Post Eruption Research Articles

Analysis of phreatic events at Ruapehu volcano, New Zealand using a new SOM approach

We apply Self-Organising Maps (SOM) to assess the low level seismic activity prior to small scale phreatic events at Ruapehu volcano New Zealand. The SOM approach allows an automatic pattern recognition, virtually independent from a priori knowledge. Volcanic tremor spectra are randomly presented to the network in a competitive iterative training process, followed by a hierarchical clusterization of the SOM nodes. Spectra are then projected, ordered by time, to clusters on the map. A coherent time evolution of the data through the clusters can highlight the existence of different regimes and the transitions between them. Two Ruapehu events were examined: a phreatic event on 4 October 2006 which displaced the crater lake producing a 4m high wave on the lake edge, and the more energetic 25 September 2007 phreatic eruption. The SOM analysis provides a classification of tremor spectral patterns that clusters into three regimes that we label by colours. The pattern for both eruptions is consistent with a pre-eruption spectral pattern including enhanced spectral energy in the range of 4 to 6Hz — labelled ‘green tremor’. This gives way to spectra having broader energy between 2 and 6Hz, the so called ‘red tremor’ just prior to the eruption. The post eruption pattern includes spectral peaks at generally lower frequencies of 2 to 4Hz — the so called ‘blue tremor’. Clusterization into only three groups yields highly non-unique solutions which cannot explain the variety of processes operating at Ruapehu over long time periods. Regardless, the approach highlights noteworthy similarities that may be explained by a pattern of slow pressurisation under a hydrothermal or magmatic seal – ‘green’ – followed by seal failure – ‘red’ – and subsequent de-pressurisation – ‘blue’ – for the two events studied. Although the application shown here is limited, we think it demonstrates the power of this classification approach.

Clinical treatment approach of a child with molar incisor hypomineralization (MIH) combined with malocclusion

Introduction. Molar incisor hypomineralization (MIH) was defined as “hypomineralisation of systemic origin of permanent first molars, frequently associated with affected incisors”. MIH includes the presence of demarcated opacity, post eruptive enamel breakdown, atypical restoration . Ohe approach to management suggested: risk identification, early diagnosis, remineralization for prevention of caries and post eruption breakdown, restorations. The clinicians very seldom notice that children with MIH usually have both- hypomineralisation and malocclusions, and they do not discuss combine treatment plan. Aim. To present our interdisciplinary approach to a patient with MIH, combined with malocclusion.

Empirical normalization for the effect of volcanic stratospheric aerosols on AVHRR NDVI

The 1982 El Chichon and 1991 Mount Pinatubo volcanic eruptions produced large volumes of stratospheric aerosols that affected the environmental indices estimated from the Advanced Very High Resolution Radiometer (AVHRR) sensor. As a result the Normalized Difference Vegetation Index (NDVI) used to derive several vegetation health products exhibits a negative bias between approximately 20°N and 20°S during the post eruption years. In this work a statistical method based on Empirical Distribution Functions (EDF) and simple assumptions regarding the state of global vegetation is used to reduce these biases. Results show that the statistical technique effectively reduces the biases allowing the construction of consistent time series from this historical dataset for climate studies.

Effects of Water Fluoride Exposure at Crown Completion and Maturation on Caries of Permanent First Molars

Pre-eruptive fluoride exposure has been shown to be important for caries prevention. This paper aimed to determine the relative effects of water fluoride exposure during crown completion (CC) and maturation on caries experience in first permanent molars. Parental questionnaires covering residential history were linked to oral examinations of 19,885 6- to 15-year-old Australian children conducted in 1992 by the School Dental Services of South Australia and Queensland. The percentage of lifetime exposed to optimally fluoridated water at CC, maturation (MAT) and post-eruption (POST) was calculated. Combined exposure variables describing different levels of CC, maturation and post-eruption were created using a threshold exposure of 50%. Compared to the reference of CC <50%/MAT <50%/POST <50%, the categories CC ≧50%/MAT <50%/POST ≧50% [rate ratio (RR) 0.52], CC ≧50%/MAT ≧50%/POST <50% (RR 0.61) and CC ≧50%/MAT ≧50%/POST ≧50% (RR 0.67) had the strongest caries-preventive effect, followed by CC ≧50%/MAT <50%/POST <50% (RR = 0.79) and CC <50%/MAT ≧50%/POST ≧50% (RR = 0.81) in negative binomial regression models (p < 0.05). The categories CC <50%/MAT ≧50%/POST <50% (RR = 0.85) and CC <50%/MAT <50%/POST ≧50% (RR = 0.84) had weaker, non-significant caries-preventive effects. In conclusion a high exposure at CC was important for caries prevention irrespective of the effect of exposure at maturation and post-eruption. The strongest caries-preventive effect was produced by a high exposure at CC supplemented by a high exposure at maturation and/or post-eruption, but the latter two phases could not produce a significant caries-preventive effect on their own. Since most of the caries occurred on pit and fissure surfaces, the findings relate to this class of lesion.

Long-term response of spring flora to chronic herbivory and deer exclusion in Great Smoky Mountains National Park, USA

Chronic herbivory by white-tailed deer ( Odocoileus virginianus Zimmerman) can have profound impacts on the function and structure of forest ecosystems. We examined the combined influence of intense herbivory associated with a deer population eruption and chronic herbivory by the post eruption population on the spring flora of Cades Cove, Great Smoky Mountains National Park. During the 1970s the deer population reached a peak of 43 deer per km 2, from which it has slowly declined in recent decades. To examine the influence of intense herbivory, we compared the abundance and flowering rates of early flowering plants in Cades Cove to a nearby reference site with similar bedrock geology, vegetation, and disturbance history but contrasting history of deer abundance. Our results suggest that significant changes ( p ⩽ 0.05) in the diversity, evenness, and species richness of the spring flora occurred during the eruptive phase. Trillium spp. and other liliaceous species appeared to be disproportionately impacted. Comparisons between control and exclosure plots established after the deer population eruption indicate that recovery has been largely restricted to species that were able to persist under intense herbivory. These species have increased in number in exclosures, suggesting continued impacts by deer on the plant community outside the exclosures. Little to no recolonization by browse sensitive species was observed. Consequently, to restore the natural diversity of early flowering plants once present in Cades Cove, active restoration may be necessary in addition to maintaining deer densities below current levels.

Relative effects of pre‐ and post‐eruption water fluoride on caries experience by surface type of permanent first molars

To determine the relative pre- and post-eruption exposure effects of fluoridated water on the caries experience of different surface types of first permanent molars. Parental questionnaires covering residential history of participants were linked to the oral examinations of 6-15-year-old Australian children conducted in 1992 by the School Dental Services of South Australia and Queensland. Percentage of lifetime exposed to optimally fluoridated water pre- (PRE) and post-eruption (POST) was calculated with respect to tooth eruption age. Combined pre- and post-eruption categories were created to test PRE against POST exposure: PRE and POST = 0, PRE < POST, PRE = POST and in the range 0-90% of lifetime exposure, PRE > POST and, PRE and POST >or= 90% lifetime exposure. These categories were used as indicator variables in linear regression models with PRE and POST = 0 as reference in an analysis of first permanent molar DMFS scores overall and by surface type. Participation rates were 69.7% in South Australia (n = 9690) and 55.6% in Queensland (n = 10 195). Compared with the reference, the categories PRE > POST (beta = -0.033), PRE = POST (beta = -0.028) in the range 0-90% and, PRE and POST >or= 90% (beta = -0.055) showed significantly lower caries overall (P < 0.01), with a similar pattern for pit and fissure surface caries (beta = -0.035, -0.031 and -0.052, respectively). Only a high PRE and POST exposure decreased caries levels significantly in the approximal (beta = -0.038; P < 0.01) and free smooth surfaces (beta = -0.023; P = 0.03). Pre-eruption exposure was important for a caries preventive effect on first permanent molars in children 6-15 years old since post-eruption exposure alone could not lower caries levels significantly. For pit and fissure surfaces, a high pre-eruption exposure could decrease caries levels significantly. However, for other surface types, only a high pre- and post-eruption exposure produced a caries preventive effect.

Study of enamel density

Objective To measure mineral concentration distributions within teeth with idiopathic enamel hypomineralisation, a condition in which developmental defects are seen in first permanent molars, and/or incisors. Design X-ray microtomographic and 3D x-ray microscopy. Setting UK University, 2001. Materials and methods X-ray microtomographic measurements of the extent of hypomineralisation in two affected molars and two contralateral controls extracted from the same patient. Results The control molars were visibly normal. The affected molars showed hypomineralised yellow opaque enamel with regions of breakdown. X-ray microtomographic images showed; a 20% reduction in mineral concentration of affected enamel (most cases involved full enamel thickness); hypomineralised enamel had a mineral concentration gradient opposite to that of normal enamel; regions of hypomineralisation distributed randomly throughout affected teeth, (apart from cervical region which was less severely affected). Conclusions The pattern of mineral concentration suggests a disturbance during the maturation process. Differences in susceptibility of the ameloblasts during different stages of dental development may explain the asymmetric distribution of the defects. Topical fluoride applications may help promote post eruption maturation of the surface layer in these teeth. The use of fissure sealants and adhesive materials appears to prevent further breakdown.

3D X-ray microscopic study of the extent of variations in enamel density in first permanent molars with idiopathic enamel hypomineralisation.

To measure mineral concentration distributions within teeth with idiopathic enamel hypomineralisation, a condition in which developmental defects are seen in first permanent molars, and/or incisors. X-ray microtomographic and 3D x-ray microscopy. UK University, 2001. X-ray microtomographic measurements of the extent of hypomineralisation in two affected molars and two contralateral controls extracted from the same patient. The control molars were visibly normal. The affected molars showed hypomineralised yellow opaque enamel with regions of breakdown. X-ray microtomographic images showed; a 20% reduction in mineral concentration of affected enamel (most cases involved full enamel thickness); hypomineralised enamel had a mineral concentration gradient opposite to that of normal enamel; regions of hypomineralisation distributed randomly throughout affected teeth, (apart from cervical region which was less severely affected). The pattern of mineral concentration suggests a disturbance during the maturation process. Differences in susceptibility of the ameloblasts during different stages of dental development may explain the asymmetric distribution of the defects. Topical fluoride applications may help promote post eruption maturation of the surface layer in these teeth. The use of fissure sealants and adhesive materials appears to prevent further breakdown.

Relative effects of pre- and posteruption water fluoride on caries experience of permanent first molars.

Previous studies have attributed the caries-preventive effects of preeruption (PRE) and posteruption (POST) exposure to fluoridated water based on data collected before and after the commencement or discontinuation of water fluoridation. This study aims to determine the relative pre- and posteruption exposure effects of fluoridated water on caries experience of 6-15-year-old Australian children based on individual residential histories. Parental questionnaires covering residential history of participants were linked to their oral examinations conducted between June 1991 and May 1992 by the School Dental Services of South Australia and Queensland. Percentage of lifetime exposed to optimally fluoridated water PRE and POST was calculated with respect to the eruption age for first permanent molars. Combined pre- and posteruption categories were created to test PRE against POST exposure: PRE & POST = 0, PRE < POST, PRE = POST in the range 0-90 percent of lifetime exposure, PRE > POST, and PRE & POST > or = 90 percent lifetime exposure. These categories were used as indicator variables with PRE and POST = 0 as reference in an analysis of first permanent molar DMFS scores. The linear regression model controlled for important potential confounders. Participation rates were 69.7 percent in South Australia and 55.6 percent in Queensland with 9,690 and 10,195 participants, respectively. Pre- and posteruption exposures were strongly correlated (r =. 74; P < .01). Compared to the reference, the categories PRE > POST, PRE = POSTin the range 0-90 percent, and PRE and POST > or = 90 percent showed significantly lower caries levels. The findings indicated that preeruption exposure was required for a caries-preventive effect and that exposure after eruption alone did not lower caries levels significantly. However, the maximum caries-preventive effects of fluoridated water were achieved by high pre- and posteruption exposure.

Satellite observations of the April 1993 eruption of Lascar volcano

The largest historic eruption of the Lascar volcano, Chile, occurred during April 1993. The eruption lasted two days, producing pyroclastic flows, covering an 18.5km2 area, and a major ash plume, leading to widespread ashfall. Here we demonstrate how combined observations from the Japanese Earth Observation (JERS-1) and the National Oceanographic and Atmospheric Administration (NOAA) satellites were used to document this eruption. These two satellite platforms provide complementary data, giving high resolution spatial (JERS-1), spectral (JERS-1) and temporal information (NOAA). Such an integrated remote sensing approach offers a valuable means of easily and safely monitoring large, dangerous, volcanic eruptions and post eruption processes.

Transient phenomena in the energetic behind-the-limb solar flare of september 29, 1989

The powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays.

Transient Phenomena in the Energetic Behind-the-Limb Solar Flare of September 29, 1989

AbstractThe powerful cosmic ray flare of Sept. 29, 1989 occurred behind the limb and was observed over a wide spectral range. The analysis of optical, radio, and other relevant data suggest two phases of energy release. After an impulsive phase a prolonged post eruption energy release occurred in an extended region of the corona following the eruption of a large coronal mass ejection (CME). This phase is responsible for numerous coronal and interplanetary phenomena including the ground-level increase of cosmic rays.

Was Fritz Zwicky's "Type V" SN 1961V a Genuine Supernova?

view Abstract Citations (69) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Was Fritz Zwicky's "Type V" SN 1961V a Genuine Supernova? Filippenko, Alexei V. ; Barth, Aaron J. ; Bower, Geoffrey C. ; Ho, Luis C. ; Stringfellow, Guy S. ; Goodrich, Robert W. ; Porter, Alain C. Abstract In 1989, Goodrich and collaborators suggested that SN 1961V, a very peculiar Type II (Zwicky's "Type V") supernova, was not the final explosion of a star at the end of its life, but rather the giant eruption of a massive, luminous blue variable, like n Car. To test this hypothesis, we have used the Hubble Space Telescope to obtain optical images of the site of SN 1961V. There is a cluster of faint (V ~ 24-25 mag), blue [(V-I)_0_ = -0.4-0.5 mag] stars around the general location of the supernova. We also see a very faint (V = 25.6 +/- 0.3 mag), much redder [(V-I)_0_ = 1.7 mag] star barely resolved from one of the blue stars. Its brightness and colors are consistent with those of a highly reddened O-type star, as predicted by Goodrich et al. Moreover, it is the star formally closest to the known radio position of SN 1961V; the coordinates are identical, to within the uncertainties. Thus, we tentatively identify this as the post eruption star of SN 1961V; it survived the giant eruption, which was not a genuine supernova, and it is now red due to a substantial envelope of dust (A_V_ ~ 4.1 mag). However, the current data do not allow us to eliminate the possibility that this star is an unrelated red supergiant or a peculiar supernova remnant. Alternatively, the blue object adjacent to it may be the actual post- eruption star of SN 1961V. If so, the envelope of dust is not as thick: A_V_ ~ 2.2-3.2 mag, but perhaps somewhat larger if the object's colors are significantly affected by a blue light echo of SN 1961V. Publication: The Astronomical Journal Pub Date: November 1995 DOI: 10.1086/117687 Bibcode: 1995AJ....110.2261F Keywords: SUPERNOVAE: INDIVIDUAL: SN 1961V; CATACLYSMIC VARIABLES full text sources ADS | data products SIMBAD (17) NED (2) MAST (1) ESA (1)

Solar Mesosphere Explorer satellite measurements of El Chichón stratospheric aerosols: 1. Cloud morphology

Data from the Solar Mesosphere Explorer (SME) is used to track the time, latitude, and altitude (above 18 km) development of the aerosol cloud injected into the stratosphere by the eruption of el Chichón. This unique data set, using scattering data from the near‐infrared (1.27 and 1.87 μm) and visible (440 nm) spectrometers on SME, covers the period from the initial injection in April 1982 through the end of 1986. Although the bulk of the mass is contained in the latitude band from 10°S to 30°N for the entire duration of the measurements, transport of material to high latitudes is apparent in the data in the post eruption period. The times of aerosol density maxima vary greatly as a function of altitude and latitude.

Paleomagnetism of the Upper Cretaceous Mount Somers Volcanics, Canterbury, New Zealand

The Mount Somers Volcanics of mid Canterbury in eastern South Island are a high-K calcalkaline andesite–dacite–rhyolite suite erupted subaerially approximately 95 Ma ago during the long Late Cretaceous episode of normal geomagnetic field. Thermoremanent magnetic directions at 46 sites, corrected for post–eruption tectonic tilt, are stable and group well (a95= 3·8°, K = 31·7) with a very steep mean inclination (I = –85°, D = 354°). The resulting paleomagnetic South Pole position is at 52° S 174° E, indicating that Canterbury was within 10° of the South Pole 95 Ma ago, and that little finite rotation of Canterbury relative to the South Pole has occurred since. The Mount Somers Volcanics were erupted prior to the separation of eastern New Zealand from West Antarctica along the Pacific–Antarctic ridge. They provide a mid–Cretaceous pole position that can be compared with pole positions of similar age from Australia and with the polar–wander path previously reported for the Chatham Islands over the past 75 Ma. The Mount Somers pole fits neatly onto the New Zealand polar-wander path, which is consistent with the Australian polarwander path when convergent displacements across the Pacific-Indian plate boundary, and spreading of the Tasman Sea, are allowed for. The paleomagnetic data also support the proposition that regional folding and oroclinal bending of the pre-Cretaceous Torlesse basement rocks mainly predates the extrusion of the Mount Somers Volcanics and took place primarily during the Early Cretaceous Rangitata Orogeny and not during the Cenozoic as implied in recent plate-tectonic reconstructions.

The Magnetic and Opaque Petrological Response of Basalts to Regional Hydrothermal Alteration

Summary The alteration state of basalt lavas is shown to be largely the result of the combined action of two alteration processes, deuteric oxidation and regional hydrothermal alteration. The former process is well described in the literature while the latter is shown here to be another widespread source of lava alteration. The environment of regional hydro-thermal alteration is that of the zeolite metamorphic facies, with temperatures of up to 300 °C, and abundant groundwater being the major elements. Independent and rapid spatial variation of the two alteration processes results in the wide range of observed lava properties. Microscopically undetectable titanomagnetite alteration, indicated by steady rise in strong field Curie point, is the first response of a non-deuterically oxidized basalt to regional hydrothermal alteration. With more extreme alteration, titanohematite etc. is seen to pseudomorph titanomagnetite grains. Ilmenite also shows very distinctive mineralogical changes. Initially, high deuteric oxidation specimens appear to be immune magnetically to moderate alteration but these too eventually succumb when conditions are extreme enough for the formation of prehnite in the rock. The geophysical implications of this widespread post eruption lava alteration process is discussed. We conclude that it is probably possible to obtain information on the original TRM of basalts at least in many cases but that the implications for potassium-argon dating need serious investigation.