Geological and hydrogeological assessment of the Brito Formation: Municipio de Tola,Nicaragua

Hydrogeology Journal - There are sparse hydrogeological data and insufficient hydrogeological knowledge in many areas of the world reliant on groundwater. Nicaragua’s Pacific coast is one...     

Public perception of cold weather events as evidence for and against climate change

It has been argued that public doubts about climate change have been exacerbated by cold weather events seen as a form of disconfirming evidence for anticipated ‘warming’. Although a link between perceptions of climate and weather is well-established, such assumptions have not been empirically tested. Here we show, using nationally representative data, that directly following a period of severe cold weather in the UK, three times as many people saw these events as pointing towards the reality of climate change, than as disconfirming it. This we argue was a consequence of these cold winters being incorporated into a conceptualisation of extreme or ‘unnatural’ weather resulting from climate change. We also show that the way in which people interpret cold weather is associated with levels of pre-existing scepticism about climate change, which is in turn related to more general worldviews. Drawing attention to ‘extreme’ weather as a consequence of climate change can be a useful communication device, however this is problematic in the case of seasonal cold.     

On the Application of Mwp in the Near Field and the March 11, 2011 Tohoku Earthquake

Tsunami Warning Centers issue rapid and accurate tsunami warnings to coastal populations by estimating the location and size of the causative earthquake as soon as possible after rupture initiation. Both US Tsunami Warning Centers have therefore been using Mwp to issue Tsunami Warnings 5–10 min after Earthquake origin time since 2002. However, because Mwp (Tsuboi et al., Bulletin of the Seismological society of America 85:606–613, 1995) is based on the far-field approximation to the P-wave displacement due to a double couple point source, we should only very carefully apply Mwp to data obtained in the near field, at distances of less than a few wavelengths from the fault. On the other hand, the surface waves from Great Earthquakes, including those that occur just offshore of populated areas, such as the 2011 Tohoku earthquake, clip seismographs located near the fault. Because the first arriving P-waves from such large events are often on scale, Mwp should provide useful information, even for these Great Earthquakes. We therefore calculate Mwp from 18 unclipped STS-1 broadband P-wave seismograms, recorded at 2–15° distance from the Tohoku epicenter to determine if Mwp can usefully estimate Mw for this earthquake, using data obtained close to the epicenter. In this case there should be a good chance to get reliable Mwp values for stations at epicentral distances of 9–10°, since the source duration for the Tohoku earthquake is less than 200 s and the time window used to estimate Mwp is 120 s in duration. Our analysis indicates that Mwp does indeed give reliable results (Mw ~ 9.1) beginning at about 11° distance from the epicenter. The values of Mwp from seismic waveforms obtained at 11–15° epicentral distance from the Mw 9.1 off the east coast of Tohuku earthquake of March 11, 2011 fell within the range 9.1–9.3, and were available within 4–5 min after origin time. Even the Mwp values of 7.7–8.4, obtained at less than 5° epicentral distance, exceed the PTWC’s threshold of Mw 7.6 for issuing a regional tsunami warning to coastal populations within 1,000 km of the epicenter, and of Mw 6.9 for issuing a local tsunami warning to the coastal populations of Hawaii.     

Flow separation at the inner (convex) and outer (concave) banks of constant‐width and widening open‐channel bends

There is a paucity of data and insight in the mechanisms of, and controls on flow separation and recirculation at natural sharply‐curved river bends. Herein we report on successful laboratory experiments that elucidate flow structure in one constant‐width bend and a second bend with an outer‐bank widening. The experiments were performed with both a flat immobile gravel bed and mobile sand bed with dominant bedload sediment transport. In the constant‐width bend with immobile bed, a zone of mainly horizontal flow separation (vertical rotational axis) formed at the inner bank that did not contain detectable flow recirculation, and an outer‐bank cell of secondary flow with streamwise oriented rotational axis. Surprisingly, the bend with widening at the outer bank and immobile bed did not lead to a transverse expansion of the flow. Rather, flow in the outer‐bank widening weakly recirculated around a vertical axis and hardly interacted with the inner part of the bend, which behaved as a constant‐width bend. In the mobile bed experiment, downstream of the bend apex a pronounced depositional bar developed at the inside of the bend and pronounced scour occurred at the outside. Moreover the deformed bed promoted flow separation over the bar, including return currents. In the constant‐width bend, the topographic steering impeded the generation of an outer‐bank cell of secondary flow. In the bend with outer‐bank widening, the topographic steering induced an outward expansion of the flow, whereby the major part of the discharge was conveyed in the central part of the widening section. Flow in the outer‐bank widening was highly three dimensional and included return currents near the bottom. In conclusion, the experiments elucidated three distinct processes of flow separation common in sharp bends: flow separation at the inner bank, an outer‐bank cell of secondary flow, and flow separation and recirculation in an outer‐bank widening. Copyright © 2012 John Wiley & Sons, Ltd.     

Mesozoic exhumation history and palaeolandscape of the Iberian Massif in eastern Galicia from apatite fission-track and (U+Th)/He data

Apatite fission-track (AFT) and (U+Th)/He (AHe) data, combined with time–temperature inverse modelling, reveal the cooling and exhumation history of the Iberian Massif in eastern Galicia since the Mesozoic. The continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins. The data provide constraints on the 10⁷ timescale longevity of a relict paleolandscape. AFT ages range from 68 to 174 Ma with mean track lengths of 10.7 ± 2.6 to 12.6 ± 1.8 μm, and AHe ages range from 73 to 147 Ma. Fastest exhumation (≈0.25 km/Ma) occurred during the Late Jurassic to Early Cretaceous main episode of rifting in the adjacent western and northern margins. Exhumation rates have decreased since then and have been approximately one order of magnitude lower. Across inland Galicia, the AFT data are consistent with Early Cretaceous movement on post-Variscan NE trending faults. This is coeval with an extensional episode offshore. The AHe data in this region indicate less than 1.7 km of denudation in the last 100 Ma. This low exhumation suggests the attainment of a mature landscape during Late Cretaceous post-rift tectonic stability, whose remains are still preserved. The low and steady rate of denudation prevailed across inland Galicia despite minor N–S shortening in the northern margin since ≈45 Ma ago. In north Galicia, rock uplift in response to NW strike-slip faulting since Early Oligocene to Early Miocene has caused insufficient exhumation (<3 km) to remove the Mesozoic cooling signal recorded by the AFT data.     

Microbial enzymatic response to catchment‐scale variations in supply of dissolved organic carbon

A suite of exoenzyme activities was assayed in three New Zealand streams draining pasture, native forest, and a pine catchment. There were differences among catchments in activity of three of the five enzymes assayed (cello‐biohydrolase, N‐acetylglucosaminidase, and dihydroxylphenylalanine oxidation). A principal components analysis (PCA) demonstrates that patterns of enzyme activity can be used to separate the three stream types. An experimental addition of algal‐leachate, leaf‐litter leachate, and high dissolved organic carbon (DOC) water from a small seep also resulted in marked shifts in epilithic enzyme activities 1 day after DOC additions. Oxidative enzymes showed a particularly strong response to additions of humic DOC. As for the field samples, a PCA showed large differences among treatments indicating that exoenzyme patterns can be used to examine which DOC sources predominate in different streams. Application of this approach to describing differences among streams will require detailed seasonal sampling together with longer‐term experiments.     

A Robust Surface Matching Technique for Integrated Monitoring of Coastal Geohazards

At the dynamic coastal fringe, numerous processes interact with local morphology. In soft-cliff environments, this can often lead to the occurrence of coastal geohazards. These can pose a major threat to property and cultural heritage, and an effective monitoring strategy is therefore essential. While contemporary monitoring techniques have been applied, these are often unsuitable in isolation. This paper presents an integrated approach, with the development of weighted surface matching software enabling reliable dataset fusion and multi-temporal change detection, even where significant surface differences exist. Evaluation of this approach is presented and discussed.