[show abstract][hide abstract] ABSTRACT: A newly developed ultraviolet (UV) imaging camera offers a new approach to the ground-based surveillance of volcanic sulphur dioxide (SO 2). Using highly sensitive 2-dimensional CCD technology and a bandpass filter centred in the UV region where SO 2 selectively absorbs UV light, the camera is able to quantify SO 2 within a gas plume in great detail. This study presents results from Sakurajima and Satsuma-Iojima volcanoes, where image sequences were obtained at an unprecedented temporal resolution and revealed interesting variations in SO 2 emission rate. The SO 2 retrieval technique is also discussed with respect to atmospheric scattering and the use of different UV wavelength filters.
[show abstract][hide abstract] ABSTRACT: Ammonites with bivalves or worm tubes attached are relatively rare among the abundant specimens in the Lower Jurassic (Sinemurian) mudstones at Bishop's Cleeve, Gloucestershire, UK, but provide evidence for ammonite taphonomy, environmental conditions and biological interactions between ammonites and epifauna. Epifauna attached only to one side or within the body chambers of ammonites usually indicate post-mortem attachment. Epifauna on both sides of, or overgrown by, ammonites attached in vivo. One large example of Oxynoticeras has at least 51 encrusting bivalves attached exclusively to one side indicating it formed a ‘benthic island’. Four, presumably annual, bivalve cohorts are recognized, with variation in preferred orientation in each cohort suggesting that current direction varied. Both the ammonite and its epifauna were buried by a single sedimentation event. Other informative examples include a Cheltonia that overgrew an epifaunal bivalve, and an example of Bifericeras which bears two clusters of four worm tubes, one of which apparently attached in vivo, the other post-mortem. Other examples bear too few specimens to be certain of the timing of attachment, but most probably attached post-mortem.
Proceedings of the Geologists Association 06/2012; 123(3):508–519.
[show abstract][hide abstract] ABSTRACT: No magmatic deformation signals have been reported from the Central
American Arc, in contrast to other arcs with similar levels of volcanic
activity. We test whether this is a result of the ambiguities in
interpreting interferometric data from tropical volcanoes, or may be
indicative of differences in volcanic processes between Central America
and other parts of the world. Arc-scale comparison of volcano
deformation requires an understanding of both the limits of InSAR
measurements, and consistent criteria for identifying volcano
deformation caused by a range of magmatic and structural processes. We
present a systematic method to distinguish between atmospheric or
geometric artefacts and actual ground deformation, based on identifying
diagnostic characteristics for artefacts in the spatial and temporal
structure of phase. We use evidence from a range of tools, including
stacking, time series analysis, and tests of phase measurements for an
ALOS dataset spanning 2007-2010. We expect to detect permanent
deformation of a magnitude above 1-2 cm for most Central American
volcanoes, corresponding to an average steady deformation rate of ~0.7
cm/yr. Any short-lived, transient deformation, however, may have to
exceed up to 8 cm to be identifiable. These upper limits on deformation
have different implications for open and closed system volcanoes. Over
three quarters of InSAR volcano measurements made in the Aleutians and
Andes would still have been measureable with the same limits as in
Central America, implying that the apparent lack of deformation
represents a real difference in volcanic processes. A systematic
approach to the identification of volcanic deformation signals and
associated uncertainty will be increasingly important for handling large
data sets as the volume of InSAR data acquired increases.