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.
•The 2014–2015 Holuhraun lava covered ~84km2 and has a bulk volume of ~1.44km3.•Lava transport, tube formation and evolution of the flow field are documented.•The eruption had an average discharge of ~90m3/s and is divided into 3 phases.•In phase 1–2 eight large ‘a’ā flows formed via open lava channels.•In phase 3 lava was mainly transported in tubes that created spiny pāhoehoe lobes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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.
•The pahoehoe-′a′ā transition•Inflated lava flows•Lava tubes and channels•Laboratory simulations and numerical modeling of lava flow morphologies•Outstanding questions
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
When a lava flow enters a body of water, either a lake, sea, river or ocean, explosive interaction may arise. However, when it is an 'a'ā lava flow entering water, a more complex interaction occurs, ...that is very poorly described and documented in literature. In this paper, we analysed the 2–4 ka San Bartolo lava flow field emplaced on the north flank of Stromboli volcano, Italy. The lava flow field extends from ~ 650 m a.s.l. where the eruptive fissure is located, with two lava channels being apparent on the steep down to the coast. Along the coast the lava flow field expands to form a lava delta ~ 1 km wide characterised by 16 lava ‘Flow’ units. We performed a field survey to characterise the features of lava entering the sea and the associated formation of different components and magnetic measurements to infer the flow fabrics and emplacement process of the lava flow system. We measured the density, porosity and connectivity of several specimens to analyse the effect of lava-water interaction on the content in vesicles and their connectivity and conducted a macroscopic componentry analysis (clast count) at selected sites to infer the character of the eroded offshore segment of the lava flow field and its component flow units. The collected data allowed us to define the main components of a lava delta fed by 'a'ā lava flows, with its channels, littoral units, ramps, lava tubes, and inflated pāhoehoe flows controlled by the arterial 'a'ā flow fronts. The spatial organisation of these components allowed us to build a three-step descriptive model for 'a'ā entering a water. The initial stage corresponds to the entry of channel-fed 'a'ā lava flow into the sea which fragments to form metric blocks of 'a'ā lava. Continued lava supply to the foreshore causes flow units to stall while spreading over this substrate. Subsequent 'a'ā lava flow units ramp up behind the stalled flow front barrier. Lava tubes extending through the stalled flow barrier feed the seaward extension of a bench made of several pāhoehoe flow units.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Lava flow hazards are usually thought to end when the erupting vent becomes inactive, but this is not always the case. At Kīlauea in August 2014, a spiny ʻaʻā flow erupted from the levee of a crusted ...perched lava lake that had been inactive for a month, and the surface of the lava lake subsided as the flow advanced downslope over the following few days. Topography constructed from oblique aerial photographs using structure-from-motion (SfM) software shows that the volume of the flow (∼68,000 m3) closely matches the volume of subsidence of the crusted lava lake (∼64,000 m3). The similarity of these volumes, along with the textural characteristics of the lava, shows that the lava that fed the flow had been stored beneath the surface of the perched lava lake, and that the flow was not generated by reactivation of the vent. This extends the duration of the local lava flow hazard presented by perched lava lakes and similar flow field structures that store lava, such as rootless shields. The flow probably occurred because the density of the lava beneath the crusted surface of the perched lava lake increased through loss of gas bubbles until it was able to penetrate the less-dense levee, which was composed of relatively vesicular overflows. The flow is thus equivalent to the lava seeps described previously at Kīlauea and elsewhere. We present a simple physical model for the pressure change at the base of a densifying body of lava, which we apply to this case study, and which could be applied to similar scenarios elsewhere.
•Spiny lava flow broke through levee of perched lake inactive for about one month.•Surface of inactive perched lava lake subsided at same time.•Topographic modeling shows lava flow volume matches lava lake subsidence volume.•Breakout caused by densification of stored lava rather than by vent reactivation.•Extends duration of hazards posed by flow field structures that store lava.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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.
•The Tiretaine lava flows extended from flat onto steep topography of a UNESCO site•Facies analysis allows association of topographic effects and flow field morphology•On the proximal plateau sustained, low effusion rate flow built a pahoehoe flow field•Flow field margin failure fed a short period of high effusion rate channelized aa•This body was valley-contained and ponded behind a lava dam
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Continental rifting is the means by which strong continental lithosphere is faulted, weakened, and ruptured to form a new ocean basin. This process evolves temporally and spatially, and is ...accompanied by significant seismicity and often crustal intrusion of mantle-derived magmas in its penultimate stages, which facilitate further extension through crustal thermo-mechanical weakening. Understanding the relationship between magmatism and extension in rifts is paramount for developing new models of tectonic evolution that account for the effects of magmas during the rifting process. This thesis investigates the magmatic character of the late-stage Main Ethiopian Rift (MER), the northernmost sector of the East African Rift System. A subject of intense geophysical examination, the MER hosts volcano-tectonic segments that accommodate the bulk of extensional strain. Past literature has highlighted the anomalous nature of the mantle and the presence of both solid and molten intrusions in the rifting crust under these segments. To verify geophysical evidence, new independent petrological observations of melt generation and crustal magmatic storage and transport are necessary. I explore magmatism in the MER by analysing erupted basalts from scoria cones. Geochemical analyses of these materials, including whole rocks, olivine crystals, and olivine-hosted melt inclusions, are used to explore melt generation, crystal fractionation, and cationic diffusion within crystals. The three principal studies outlined in this thesis demonstrate that heterogeneous melts, derived from a hot mantle that is geochemically and lithologically enriched relative to ambient mantle, are stalled and stored in a mid-crustal weak layer prior to eruption. Significant degassing of CO2 occurs within this layer. Eruptions are triggered by the intrusion of hot mafic dykes in the months leading up to cone-forming events. These results provide new constraints on the temperature and composition of the sub-MER mantle, the storage conditions of rift magmas, and the timescales of processes that trigger eruptions.
Between 2015 and 2021, Nyiragongo's lava lake level experienced a linear increase punctuated by fast intermittent drops. These drops occurred synchronously to seismic swarm at approximately 15 km ...below the surface and extending laterally NE from the volcano. To interpret these lava lake level patterns in terms of reservoirs pressure evolution within Nyiragongo, we consider the following simplified plumbing system: a central reservoir is fed by a constant flux of magma, distributing the fluid up into the lava lake and laterally into a distal storage zone. Magma transport is driven by a pressure gradient between the magma storage bodies, accommodating influx and outflow of magma elastically, and the lava lake. Lateral transport at depth occurs through a hydraulic connection for which the flow resistance is coupled to the magma flux. When the right conditions are met, lateral magma transport occurs intermittently and triggers intermittent lava lake level drops matching the observations.
Plain Language Summary
The level of lava lakes fluctuates in response to magma motion in the underlying crust. Prior to the May 2021 flank eruption, Nyiragongo's lava lake level displayed a series of rapid drops in concert with ∼15 km deep earthquakes likely caused by crustal magma movements deforming and fracturing the surrounding rocks. The present work studies the simplified physics of magma motion at depth draining the lava lake. We show that a valve‐like mechanism either preventing or enabling deep magma flow can cause successive lava lake level drops as observed between 2015 and 2021 at Nyiragongo.
Key Points
Nyiragongo 2015–2021 successive lava lake level drops modeled as the result of ∼15 km deep lateral transport of magma
Nyiragongo's modeled central reservoir distributes the fluid up into the lava lake and laterally into a distal storage zone
Lava lake overflows exert top‐down control on magma transport phenomena occurring in the deeper part of the plumbing system
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Multiple lava flows have profoundly shaped the landscape of Terkhiin Tsagaan Lake (TTL) in central Mongolia, influencing its level and extent over the Quaternary. Optically Stimulated Luminescence ...(OSL) dating of terraces unveils ages ranging from 65 to 59 ka at 2073 m, 54–51 ka at 2069 m, and approximately 46 ka at 2065 m. Additionally, cosmogenic 36Cl dating of a lava flow provides insights into the timing of the most recent volcanic eruption, dating it to 7.2 ka ago. The integration of geomorphic and geochronological evidence, along with observations of Lava-Water-Interaction features, suggests the presence of a paleolake preceding the last Holocene eruption of Khorgo Volcano. The geomorphic evolution unfolds in three stages: (i) A Pleistocene lava flow formed multiple dams across the Tariat Basin, creating temporally successive lava-dammed lakes. (ii) The paleolakes underwent fluctuations, leaving lacustrine terraces, and experiencing lower levels. (iii) Holocene eruption of Khorgo, which is one of the youngest in Central Asia, shaped the current TTL by releasing lavas over the eastern margin of the paleolake. The study contributes valuable insights into the paleoenvironmental dynamics, shedding light on the interplay between volcanic activity, climate, and landscape evolution.
•Multiple lava flows altered the level and extent of Terkhiin Tsagaan Lake in central Mongolia.•OSL dating indicates terrace ages of 65–46 ka at 2073–2065 m.•Cosmogenic 36Cl dating of a lava flow constrains the last eruption to 7.2 ka ago.•Geomorphic evidence and Lava-Water-Interaction features are abundant around volcanic areas.•The paleolake existed prior to the last eruption of Khorgo Volcano.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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