuff rings, spatter cones and extensive lava flow fields. It also contains several silicic lava domes and associated block-and-ash fans whose deposits fill inter-cone regions. Some of the field’s volcanoes are inferred to have been erupted as recently as about 1000 AD, based on historic documents and geomorphologic evidence. There are no data available to directly support or better constrain the timing of the latest eruptions of the field. The area is also one of the highest regions of Saudi Arabia with a plateau at about 1500 m above sea level, topped by Jabal Abyad (2093 m) and Jabal Quidr (2022 m) volcanoes. Due to the elevation, Harrat Khaybar has a cold arid climate with a unique ecosystem and landscape. The region’s high aesthetic value is derived from the bright white colour of several of its volcanoes which are dominantly rhyolitic ash. These edifices are strikingly different from the dark-coloured lava fields (harrats) of Arabia. Based on appearance, Harrat Khaybar has geoheritage value and could be a major geoconservation and geoeducation region of Arabia. Geological research in the region started only recently and is restricted to geological mapping and geochemical studies. Interest has recently increased because of the recognition of the field’s potential volcanic hazards. There is a push to establish a geoheritage inventory of Harrat Khaybar with the aim of assessing the geoheritage framework of the region and developing more geotourism, geoeducational programmes and a geopark. Key volcanic geotopes and their geosites provide unique opportunities for a stand-alone geopark offering geoeducation and geotourism programmes in the region. The concept has been proposed to the geoheritage resource management of Harrat Rahat just south of Harrat Khaybar and Al Madinah City and could serve as a link between the two historically active volcanic fields located near Al Madinah.

Subsurface architecture of Las Bombas volcano circular structure (Southern Mendoza, Argentina) from geophysical studies

The Plio-Pleistocene Llancanelo volcanic field is located in the south-eastern region of the province of Mendoza, Argentina. This wide back-arc lava plateau, with hundreds of monogenetic pyroclastic cones, covers a large area behind the active Andean volcanic arc. Here we focus on the northern Llancanelo volcanic field, particularly in Las Bombas volcano. Las Bombas volcano is an eroded, but still recognizable, scoria cone located in a circular depression surrounded by a basaltic lava flow, suggesting that Las Bombas volcano was there when the lava flow field formed and, therefore, the lava flow engulfed it completely. While this explanation seems reasonable, the common presence of similar landforms in this part of the field justifies the need to establish correctly the stratigraphic relationship between lava flow fields and these circular depressions. The main purpose of this research is to investigate Las Bombas volcano 3D subsurface architecture by means of geophysical methods. We carried out a paleomagnetic study and detailed topographic, magnetic and gravimetric land surveys. Magnetic anomalies of normal and reverse polarity and paleomagnetic results point to the occurrence of two different volcanic episodes. A circular low Bouguer anomaly was detected beneath Las Bombas scoria cone indicating the existence of a mass deficit. A 3D forward gravity model was constructed, which suggests that the mass deficit would be related to the presence of fracture zones below Las Bombas volcano cone, due to sudden degassing of younger magma beneath it, or to a single phreatomagmatic explosion. Our results provide new and detailed information about Las Bombas volcano subsurface architecture.

The rheological evolution of the 2014/2015 eruption at Holuhraun, central Iceland

In the period from August 29, 2014, to February 27, 2015, the largest basaltic eruption of the last 200 years in Iceland occurred within the tectonic fissure swarm between the Barðarbunga-Veiðivotn and the Askja volcanic systems. The eruption took place in the Holuhraun lava field, 45 km northeast of the Barðarbunga volcano and 20 km south of the Askja volcano. It emplaced over 1.2 km3 dense rock equivalent (DRE) of lava in an area of very low topographic relief. In light of the minimal topographic forcing, lava flow emplacement can be viewed as having been effectively controlled by the lava’s temperature-dependent rheology. Here we combine field and remote sensing data collected during the week of the 17th to 22nd of November 2014 to constrain the lava’s flow path, its velocity, deformation rate and thermal evolution during emplacement. We combine these with measurements of the pure liquid viscosity and the sub-liquidus rheological evolution of the lava during crystallization. Sub-liquidus experiments were performed at a range of constant cooling and shear rates, to mimic the conditions experienced by the lava during emplacement. These data can also be used to infer flow conditions of partly degassed magma within dike-swarms during transport towards the surface. The data show that the effective viscosity of the lava drastically increases until reaching a specific sub-liquidus temperature, the “rheological cutoff temperature” (T cutoff). This departure to high viscosity is a consequence of the onset of crystallization and is found to be primarily controlled by the imposed cooling rate. Our data indicate that shear rate exerts a second-order effect on this rheological departure and T cutoff. We discuss the experimental dataset in the context of the reconstructions of the natural emplacement conditions and describe the implications for the 2014–2015 lava flow field at Holuhraun as well as lava flow modelling in general.

Long-term ground displacement observations using InSAR and GNSS at Piton de la Fournaise volcano between 2009 and 2014

Monitoring ground surface displacement of volcanoes over a long period of time helps improve understanding of the volcano structure, dynamics and mechanisms. In this paper, we investigate the spatio-temporal behavior of the long-term displacement field at Piton de la Fournaise volcano (La Réunion Island) by means of X-band InSAR and GNSS time series analysis from 2009 to 2014. We propose a new correction approach based on principal component analysis to mitigate the long-wavelength artifact in the interferograms over the study area. Our results show that most of the volcanic edifice including the Central Cone, the Eastern Flank and recent lava flow fields was affected by varying degrees of ground motion. More importantly, a widespread sector (~20km2) affected by time-dependent downward and eastward motion was observed on the Eastern Flank of Piton de la Fournaise. The combined analysis of InSAR and GNSS time series and previous studies allows us to confirm that this large mobile sector on the Eastern Flank underwent deformation for at least 7years following the end of the large March–April 2007 eruption, including a stage of transient strain from the end of eruption to February 2011, followed by a stage of steady-state strain until late 2014. Several possible origins, including a pre-existing structural discontinuity, summit stress associated with magmatism, and activated fault movement are explored to explain the observed widespread long-term seaward motion that is considered to be direct evidence of potential flank instability.

Multiple coincident eruptive seismic tremor sources during the 2014–2015 eruption at Holuhraun, Iceland

We analyze eruptive tremor during one of the largest effusive eruptions in historical times in Iceland (2014/2015 Holuhraun eruption). Seismic array recordings are compared with effusion rates deduced from Moderate Resolution Imaging Spectroradiometer recordings and ground video monitoring data and lead to the identification of three coexisting eruptive tremor sources. This contrasts other tremor studies that generally link eruptive tremor to only one source usually associated with the vent. The three sources are (i) a source that is stable in back azimuth and shows bursts with ramp‐like decrease in amplitude at the beginning of the eruption: we link it to a process below the open vents where the bursts correlate with the opening of new vents and temporary increases in the lava fountaining height; (ii) a source moving by a few degrees per month while the tremor amplitude suddenly increases and decreases: back azimuth and slowness correlate with the growing margins of the lava flow field, whilst new contact with a river led to fast increases of the tremor amplitude; and (iii) a source moving by up to 25° southward in 4 days that cannot be related to any observed surface activity and might be linked to intrusions. We therefore suggest that eruptive tremor amplitudes/energies are used with caution when estimating eruptive volumes, effusion rates, or the eruption explosivity as multiple sources can coexist during the eruption phase. Our results suggest that arrays can monitor both the growth of a lava flow field and the activity in the vents.

Lava field evolution and emplacement dynamics of the 2014–2015 basaltic fissure eruption at Holuhraun, Iceland

The 6-month long eruption at Holuhraun (August 2014–February 2015) in the Bárðarbunga-Veiðivötn volcanic system was the largest effusive eruption in Iceland since the 1783–1784 CE Laki eruption. The lava flow field covered ~84km2 and has an estimated bulk (i.e., including vesicles) volume of ~1.44km3. The eruption had an average discharge rate of ~90m3/s making it the longest effusive eruption in modern times to sustain such high average flux. The first phase of the eruption (August 31, 2014 to mid-October 2014) had a discharge rate of ~350 to 100m3/s and was typified by lava transport via open channels and the formation of four lava flows, no. 1–4, which were emplaced side by side. The eruption began on a 1.8km long fissure, feeding partly incandescent sheets of slabby pāhoehoe up to 500m wide. By the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly pāhoehoe and ‘a’ā. The latter became the dominating morphology of lava flows no. 1–8. The second phase of the eruption (Mid-October to end November) had a discharge of ~100–50m3/s. During this time the lava transport system changed, via the formation of a <1km2 lava pond ~1km east of the vent. The pond most likely formed in a topographical low created by a the pre-existing Holuhraun and the new Holuhraun lava flow fields. This pond became the main point of lava distribution, controlling the emplacement of subsequent flows (i.e. no. 5–8). Towards the end of this phase inflation plateaus developed in lava flow no. 1. These inflation plateaus were the surface manifestation of a growing lava tube system, which formed as lava ponded in the open lava channels creating sufficient lavastatic pressure in the fluid lava to lift the roof of the lava channels. This allowed new lava into the previously active lava channel lifting the channel roof via inflation. The final (third) phase, lasting from December to end-February 2015 had a mean discharge rate of ~50m3/s. In this phase the lava transport was mainly confined to lava tubes within lava flows no. 1–2, which fed breakouts that resurfaced >19km2 of the flow field. The primary lava morphology from this phase was spiny pāhoehoe, which superimposed on the ‘a’ā lava flows no. 1–3 and extended the entire length of the flow field (i.e. 17km). This made the 2014–2015 Holuhraun a paired flow field, where both lava morphologies had similar length. We suggest that the similar length is a consequence of the pāhoehoe is fed from the tube system utilizing the existing ‘a’ā lava channels, and thereby are controlled by the initial length of the ‘a’ā flows.

A28 Large Off-axis Lava Flow Field from the southern East Pacific Rise at 14°S : Preliminary Report of NIRAI-KANAI Cruise Leg 1, YK04-07 Yokosuka/Shinkai dives

A28 Large Off-axis Lava Flow Field from the southern East Pacific Rise at 14°S : Preliminary Report of NIRAI-KANAI Cruise Leg 1, YK04-07 Yokosuka/Shinkai dives

The Role of Cultural and Indigenous Values in Geosite Evaluations on a Quaternary Monogenetic Volcanic Landscape at Ihumātao, Auckland Volcanic Field, New Zealand

The Ihumātao Peninsula is located within the wider Mangere region in South Auckland, New Zealand. Significant sites of geological, cultural and ecological value are a recorded feature of this area. One of the most significant sites in the region is the Otuataua Stonefields Historic Reserve (OSHR). Geologically, this area is a Quaternary lava flow field with tuff rings, scoria and spatter cones. It sits within the Auckland Volcanic Field (AVF), and the landscape of the OSHR and the wider Ihumātao Peninsula may be seen as the physical expression of a unique convergence of ecological, geological and cultural values. Geosite evaluation methods applied to the Ihumātao Peninsula, following two distinct methods, shed light on potential high geoheritage values the region holds. These values may be looked at as a good base to develop effective geoeducational, geoconservational and geotouristic programs. The study also showed that implementing management strategies to add and conserve geosite values in the region could provide positive outcomes; however, reduction of its main geosite values would be inevitable and irreversible should proposed urban development take place on a block of land immediately bordering the OSHR. The Ihumātao Peninsula is one of several areas of South Auckland where urbanization has left significant areas relatively untouched until the present, whereby they are now threatened by intense housing and industrial development. The geological features of these areas unquestionably hold geological heritage values, allowing understanding of the interplay between low coastal land and rising basaltic magma. This interplay has resulted in a landscape potentially featuring the greatest volcanic geodiversity of the entire AVF. In addition, this relatively undeveloped land provides an unbroken physical and cultural record dating to arrival of the first humans in New Zealand. Of particular note is the physical artefacts and archaeological sites telling a story of settlers attracted to, utilizing and shaping this discrete region of the AVF. Geosite evaluations demonstrate that high geoheritage values of regions like the Ihumātao Peninsula are influenced by the strong cultural link between the community (in particular the indigenous population) and the volcanic landscape. These cultural factors could be given more weight in currently used geosite evaluation methods, enabling such geoheritage values to be demonstrated in a more explicit and meaningful way and providing a basis for further community education and protection of specific sites within the geographical context of the Ihumātao Peninsula.

Morphologic and thermophysical characteristics of lava flows southwest of Arsia Mons, Mars

The morphologic and thermophysical characteristics of part of the extensive lava flow fields southwest of Arsia Mons (22.5–27.5°S, 120–130°W) have been examined using a combination of orbital VNIR and TIR datasets. THEMIS images provide context for the regional geology and record diurnal temperature variability that is diverse and unusual for flow surfaces in such close proximity. CTX images were used to distinguish dominant flow types and assess local age relationships between individual lava flows. CTX and HiRISE images provide detailed information on flow surface textures and document aeolian effects as they reveal fine-grained deposits in many low-lying areas of the flow surfaces as well as small patches of transverse aeolian ridges. Although this region is generally dust-covered and has a lower overall thermal inertia, the THEMIS data indicate subtle spectral variations within the population of lava flows studied. These variations could be due to compositional differences among the flows or related to mixing of flow and aeolian materials. Specific results regarding flow morphology include: a) Two main lava flow types (bright, rugged and dark, smooth as observed in CTX images) dominate the southwest Arsia Mons/NE Daedalia Planum region; b) the bright, rugged flows have knobby, ridged, and/or platy surface textures, commonly have medial channel/levee systems, and may have broad distal lobes; c) the dark, smooth flows extend from distributary systems that consist of combinations of lava channels, lava tubes, and/or sinuous ridges and plateaus; and d) steep-sided, terraced margins, digitate breakout lobes, and smooth-surfaced plateaus along lava channel/tube systems are interpreted as signatures of flow inflation within the dark, smooth flow type. These flows exhibit smoother upper surfaces, are thinner, and have more numerous, smaller lobes, which, along with their the channel-/tube-fed nature, indicate a lower viscosity lava than for the bright, rugged flows. Flow patterns and local interfingering and overlapping relationships are delineated in CTX images and allow reconstruction of the complex flow field surfaces. Darker channel-/tube-fed flows are generally younger than adjacent thicker, bright, rugged flows; however, the diversity and complexity of temporal relationships observed, along with the thermophysical variability, suggests that lava sources with different eruptive styles and magnitudes and/or lavas that experienced different local emplacement conditions were active contemporaneously.