Open Fissures Research Articles

Possible relation between the sudden sinking of river Iška and the sequence of weak earthquakes in September-October 2010 near Iška vas (central Slovenia)

During heavy rainfalls between September 17 and 19, 2010 large part of Slovenia has suffered extensive floods that last for nearly two weeks. For the river Iška record discharge of 59.3 m3/s was measured on September 19 on the gauging station in Iška vas located at the southern rim of Ljubljansko barje. In the first hour of September 21, 2010 two weak earthquakes (ML=0.6 and ML=0.2) occurred within one minute near Iška vas. They were felt by some inhabitants who reported also a rumbling noise (brontides). During the flood recession period, the water of river Iška started to sink into the gravely stream bed or rocky left banks and the gauging profile completely dried on September 23, day and a half after the first earthquake. Water reappeared again on September 25. In the period September 21 − October 4 additional seven weak earthquakes occurred in the same area. All earthquakes from this series occurred at or near the surface and deviate in hypocentral depth from the seismicity pattern characteristic for the southern rim of Ljubljansko barje, which was analysed for comparison. The epicentres of the first two earthquakes are in good agreement with the location of the dried river bed. It is therefore probable that both phenomena are related. Analyses of seismograms have shown that it is not likely that the observed events are collapse earthquakes, but they are tectonic events. Although earthquakes were relatively weak, it seems that they could be accompanied by small near-surface tectonic movements, because they occurred at the position of a known fault. These movements are probably connected to the opening of pre-existing fissures in the karstified valley bottom, although the primary reason for sinking of the river is that high waters removed the clogged river bed that enables intensive sinking into the river bottom during the flood.

Dating brittle tectonic movements with cleft monazite: Fluid‐rock interaction and formation of REE minerals

AbstractTwo millimeter‐sized hydrothermal monazites from an open fissure (cleft) that developed late during a dextral transpressional deformation event in the Aar Massif, Switzerland, have been investigated using electron microprobe and ion probe. The monazites are characterized by high Th/U ratios typical of other hydrothermal monazites. Deformation events in the area have been subdivided into three phases: (D1) main thrusting including formation of a new schistosity, (D2) dextral transpression, and (D3) local crenulation including development of a new schistosity. The two younger deformational structures are related to a subvertically oriented intermediate stress axis, which is characteristic for strike slip deformation. The inferred stress environment is consistent with observed kinematics and the opening of such clefts. Therefore, the investigated monazite‐bearing cleft formed at the end of D2 and/or D3, and during dextral movements along NNW dipping planes. Interaction of cleft‐filling hydrothermal fluid with wall rock results in rare earth element (REE) mineral formation and alteration of the wall rock. The main newly formed REE minerals are Y‐Si, Y‐Nb‐Ti minerals, and monazite. Despite these mineralogical changes, the bulk chemistry of the system remains constant and thus these mineralogical changes require redistribution of elements via a fluid over short distances (centimeter). Low‐grade alteration enables local redistribution of REE, related to the stability of the accessory phases. This allows high precision isotope dating of cleft monazite. 232Th/208Pb ages are not affected by excess Pb and yield growth domain ages between 8.03 ± 0.22 and 6.25 ± 0.60 Ma. Monazite crystallization in brittle structures is coeval or younger than 8 Ma zircon fission track data and hence occurred below 280°C.

From slots to tubes: The influence of dimensionality on fracture dissolution models

We briefly review the models of fracture dissolution process, discussing the experimental and numerical evidence showing that this phenomenon is inherently two-dimensional and hence cannot be accurately described by one-dimensional models. The physical reason for this incompatibility is that a dissolution front in a single rock fracture is potentially unstable to small variations in local permeability, leading to spontaneous formation of dissolution channels in the rock. This leads to a dramatic increase of fissure opening rates, which must be taken into account not only in the estimation of karstification times but also in the assessment of ground subsidence, dam collapse or toxic seepage risks.

Experimental investigation on fracture coalescence behavior of red sandstone containing two unparallel fissures under uniaxial compression

Natural rock usually contains a lot of flaws, such as fissures, joints, weak surfaces and faults, which have a significant effect on the strength, deformability and crack coalescence behaviors of rock material [1–5]. In order to improve the understanding of fracture mechanism of rock engineering containing intermittent structures, a lot of experimental studies have been performed for all kinds of rock materials or rock-like materials containing two fissures [6–10]. Wong and Chau [6] investigated the crack propagation and coalescence on rock-like materials containing two inclined open or closed fissures, which obtained three main modes of crack coalescence in two fissured specimens under uniaxial compression. Feng et al. [7] carried out a number of experimental studies to explore the mechanism of multi-crack interaction in limestone specimens (the size of the specimen was 15 30 3 mm) with two fissures of different geometries under the coupled uniaxial compressive stress and chemical solutions with different ionic concentrations and pH values. Yang et al. [8] made uniaxial compression tests for cylindrical marble specimens with different pre-existing fissures, which analyzed the effect of fissure geometry on strength and deformation failure behaviors of brittle marble material. Wong and Einstein [9] summarized the effects of the flaw angle, ligament angle and length on the cracking processes and coalescence patterns of Carrara marble specimens containing two open fissures and used a high speed camera to observe the specimens at a macroscopic scale. Yang [10] performed an experimental study on the influence of coplanar fissure angle on the strength, deformation

In Vivo Performance of Two Devices for Occlusal Caries Detection

The aim of this in vivo study was to compare the performance of light-emitting diode (LED)- and laser fluorescence (LF)-based devices with that of visual inspection (VI) in the diagnosis of occlusal caries. A total of 156 occlusal surfaces were investigated. Each occlusal surface was assessed with LED- and LF-based devices after a VI was performed. Pit and fissure opening was applied to the occlusal surfaces in which opacity or discoloration was distinctly visible after airdrying. The inter-examiner reliability of caries examination was assessed using the weighted κ statistics. The sensitivity, specificity, and accuracy of occlusal caries diagnosis using these methods were calculated according to the appropriate thresholds. Acceptable inter-examiner agreement was found for the LED- and LF-based devices and VI (κ=0.61, κ=0.76, and κ=0.87, respectively). Higher specificity values were achieved at a T2 threshold for the LF-based device (0.76 and 0.80) and at a T1 threshold for the LED-based readings (0.60 and 0.62) and VI (0.90 and 0.93) for both observers. With regard to VI, higher sensitivity values were found at both thresholds for the two observers in comparing the three caries detection methods (0.98 at T1 and 0.96 at T2). The accuracy values for T1 were higher than those for the T2 values, for all three caries detection methods. Caries lesions may be detected more accurately than clinically sound areas by both caries detection devices.

Extension of continental crust by anelastic deformation during the 2011 Tohoku-oki earthquake: The role of extensional faulting in the generation of a great tsunami

Observations of seafloor morphologies and environments made before and after the 2011 Tohoku-oki earthquake reveal open fissures, generated during the earthquake, where the fault trace is interpreted on seismic profiles to intersect the seafloor. Anomalously high heat flow was observed at a landward-dipping normal fault in August 2011, five months after the earthquake, but by August 2012 heat flow measured at the same station had decreased to close to the background value, which suggests that the normal fault ruptured during the 2011 earthquake. These seafloor observations and measurements demonstrate deformation that was both extensional and anelastic within the overriding continental plate during the 2011 earthquake. Seismic profiles as well as seafloor bathymetry data in the tsunami source area further demonstrate that landward-dipping normal faults (extensional faults) collapse the continental framework and detach the seaward frontal crust from the landward crust at far landward from the trench. The extensional and anelastic deformation (i.e., normal faulting) observed in both seafloor observations and seismic profiles allows the smooth seaward movement of the continental crust. Seaward extension of the continental crust close to the trench axis in response to normal faulting is a characteristic structure of tsunami source areas, as similar landward-dipping normal faults have been observed at other convergent plate margins where tsunamigenic earthquakes have occurred. We propose that the existence of a normal fault that moves the continental crust close to the trench can be considered one indicator of a source area for a huge tsunami.

A New Coal Permeability Prediction Method Based on Experiment and Dimension Analysis

Summary This paper aims to investigate the effect of temperature and effective stress on coal permeability. Through the experiment, we find a reversal phenomenon in which the coal permeability presents different change trends as temperature increases at two sides of the reverse point. The term “critical effective stress” refers to the effective stress at the reverse point. When effective stress is lower than the critical effective stress, the outward expansion effect of the coal block caused by grain and gas swell is greater than compaction effect as temperature increases under low effective stress condition. Therefore, the coal expands primarily outward, which results in fissure opening and permeability increase. When effective stress is higher than the critical effective stress, high effective stress limits the coal's outward expansion. The coal expands inward with increasing temperature, thus causing fissure closure and permeability decrease. On the basis of dimension analysis and regression analysis, combined with experimental data, this paper develops a high-precision semitheoretical coal permeability model of Qinshui basin in China. Simultaneously, what this paper presents is a permeability prediction method: measuring coal core permeability and performing dimension analysis and regression analysis. With this work done, we can establish a similar permeability model suitable for other target zones. Thus, the analytical method presented in this paper provides a basis for coal permeability prediction.

脳動脈瘤クリッピングの基本

To improve the safety of aneurysmal clipping as well as to develop neurosurgical skills of residents simultaneously, we present the technical details and setting adopted in our institution. Between 2006 and 2011, we experienced 379 aneurysmal clipping surgeries (209 ruptured, 170 unruptured) at Fuji Brain Institute and Hospital. With daily thorough in-vitro microsurgical training, we performed standard-sized craniotomies with open fissures such as the sylvian fissure or interhemispheric fissure, to obtain a safe wide surgical field for clipping to compensate for the lack of experience in young neurosurgeons. We made every effort to be meticulous rather than fast to maintain treatment safety. To enhance the understanding for the surgical setting, method and strategy, we standardized procedures in detail to maximize the practice effect for residents with a limited amount of surgical experience. We discuss our institutional experiences in developing the surgical skills of young neurosurgeons, with the aim of having residents perform real neurosurgical micro-operations under the supervision of a staff doctor without compromising safety.

Unilateral subfrontal approach to anterior communicating artery aneurysms: A review of 28 patients

Dear Editor, The authors present the named “unilateral subfrontal approach” for anterior communicating aneurysms, analyzed in a small clinical series. The authors present this approach mainly as an alternative to the pterional approach. This approach was previous described as the “superciliar keyhole approach” or the “lateral supraorbital approach” for the treatment not only of vascular disease but also for tumors.[2] The authors present their approach as a “tailored” pterional approach. Nevertheless, there are some aspects that are subject of criticism as the rutinary use of external ventriculostomy or lumbar drainage; these are procedures that carry additional risks: Intraoperative rebleeding, frontal lobe lesion among others. We strongly recommend the microsurgical wide opening of the basal cisterns and the fenestration of the lamina terminalis to obtain CSF drainage and brain relaxation during the surgery, we do not see the silvian fissure opening as an additional source of complications as the authors pointed out. Additionally, these microsurgical simple procedures are implicated in the prevention of the hydrocephalus and vasospasm in the subarachnoid hemorrhage secondary to ruptured aneurysms.[1] The four advantages that the authors provided are at least uncertain. In the number 4 we can say that the pterional approach provide a corridor to see up to the contralateral middle cerebral artery bifurcation. Another important issue is that they have a 50% of resection of the gyrus rectus in unruptured and 61% in ruptured aneurysms, so the approach does not avoid this designed resection of the frontal lobe; we only use a small gyrus rectus resection in the anterior communicating artery (ACoA) aneurysms superiorly projected located between the two A2 segments, especially in the large or giant lesions, in all the other cases we split the interhemispheric cistern, which is possible using the pterional approach. The authors point out that the pterional approach leave a cosmetic defect at the level of the pterion, but in their own series the leave two burr holes in the frontal bone visible in the forehead. Salma et al.[3] recently published a cadaveric anatomical study comparing this two approaches, in their paper they analyzes the qualitative and quantitative anatomic evaluation between this two approaches, showing that this kind of approach can eventually reduce the temporalis muscle trauma, and offers and equivalent access and exposure of the anterior communicating artery complex, optic nerve, optic chiasm, and sellar areas. However, like all the anatomical cadaveric models, they do not consider the role of the cisternal and ventricular opening using these anatomical corridors as the natural pathways to reach the pathology, in this case ACoA aneurysms. We think that in patient's ruptured aneurysms with hematoma or subarachnoid hemorrhage (SAH) of high Fisher grade this approach is not a good choice, because it does not allow a wide opening of the sylvian fissure for cleansing the blood clots and relaxing the brain. Hence, this approach would be useful just for treating the aneurysm, but not to deal with the SAH, without reducing neither the risk of vasospasm nor the hydrocephalus.

How travertine veins grow from top to bottom and lift the rocks above them: The effect of crystallization force

Travertine mounds form at the mouth of springs where CO 2 degassing drives carbonate precipitation from water flowing from depth. Building of such mounds commonly involves the successive stratigraphic deposition of carbonate layers that precipitate from waters rising from depth along vertical to horizontal open fissures that are episodically sealed by radiating crystals. Much more intriguing structures can also be observed, such as widespread horizontal white veins of carbonate with vertical aragonite fibers, parallel or oblique to the stratigraphic travertines, which extend laterally over distances of several tens of meters and could represent up to 50% of the total volume of the travertine mound. Using highly precise U-Th dating, the growth direction of these horizontal veins is shown to be from top to bottom, and this fact clearly indicates that they developed within the mound over a period of ∼1000 yr for the vein analyzed. A vein growth mechanism is proposed that is able to uplift the rock above the vein thanks to the force of crystallization. The possible development of such structures in other places and the consequences of reverse growth direction when interpreting travertine data are discussed.

Controls on reservoir compartmentalization of an Upper Permian tight gas field in Germany and links to a modern analogue in the Western US

This study focuses on the reservoir characteristics of a Permian tight gas field in the Southern Permian Basin, Eastern Frisia, Germany. To improve the understanding of the reservoir, 3D seismic, wireline and core data were compared with a reservoir analogue in the Panamint Valley, United States. Depositional environments of the Permian Upper Rotliegend II include perennial saline lakes, coastal parallel sand belts comprising wet, damp and dry sand flats and aeolian dunes with interdune deposits. Polygonal patterns at different scales were observed on seismic horizon slices in the reservoir intervals and the overlying Zechstein. Outlines of superordinate polygons coincide with interpreted faults. Similar polygonal networks were identified on modern dry lakes in the western United States. The kilometre-long, up to 1.20 m deep open fissures in the Panamint Valley are interpreted to originate from the combined effects of synaeresis and tectonics. Subsequently, the fissures were filled with aeolian sediment. Vegetation growth confined to the lineaments indicates enhanced fluid circulation. Such fissures systems may serve as weakness zones and fault grain and impact reservoir quality in terms of hydraulic connectivity of reservoir compartments. For the Rotliegend reservoirs, original porosities and permeabilities of these zones were reduced to a minimum by enhanced cementation along the fluid migration pathways. Permeability barriers and reservoir compartmentalization, which can be clearly depicted on seismic attribute volumes, are a potential result of this development.

Pax2 regulates a fadd-dependent molecular switch that drives tissue fusion during eye development

Tissue fusion is an essential morphogenetic mechanism in development, playing a fundamental role in developing neural tube, palate and the optic fissure. Disruption of genes associated with the tissue fusion can lead to congenital malformations, such as spina bifida, cleft lip/palate and ocular coloboma. For instance, the Pax2 transcription factor is required for optic fissure closure, although the mechanism of Pax2 action leading to tissue fusion remains elusive. This lack of information defining how transcription factors drive tissue morphogenesis at the cellular level is hampering new treatments options. Through loss- and gain-of-function analysis, we now establish that pax2 in combination with vax2 directly regulate the fas-associated death domain (fadd) gene. In the presence of fadd, cell proliferation is restricted in the developing eye through a caspase-dependent pathway. However, the loss of fadd results in a proliferation defect and concomitant activation of the necroptosis pathway through RIP1/RIP3 activity, leading to an abnormal open fissure. Inhibition of RIP1 with the small molecule drug necrostatin-1 rescues the pax2 eye fusion defect, thereby overcoming the underlying genetic defect. Thus, fadd has an essential physiological function in protecting the developing optic fissure neuroepithelium from RIP3-dependent necroptosis. This study demonstrates the molecular hierarchies that regulate a cellular switch between proliferation and the apoptotic and necroptotic cell death pathways, which in combination drive tissue morphogenesis. Furthermore, our data suggest that future therapeutic strategies may be based on small molecule drugs that can bypass the gene defects causing common congenital tissue fusion defects.

Remarks on axisymmetric modeling of deep tunnels in argillaceous formations: I: Plastic clays

The paper analyses the response of argillaceous formations to the excavation of deep tunnels, focusing on the role of hydro-mechanical behavior. First, two different types of geologic formations are identified: plastic, soil-like, and stiff, rock-like, argillaceous formations. This paper is specifically concerned with deep tunnels in plastic clays. In particular, the influence of pore pressure changes on the stability of the excavation and on the loading of the support systems is investigated. The state of stress and deformation is analyzed in the short- and long-term, by applying analytical and numerical solutions to the idealized situation of an axisymmetric tunnel. General remarks on the influence of hydro-mechanical coupling, artificial boundary conditions and lining permeability are presented. Theoretical predictions are compared with measurements made in some tunnels excavated in the Boom clay formation at Mol (Belgium). The suggestions provided in the paper may contribute to refining practical design approaches, hence filling the gap between the application of advanced hydro-mechanical models and conventional uncoupled elasto-plastic models. In a companion paper, the behavior of rock-like materials is considered. In particular, the effect of scaly structure, typical of many deep argillaceous formations, and fissure opening around the tunnel walls is examined. Results of conventional and novel models, purposely formulated to analyze such situations, are compared.

Remarks on axisymmetric modelling of deep tunnels in argillaceous formations. II: Fissured argillites

In a companion paper, basic differences between the hydro-mechanical behaviour of plastic and stiff clay formations were highlighted and some issues, such as the influence of hydro-mechanical coupling and boundary conditions, were pointed out.This paper focuses on the effect of the scaly structure, frequently caused by tectonic shearing, typical of many relatively old and deep-sited argillaceous formations. Different engineering models for the prediction of short- and long-term response to tunnel excavation are compared. The proposed approaches consider some typical features of the hydro-mechanical behaviour of the plastic annulus around the tunnel, focusing on the influence of fissure opening, which may cause loss of saturation, in the short-term, and a general increase in permeability in the long-term. The case of the Raticosa tunnel (Italy), excavated through tectonised argillites, is chosen as an example case to apply the proposed approaches and investigate the aforementioned issues.Laboratory test results and in situ measurements are also discussed. The interpretation of convergence measurements, with the help of empirical correlations and the results of hydro-mechanical analyses, highlights the relevance of time-dependent creep deformation, which could therefore be tentatively distinguished from deformation due to consolidation.The potential of an “observational” approach in which early tunnel convergence measurements are used to predict the total final increment in convergence due to time-dependent deformation is also discussed.

Geology and tectonics of the southwestern boundary of the unstable sector of Mt. Etna (Italy)

The Etna volcano is known to be unstable and gradually moving downslope toward east and south. The study of the local geology and structure of these unstable flanks and of their boundaries is important to understand the evolution of the flank instability and the stress field driving the spreading of the edifice. In this paper we present the geological evolution of the lower south-western sector of Mount Etna base on a detailed field survey at 1:10,000 scale. This area located at the boundary of the unstable south-eastern flank of the volcano is affected by the active Ragalna Fault and by distinctive eruptive fissures (Monte Calvario formation, 18–15 ka). The Monte Calvario formation is made of viscous lavas often associated to breccia and autoclastic lava facies fed by a set of eruptive fissures NE–SW oriented. Their emplacement occurred immediately before the Ellitico caldera collapse, marking a previously poorly constrained shift in the feeding system of the volcano. The orientation of these eruptive fissures and lineaments, and the geometry of the sedimentary substratum modeled from subsurface data, indicate that the area was dominated by a local stress field consistent with the lateral spreading of Mount Etna since at least from the final Ellittico phase (about 18 ka) with a nearly constant mean displacement rate. These data give new insights into the geology and structure of the flank instability at Etna. The main geologic hazard of the studied area is not related to the opening of a new eruptive fissures, but it is posed by the presence into Il Calvario quarry of fluoro-edenite, an asbestiform mineral that caused an high mortality rate for respiratory system cancer in Biancavilla town. In fact the Monte Calvario formation groups other eruptive fissures with similar volcanological and geochemical characteristics, where hydrothermal alteration occurred with the likely formation of health-threatening minerals.

Discussion on ‘Hyper-permeable granite: lessons from test pumping in the Eastgate Geothermal Borehole, Weardale, UK’ by P.L. Younger & D.A.C. Manning

The authors have described some unexpected properties from a mineralized fracture system associated with Slitt Vein in the Weardale Granite. They ask whether the presence of open fissures might be more commonplace in granites than is currently supposed. Their suggestion that the main cavity, intersected at 410–413 m in the granite, might result from dissolution by deep weathering at the Carboniferous–Devonian unconformity is interesting, but other possibilities exist. The borehole was sited on a complex quartz–fluorspar mineral vein, and had passed through several mineral-filled veins. Examples of dissolution of one phase of ‘Pennine Style’ mineralization and replacement by …

Normal Faulting during the August 1989 Earthquakes in Central Afar: Sequential Triggering and Propagation of Rupture along the Dobi Graben

In August 1989, an earthquake sequence including ten events with 6:3 ! M ! 5:5 in the first two days produced widespread ground deformation in the Dobi graben of central Afar. Numerous surface breaks with complex geometry, including fresh scarplets with vertical throws up to 30 cm high and open fissures up to 30 cm wide, were observed. Coseismic slip incremented the deformation (normal faulting, block tilting, and counterclockwise rotation of basaltic slices) accumulated in the last 2 m.y. in the transfer zone between the Dobi and Hanle grabens. By combining maps of surface ruptures, relative event relocations with the local Djibouti network, published focal mechanisms, and source sizes, we tentatively relate most of the main- shocks of the sequence to slip on individual faults. The largest shocks at 11h16 on 20 August 1989 (MS 6:2) and at 1h09 on 21 August 1989 (MS 6:3) ruptured southern segments of the southwestern bounding fault of the graben. A dozen other faults also slipped along the edges of, and inside, the graben. On average, triggered seismic fault- ing propagated about 35 km northwestward along the graben in about 20 hr. Slip on the main faults was coupled with slip on secondary antithetic faults branching from them at depth. Although the Dobi earthquakes ruptured part of the fault array between the Asal rift (1978 sequence) and the Serdo region (1969 sequence), an approximately 50-km-long gap subsists along the Der'ela half-graben. We infer the patterns of sur- face faulting in the Dobi sequence, which coinvolved bookshelf-faulting about both horizontal and vertical axes, to typify the complexity of coseismic stress release in central Afar and in other active zones of distributed extension (e.g., Iceland, Abruzzi, Basin and Range). Online Material: Additional photos and descriptions of surface effects of the Dobi earthquake sequence.

Magnetic features of the magmatic intrusion that occurred in the 2007 eruption at Stromboli Island (Italy)

Significant changes in the local magnetic field marked the resumption of eruptive activity at Stromboli volcano on February 27, 2007. After differential magnetic fields were obtained by filtering out external noise using adaptive filters and seasonal thermal noise using temperature data, we identified step-like changes of 1–4 nT coincident with the opening of eruptive fissures in the upper part of the Sciara del Fuoco. The magnetic variations detected at two stations are closely related to the propagation of a shallow NE–SW magmatic intrusion extending beyond the summit craters area. These observations are consistent with those calculated using piezomagnetic models in which stress-induced changes in rock magnetization are produced by the magmatic intrusion. No significant magnetic changes were observed when the first fractures opened along the NE crater rim. Indeed, the stress-induced magnetization caused by this magmatic activity is expected to be too low because of the structural weakness and/or thermal state of the summit area. The continuous long-term decay characterizing the post-eruptive magnetic pattern can be related to a time-dependent relaxation process. A Maxwell rheology was assumed and the temporal evolution of the piezomagnetic field was evaluated. This allowed us to estimate the rheological properties of the medium; in particular, an average viscosity ranging between 1016 and 1017 Pa⋅s was a relaxation time τ of about 38 days.

Infrasound from the 2007 fissure eruptions of Kīlauea Volcano, Hawai'i

[1] Varied acoustic signals were recorded at Kīlauea Volcano in mid-2007, coincident with dramatic changes in the volcano's activity. Prior to this time period, Pu'u 'Ō'ō crater produced near-continuous infrasonic tremor and was the primary source of degassing and lava effusion at Kīlauea. Collapse and draining of Pu'u 'Ō'ō crater in mid-June produced impulsive infrasonic signals and fluctuations in infrasonic tremor. Fissure eruptions on 19 June and 21 July were clearly located spatially and temporally using infrasound arrays. The 19 June eruption from a fissure approximately mid-way between Kīlauea's summit and Pu'u 'Ō'ō produced infrasound for ∼30 minutes—the only observed geophysical signal associated with the fissure opening. The infrasound signal from the 21 July eruption just east of Pu'u 'Ō'ō shows a clear azimuthal progression over time, indicative of fissure propagation over 12.9 hours. The total fissure propagation rate is relatively slow at 164 m/hr, although the fissure system ruptured discontinuously. Individual fissure rupture times are estimated using the acoustic data combined with visual observations.

Riding the Narrow Tracks of Moral Life: Commercial Motorbike Riders in Makeni, Sierra Leone

Contrary to the postwar paradigm of demobilization and reintegration of ex-combatants and ideals of coming-of-age under elders' guidance, some Sierra Leonean ex-combatants and other young men took another way: by remobilizing and providing transportation on motorbikes, they nowadays enhance the physical and social mobility of others and themselves. Depicted nevertheless as transgressing local morals, they try to find ways to conjoin the expectations of others with their own aspirations. Oscillating between avoidance and compliance with claimed norms, negotiating and extending them, they fill ruptures and gaps within society while they broaden and open fissures further. This article is about those men's ethical mobility and the obstacles to it: congestion, denied mobility, and difficulties of avoiding potholes and not losing the right track while navigating a constantly transforming social landscape.