Eruptive styles and inferences about plumbing systems at Hidden Cone and Little Black Peak scoria cone volcanoes (Nevada,U.S.A.)

We describe two small scoria cone volcanoes, Hidden Cone and Little Black Peak (ages between ~320–390 ka), in the Southwestern Nevada Volcanic Field and discuss their eruption mechanisms and inferences about their plumbing systems. Cone-forming pyroclastic deposits are consistent with eruptive styles ranging from Strombolian to violent Strombolian, and lavas emanated from near the bases of the cones. The volcanoes are monogenetic (rather than polycyclic, as allowed by previous geomorphic interpretations). Vents at each volcano appear to coincide with pre-existing normal faults, consistent with observations at older, deeply eroded volcanoes in the region. The existence of these two volcanoes on a topographically high area (particularly Hidden Cone) provides evidence for short feeder dike lengths (~500 m at the surface). We infer that this short length reflects the small length scale of the mantle source region that was tapped to feed each volcano. Editorial responsibility: J Stix     

Numerical simulation of the summer wake of Rottnest Island, Western Australia

During the summer, a northward, wind-driven current dominates the Rottnest Island region in southwestern Australia. Field studies have shown that the interaction between Rottnest Island and the northward current generates upwelling at the western end of the island, which is advected downstream, resulting in isotherm doming in the wake region. Flow curvature-induced secondary circulation has been proposed as the dominant mechanism responsible for this upwelling. Here, a three-dimensional numerical model, together with field observations, was used to undertake a detailed investigation of the three-dimensional flow structure in the wake region. Comparison of the observed upwelling pattern and the simulated flows revealed the island's dominant role in generating upwelling. This result was confirmed with the use of idealized numerical experiments. The modeling results confirmed the presence of secondary circulation, generated as a result of flow curvature at the western end of the island, which caused strong upwelling and extended downstream.     

Errors and uncertainty in physically-based rainfall-runoff modelling of catchment change effects

The error in physically-based rainfall-runoff modelling is broken into components, and these components are assigned to three groups: (1) model structure error, associated with the model’s equations; (2) parameter error, associated with the parameter values used in the equations; and (3) run time error, associated with rainfall and other forcing data. The error components all contribute to “integrated” errors, such as the difference between simulated and observed runoff, but their individual contributions cannot usually be isolated because the modelling process is complex and there is a lack of knowledge about the catchment and its hydrological responses. A simple model of the Slapton Wood Catchment is developed within a theoretical framework in which the catchment and its responses are assumed to be known perfectly. This makes it possible to analyse the contributions of the error components when predicting the effects of a physical change in the catchment. The standard approach to predicting change effects involves: (1) running “unchanged” simulations using current parameter sets; (2) making adjustments to the sets to allow for physical change; and (3) running “changed” simulations. Calibration or uncertainty-handling methods such as GLUE are used to obtain the current sets based on forcing and runoff data for a calibration period, by minimising or creating statistical bounds for the “integrated” errors in simulations of runoff. It is shown that current parameter sets derived in this fashion are unreliable for predicting change effects, because of model structure error and its interaction with parameter error, so caution is needed if the standard approach is to be used when making management decisions about change in catchments.     

Cracking up: faulting on Earth and Mars

Joyce Vetterlein and Gerald P Roberts describe research in progress on the structural evolution of Cerberus Fossae, Mars, with implications for cryosphere cracking in recent Mars history.     

Telegraph Messenger Boys: Crossing the Borders between History of Technology and Human Geography*

Historians of telegraphy have traditionally focused on the system‐builders who invented wire communications technologies and incorporated them into profit‐making enterprises. Geographers of communications have traditionally traced the changes that the telegraph network wrought on the rank‐size of cities and the speed of business. Both have ignored the history of the telegraph messenger boys and the “lived geography” of the telegraph network. This article summarizes a study of telegraph messengers as both active components of technological systems and laboring agents within produced urban spaces, bringing together the fields of both history of technology and human geography.     

Proximal stratigraphy and syn-eruptive faulting in rhyolitic Grants Ridge Tuff, New Mexico, USA

Proximal deposits of the 3.3 Ma Grants Ridge Tuff, part of a 5-km³ topaz rhyolite sequence, are composed of basal pyroclastic flow, surge, and fallout deposits, a thick central ignimbrite, and upper surge and fallout deposits. Large lithic blocks (≤2 m) of underlying sedimentary and granitic bedrock that are present in lower pyroclastic flow and fallout deposits indicate that the eruptive sequence began with explosive, conduit-excavating eruptions. The massive, nonwelded central ignimbrite displays evidence for postemplacement deformation. The upper pyroclastic surge deposits are dominated by fine ash, some beds containing accretionary lapilli, soft-sediment deformation features, and mud-coated lithic lapilli, indicating an explosive, hydromagmatic component to these later eruptions. The upper fall and surge deposits are overlain by fluvially reworked volcaniclastic deposits that truncate the primary section with a relatively planar surface. The proximal, upper pyroclastic surge and Plinian fall deposits are preserved only in small grabens (5–8 m deep and wide), where they subsided into the ignimbrite and were protected from reworking. The pyroclastic surge and fall deposits within the grabens are offset by numerous small normal faults. The offset on some faults decreases upward through the section, indicating that the faulting process may have been syn-eruptive. Several graben-bounding faults extend downward into the ignimbrite, but the uppermost, fluvially reworked tephra layers are not cut by these faults. The faulting mechanism may have been related to settling and compaction of the 60 m thick, valley-filling ignimbrite along the axis of the paleovalley. Draping surge contacts against the graben faults and brittle and soft-style disruption of the upper pyroclastic surge beds indicate that subsidence was ongoing during the emplacement of the upper eruptive sequence. Seismicity accompanying the late-stage hydromagmatic explosions may have contributed to the abrupt settling and compaction of the ignimbrite.     

Segment boundaries, the 1894 ruptures and strain patterns along the Atalanti Fault, Central Greece

The Atalanti Fault is a large active normal fault segment inside the Gulf of Evia Rift system (Central Greece), that last ruptured during the April 1894 earthquake sequence. Using structural and geomorphological interpretations of digitally processed Landsat TM satellite imagery, two regions of i) low topography, ii) minimum hinterland development and iii) transverse bedrock ridge development, 34 kilometres apart were identified; these regions are suggested to be segment boundaries constraining the length of the fault. From throw profiles and displaced syn-rift strata, we estimate a minimum slip of 810m at the central region of the fault (Tragana), increasing to a value of 1200 meters within the Asprorema embayment area. These figures averaged over a time span of 3 million years (age of oldest offset syn-rift), yield mean slip rates of at least 0.27 to 0.4 mm/year.Field studies were also conducted along the length of the Atalanti Fault Segment to reexamine and map the 1894 ruptures. The surface break is only preserved locally where the footwall comprises a resistant bedrock lithology (limestone), whilst the rest of the rupture noted in historical records propagated along the contact with the volcanic pre-rift, as well as within the syn-rift, and has since been eradicated due to man-made changes in surface morphology. The surface breaks appear not to have crossed over the segment boundaries that we propose, but seem to have ruptured the full length of the Atalanti Fault Segment, that is, 34km. These observations suggest that the 1894 rupture is the longest mapped within Central Greece. However, it remains unclear whether the ruptures were produced solely by the 27/4/1894 earthquake, or by two events, one week apart. We discuss the implications for fault-behavioural models and seismic hazards for the Atalanti area.     

Optical dating of Holocene sediments from a variety of geomorphic settings using single grains of quartz

This paper presents an improved method for the optical dating of Holocene sediments from a variety of geomorphic settings. We have measured the equivalent dose (D_e) in individual grains of quartz, using green laser light for optical stimulation, and have simulated the D_e distributions for multiple-grain ‘synthetic’ aliquots using the single-grain data. For 12 samples of known (independent) age, we show that application of a ‘minimum age model’ to the single-grain and ‘small’ (10-grain) aliquot D_e data provides the most accurate estimate of the burial dose for nine of the samples examined (3 aeolian, 5 fluvial, and 1 marine). The weighted mean D_e (as obtained using the ‘central age model’) gives rise to burial age overestimates of up to a factor of 10 for these nine samples, whether single grains, small aliquots, or ‘large’ (100-grain) aliquots are used. For the other three samples (two aeolian and one fluvial), application of either the minimum age model or the central age model to the single-grain, small aliquot, and large aliquot D_e data yields burial ages in accord with the independent age control. We infer that these three samples were well bleached at the time of deposition. These results show that heterogeneous bleaching of the optical dating signal is commonplace in nature, and that aeolian transport offers no guarantee that the sample will be well bleached at the time of deposition. We also show that grains sensitive to infrared (IR) stimulation can give rise to low D_e values, which will result in significant underestimation of the burial dose and, hence, of the age of deposition. We demonstrate that use of a modified single-aliquot regenerative-dose protocol incorporating IR stimulation prior to green light stimulation deals effectively with contamination by IR-sensitive grains. We conclude that application of the modified protocol to single grains or small aliquots of quartz, using the lowest D_e population to estimate the burial dose, is the best means of obtaining reliable ages for Holocene sediments from a wide range of depositional environments.     

Wealth from waste: local and regional economic development and the environment

Sustainable economic development strategies promote mutually-beneficial environmental, social and economic progress. Such strategies now form an essential basis for local and regional development. Various models of sustainable economic and environmental industry development have been introduced in recent years, some of which have proved to be of particular value. The theory and practice of sustainable economic development has made rapid progress, and this approach to local and regional development is now generally accepted as offering the opportunity to solve a range of environmental and economic problems and to promote new economic activities that can generate jobs in socially excluded communities.