Search

International audience; Lava flows often erupt onto eroded landscapes, flowing across plateaus, into valleys and basins, and down escarpments. With the Tiretaine lava flow system in the Chaîne des Puys (Central France), lava flowed over the complex topography of an ancient rift margin. Erupted 41.3 ± 1.3 ka ago onto the granite plateau of the Massif Central, flow initially advanced over a surface that sloped 2°E. On reaching a fault scarp that delimits the plateau, flows descended the 6° slopes of a ravine that cuts the scarp E-W. In part 1 of this work we thus consider the case where lava is emplaced onto relatively flat terrain, then passes over a break-in-slope onto steeper slopes. To do this, we carried out mapping and facies analysis down this ∼6-km-long system, collecting 24 samples on which we completed textural and geochemical analyses. Results reveal three lava facies: (i) a 3 × 2 km proximal zone of inflated pāheohoe with a thickness of 25–50 m; (ii) a channelized medial zone with simple rubble levees nested in the ravine; and (iii) a valley-ponded distal zone with tubes and well-formed columnar jointing.Through simple mass balance calculations, and analogy with systems displaying similar facies, we find that the proximal inflated zone was fed at relatively low (1–5 m3/s) effusion rates. This built the proximal portion of the flow field over a period of 1–6 years, forming a volume of flow-field stored, degassed lava. Failure of the eastern edge of the proximal flow field at the head of the Tiretaine ravine fed high (215–315 m3/s) effusion rate flow down the ravine, to build a channelized flow system in just a few hours. However, the presence of a lava dam at the mouth of the ravine impeded further flow and resulted in ponding. This ponded volume then cooled in-place over a period of 10–11 years. Breaks-in-slope, and the resulting lava–topography interaction, thus created a system of reservoirs and transfers, with different flow rates, dynamics and emplacement time scales. For our case, where the lava flow system is mostly in a UNESCO World Heritage site, the study provides scientific support for Geoheritage efforts, outreach, and initiatives to support protection of geologically important sites. Previous article in issue

During emplacement, lavas modify the pre-existing topography and release a large amount of heat. In spite of the relevance of both heat and mass release, combined morphological and thermal analyses have been seldom carried out at a flow-field scale. Here, we consider a channelised lava flow unit formed at Mt Etna during the 2001 flank eruption, and we show that, by combining a morphological analysis of the pre- and post-emplacement topography with the analysis of the syn-eruptive thermal signature, critical insights about the processes driving mass and heat dissipation can be derived. Our results suggest that, in the considered lava flow, the pre-emplacement slope controls heat dissipation and can influence the thickness of the final lava deposit, with possible implications for hazard assessment. The width of the lava channel, instead, appears less sensitive to the pre-emplacement slope, and tends to regularly increase with increasing distance from the vent.

Most lava flows have been emplaced away from the watchful eyes of volcanologists, so there is a desire to use solidified lava-flow morphologies to reveal important information about the eruption that formed them. Our current understanding of the relationship between solidified basaltic lava morphology and the responsible eruption and emplacement processes is based on decades of fieldwork, laboratory analyses and simulations, and computer models. These studies have vastly improved our understanding of the complex interactions between the solids, liquids, and gases that comprise cooling lava flows. However, the complex interactions (at millimeter and sub-millimeter scales) between the temperature-dependent abundances of the distinct phases that comprise a lava flow and the final morphology remain challenging to model and to predict. Similarly, the complex behavior of an active pahoehoe flow, although almost ubiquitous on Earth, remains difficult to quantitatively model and precisely predict.

Understanding the thermo-rheological regime and physical character of lava while it is flowing is crucial if we are to adequately model lava flow emplacement dynamics. We present measurements from simultaneous sampling and thermal imaging across the full width of an active channel at Piton de la Fournaise (La Réunion, France). Our data set involves measurements of flow dynamics at three sites down-channel from the vent. Quantification of flow velocities, cooling rates, sample texture, and rheology allows all thermo-rheological parameters to be linked, and down- as well as cross-channel variations to be examined. Within 150 m from the vent, we recorded an unexpected velocity increase (from 0.07 to 0.1 m/s), in spite of cooling rates of 0.19–0.29 °C/m and constant slope. This change requires a switch from a Newtonian-dominated regime to a Bingham plug–dominated regime. Sample analysis revealed that the plug consists of foam-like lava, and the shear zones involve vesicle-poor (low-viscosity) lava. With distance from the vent, shear zones develop, carrying the vesicular plug between them. This causes flow to initially accelerate, helped by bubble shearing in narrow lateral shear zones, until cooling takes over as the main driver for viscosity increase and, hence, velocity decrease.

INTRODUCTION The 2018 flank eruption and summit collapse of Kīlauea Volcano was one of the largest and most destructive volcanic events in Hawai‘i in the past 200 years. The eruption occurred on the volcano’s lower East Rift Zone (ERZ), draining magma at a high rate from the summit reservoir and triggering incremental collapse of the overlying caldera floor. Lava flows erupted for 3 months, destroying several residential subdivisions and burying miles of roads. The eruption rate exhibited cyclic behavior on multiple time scales, resulting in repeated lava breakouts and overflows. Multidisciplinary observations provide insight into the nature of these variations, driving forces in the magmatic system, and implications for hazard. RATIONALE Volumetric eruption rate is a primary control on the vigor and hazard of lava flows, but the processes that control its temporal variations are not well understood because of limited observational data. We integrated field observations, photos and video from time-lapse cameras and unmanned aircraft systems, seismic tremor, and infrasound to track the time scales and magnitude of fluctuations in eruption rate at the primary vent for the 2018 eruption on Kīlauea’s LERZ. We combined these data with documentation of summit caldera collapses to investigate the origins and impacts of these fluctuations. RESULTS Cyclic variations in eruption rate occurred on two disparate time scales. First, short-term fluctuations (“pulses”) in eruption vigor had periods of 5 to 10 min, but had no major implications for lava flow hazard. Flow rate in the lava channel was inversely related to fountaining and outgassing intensity at the vent. Second, long-term fluctuations (“surges”) had periods of 1 to 2 days and began within minutes of episodic caldera collapse events at the summit, 40 km upslope. These surges triggered overflows from the channel that produced hazardous enlargement of the lava flow field, which could be forecast several hours in advance. We also show that seismic tremor and infrasound were correlated with lava flow eruption rates. CONCLUSION We conclude that the two types of eruption rate cycles were controlled by two distinct processes. Short-term pulses were driven by changes in outgassing efficiency of the lava at shallow depths. Long-term surges in eruption rate were driven by pressure transients induced by the summit collapses and transmitted through the magma conduit over a distance of 40 km. The pressure-driven surges in eruption rate demonstrate that the episodic rhythm of summit caldera collapse sequences may be imparted on the accompanying flank eruption. The surges also help to constrain the efficient hydraulic connection between Kīlauea’s summit magma system and rift zones and demonstrate that pressure communication over distances of 40 km can occur on a time scale of minutes. Seismic tremor and infrasound may be effective proxies for lava flow eruption rates, allowing for improved tracking of lava flow hazards. Our multidisciplinary data provide a clear link between eruption rate fluctuations and their driving processes in the magmatic system.

International audience; To examine whether there was any physical or thermal interaction between trees and lava when a lava flow inundates a forest we studied the Kīlauea's July 1974 lava flow. We mapped the location of ∼600 lava-trees and the lava type (pāhoehoe versus 'a'ā), and sampled an additional ten lava-trees for chemical and textural analysis to infer flow viscosity and dynamics. The emplacement event lasted 3.5 hours and markers on the outer surface of the lava-trees allowed us to define initial high effusion rate and velocity (∼400 m 3 /s and 5-10 m/s) that then declined to 9 m 3 /s and 4 m/s during a waning phase. We find that lava passing through the forest underwent an initial cooling rate of 4 °C/km which increased to 10 °C/km late in the eruption. This is no different to cooling rates recorded at Kīlauea for tree-free cases. There thus appears to be no effect on cooling for this case. The lava-trees did, though, form a network of vertical cylinders obstacles and evidence for local diversion of flow lines are noticed. However, this varies with lava type, as almost no lava-trees form in ʻaʻā. We find a relation between the percentage of ʻaʻā and the number of lava-trees per hectare. The pāhoehoe-ʻaʻā transition for this flow occurs at a viscosity of 10 3 Pa s and this appears to be a threshold be low which lava-trees can form so as to behave as a network of obstacles, and above which they cannot

Cooling and dynamics of lava flowing in a rectangular channel driven by the gravity force is numerically modeled. The purpose is to evaluate the thermal process as a function of time involving the liquid lava in contact with the solid boundary that flanks lava. Lava rheology is dependent on temperature and strain rate according to a power law function. The model couples dynamics and thermodynamics inside the lava channel and describes the thermal evolution of the solid boundary enclosing the channel. Numerical tests indicate that the solution of the thermo-dynamical problem is independent of the mesh. The boundary condition at the ground and at the levees is treated assuming a solid boundary around the lava flow across which lava can exchange heat by conduction. A far field thermal boundary condition allows to overcome the assumption of constant temperature or constant heat flow as boundary conditions, providing more realistic results. The effect of viscous heating is evaluated and discussed .

International audience; 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 ´áā 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 ´áā 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.

Lava flow hazard modelling requires detailed geological mapping, and a good understanding of emplacement settings and the processes involved in the formation of lava flows. Harrat Rahat, Kingdom of Saudi Arabia, is a large volcanic field, comprising about 1000 predominantly small-volume volcanoes most of which have emitted lava flows of various lengths. A few eruptions took place in this area during the Holocene, and they were located in the northern extreme of the Harrat Rahat, a close proximity to critical infrastructure and population living in Al-Madinah City. In the present study, we combined field work, high resolution digital topography and morphometric analysis to infer the emplacement history of the last historical event in the region represented by the 1256 AD Al-Madinah lava flow field. These data were also used to simulate 1256 AD-type lava flows in the Harrat Rahat by the MAGFLOW lava flow emplacement model, which is able to relate the flow evolution to eruption conditions. The 1256 AD lava flow field extent was mapped at a scale of 1:1000 from a high resolution (0.5 m) Light Detection And Ranging (LiDAR) Digital Terrain Model (DTM), aerial photos with field support. The bulk volume of the lava flow field was estimated at 0.4 km3, while the source volume represented by seven scoria cone was estimated at 0.023 km3. The lava flow covered an area of 60 km2 and reached a maximum length of 23.4 km. The lava flow field comprises about 20.9% of pāhoehoe, 73.8% of 'a'ā, and 5.3% of late-stage outbreaks. Our field observation, also suggests that the lava flows of the Harrat Rahat region are mainly core-dominated and that they formed large lava flow fields by amalgamation of many single channels. These channels mitigated downslope by topography-lava flow and channel–channel interactions, highlighting this typical process that needs to be considered in the volcanic hazard assessment in the region. A series of numerical lava flow simulations was carried out using a range of water content (0.1–1 wt.%), solidification temperature (800–600 °C) and effusion curves (simple and complex curves). These simulations revealed that the MAGFLOW code is sensitive to the changes of water content of the erupting lava magma, while it is less sensitive to solidification temperature and the changes of the shape of effusion curve. The advance rate of the simulated lava flows changed from 0.01 to 0.22 km/h. Using data and observations from the youngest volcanic event of the Harrat Rahat as input parameters to MAGFLOW code, it is possible to provide quantitative limits on this type of hazard.

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 (Φrad) 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, The first author has been supported by the Indonesia Endowment Fund for Education (LPDP), Institute of Earth Science and Vinir Vatnajökuls during his Ph.D. project. Authors also would also like to thank anonymous reviewers for their constructive comments for the manuscript.

We used light detection and ranging (LiDAR) data to calculate roughness patterns (homogeneity, mean-roughness, and entropy) for five lava types at two different resolutions (1.5 and 0.1 m/pixel). We found that end-member types (ʻaʻā and pāhoehoe) are separable (with 95% confidence) at both scales, indicating that roughness patterns are well suited for analyzing types of lava. Intermediate lavas were also explored, and we found that slabby-pāhoehoe is separable from the other end-members using 1.5 m/pixel data, but not in the 0.1 m/pixel analysis. This suggests that the conversion from pāhoehoe to slabby-pāhoehoe is a meter-scale process, and the finer roughness characteristics of pāhoehoe, such as ropes and toes, are not significantly affected. Furthermore, we introduce the ratio $$ \frac{ENT}{HOM} $$ (derived from lava roughness) as a proxy for assessing local lava flow rate from topographic data. High entropy and low homogeneity regions correlate with high flow rate while low entropy and high homogeneity regions correlate with low flow rate. We suggest that this relationship is not directional, rather it is apparent through roughness differences of the associated lava type emplaced at the high and low rates, respectively.

As for many other effusive volcanoes, Mount Cameroon (MC) is a volcano for which only limited information exists on lava flow properties and emplacement dynamics for recent eruptions. This study provides new quantitative constraints for rheological and dynamic characteristics of lava flow effusion for the 1982 and 2000 eruptive events, used to calibrate the FLOWGO thermo-rheological model for these lava flows. The FLOWGO 1-D physical model is used to simulate down-flow evolution of the geometry and rheology of channel-contained cooling-limited lava flows. Morphometric data from historical lava flows were acquired from the field, e.g. channel geometry, levee and background slope, in order to estimate lava yield strength, velocity and effusion rate. Lava density and viscosity were also estimated from compositional data and laboratory methods. To account for uncertainty in the input rheological and geometrical data, three end-member scenarios were used to bracket the potential range in lava channel initial dimension, initial lava temperature and phenocryst content. For each of these scenarios, two crustal growth models were used: one assuming strong insulation due to lava flow surface crusting, the other a much lower crusting rate. Twelve numerical simulations were made per flow and the results were compared against the channel geometry, microlite content, yield strength and viscosity estimates from field and laboratory investigations. Best-fit models where obtained for both the 1982 and 2000 lava flows using a low rate of surface crusting, high initial temperature and low phenocryst content. Model-predicted lengths were within 5% of the actual lengths. Modelled mean effusion rates for the 1982 (52–64 m 3 s − 1 ) and 2000 (10 m 3 s − 1 ) flows closely matched field data derived estimations (26–68 and 9.5 m 3 s − 1 respectively). FLOWGO model results are highly sensitive to initial channel dimensions, phenocryst content and the FLOWGO model is unable to reproduce the observed rapid near-vent increase in microlite content. Near-vent rapid cooling induced by lava degassing is yet to be fully documented and integrated into numerical lava flow models such as FLOWGO, but obtained results already provide valuable insights for lava flow hazard assessment at Mount Cameroon.

The 120 m-wide Khedrai Dam lava channel is one of the widest recorded in the Deccan Volcanic Province. Like many recent ones, this channel also has a pair of linear marginal levees made of breccia and confines the channelfill lava. It is resting over a pahoehoe flow (substrate) of basalt studded with plagioclase megacrysts, also known as the Giant Plagioclase Basalt (GPB). The channel-fill lava, which makes the lining at the edges and basal portion of the channel, is a comb-layered basalt (Cl-B) characterized by alternating layers rich in curved, branching augite crystals and laths of plagioclase — a texture indicative of high order of supercooling and rapid cooling rates. The dominant and centrally filling lava of this channel is a plagioclase-phyric basalt (Pp-B) that has a wide variation in phenocryst number from megacryst-poor to megacryst-rich. Occurrence of centimetre to decimetre size angular fragments of Cl-B within Pp-B fill indicates mechanical dislodgements of channel-lining by flowing lava. This also suggests that the channel was reactivated before it finally lost its hydraulic gradient and solidified.

Kalaupapa Peninsula, along the northern coast of East Moloka‘i volcano, is a remarkably well-preserved example of rejuvenated-stage volcanism from a Hawaiian volcano. Mapping of lava flows, vents and other volcanic constructs reveals a diversity of landforms on this small monogenetic basaltic shield. The late-stage lava distributary system of this shield is dominated by a prominent lava channel and tube system emanating from the primary vent, Kauhakō crater. This system, along with several smaller examples, fed five prominent rootless vents downslope from Kauhakō. This map shows the subaerial part of this volcanic construct at 1:30,000 scale and encompasses an area of approximately 20.6 km2.

Bends in lava channels are often observed in volcanic fields. The curvature of a channel affects flow dynamics and surface morphology and may be a trigger for the formation of lava tube. We propose a model to describe the effects of curvature on velocity, shear stress and the formation of crust at the flow surface. Lava is described as a Newtonian, homogeneous, isotropic and incompressible fluid. The steady-state solution of the Navier-Stokes equation is found for a unidirectional flow, in cylindrical coordinates. The flow levees are described as arcs of concentric circumferences, with their centres in the origin of the coordinate system. Under the assumption that the gravity force has no radial component, in the bend the fluid moves parallel to the levees. The velocity is assumed to depend on the radial coordinate only. As an effect of curvature, velocity and shear stress are asymmetric with respect to the centre of the channel. The maximum of surface velocity is shifted toward the internal levee, and the shear stress has larger values close to the internal levee. This effect is greater for wider channels. Heat radiation and convection into the atmosphere are considered as the main cooling mechanisms and the temperature distribution along the channel is calculated. Crust formation at the flow surface is considered under the assumption that solid lava is a plastic body. The amount of crust coverage is mainly controlled by the channel width: narrow channels have a greater coverage than wide channels for a given radius of curvature. The effect of a bend is to favour the crust growth toward the internal levee, while the crust coverage toward the external levee decreases. The presence of a bend in a lava channel may favour the formation of a lava tube. The analytical solution will serve as a benchmark for numerical models. Understanding the mechanism of formation of lava tubes is crucial to the simulation of actual lava flows and to evaluation of the associated hazard.

During long-lived basaltic eruptions, overflows from lava channels and breaching of channel levees are important processes in the development of extensive 'a'ā lava flow-fields. Short-lived breaches result in inundation of areas adjacent to the main channel. However, if a breach remains open, lava supply to the original flow front is significantly reduced, and flow-field widening is favoured over lengthening. The development of channel breaches and overflows can therefore exert strong control over the overall flow-field development, but the processes that determine their location and frequency are currently poorly understood. During the final month of the 2008–2009 eruption of Mt. Etna, Sicily, a remote time-lapse camera was deployed to monitor events in a proximal region of a small ephemeral lava flow. For over a period of ~10 h, the flow underwent changes in surface elevation and velocity, repeated overflows of varying vigour and the construction of a channel roof (a required prelude to lava tube formation). Quantitative interpretation of the image sequence was facilitated by a 3D model of the scene constructed using structure-from-motion computer vision techniques. As surface activity waned during the roofing process, overflow sites retreated up the flow towards the vent, and eventually, a new flow was initiated. Our observations and measurements indicate that flow surface stagnation and flow inflation propagated up-flow at an effective rate of ~6 m h−1, and that these processes, rather than effusion rate variations, were ultimately responsible for the most vigorous overflow events. We discuss evidence for similar controls during levee breaching and channel switching events on much larger flows on Etna, such as during the 2001 eruption.

In late 2007, a perched lava channel, built up to 45 m above the preexisting surface, developed during the ongoing eruption near Pu‘u ‘Ō‘ō cone on Kīlauea Volcano’s east rift zone. The lava channel was segmented into four pools extending over a total of 1.4 km. From late October to mid-December, a cyclic behavior, consisting of steady lava level rise terminated by vigorous spattering and an abrupt drop in lava level, was commonly observed in pool 1. We use geologic observations, video, time-lapse camera images, and seismicity to characterize and understand this cyclic behavior. Spattering episodes occurred at intervals of 40–100 min during peak activity and involved small (5–10-m-high) fountains limited to the margins of the pool. Most spattering episodes had fountains which migrated downchannel. Each spattering episode was associated with a rapid lava level drop of about 1 m, which was concurrent with a conspicuous cigar-shaped tremor burst with peak frequencies of 4–5 Hz. We interpret this cyclic behavior to be gas pistoning, and this is the first documented instance of gas pistoning in lava well away from the deeper conduit. Our observations and data indicate that the gas pistoning was driven by gas accumulation beneath the visco-elastic component of the surface crust, contrary to other studies which attribute similar behavior to the periodic rise of gas slugs. The gas piston events typically had a gas mass of about 2,500 kg (similar to the explosions at Stromboli), with gas accumulation and release rates of about 1.1 and 5.7 kg s−1, respectively. The time-averaged gas output rate of the gas pistoning events accounted for about 1–2% of the total gas output rate of the east rift zone eruption.

A series of fluid-carved channels in the Sulci Gordii region of Mars were investigated. Numerous channel networks exist in Sulci Gordii, part of the Olympus Mons aureole, and this area comprises some of the youngest volcanic terrain on Mars. The channels ranged in length from 43 to 155 km, with widths of 128–288 m. The morphology of the channels was analysed assuming both lava and water as possible agents. For three of the four channels studied, water appears to be the likely agent, while one channel is probably lava-formed. For the water-formed channels, discharge rates were estimated at 8000–36 000 m3 s?1. The lava channel was probably formed from short-lived episodic activity by a low-viscosity lava. The age of the channels and surrounding area was estimated using crater counting to be 100 Ma. Water has appeared to have flowed for almost 150 km under the climatic conditions at this time. There is some evidence for later tectonic activity, possibly as recent as 10 Ma, but crater-dating accuracy was limited by the lack of high-resolution images of some areas. Sulci Gordii is therefore a dynamic site with evidence of hydrological and volcanic activity extending into the recent geological past.

The Moran nickel orebody was discovered in 2008 when underground drill-hole LSU-152 intersected a 12.3 m thick interval of mineralisation with an average grade of 6.0% Ni. The discovery drill-hole had been designed to test a strong conductor detected by transient electromagnetic surveys read in drill-holes that had passed above and below Moran. Moran is located approximately 1.1 km south of the Long orebody. Both orebodies are interpreted to be hosted within the same komatiite lava channel. The exploration program was premised on the observation that fertile komatiite lava channels are often mineralised over significant distances. Diamond drill-holes were drilled from underground mine workings in order to test the target lava channel to the south of Long over 1.7 km of strike. Recognition of potential ore-hosting environments, integrated with conductor models developed from DHTEM data, were keys to success.

A lava channel identified on the wall of an Elysium Planitia impact crater is investigated to identify the dominant erosion mechanism, mechanical vs. thermal, acting during channel formation. Observations of channel morphology are used to supplement analytical models of lava channel formation in order to calculate the duration of channel formation, the velocity of the lava flowing through the channel, and the erosion rate in each erosion regime considered. Results demonstrate that the channel observed in the Elysium Planitia impact crater formed primarily due to mechanical erosion. In a more general sense, results of this study suggest that lava channels can form primarily due to thermal erosion in the presence of more gradual slopes and more consolidated substrates whereas lava channels can form primarily due to mechanical erosion in the presence of more energetic flows on steeper slopes and more poorly consolidated substrates. Therefore, both erosion regimes must be considered when analyzing origins of eroded lava channels that cut through strata of different strengths.

We use a kinematic GPS and laser range finder survey of a 200 m-long section of the Muliwai a Pele lava channel (Mauna Ulu, Kilauea) to examine the construction processes and flow dynamics responsible for the channel–levee structure. The levees comprise three packages. The basal package comprises an 80–150 m wide ′a′a flow in which a ∼2 m deep and ∼11 m wide channel became centred. This is capped by a second package of thin (

Arnus Vallis (AV) is a >300-km-long sinuous, rille located on the northeastern flank of the Syrtis Major volcano on Mars. Observational evidence presented here suggests that AV formed as an open lava channel that was at least partly incised into the pre-existing terrain. The lava source area consists of a sub-circular pit at the southwestern end of a 7-km-long straight section of channel. AV trends down slope from this source with an average bottom slope of 0.26% or 0.14°. Width varies from ∼1 km at the source to ∼0.6 km near the distal end, with a mean of 0.76 km. Depth decreases from ∼180 m at the source to ∼25 m near the distal end. The AV terminus is obscured by a large impact crater. We suggest that the material that flowed in AV must have been a relatively high temperature, low viscosity lava dynamically and perhaps compositionally similar to terrestrial komatiite or some lunar basalt lavas. If correct, this finding has implications for the mode of construction of Syrtis Major.

Widespread igneous activity, showing striking mineralogical, petrographical and chemical commonalities with terrestrial komatiites and ferropicrites, intensely affected, reshaped and buried the primary Martian crust. This study evaluates whether the igneous activity on Mars may have led to the formation of orthomagmatic Ni–Cu±(PGE) sulphide mineralisation similar to that associated with terrestrial komatiites and ferropicrites. Particular focus is laid on two different components of the Martian Ni–Cu±(PGE) sulphide mineral system: 1) the potential metal and sulphur fertility of mantle sources and derived melts, and 2) the physicochemical processes that enable sulphide supersaturation and batch segregation of metal-rich sulphide liquids. We show that potentially metal-rich Martian mantle melts likely reach sulphide saturation within 30 wt.% crystal fractionation. This value is comparable to that calculated for the mineralised ferropicrites at Pechenga, Russia. However, the majority of known world-class Ni–Cu±(PGE) sulphide deposits associated with terrestrial komatiites and ferropicrites originated due to the assimilation of crustal sulphur-rich substrate, thus promoting the attainment of sulphide supersaturation and batch segregation of metal-rich sulphide liquids during early stages of magma evolution. Given the high sulphur inventory of Martian crustal reservoirs, ranging from sulphide bearing magmatic rocks to sulphate-rich soils, regoliths and sedimentary deposits, it is likely that mantle-derived melts assimilated significant amounts of crustal sulphur during ascent and emplacement. It is proposed that channelled lava flows, which potentially emplaced and incised into sulphur-rich crustal lithologies, may have led to the formation of orthomagmatic Ni–Cu±(PGE) sulphide mineralisation on Mars.

A short length of channel on Pico Partido volcano, Lanzarote, provides us the opportunity to examine the dynamics of lava flowing in a channel that extends over a sudden break in slope. The 1–2-m-wide, 0.5–2-m-deep channel was built during the 1730–1736 eruptions on Lanzarote and exhibits a sinuous, well-formed channel over a steep (11° slope) 100-m-long proximal section. Over-flow units comprising smooth pahoehoe sheet flow, as well as evidence on the inner channel walls for multiple (at least 11) flow levels, attest to unsteady flow in the channel. In addition, superelevation is apparent at each of the six bends along the proximal channel section. Superelevation results from banking of the lava as it moves around the bend thus causing preferential construction of the outer bank. As a result, the channel profile at each bend is asymmetric with an outer bank that is higher than the inner bank. Analysis of superelevation indicates flow velocities of ~8 m s–1. Our analysis of the superelevation features is based on an inertia-gravity balance, which we show is appropriate, even though the down-channel flow is in laminar flow. We use a viscosity-gravity balance model, together with the velocities calculated from superelevation, to obtain viscosities in the range 25–60 Pa s (assuming that the lava behaved as a Newtonian liquid). Estimated volume fluxes are in the range 7–12 m3 s–1. An apparent down-flow increase in derived volume flux may have resulted from variable supply or bulking up of the flow due to vesiculation. Where the channel moves over a sharp break in slope and onto slopes of ~6°, the channel becomes less well defined and widens considerably. At the break of slope, an elongate ridge extends across the channel. We speculate that this ridge was formed as a result of a reduction in velocity immediately below the break of slope to allow deposition of entrained material or accretion of lava to the channel bed as a result of a change in flow regime or depth.

An open channel lava flow on Mt. Etna (Sicily) was observed during May 30–31, 2001. Data collected using a forward looking infrared (FLIR) thermal camera and a Minolta-Land Cyclops 300 thermal infrared thermometer showed that the bulk volume flux of lava flowing in the channel varied greatly over time. Cyclic changes in the channel's volumetric flow rate occurred over several hours, with cycle durations of 113–190 min, and discharges peaking at 0.7 m3 s−1 and waning to 0.1 m3 s−1. Each cycle was characterized by a relatively short, high-volume flux phase during which a pulse of lava, with a well-defined flow front, would propagate down-channel, followed by a period of waning flow during which volume flux lowered. Pulses involved lava moving at relatively high velocities (up to 0.29 m s−1) and were related to some change in the flow conditions occurring up-channel, possibly at the vent. They implied either a change in the dense rock effusion rate at the source vent and/or cyclic-variation in the vesicle content of the lava changing its bulk volume flux. Pulses would generally overspill the channel to emplace pāhoehoe overflows. During periods of waning flow, velocities fell to 0.05 m s–1. Blockages forming during such phases caused lava to back up. Occasionally backup resulted in overflows of slow moving ‘a‘ā that would advance a few tens of meters down the levee flank. Compound levees were thus a symptom of unsteady flow, where overflow levees were emplaced as relatively fast moving pāhoehoe sheets during pulses, and as slow-moving ‘a‘ā units during backup. Small, localized fluctuations in channel volume flux also occurred on timescales of minutes. Volumes of lava backed up behind blockages that formed at constrictions in the channel. Blockage collapse and/or enhanced flow under/around the blockage would then feed short-lived, wave-like, down-channel surges. Real fluctuations in channel volume flux, due to pulses and surges, can lead to significant errors in effusion rate calculations.

The widespread komatiitic Reliance lithostratigraphic unit of the late Archean Bulawayan Supergroup consists of many submarine flow fields directly or indirectly overlying the sedimentary Manjeri unit, which varies from a generally carbonaceous, sulfide-rich, deep-water, basinal facies in the north and west parts of the Zimbabwe craton to a generally sulfide poor, shallow-water, platformal facies in the south and east. The flow fields are associated with high-level subvolcanic feeder sills, intruded into pre-Manjeri basement made up of the conformable, sulfide-bearing, felsic Koodoovale unit and older, barren, granitoid-greenstone crust in the north and west, and south and east, respectively. The sills and flow fields together constitute largely discrete sill-flow complexes, very approximately 100 km in diameter, of which five are well preserved in the north and west, and three in the south and east parts of the craton. The Reliance sills, up to 40 km in diameter and 2,000 m thick, some composite and locally overlapping to slightly discordant, mostly comprise a thick lower dunite-peridotite and a relatively thin to intermittent upper pyroxenite-gabbro. Other larger, probably related, sills intruded at greater structural depths link adjacent complexes and form midcrustal magma chambers. The Reliance sills are interpreted as an interconnected system of "flow-through" feeders at different crustal levels. The Reliance flow fields are 33 to 85 km in diameter and up to 2,500 m thick, dominantly of komatiitic basalt composition, of very low height/breadth aspect ratio, locally linked to the sills via structures interpreted as fissure vents and partly extrusive cryptodomes, and thin out toward their lateral margins. Most display a simple, coherent, volcanological growth sequence (from sheet and/or channelized sheet flows and lava channel complexes in lower and proximal positions to marginal lava lobes in upper and distal positions), comparable in general organization and probable emplacement processes to those of Hawaiian and flood-basalt flow fields. Flow-field development was influenced by episodic eruption, preexisting topographies, and penecontemporaneous sedimentation and felsic and mafic volcanism, and some flow fields in the south and east were partly emergent. Sills in the north and west are weakly mineralized, but those in the south and east are barren. The principal Reliance nickel sulfide deposits are confined to flow fields in the north and west, occur within lava channel complexes (Trojan and Shangani mines, Damba-Silwane and Hunters Road prospects) and a fissure vent (Epoch mine), and include type 1 basal sequences of massive to matrix to disseminated sulfides (lowermost flows Trojan, Shangani) and type 2 central accumulations of weakly disseminated sulfides (Hunters Road, upper flows Trojan, Shangani). Epoch and Shangani occupy central flow-field positions, whereas Hunters Road and Damba-Silwane are proximal; Trojan may be either distal or proximal. Field evidence does not directly support the origin of the Reliance deposits solely by magmatic erosion of sulfidic substrate during flow emplacement, as proposed for komatiite-hosted nickel deposits elsewhere. Instead, the deposits’ origin and asymmetric distribution across the craton may be mainly due to assimilation of sulfidic felsic wall rocks during magma passage through the subvolcanic sills in the north and west, possibly combined with sulfur degassing, due to very shallow water lava emplacement in the south and east.