Lava Flow Emplacement Research Articles

The effects of undercooling and deformation rates on the crystallization kinetics of Stromboli and Etna basalts

We have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from Stromboli (pumice from the March 15, 2007 paroxysmal eruption) and Etna (1992 lava flow). Isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate (T = 1,157–1,187 °C and $$ \dot{\gamma }_{i} $$ = 4.26 s−1 for Stromboli; T = 1,131–1,182 °C and $$ \dot{\gamma }_{i} $$ = 0.53 s−1 for Etna). Melt viscosity increased due to the decrease in temperature and the increase in crystal content. The mineralogical assemblage comprises Sp + Plg (dominant) ± Cpx with an overall crystal fraction (ϕ) between 0.06 and 0.27, increasing with undercooling and flow conditions. Both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process. Plagioclase nucleation incubation time strongly decreases with increasing ΔT and flow, while slow diffusion-limited growth characterizes low ΔT—low deformation rate experiments. Both Stromboli (high strain rate) and Etna (low strain rate) plagioclase growth rates (G) display relative small variations with Stromboli showing higher values (4.8 ± 1.9 × 10−9 m s−1) compared to Etna (2.1 ± 1.6 × 10−9 m s−1). Plagioclase average nucleation rates J continuously increase with undercooling from 1.4 × 106 to 6.7 × 106 m−3 s−1 for Stromboli and from 3.6 × 104 to 4.0 × 106 m−3 s−1 for Etna. The extremely low value of 3.6 × 104 m−3 s−1 recorded at the lowest undercooling experiment for Etna (ΔT = 20 °C) indicates that the crystallization process is growth-dominated and that possible effects of textural coarsening occur. G values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions. Stirring of the melt, simulating magma flow or convective conditions, facilitates nucleation and growth of crystals via mechanical transportation of matter, resulting in the higher J and G observed. Any modeling pertaining to magma dynamics in the conduit (e.g., ascent rate) and lava flow emplacement (e.g., flow rate, pāhoehoe–‘a‘ā transition) should therefore take the effects of dynamic crystallization into account.

Morpho-Structure of the 1982 Lava Flow Field at Mount Cameroon Volcano, West-Central Africa

Basaltic eruptions have been observed to produce structurally complex, compound 'a'ā lava flow fields but their morphometry has only rarely been systematically documented. We document the morphology and structures that developed during the emplacement of the 1982 basaltic lava flow field at Mount Cameroon (MC) volcano over a period of one month. Topographic cross-sections (13 in total) were made from the main vent (~2700 m above sea level (a.s.l)) down to a distance of 5.5 km on the cooled lava surface. Details obtained from these cross-sections include: channel width and depth, levee slope, lava surface morphology and structures. These details enabled us to describe the physical characteristics of the 1982 lava flow field. The inclined (12° - 19°) underlying slopes on which this flow field was emplaced resulted in a characteristic channelized basaltic 'a'ā flow field morphology. This includes a proximal zone characterised by reduced flow width and depth with no subsidiary channels. Slab-crusted lava dominates the proximal channel distinctively bent into convex upward shapes. 7 secondary vents were observed for the first time ~2.5 km from the main vent, with heights of 3 - 15 m. This is a very significant observation since it points to the fact that the flow field emplacement may have been a product of 2 eruption sites as observed at other historical MC lava flow fields. This supposition was ruled out by further evidence obtained from other surface features within the flow field. The presence of these secondary vents still has an important bearing in lava flow hazard assessment. Field observations also revealed the presence of tumulus. This is a novel feature for MC lava flow fields. It displayed a close similarity to those observed at other basaltic volcanoes occurring in association with clinker 'a'ā lava, lava tubes, squeeze-ups and pressure ridges. Channels are well-defined, bounded by levees. Accretional and overflow levees dominate in this flow field. This lava flow-field attained a final length of 7.5 km, an area of 2.6 × 106 m2 and volume of 1.3 × 107 m3. The presence of tumulus indicates internal inflation together with structures such as pressure ridges and squeeze-ups which are also attributed to compressive forces. Our observations suggest that real-time monitoring of compound lava flow fields evolution at MC may reveal the emplacement mechanisms of complex structures such as the secondary vents (~2180 - 2011 m a.s.l.) observed within the flow field. In addition, documenting the occurrence, morphology and link between lava tubes, tumulus and squeeze-ups may allow us to determine the risk of reactivation of a stalled flow front. This will thereby enhance the ability to track and assess hazards posed by lava flow emplacement from MC-like volcanoes.

Viscosity changes during crystallization of a shoshonitic magma: new insights on lava flow emplacement

Viscosity changes during crystallization of a shoshonitic magma: new insights on lava flow emplacement

Chapter 12 Geological history of the Panarea volcanic group (eastern Aeolian archipelago)

Abstract The Panarea volcanic group is made up of dome-fields that are the subaerial culminations of a largely dissected volcanic complex mostly located below sea level. The correlation of marine isotope stage (MIS) 5 marine terrace deposits and numerous tephra layers, combined with the available radiometric ages, shows that the Panarea dome-fields mostly developed between c. 155–149 and 124–118 ka through the emplacement of successive lava domes, lava flows and minor pyroclastic products, interrupted by dormant periods and episodes of faulting in a context of regional uplift, plus volcano-related deformation. Recurrent explosive phases subsequently occurred in the area of minor islets at c. 100 ka (Punta Falcone), 67–56 ka (p 1 ) and 24–8.7 ka (Drauto), together with the emission of the c. 54 ka Basiluzzo dome. The Panarea volcanic group is presently in a quiescent state with fumarolic activity and episodic gas outbursts. Panarea rocks show basaltic andesite and high-K basaltic andesite to high-K dacite and rhyolite compositions, with minor shoshonites. Radiogenic isotope signatures range between those typical of the western Aeolian islands and Stromboli. This reveals a heterogeneous mantle source, which resulted from migration of more primitive asthenospheric mantle from the west during slab rollback, and its admixture with more strongly contaminated Stromboli-type resident mantle. DVD: The 10 000 scale geological map of Panarea is included on the DVD in the printed book and can also be accessed online at http://www.geolsoc.org.uk/Memoir37-electronic . Also included is a full geochemical data set for the Panarea volcanic group.

40Ar/39Ar geochronology of the Neogene-Quaternary Harrat Al-Madinah intercontinental volcanic field, Saudi Arabia: Implications for duration and migration of volcanic activity

New 40Ar/39Ar ages, based on incremental heating techniques for groundmass separates of 25 samples, are presented for the Harrat Al-Madinah volcanic field, part of Harrat Rahat in the north western part of the Arabian plate. This area is an active volcanic field characterized by the occurrence of two historical eruptions approximately in 641 and 1256AD. Field investigations of the main volcanic landforms indicate dominantly monogenetic strombolian eruptions, in addition to local more explosive eruptions. The lavas consist mainly of olivine basalt and hawaiite flows with minor evolved rocks of mugearite, benmoreite, and trachyte that occur mainly as domes, tuff cones and occasionally as lava flows. Previous K/Ar dating shows that the Harrat Al-Madinah lava flows and associated domes comprise seven units spanning an age range of ca. 1.7Ma–Recent. The new 40Ar/39Ar age determinations confirm, to a great extent, the previously obtained K/Ar ages in the sense that no major systematic biases were found in the general stratigraphy of the different flow units. However, the 40Ar/39Ar plateau ages show that volcanism in this area began in the Neogene (∼10Ma) and continued to Recent, with the most voluminous eruptions occurring in the Quaternary. Neogene volcanism occurred in at least three pulses around 10, 5 and 2Ma, whereas Quaternary volcanism produced at least seven units reflecting lava flow emplacement in the time period of 1.90Ma–Recent. Thus, the whole duration of volcanic activity in the Harrat Al-Madinah (10Ma–Recent) appears much longer than that previously identified. The longevity of volcanism in the same part of the moving Arabian plate and absence of evidence for uni-directional migration of volcanic activity indicate that there is no fixed plume beneath this region. The NNW-trending distribution of the volcanic vents is parallel to the Red Sea, and suggests their origin is related to periodic extensional episodes along the reactivated Red Sea fault system.

A 3-D genetic approach to high-resolution geological modelling of the volcanic infill of a paleovalley system. Application to the Volvic catchment (Chaîne des Puys, France)

Abstract The Volvic natural mineral water is catched in a complex volcanic aquifer located in the northern part of the “Chaîne des Puys” volcanic system (Auvergne, France). In the watershed, water transits through scoria cones and basaltic to trachybasaltic lava flows. These aa lava flows, emitted by strombolian cones between 75,000 and 10,000 years ago, are emplaced in deep paleovalleys incised within the variscan crystalline bedrock. The volcanic infill is highly heterogeneous. In order to build a hydrogeological model of the watershed, a simple but robust methodology was developed to reconstruct the bedrock morphology and the volcanic infill in this paleovalley context. This methodology, based on the combination of genetic and geometric approaches, appears to be rather efficient to define both the substratum and the lava flows geometry. A 3D geological model is then proposed. It synthesizes the data from 99 boreholes logs, 2D geoelectric profiles, morphologic clues, datings and petrographic data. A genetic approach, integrating aa lava flow morphology and emplacement behaviour, was used to reconstruct the chronology of the volcanic events and lava flow emplacement from the upper part of the Dômes plateau to the Limagne plain. The precision of the volcanic reconstruction is discussed: the main limitation of the methodology are related to the homogeneity of the petrographic and geochemical composition of the lava flows succession (except for the trachyandesitic Nugere lava), the spatially variable borehole density, the lack of a real petrographical and geological description on most of the available geological logs. Nevertheless, the developed methodology combining spatial and genetic approaches appears to be well adapted to constrain complex lava flow infill geometries in paleovalley context.

Tracking lava flow emplacement on the east rift zone of Kīlauea, Hawai‘i, with synthetic aperture radar coherence

Lava flow mapping is both an essential component of volcano monitoring and a valuable tool for investigating lava flow behavior. Although maps are traditionally created through field surveys, remote sensing allows an extraordinary view of active lava flows while avoiding the difficulties of mapping on location. Synthetic aperture radar (SAR) imagery, in particular, can detect changes in a flow field by comparing two images collected at different times with SAR coherence. New lava flows radically alter the scattering properties of the surface, making the radar signal decorrelated in SAR coherence images. We describe a new technique, SAR Coherence Mapping (SCM), to map lava flows automatically from coherence images independent of look angle or satellite path. We use this approach to map lava flow emplacement during the Pu‘u ‘Ō‘ō‐Kupaianaha eruption at Kīlauea, Hawai‘i. The resulting flow maps correspond well with field mapping and better resolve the internal structure of surface flows, as well as the locations of active flow paths. However, the SCM technique is only moderately successful at mapping flows that enter vegetation, which is also often decorrelated between successive SAR images. Along with measurements of planform morphology, we are able to show that the length of time a flow stays decorrelated after initial emplacement is linearly related to the flow thickness. Finally, we use interferograms obtained after flow surfaces become correlated to show that persistent decorrelation is caused by post‐emplacement flow subsidence.

Charting thermal emission variability at Pele, Janus Patera and Kanehekili Fluctus with the Galileo NIMS Io Thermal Emission Database (NITED)

Using the NIMS Io Thermal Emission Database (NITED), a collection of over 1000 measurements of radiant flux from Io’s volcanoes (Davies, A.G. et al. [2012]. Geophys. Res. Lett. 39, L01201. doi:10.1029/2011GL049999), we have examined the variability of thermal emission from three of Io’s volcanoes: Pele, Janus Patera and Kanehekili Fluctus. At Pele, the 5-μm thermal emission as derived from 28 night time observations is remarkably steady at 37±10GWμm−1, re-affirming previous analyses that suggested that Pele an active, rapidly overturning silicate lava lake. Janus Patera also exhibits relatively steady 5-μm thermal emission (≈20±3GWμm−1) in the four observations where Janus is resolved from nearby Kanehekili Fluctus. Janus Patera might contain a Pele-like lava lake with an effusion rate (QF) of ≈40–70m3s−1. It should be a prime target for a future mission to Io in order to obtain data to determine lava eruption temperature. Kanehekili Fluctus has a thermal emission spectrum that is indicative of the emplacement of lava flows with insulated crusts. Effusion rate at Kanehekili Fluctus dropped by an order of magnitude from ≈95m3s−1 in mid-1997 to ≈4m3s−1 in late 2001.

Sensitivity analysis of the MAGFLOW Cellular Automaton model for lava flow simulation

MAGFLOW is a physics-based numerical model for lava flow simulations based on the Cellular Automaton approach that has been successfully used to predict the lava flow paths during the recent eruptions on Mt Etna. We carried out an extensive sensitivity analysis of the physical and rheological parameters that control the evolution function of the automaton and which are measured during eruptive events, in an effort to verify the reliability of the model and improve its applicability to scenario forecasting. The results obtained, which include Sobol' sensitivity indices computed using polynomial chaos expansion, confirm the consistency of MAGFLOW with the underlying physical model and identify water content and solidus temperature as critical parameters for the automaton. Additional tests also indicate that flux rates can have a strong influence on the emplacement of lava flows, and that to obtain more accurate simulations it is better to have continuous monitoring of the effusion rates, even if with moderate errors, rather than sparse accurate measurements.

An emergent strategy for volcano hazard assessment: From thermal satellite monitoring to lava flow modeling

Spaceborne remote sensing techniques and numerical simulations have been combined in a web-GIS framework (LAV@HAZARD) to evaluate lava flow hazard in real time. By using the HOTSAT satellite thermal monitoring system to estimate time-varying TADR (time averaged discharge rate) and the MAGFLOW physics-based model to simulate lava flow paths, the LAV@HAZARD platform allows timely definition of parameters and maps essential for hazard assessment, including the propagation time of lava flows and the maximum run-out distance. We used LAV@HAZARD during the 2008–2009 lava flow-forming eruption at Mt Etna (Sicily, Italy). We measured the temporal variation in thermal emission (up to four times per hour) during the entire duration of the eruption using SEVIRI and MODIS data. The time-series of radiative power allowed us to identify six diverse thermal phases each related to different dynamic volcanic processes and associated with different TADRs and lava flow emplacement conditions. Satellite-derived estimates of lava discharge rates were computed and integrated for the whole period of the eruption (almost 14months), showing that a lava volume of between 32 and 61million cubic meters was erupted of which about 2/3 was emplaced during the first 4months. These time-varying discharge rates were then used to drive MAGFLOW simulations to chart the spread of lava as a function of time. TADRs were sufficiently low (<30m3/s) that no lava flows were capable of flowing any great distance so that they did not pose a hazard to vulnerable (agricultural and urban) areas on the flanks of Etna.

Komatiites of the Wildara-Leonora Belt, Yilgarn Craton, WA: The missing link in the Kalgoorlie Terrane?

The Wildara-Leonora Belt in the Kalgoorlie Terrane is located between the world-class nickel provinces of the Agnew-Wiluna Belt to the North and the Kambalda Domain to the South. It extends from the Wildara station to the gold mining center of Leonora and consists of a deformed package of mafic, komatiitic and sedimentary rocks. This package of rocks, which hosts a number of small nickel–sulfide occurrences, has been explored extensively for komatiite-hosted nickel deposits, most recently within the Sullivans Unit in the South-East of the Wildara-Leonora Belt. Lithostratigraphic similarities together with shared physical, geochemical and textural properties support a common affiliation between the Wildara-Leonora and the Agnew-Wiluna Belts. On this evidence, the Wildara-Leonora Belt represents the Southern extension of the largest komatiite-hosted nickel camp in the world. The apparently lesser prospectivity for nickel sulfide deposits is interpreted as a consequence of contrasting volcanic facies assemblages.Komatiites in the Wildara-Leonora Belt present geochemical and volcanological characteristics consistent with turbulent lava flow emplacement. However, compared with the Agnew-Wiluna Belt, the Wildara-Leonora Belt komatiites are not spatially associated with felsic volcanic units, but rather overlie a thick sequence of pillowed basalts and sulfidic sediments. The lower proportion of adcumulate, greater degrees of fractionation and lower degrees of contamination are consistent with komatiites in the Wildara-Leonora Belt having been emplaced in a more distal position to the rift environment, with lower magma flux and more tranquil emplacement than the Agnew-Wiluna Belt komatiites, and consequently having lower potential for giant nickel sulfide deposits such as those at Perseverance and Mt. Keith.

The morphological evolution of the Sciara del Fuoco since 1868: reconstructing the effusive activity at Stromboli volcano

The morphological evolution of the Sciara del Fuoco, Stromboli, is described from a time series dataset formed by Digital Elevation Models and orthophotos derived by digitising historical contour maps compiled in 1868 and 1937 and by processing data from aerial surveys carried out between 1954 and 2009. All maps were co-registered in the same reference system and used to build a quantitative reconstruction of the morphological changes of the Sciara del Fuoco slope. The changes mainly relate to the emplacement of many lava flows and their successive erosion. A comparative quantitative analysis yields estimates of areas and volumes of the lava fields formed on the sub-aerial part of the Sciara del Fuoco during a number of effusive events between 1937 and 2001, some of them never assessed before. The results of the analysis constrain the interpretation of the evolution and the magnitude of the recent effusive activity at the Stromboli volcano. Despite some uncertainties due to widely spaced observation periods, the results integrate all available topographic knowledge and contribute to an understanding of the main characteristics of the recent effusive eruptive styles at Stromboli volcano.

Identifying potentially active volcanoes in the Andes: Radiometric evidence for late Pleistocene-early Holocene eruptions at Volcán Imbabura, Ecuador

Recent eruptions from volcanoes with no previously known historical activity in Chile and Indonesia have raised the importance of the early identification of potentially active centers for the purpose of hazard assessment. Here we bring radiometric evidence ( 14 C, 39Ar– 40Ar) of previously unrecognized but significant magmatic activity at partly eroded Imbabura volcano (Ecuador) in late Pleistocene to early Holocene times, on whose perimeter live more than 300,000 persons. Following an effusive stage from 50 to 30 ka with the emplacement of andesitic lava flows on different flanks of its edifice, the activity became explosive with the generation of andesitic block-and-ash flows on its eastern side, beginning at ~ 35 ka cal BP. Subsequently a flank collapse associated with a volcanic blast occurred on the volcano's SW flank at ~ 30 ka cal BP. The resulting debris avalanche and blast breccias cover an area now heavily populated around San Pablo Lake and its source was later concealed by successive dome building episodes at Huarmi which produced ~ 2.8 km 3 of silicic andesite. Renewed dome activity at the edifice's Taita summit occurred at ~ 17 ka cal BP and continued intermittently into early Holocene times, as indicated by pyroclastic flow deposits overlying a palaeosoil dated at ~ 9 ka cal BP. In summary, this study reveals an eruptive behavior characterized by a low recurrence rate but with quite large eruptions, a pattern which is also observed at other silicic volcanoes of Ecuador's Western Cordillera. It is now imperative to reconsider the origin and source of the many tephra layers catalogued in Holocene lacustrine sediments in the Imbabura area. Tephra and lava volume estimates for Imbabura volcano converted to Dense Rock Equivalent values yield a minimum magmatic output rate of 0.13 km 3/ka in the past 35,000 years, which argues for sustained magma production for this volcano in recent geological times. The Imbabura example thus raises the question of how to improve population preparedness for volcanoes with infrequent eruptions, and how to guide authorities' decisions concerning the development of urban areas and infrastructures near presently inactive but potentially highly dangerous volcanoes.

Application of seismic and sequence stratigraphic concepts to a lava‐fed delta system in the Faroe‐Shetland Basin, UK and Faroes

ABSTRACTDetailed seismic stratigraphic analysis of 2D seismic data over the Faroe‐Shetland Escarpment has identified 13 seismic reflection units that record lava‐fed delta deposition during discrete periods of volcanism. Deposition was dominated by progradation, during which the time shoreline migrated a maximum distance of ∼44 km in an ESE direction. Localised collapse of the delta front followed the end of progradation, as a decrease in volcanic activity left the delta unstable. Comparison with modern lava‐fed delta systems on Hawaii suggests that syn‐volcanic subsidence is a potential mechanism for apparent relative sea level rise and creation of new accommodation space during lava‐fed delta deposition. After the main phase of progradation, retrogradation of the delta occurred during a basinwide syn‐volcanic relative sea level rise where the shoreline migrated a maximum distance of ∼75 km in a NNW direction. This rise in relative sea level was of the order of 175–200 m, and was followed by the progradation of smaller, perched lava‐fed deltas into the newly created accommodation space. Active delta deposition and the emplacement of lava flows feeding the delta front lasted ∼2600 years, although the total duration of the lava‐fed delta system, including pauses between eruptions, may have been much longer.

Hazard assessment at Mount Etna using a hybrid lava flow inundation model and satellite-based land classification

Using a lava flow emplacement model and a satellite-based land cover classification, we produce a map to allow assessment of the type and quantity of natural, agricultural and urban land cover at risk from lava flow invasion. The first step is to produce lava effusion rate contours, i.e., lines linking distances down a volcano’s flank that a lava flow will likely extend if fed at a given effusion rate from a predetermined vent zone. This involves first identifying a vent mask and then running a downhill flow path model from the edge of every pixel around the vent mask perimeter to the edge of the DEM. To do this, we run a stochastic model whereby the flow path is projected 1,000 times from every pixel around the vent mask perimeter with random noise being added to the DEM with each run so that a slightly different flow path is generated with each run. The FLOWGO lava flow model is then run down each path, at a series of effusion rates, to determine likely run-out distance for channel-fed flow extending down each path. These results are used to plot effusion rate contours. Finally, effusion rate contours are projected onto a land classification map (produced from an ASTER image of Etna) to assess the type and amount of each land cover class falling within each contour. The resulting maps are designed to provide a quick look-up capability to assess the type of land at risk from lava extending from any location at a range of likely effusion rates. For our first (2,000 m) vent zone case used for Etna, we find a total of area of ~680 km2 is at risk from flows fed at 40 m3 s−1, of which ~6 km2 is urban, ~150 km2 is agriculture and ~270 km2 is grass/woodland. The model can also be run for specific cases, where we find that Etna’s 1669 vent location, if active today, would likely inundate almost 11 km2 of urban land, as well as 15.6 km2 of agricultural land, including 9.5 km2 of olive groves and 5.2 km2 of vineyards and fruit/nut orchards.

Present‐Day Volcanism on Venus: Evidence from Microwave Radiometry

We present new evidence for volcanic eruptions and lava flow emplacement on Venus within the last several decades. An integrated study of a radar‐dark lava flow unit in Bereghinia Planitia on Venus (∼28°E, ∼39°N) based on Magellan data obtained in 1993 reveals a significant apparent microwave thermal emission excess, consistent with increased subsurface temperature due to very recent lava flow emplacement. The flow unit occupies the stratigraphically youngest position in the area and in part is more than 15 years old because it was also observed in the radar map obtained by Pioneer‐Venus in 1978. Analysis of lava flow cooling rates and geological characteristics point to flow material of mafic composition. Future missions can employ this microwave radiometry technique to search for and monitor active volcanism on Venus.

Benefits of the Proposed Magia Mission for Lunar Geology

Age of geological units, surface mineralogical composition, volcanism, tectonics and cratering are major keys for unravelling the geodynamic and geological history of a planet. Thanks to the extensive exploration of the 1960s and 1970s and the compositional mapping of the 1990s missions (Galileo, Clementine and Luna Prospector), the Moon has a unique geological dataset among the extraterrestrial Solar System bodies. The recent and on-going missions, along with the future plans for lunar exploration, will together acquire an extraordinary amount of data. This should provide a solid basis to meet broad objectives like the constraints on the heterogeneity of Lunar composition and the presence of water deposits, the understanding of volcanic and tectonic evolution as well as more specific issues such as the genetic classification of volcanic domes, origin of the dark-halos craters, lava flow emplacement mechanisms, and the kinematics and deformational styles of tectonic structures. The Italian small mission MAGIA (Missione Altimetrica Gravimetrica geochImica lunAre) will be equipped with an integrated context camera and imaging spectrometer, a high resolution camera and a radar altimeter. The spatial and spectral resolution of these instruments will provide data products complementing past and ongoing Lunar mission data, particularly for the polar regions where a full resolution coverage is planned. A general review of some still unanswered questions on lunar surface composition, cold traps, volcanism, tectonics and cratering records is presented here in order to illustrate the potential contribution of MAGIA to these subjects.

Pressure sources versus surface loads: Analyzing volcano deformation signal composition with an application to Hekla volcano, Iceland

The load of lava emplaced over periods of decades to centuries induces a gradual viscous response of the Earth resulting in measurable deformation. This effect should be considered in source model inversions for volcanic areas with large lava production and flow emplacement in small centralized regions. If deformation data remain uncorrected, constructive load and pressure source interference may result in an overestimate of depth and volume of a magma reservoir whereas destructive signal interference may cause these values to be underestimated. In both cases the source geometry preference could be biased. The ratio of horizontal and vertical displacements aids the identification of composite signals. We provide a method to quantify and remove the lava load deformation signals, using deformation at Hekla volcano, Iceland as an example.

Emplacement of the mid-Miocene Yatta lava flow, Kenya: Implications for modelling long channelled lava flows

The emplacement of the 13.51 m.y. old Yatta lava flow in Kenya has been investigated using evidence from field observations combined with a novel method of modelling length-dominated lava flows along channels. The Yatta lava erupted as an individual flow from a single vent on the eastern rim of the present-day East African Plateau during the extensive volcanism that occurred in mid-Miocene times. It then followed an old river valley for nearly 300 km, thus forming one of the longest phonolitic lava flows on Earth. For our modelling we combined a composition and temperature dependent viscosity equation with empirical cooling and morphological relationships. By using an average channel width and the known length of the Yatta lava flow but varying the mean thickness and underlying topography, we have improved flow rate calculations for the internal part of the lava, close to the front of the lava flow. Within this zone the lava's motion was treated as steady, uniform, and laminar, following a stepwise cooling from the eruption temperature to the temperature at the cessation of flow. Comparison of eight different compositions ranging from basaltic to rhyolitic has revealed that the length-dominated Yatta lava flow emplacement was rapid (~ 7 days), approximately isothermal (cooling at 0.71 °C/km), and the result of high effusion rates (~ 7900 m 3/s). This study shows that morphology of a lava flow, and in particular its length, is not a simple function of rheological properties and effusion rate, but is also affected by many other parameters. Small changes in H 2O compounds in the lava chemistry can affect melt viscosity significantly and thus lava flow morphology. Therefore H 2O content, together with slope angle and the mean lava flow thickness, ultimately control the length of a lava flow within a channel.

Late Pleistocene: Holocene record of environmental changes in Lake Zirahuen, Central Mexico

Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC), and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19° 26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time scale is based on ten AMS 14C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP, followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP. This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability. Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this region.