Pahoehoe Flow Fields Research Articles

Lithostratigraphy and volcanology of the Serra Geral Group, Paraná-Etendeka Igneous Province in Southern Brazil: Towards a formal stratigraphical framework

The volcanic rocks of the Lower Cretaceous Paraná-Etendeka Igneous Province, in Brazil, are grouped in the Serra Geral Group. The province can be chemically divided into low-TiO2, and high-TiO2. In southern Brazil, the low-TiO2 lava pile reaches a thickness of ~1km and is formed of heterogeneous lava packages here divided into four lava formations. Torres Formation (TF) is characterized by chemically more primitive basaltic (>5wt% MgO) compound pahoehoe flow fields; these lavas stratigraphically overly aeolian sandstones of Botucatu Formation and represent the onset of the volcanic activity. Vale do Sol Formation (VSF) groups vertically stacked sheet-like rubbly pahoehoe basaltic andesites (SiO2>51wt%; MgO<5wt%). These lavas covered the former basalts in the Torres Syncline axis and pinch out towards southwest and represent the most voluminous mafic lava flows. Dacites and rhyolites of Palmas Formation (PF) overlay VSF flows in the central and eastern outcrop area and rest directly upon TF lavas in the west. The acidic units were emplaced as lava domes and widespread tabular lava flows. Esmeralda Formation (EF) is the upper stratigraphic unit and it is formed by a basaltic pahoehoe flow field emplaced during the waning phase of volcanic activity of the low-TiO2 lava sequence. Sedimentary interbeds are preserved throughout the whole lava pile and were deposited during quiescence periods of volcanic activity, and represent important stratigraphic markers (e.g. TF-VSF contact). The newly proposed stratigraphy provides promptly recognized stratigraphic units in a regional framework of fundamental importance for future correlations and provide vital information in the understanding of how the Paraná-Etendeka Igneous Province evolved through time.

Stratigraphical framework of basaltic lavas in Torres Syncline main valley, southern Parana-Etendeka Volcanic Province

The Paraná-Etendeka Volcanic Province records the volcanism of the Early Cretaceous that precedes the fragmentation of the South-Gondwana supercontinent. Traditionally, investigations of these rocks prioritized the acquisition of geochemical and isotopic data, considering the volcanic stack as a monotonous succession of tabular flows. Torres Syncline is a tectonic structure located in southern Brazil and where the Parana-Etendeka basalts are well preserved. This work provides a detailed analysis of lithofacies and facies architecture, integrated to petrographic and geochemical data. We identified seven distinct lithofacies grouped into four facies associations related to different flow morphologies. The basaltic lava flows in the area can be divided into two contrasting units: Unit I - pahoehoe flow fields; and Unit II - simple rubbly flows. The first unit is build up by innumerous pahoehoe lava flows that cover the sandstones of Botucatu Formation. These flows occur as sheet pahoehoe, compound pahoehoe, and ponded lavas morphologies. Compound lavas are olivine-phyric basalts with intergranular pyroxenes. In ponded lavas and cores of sheet flows coarse plagioclase-phyric basalts are common. The first pahoehoe lavas are more primitive with higher contents of MgO. The emplacement of compound pahoehoe flows is related to low volume eruptions, while sheet lavas were emplaced during sustained eruptions. In contrast, Unit II is formed by thick simple rubbly lavas, characterized by a massive core and a brecciated/rubbly top. Petrographically these flows are characterized by plagioclase-phyric to aphyric basalts with high density of plagioclase crystals in the matrix. Chemically they are more differentiated lavas, and the emplacement is related to sustained high effusion rate eruptions. Both units are low TiO2 and have geochemical characteristics of Gramado magma type. The Torres Syncline main valley has a similar evolution when compared to other Large Igneous Provinces, with compound flows at the base and simple flows in the upper portions. The detailed field work allied with petrography and geochemical data are extremely important to identify heterogeneities inside the volcanic pile and allows the construction of a detailed lithostratigraphical framework.

Lithofacies analysis of basic lava flows of the Paraná igneous province in the south hinge of Torres Syncline, Southern Brazil

The Paraná igneous province records the volcanism of the earlier Cretaceous that preceded the fragmentation of the Gondwana supercontinent. Historically, investigations of these rocks prioritized the acquisition of geochemical and isotopic data, considering the volcanic pile as a monotonous succession of tabular flows. This work provides a detailed analysis of the emplacement conditions of these basic volcanic rocks, applying the facies analysis method integrated to petrographic and geochemical data. The Torres Syncline is a NW–SE tectonic structure, located in southern Brazil, where a thick sequence of the Paraná–Etendeka volcanic rocks is well preserved. This study was performed in the south hinge of the syncline, where the basaltic lava flows are divided into three lithofacies associations: early compound pahoehoe, early simple pahoehoe and late simple rubbly. The first lavas that erupted were more primitive compound pahoehoe flow fields composed of olivine basalts with higher MgO contents and covered the sandstones of the Botucatu Formation. The emplacement of compound pahoehoe flow fields is possibly related to intermittent low effusion rates, whereas the emplacement of simple pahoehoe is related to sustained low effusion rates with continuous supply. The thick simple rubbly lavas are associated with high effusion rates and were formed during the main phase of volcanism in the area. The absence of paleosoils between the lavas and lithofacies associations suggests that the successive emplacement of the lava flows occurred in a relatively short time gap. Geochemically, the lithofacies associations are low-TiO2 and belong to Gramado magma type. The lavas of the south hinge of the Torres Syncline have a similar evolution when compared to other Continental Basaltic Provinces with earlier compound flows at the base and thicker simple flows in the upper portions.

Pahoehoe–a′a transitions in the lava flow fields of the western Deccan Traps, India-implications for emplacement dynamics, flood basalt architecture and volcanic stratigraphy

Unlike pahoehoe, documentation of true a′a lavas from a modern volcanological perspective is a relatively recent phenomenon in the Deccan Trap (e.g. Brown et al., 2011, Bull. Volcanol. 73(6): 737–752) as most lava flows previously considered to be a′a (e.g. GSI, 1998) have been shown to be transitional (e.g. Rajarao et al., 1978, Geol. Soc. India Mem. 43: 401–414; Duraiswami et al., 2008 J. Volcanol. Geothermal. Res. 177: 822–836). In this paper we demonstrate the co-existence of autobrecciation products such as slabby pahoehoe, rubbly pahoehoe and a′a in scattered outcrops within the dominantly pahoehoe flow fields. Although volumetrically low in number, the pattern of occurrence of the brecciating lobes alongside intact ones suggests that these might have formed in individual lobes along marginal branches and terminal parts of compound flow fields. Complete transitions from typical pahoehoe to ‘a′a lava flow morphologies are seen on length scales of 100–1000m within road and sea-cliff sections near Uruli and Rajpuri. We consider the complex interplay between local increase in the lava supply rates due to storage or temporary stoppage, local increase in paleo-slope, rapid cooling and localized increase in the strain rates especially in the middle and terminal parts of the compound flow field responsible for the transitional morphologies. Such transitions are seen in the Thakurwadi-, Bushe- and Poladpur Formation in the western Deccan Traps. These are similar to pahoehoe–a′a transitions seen in Cenozoic long lava flows (Undara ∼160km, Toomba ∼120km, Kinrara ∼55km) from north Queensland, Australia and Recent (1859) eruption of Mauna Loa, Hawaii (a′a lava flow ∼51km) suggesting that flow fields with transitional tendencies cannot travel great lengths despite strong channelisation. If these observations are true, then it arguably limits long distance flow of Deccan Traps lavas to Rajahmundry suggesting polycentric eruptions at ∼65Ma in Peninsular India.

Effect of slope on development of pahoehoe flow fields: Evidence from Mount Etna

We describe and compare two types of pahoehoe on Mount Etna: one similar to an Hawaiian inflated flow field consisting of tumuli, lava rises and lava rise pits; and the other a coalescing complex of rootless centres of ephemeral boccas fed from lava tubes and superimposed on an initial 'a'a flow field. The former we define as a primary pahoehoe field that results from relatively slow advance rate of lava over an almost horizontal surface. The latter is a result of an eruption of long enough duration to allow tube formation over a substantial portion of the flow field over steeper slopes; at breaks in slope in the underlying topography centres of ephemeral boccas develop giving rise to low effusion rate pahoehoe lavas covering the original channelled 'a'a surface. These we refer to as secondary pahoehoe flow fields.

Monitoring active volcanism with the Autonomous Sciencecraft Experiment on EO-1

The ability to monitor and rapidly react to remote detection of volcanic activity has been greatly improved through use of the Autonomous Sciencecraft Experiment (ASE), an advanced software application installed on a spacecraft in Earth orbit. ASE is a NASA New Millennium Program experiment demonstrating science-driven autonomous command and control of a spacecraft. Flying on the Earth Observing-1 ( EO-1) spacecraft, ASE successfully detected thermal emission from the Mt. Erebus lava lake on 7 May 2004, having analyzed a Hyperion hyperspectral data product on board the spacecraft. EO-1 was re-tasked by ASE to obtain a follow-up observation 7 h later and sent a notification of detection of volcanic activity to the ground. The entire process was carried out autonomously. Initial acquisition to receipt on the ground of the positive detection took less than 3 h, a process that without ASE would have taken weeks. The ASE Thermal Classifier has detected several styles of effusive volcanic activity: active lava lakes, pahoehoe flow fields, open channel flows and lava domes. ASE successfully demonstrated that science-driven spacecraft operation greatly enhances science return per returned byte through the identification of the most valuable data, allowing prioritization of downlink products and the discarding of null data sets. This technology has applications on missions elsewhere in the solar system. Modified thermal classifiers can be used for detecting and monitoring active volcanism on the jovian satellite Io, the neptunian moon Triton, and searching for active volcanism on Mars and icy satellites. The success of ASE is an incentive for future instrument and mission designers to consider on-board data-processing requirements (especially data storage capacity, number of processors and processor speed, and RAM) in order to take advantage of this flight-proven technology.

Fast emplacement of extensive pahoehoe flow-fields: the case of the 1736 flows from Montaña de las Nueces, Lanzarote

The 1730–36 Timanfaya eruption on Lanzarote, in the Canary Islands, is the second largest historical effusion on record. During its final stages, in 1736, the eruption produced the Montaña de las Nueces flow-field, consisting of sheets of pahoehoe lava that, within 4 weeks, had covered 32 km 2 and reached a maximum length of almost 21 km. The tholeiitic lavas have pahoehoe surface features, but internal structures that are normally associated with massive aa flows, suggesting that their fronts advanced as single units rather than as a collection of budding pahoehoe tongues. Volume conservation and a simple model of crustal failure suggest that the main flows advanced at about 0.02 ms −1 over the prevailing slopes of ∼1°. The rates of advance are (1) consistent with emplacement near the transition from pahoehoe to aa, and (2) about an order of magnitude greater than would have been expected by analogy with Hawaiian pahoehoe flow-fields of similar dimensions. Surface texture and morphology, therefore, is an insufficient guide for constraining the rate and style of pahoehoe emplacement, and a flow’s internal structure must be established before its characteristics are used to infer eruption conditions and potential hazard.

Surface temperature measurements of active lava flows on Kilauea volcano, Hawai′i

Systematic 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.

The morphology and formation of flow-lobe tumuli on Icelandic shield volcanoes

Three types of tumuli are recognized on monogenetic shield volcanoes in Iceland, namely (1) lava-coated tumuli, (2) upper-slope tumuli and (3) flow-lobe tumuli. Flow-lobe tumuli grade into lava rises, which are larger inflation structures, but both structures have a similar mode of emplacement. The areal distribution of flow-lobe tumuli in the flow field differs from that of lava-coated tumuli and upper-slope tumuli. Flow-lobe tumuli are frequent in the medial and distal parts of pahoehoe flow fields, whereas the other two tumulus types are more frequent in the proximal parts of the flow fields. The flow-lobe tumuli also differ from the two other tumulus types as regards their morphology: they are significantly larger, have shallower flanks, and do not have extensive outflows from the cracks. The vesicle distribution within the flow-lobe tumuli is similar to that of P-type flow lobes: a fairly dense zone is situated between the upper and lower vesicular zones. Each flow-lobe tumulus is an individual lobe that inflates and forms tension cracks in the lava crust. Major lava tubes are mostly absent from the areas where flow-lobe tumuli form and, therefore, the emplacement of flow-lobe tumuli must be related to secondary, short-lived pathways of lava. The flow-lobe tumuli inside the flow fields of Icelandic shield volcanoes are morphologically identical to those flow-lobe tumuli that are found in the margins of flow fields of other Icelandic volcanoes. These observations allow us to model the flow-lobe tumuli as morphological variants of P-type flow lobes forming along terminating secondary lava paths. Flow-lobe tumuli form at low lava-supply rates of the order of 10 −2 − 10 −5 m 3/s and are generated by inflation of the lava crust as a result of magmatic overpressure in the associated lava core. We model the tumulus as a circular elastic plate that becomes uplifted, inflated and fractured by a uniform magmatic overpressure at its bottom. We conclude that (1) the effective thickness of the lava crust that is subject to bending is 0.2–0.4 m and remains essentially constant during the formation of the tumulus, and (2) for flow-lobe tumuli that are supplied with magma from tubes that originate in overflow from the lava lake of a shield volcano, the elevation difference between the tumuli and the surface of the source lava lake is commonly around 100 m. This elevation difference can give rise to a static magmatic overpressure of 2.5 MPa in the tumulus, whereas the overpressure needed to form a typical flow-lobe tumulus is only 0.2–1 MPa.

Emplacement of the 75-km-long Carrizozo lava flow field, south-central New Mexico

The Carrizozo Lava flow field is a young, 75-km-long, compound tube-fed pahoehoe flow field located in south-central New Mexico. Topographic channeling, unusually low viscosity, and fissure vents are ruled out as possible explanations for the length of the flow field. Effusion rates are estimated using: (1) a Bingham plastic model; (2) correlations between flow morphology and effusion rate; and (3) comparison with Hawaiian pahoehoe flows. The Bingham plastic model placed no useful restrictions on the effusion rate, while empirical and theoretical correlations gave estimates between 300 and 3 × 10 5 m 3 s −1 for the effusion rate. The striking morphological similarity of the Carrizozo flow field to the compound tube-fed pahoehoe Kupaianaha flow field on Kilauea Volcano suggests an effusion rate of about 5 m 3 s −1 and an eruption duration of nearly 3 decades. This long eruption duration and a long-lived lava tube system are interpreted to be the most important factors responsible for the length of the Carrizozo flow field. Furthermore, we conclude that the Bingham plastic model does not apply to tube-fed pahoehoe flow fields and that the correlation techniques grossly overestimate their effusion rates. This indicates that effusion rates may also have been overestimated for extra-terrestrial lava flows where it is has not been possible to distinguish between pahoehoe and ‘a’a.

Chronology, Eruption Duration, and Atmospheric Contribution of the Martian Volcano Apollinaris Patera

Geologic mapping, thermal inertia measurements, and an analysis of the color (visual wavelengths) of the martian volcano Apollinaris Patera indicate the existence of two different surface materials, comprising an early, easily eroded edifice, and a more recent, competent fan on the southern flank. A chronology of six major events that is consistent with the present morphology of the volcano has been identified. We propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on Earth. A basal escarpment typically 500 m in relief and morphologically similar to the one surrounding Olympus Mons was produced between the formation of the main edifice and the fan, indicating multistage eruptions over a protracted period of time. Contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed Apollinaris Patera. Stereophotogrammetric measurements permit the volume of the volcano to be estimated at 10 5 km 3. From this volume measurement and an inferred eruption rate (1.5 × 10 -2 km 3 yr -1) we estimate the total eruption duration for the main edifice to be ∼10 7 yrs. Plausible estimates of the exsolved volatile content of the parent magma imply that greater than 10 15 kg of water vapor was released into the atmosphere as a consequence of this activity. This large amount of water vapor as well as other exsolved gases must have had a significant impact on local, and possibly global, climatic conditions.

Development of the 1990 Kalapana Flow Field, Kilauea Volcano, Hawaii

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m3/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.