191,853 research outputs found
On the Thermal Budget of Pahoehoe Lava Flows
No full textIn this thesis I investigate some aspects of the thermal budget of pahoehoe lava
flows. This is done with a combination of general field observations, quantitative
modeling, and specific field experiments. The results of this work apply to pahoehoe
flows in general, even though the vast bulk of the work has been conducted on the lavas
formed by the Pu'u 'O'o - Kupaianaha eruption of Kilauea Volcano on Hawai'i. The field
observations rely heavily on discussions with the staff of the United States Geological
Survey's Hawaiian Volcano Observatory (HVO), under whom I labored repeatedly in
1991-1993 for a period totaling about 10 months.
The quantitative models I have constructed are based on the physical processes
observed by others and myself to be active on pahoehoe lava flows. By building up these
models from the basic physical principles involved, this work avoids many of the pitfalls of
earlier attempts to fit field observations with "intuitively appropriate" mathematical
expressions. Unlike many earlier works, my model results can be analyzed in terms of the
interactions between the different physical processes. I constructed models to: (1) describe
the initial cooling of small pahoehoe flow lobes and (2) understand the thermal budget of
lava tubes.
The field experiments were designed either to validate model results or to constrain
key input parameters. In support of the cooling model for pahoehoe flow lobes, attempts
were made to measure: (1) the cooling within the flow lobes, (2) the amount of heat
transported away from the lava by wind, and (3) the growth of the crust on the lobes.
Field data collected by Jones [1992], Hon et al. [1994b], and Denlinger [Keszthelyi and
Denlinger, in prep.] were also particularly useful in constraining my cooling model for
flow lobes. Most of the field observations I have used to constrain the thermal budget of
lava tubes were collected by HVO (geological and geophysical monitoring) and the Jet
Propulsion Laboratory (airborne infrared imagery [Realmuto et al., 1992]). I was able to
assist HVO for part of their lava tube monitoring program and also to collect helicopterborne
and ground-based IR video in collaboration with JPL [Keszthelyi et al., 1993].
The most significant results of this work are (1) the quantitative demonstration that
the emplacement of pahoehoe and 'a'a flows are the fundamentally different, (2)
confirmation that even the longest lava flows observed in our Solar System could have
formed as low effusion rate, tube-fed pahoehoe flows, and (3) the recognition that the
atmosphere plays a very important role throughout the cooling of history of pahoehoe lava
flows. In addition to answering specific questions about the thermal budget of tube-fed
pahoehoe lava flows, this thesis has led to some additional, more general, insights into the
emplacement of these lava flows. This general understanding of the tube-fed pahoehoe
lava flow as a system has suggested foci for future research in this part of physical
volcanology.</p
Surface temperature measurements of active lava flows on Kilauea volcano, Hawai'i.
No full textSystematic hand-held radiometer measurements of lava surface temperatures in active flows and tubes on Kilauea volcano, Hawai′i reveal complexities that cannot be resolved in remotely sensed data from aircraft or satellites. Using portable infrared Minolta/Land Cyclops radiometers, we measured surface temperatures of flows at various distances from their sources and investigated cooling rates and the development of crust. Our measurements suggest that the upper surface of these lava flows can be split into a minimum of four thermal components: core (>1050°C), visco-elastic skin (750–900°C), rigid solid crust (<750°C), and flow margins (<175°C). For the ′a′a flows investigated, a cool rigid crust characteristically developed in the central part of channels within 30 m of the source vent and incandescent lava was exposed in the marginal shear zones of channels. This affects the heat loss and morphology of lava in active channels. Our investigations of temperature distributions on pahoehoe flow fields reveal temperature anomalies of up to 150°C above active tubes and tumuli
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Coupled subdaily and multiweek cycles during the lava dome erupt of Soufriere Hills Volcano, Montserrat
No full textObservations of volcanoes extruding andesitic lava to produce lava domes often reveal cyclic behaviour. At Soufriere Hills Volcano, Montserrat, cycles with sub-daily and multi-week periods have been recognised on many occasions. These two types of cycle have been modelled separately as stick-slip magma flow at the junction between a dyke and an overlying cylindrical conduit (Costa et al. 2012), and as the filling and discharge of magma through the elastic-walled dyke (Costa et al., 2007a) respectively. Here, we couple these two models to simulate the behaviour over a period of well-observed multi-week cycles, with accompanying sub-daily cycles, from 13 May to 21 September 1997. The coupled model captures well the asymmetrical first-order behaviour: the first 40% of the multi-week cycle consists of high rates of lava extrusion during short period/high amplitude sub-daily cycles as the dyke reservoir discharges itself. The remainder of the cycle involves increasing pressurization as more magma is stored, and extrusion rate falls, followed by a gradual increase in the period of the sub-daily cycles
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Lava dome growth and mass wasting measured by a time series of ground-based radar and seismicity observations
No full textExogenous growth of Peléean lava domes involves the addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows. These processes were investigated at the Soufrière Hills Volcano, Montserrat, between 30 March and 10 April 2006, using a ground-based imaging millimeter-wave radar, AVTIS, to measure the shape of the dome and talus surface and rockfall seismicity combined with camera observations to infer pyroclastic flow deposit volumes. The topographic evolution of the lava dome was recorded in a time series of radar range and intensity measurements from a distance of 6 km, recording a southeastward shift in the locus of talus deposition with time, and an average height increase for the talus surface of about 2 m a day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2-day lag in the equivalent change in the rockfall seismicity record. The dense rock equivalent volumetric budget of lava added and dispersed, including the respective proportions of the total for each component, was calculated using: (1) AVTIS range and intensity measurements of the change in summit lava (∼1.5 × 106 m3, 22%), (2) AVTIS range measurements to measure the talus growth (∼3.9 × 106 m3, 57%), and (3) rockfall seismicity to measure the pyroclastic flow deposit volumes (∼1.4 × 106 m3, 21%), which gives an overall dense rock equivalent extrusion rate of about 7 m3·s−1. These figures demonstrate how efficient nonexplosive lava dome growth can be in generating large volumes of primary clastic deposits, a process that, by reducing the proportion of erupted lava stored in the summit region, will reduce the likelihood of large hazardous pyroclastic flows
The influence of surface clinker on the crustal structures and dynamics of 'a'ā lava flows.
No full textSurface structures on 'a'ā and blocky lavas reflect the internal flow dynamics during emplacement and also influence the dynamics of developing flows. To investigate the effects of brittle, clinkery 'a'ā flow crusts on flow dynamics and surface structures, we conducted sand and silicone laboratory experiments that simulated the advance of lava into a preexisting channelized flow with a surface crust. Experiments carried out with relatively thin crusts produced apparently ductile surface deformation structures, while thick crusts behaved dominantly in a brittle manner. Increased crustal thickness led to increased strength under compression but favored more disruption under tension, as the flow core welled up through tensile fractures, entraining crustal material. At lava flow fronts, upwelling and entrainment would increase heat losses by radiation and advection, respectively, resulting in a positive‐feedback cooling loop. Fracturing caused heterogeneous crustal distribution near the flow front, which resulted in lobate flow advance, despite the absence of the viscoelastic layer that has previously been inferred as the primary control on flow advance and lobe formation. We therefore conclude that the influence of a purely brittle crust on the dynamics and surface morphologies of lava flows is more significant than often thought. All of the surface structures produced in the experiments have been observed on lavas or glaciers and many also on landslides and debris flows, suggesting the results can assist in the understanding of a range of natural flows
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Use of a portable topographic mapping millimetre wave radar at an active lava flow.
No full textA ground-based millimetre wave radar, AVTIS (All-weather Volcano Topography Imaging Sensor), has been developed for topographic monitoring. The instrument is portable and capable of measurements over ranges up to ∼7 km through cloud and at night. In April and May 2005, AVTIS was deployed at Arenal Volcano, Costa Rica, in order to determine topographic changes associated with the advance of a lava flow. This is the first reported application of mm-wave radar technology to the measurement of lava flux rates. Three topographic data sets of the flow were acquired from observation distances of ∼3 km over an eight day period, during which the flow front was detected to have advanced ∼200 m. Topographic differences between the data sets indicated a flow thickness of ∼10 m, and a dense rock equivalent lava flux of ∼0.20 ± 0.08 m3s−1
Application of palynological data to the chronology of the Palaeogene lava fields of the British Province: implications for magmatic stratigraphy
No full textNew high-precision ages, determined from palynomorph assemblages within intercalated sedimentary deposits, are presented for the Palaeogene lava fields (Skye, Mull and Antrim) of the British Province. These data reveal very rapid averaged eruption rates (1 m/200 yr) and the non-synchronous formation of the lava fields. Eruption of the volumetrically dominant transitional to mildly alkaline lavas of the Skye (58.25-58.0 Ma) and Mull (post 55 Ma) lava fields is separated by the eruption of the MORB-like Preshal More flows of olivine tholeiite found at the top of the preserved sequence on Skye and at the base of the Mull Lava Field. The Lower Formation of the Antrim Lava Field correlates with the Skye Lava Field and the Upper Formation correlates with the Preshal More flows. The new ages indicate that the eruption of the Preshal More flows was synchronous with the main ocean floor spreading event which occurred 500 km to the NW, at c. 55 Ma, during Chron 24r. A combined thinspot and channelized plume model may best explain the temporal and spatial distributions of the lava fields and associated subvolcanic complexes of the British Province
Identification of structural controls in an active lava dome with high resolution DEMs : Volcán de Colima, Mexico
No full textMonitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity. Internal dome structure and conditions are more difficult to elucidate, but also play vital roles. Here, we describe the exposure (following an explosion) of significant scarps in the active dome at Volcán de Colima, Mexico, that are interpreted as evidence of brittle failure planes and a complex internal dome morphology. In the first use of automated 3D computer vision reconstruction techniques (structure-from-motion and multi-view stereo, SfM-MVS) on an active volcanic dome, we derive high resolution surface models from oblique and archive photographs taken with a consumer camera. The resulting 3D models were geo-referenced using features identified in a web-sourced orthoimage; no ground-based measurements were required. In December 2010, the dome (2.14×106 m3) had a flat upper surface, reflecting an overall ductile emplacement regime. Between then and May 2011, a period of low explosivity was accompanied by a small volume loss (0.4×105 m3) and arcuate steps appeared in the dome surface, suggesting the presence of localized planes of weakness. The complex array of summit scarps was exposed following a significant explosion in June 2011, and is interpreted to be the surface expression of fault planes in the dome. The 1-m resolution DEMs indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit, and that heterogeneity within the dome may have been important during the June explosion
Icelandic analogs to Martian flood lavas
No full textWe report on new field observations from Icelandic lava flows that have the same surface morphology as many Martian flood lava flows. The Martian flood lavas are characterized by a platy-ridged surface morphology whose formation is not well understood. The examples on Mars include some of the most pristine lava on the planet and flows >1500 km long. The surfaces of the flows are characterized by (1) ridges tens of meters tall and wide and hundreds of meters long, (2) plates hundreds of meters to kilometers across that are bounded by ridges, (3) smooth surfaces broken into polygons several meters across and bowed up slightly in the center, (4) parallel grooves 1–10 km long cut into the flow surface by flow past obstacles, and (5) inflated pahoehoe margins. The Icelandic examples we examined (the 1783–1784 Laki Flow Field, the Búrfells Lava Flow Field by Lake Myvatn, and a lava flow from Krafla Volcano) have all these surface characteristics. When examined in detail, we find that the surfaces of the Icelandic examples are composed primarily of disrupted pahoehoe. In some cases the breccia consists of simple slabs of pahoehoe lava; in other cases it is a thick layer dominated by contorted fragments of pahoehoe lobes. Our field observations lead us to conclude that these breccias are formed by the disruption of an initial pahoehoe surface by a large flux of liquid lava within the flow. In the case of Laki, the lava flux was provided by surges in the erupted effusion rate. At Búrfells it appears that the rapid flow came from the sudden breaching of the margins of a large ponded lava flow. Using the observations from Iceland, we have improved our earlier thermal modeling of the Martian flood lavas. We now conclude that these platy-ridged lava flows may have been quite thermally efficient, allowing the flow to extend for >100 km under a disrupted crust that was carried on top of the flow
Seismic Stratigraphy and Geomorphology of Palaeocene Volcanic Rocks, Faroe-Shetland Basin
No full text2D and 3D seismic reflection data in the Faroe-Shetland Basin have been used to remotely study buried, large-scale Palaeocene volcanic structures emplaced during continental flood basalt volcanism in the Faroe-Shetland Basin. The flood basalts were emplaced as thick and extensive pāhoehoe lava flows from multiple sources, including fissure systems close to the Faroese shelf and from volcanic centres within the basin. This thesis has investigated the distribution and internal structure of the flood basalts based on the hypothesis that volcanic eruptions produce volcanic depositional successions that record the temporal and spatial variations of the basin into which they are emplaced. Multiple eruptions will produce cycles of volcanic deposition that are delineated by hiatal surfaces. These successions can be recognised in seismic reflection data by applying seismic stratigraphic concepts in order to gain insights into the evolution of volcanic basin-fill.
The Faroe-Shetland Basin contains a variety of depositional environments, including a deepening marine basin where continental flood basalts reached a palaeo-shoreline and constructed an extensive lava-fed delta system >1000 m thick. The delta is composed of 13 seismic reflection units whose stacking architecture primarily records variations in lava supply and accommodation. Modification of the delta front was by erosion and debris avalanches. The second environment is subaerial to shallow marine where the continental flood basalts emplaced multiple lava flows 10 - 60 m thick which coalesced to form extensive and overlapping lava flow fields. Four seismic reflection units have been recognised and record variations in source and supply of the lava flows. During reoccurring periods of volcanic quiescence, fluvial channels 350 – 500 m wide incised across the lava flow fields, constrained by flow field topography.
The volcanic depositional successions used to reconstruct the volcanic basin-fill history of the Faroe-Shetland Basin indicate that eruptive styles and volcanic structures varying significantly over relatively small areas (tens of km2). Many of the seismic observations have been compared to outcrop analogues, are scale-independent and are indicative of emplacement environment. Analysis has also led to the development of a volcanic seismic stratigraphic model as depositional patterns produced during volcanic activity are primarily driven by volcanic supply. The results presented in this thesis have many important implications for stratigraphy, hydrocarbon exploration and basin modelling in the Faroe-Shetland Basin and therefore can be applied beyond the fields of volcanology or seismic interpretation
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