Trenching studies of active faults in Kamchatka, eastern Russia: Palaeoseismic, tectonic and hazard implications

The central part of the Kamchatka Peninsula is characterized by a well defined depression associated with active volcanism, aligned NE–SW. On the east, the depression is bounded by a prominent system of active faults known as the East Kamchatka Fault Zone (EKFZ). In order to improve understanding of the behaviour and kinematic role of this fault zone a fieldwork programme, including study of trenches, was conducted in the north-central part of this system. Aerial photograph analysis, ground-truthed, indicates a westward fault dip with predominantly normal slip, while lateral offsets of river terraces and stream channels demonstrate a combined dextral component. Over 20 excavated pits and natural exposures were examined to confirm a detailed tephra succession extending from the early Holocene to recent historic eruptions. This chronological framework then provided age control on five past faulting events recognised in three trenches. These events took place at about 10.5, 6.0, 4.5 and, in a two-event succession within a short time span, at 3.3–3.2 ka BP. Event clustering may be characteristic and fault length–displacement values suggest earthquakes of M6.5, thus representing a significant new element in regional seismic hazard evaluations; additional to events generated at the subduction interface. The relatively long gap in faulting since the two most recent events may also be significant for hazard scenarios and there is a possible link between the faulting and volcanic activity in the depression. Overall, the EKFZ, together with the Nachiki Transverse Zone farther south, is thought to define a regional-scale block that is extending eastwards independently from the rest of Kamchatka.     

A novel triggerless approach for mass wasting susceptibility modeling applied to the Boston Mountains of Arkansas,USA

This research deploys a novel mass wasting susceptibility modeling approach for cases where temporal information is unavailable and circumstances are prejudiced to merit applying traditional susceptibility modeling strategies. Conventional models typically employ approaches deemed problematic for this study, e.g., biased weighted input; a “more is better” approach pertaining to voluminous inputs; neglecting geologic structural influence; and establishing temporal linkages between cause (trigger) and effect (failure) with a trigger being defined as a catalyst for failure, such as timed events like earthquakes or precipitation as well as physical changes like vegetation removal or slope disturbance. Road bias may also influence modeling dramatically when event data are derived from observations of road-related failures, which become unreliable at predicting susceptibility in regions with no roads. However, a triggerless approach can extrapolate naturally occurring susceptibility via priori knowledge of local topography and structural geology factors. Two models are then created for comparison: One model has integrated empirical Bayesian kriging and fuzzy logic considering basically local topography and structural geology, while the second model has employed a standard implementation of a weighted overlay using all available (8) input data layers. Statistical comparisons show that the first model has identified ~ 83%, compared to only ~ 28% for the latter model, of the 47 documented mass wasting events in the selected study site. These results demonstrate that the introduced triggerless approach is efficiently capable of modeling mass wasting susceptibility in areas lacking temporal datasets, which in turn can help in mitigating future geohazards.     

Persistence of clear-water,shallow-lake ecosystems: the role of protected areas and stable aquatic food webs

The roles of both landscape alteration and in-lake processes need to be considered in conservation strategies for shallow lakes in the prairie regions of North America. Here we focus on shallow lakes in west-central Minnesota, USA, highlighting the long-term ecological history and response to known landscape changes of a clear-water, macrophyte-dominated, shallow lake. Contemporary limnological data suggest the aquatic ecosystem has been very stable and fishless for the last ~15 years. Sediment proxies for primary production and ecological change confirm that a stable ecosystem likely prevailed for the last ~200 years. However, sedimentary indicators of catchment erosion detail a distinct response to land-use change during the conversion of native grassland to agricultural land, and following establishment of a protected waterfowl production area (WPA) around the lake. Post-WPA, the rate of sediment accrual decreased dramatically within 5–10 years and sources of organic matter were similar to those of the pre-settlement period. The aquatic ecosystem has been able to withstand nutrient enrichment and allochthonous inputs because stable trophic interactions have likely been in place for more than 200 years. We conclude that lack of hydrologic connectivity and isolated, small catchments are important factors in the promotion of clear-water shallow lake ecosystems, mainly because they prevent colonization by fish and associated ecological consequences. This study highlights the importance of managing both the landscape and in-lake processes to maintain stable, clear-water, shallow lakes.     

Are burnt sediments reliable recorders of geomagnetic field strength?

This study tests if burnt soils and sediments can provide reliable records of geomagnetic field strength at the time of burning by carrying out an experiment to reproduce the prehistoric use of fire on a clayish soil substratum. Rock magnetic experiments showed that in the upper 0–1 cm of the central part of the burnt surface, remanence is a thermoremanent magnetization carried by single-domain magnetite and that samples are thermally stable. Fourteen specimens from that area were subjected to paleointensity experiments with the Coe method (1967). An intensity of 42.9 ± 5.7 μT was estimated below 440°C, whereas at higher temperatures magneto-mineralogical alterations were observed. Corresponding successful microwave intensity determinations from two specimens gave a mean value of 47.6 μT. Both results are in reasonable agreement with the expected field value of 45.2 μT. Burnt soils of archeological fires thus have the potential to record accurately the paleofield strength and may be useful targets for archeointensity investigations. Coincident results obtained from two different paleointensity determination methods support this conclusion.     

Drones as tools for monitoring beach topography changes in the Ligurian Sea (NW Mediterranean)

The aim of this study was to evaluate topographic changes along a stretch of coastline in the Municipality of Borghetto Santo Spirito (Region of Liguria, Italy, north-western Mediterranean) by means of a remotely piloted aircraft system coupled with structure from motion and multi-view stereo techniques. This sector was surveyed three times over 5 months in the fall–winter of 2013–2014 (1 November 2013, 4 December 2013, 17 March 2014) to obtain digital elevation models and orthophotos of the beach. Changes in beach topography associated with storm action and human activities were assessed in terms of gain/loss of sediments and shifting of the wet–dry boundary defining the shoreline. Between the first and second surveys, the study area was hit by two storms (10–11 November 2013 and 21–22 November 2013) with waves approaching from the E–NNE, causing a shoreline retreat which, in some sectors, reached 7 m. Between the second and third surveys, by contrast, four storms (25–27 December 2013, 5–6 January 2014, 17–18 January 2014 and 6–10 February 2014) with waves propagating from the SE produced a general advancement of the shoreline (up to ~5 m) by deposition of sediments along some parts of the beach. The data also reflect changes in beach topography due to human activity during the 2013 fall season, when private beach managers quarried ~178 m³ of sediments on the emerged beach near the shoreline to accumulate them landwards. The results show that drones can be used for regular beach monitoring activities, and that they can provide new insights into the processes related to natural and/or human-related topographic beach changes.     

Activity budgets of New Zealand fur seals Arctocephalus forsteri during the breeding season

The activity budgets of territorial males, adult females, pups, and yearlings of the New Zealand fur seal Arctocephalus forsteri (Lesson, 1828) on Taumaka, Open Bay Islands, Westland, New Zealand (43° 52 S, 168° 53′ E) from 18 November 1974 to 30 January 1975 are described. Territorial males spent an average of 74.4% of their time lying down; 13.5% in a state of alertness; 4.8% on intrasexual and intersexual activities combined; and 7.3% on miscellaneous activities, including grooming, walking, and swimming. Equivalent figures for adult females, pups, and yearlings were: lying down (62.8%, 70.1%, and 66.6% respectively); alertness (4.9%, 2.8%, 6.8%); intrasexual and intersexual activities (1.1%, females only); miscellaneous (21%; 16%; 26.5%); female‐pup interactions (11%; 11.1%).

The activity budgets of all the seal classes changed as the breeding season progressed. Males spent more time alert early in the season when they were establishing and defending territories and procuring females. Intrasexual behaviour was prominent only in November and early December, whereas intersexual behaviour became more conspicuous during December, when females were in post‐partum oestrus. Females displayed little interest in intrasexual activity. Interactions with males ceased after copulation. Swimming was a prominent activity for females, as was suckling once pups were present. During the first few weeks of life pups mostly slept and suckled. Yearlings were present on the rookery only until 2 December, when they were rejected by females with new pups. Their predominant activity, when not lying down, was swimming (17.2%).     

Strengths and weaknesses of acoustic pipe microphone systems in ephemeral,sandy, gravel-bed rivers

We calibrated an acoustic pipe microphone system to monitor bedload flux in a sandy, gravel-bed ephemeral channel. Ours is a first attempt to test the limit of an acoustic surrogate bedload system in a channel with a high content of sand. Calibrations varied in quality; significant data subsetting was required to achieve R² values >0.75. Several data quality issues had to be addressed: (1) apparent pulses, which occur when a sensor records an impulse from sediment impacting the surrounding substrate rather than directly impacting the sensor, were frequent, especially at higher signal amplifications. (2) The impact sensors were frequently covered by gravel sheets. This prompted the development of a cover detection protocol that rejected part of the impact sensor record when at least one sensor was partially or fully covered. (3) Because of the lack of sensor sensitivity to impacts of sand-sized particles, which was anticipated, and the considerable sand component of bedload in this channel, a grain size-limited bedload flux was estimated. This was accomplished by sampling the bedload captured by slot samplers and evaluating the variation of grain size with increasing flow strength. This considerably improved the results when compared to attempts at estimating the flux of the entire distribution of grain sizes. This calibration is a successful first attempt, though the impact sensors required several site-specific calibration steps. A universal set of equations using impact sensors to estimate bedload transport of fine-gravel with a large content of sand remains elusive. Notwithstanding, our study demonstrates the utility of impact sensor data, producing relatively low root mean square errors that are independent of measurements of flow strength (i.e. discharge). These tools will be particularly useful in settings that would benefit from new methodologies for estimating bedload transport in sand-rich gravel-bed rivers, such as the American desert Southwest.     

A 3.5 ka record of paleoenvironments and human occupation at Angkor Borei,Mekong Delta,southern Cambodia

Microfossil and sedimentological data from a 3.1 m core extracted from a reservoir (baray) at the ancient Cambodian settlement of Angkor Borei in the Mekong Delta have provided a continuous record of sedimentation and paleoenvironments dating from about 2000 cal yr B.C. Palynological data indicate that for much of the cal. 1st and 2nd millennia B.C. mangroves dominated the regional vegetation, while extensively and regularly burnt grasslands dominated the local vegetation. Turbid, nutrient‐rich standing water characterized the core locality, perhaps suggesting a connection with rivers in the area. An abrupt change during the cal. 5th to 6th centuries A.D. involved a dramatic reduction in grasslands and the expansion of secondary forest or re‐growth taxa. These changes are synchronous with an abrupt decline in the concentration of microscopic charcoal particles in the sediments, and the colonization of the core locality by swamp forest plants. These changes are taken to indicate a shift in land‐use strategies or, possibly, a period of land abandonment. The age for the construction of the baray is interpreted to be in the 17th–19th centuries, but this dating remains speculative. Construction of the Angkor Borei baray exploited a preexisting body of standing water, so its construction was fundamentally different from the methods used at the Angkorian capital in northern Cambodia. © 2003 Wiley Periodicals, Inc.