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.     

Interruptions of the ancient Shu Civilization: triggered by climate change or natural disaster?

Environmental proxies of a stable carbon isotope, total organic carbon, free iron oxide, and particle size distribution in sediments as well as the stable carbon and oxygen isotopes in fossil human and animal teeth were used to reconstruct the history of climate change and natural disasters near the Jinsha Relic Site and to track their effect on the ancient Shu Civilization, which was established in the Chengdu Plain of southwest China during the late Holocene. In general, the late Holocene climate in the Chengdu Plain demonstrated a drying and cooling trend, with evident cooler events ~4100 and ~2700 a BP, which coincided with global climate changes. The ancient Shu Civilization was interrupted twice, and it included three stages—the Baodun (4700–3700 a BP), the Sanxingdui (3700–3150 a BP), and the Shi’erqiao (3150–2600 a BP)—that were slightly related to the abrupt climate changes that resulted from the collapse of the classic Sanxingdui Civilization, which was founded in a regional warm period. The abrupt increase in sand content in the sediment from the Jinsha Site coincided with the palaeoearthquake and palaeodam burst in the Longmen Mountains when the Baodun and Shi’erqiao desisted, indicating that a flood had occurred due to a dam burst and may likely have caused the ancient civilization’s destruction. Although the warm and humid climate, flat terrain and rich water resources prompted the prosperity of the ancient towns of Sanxingdui and Jinsha, frequent natural disasters, such as powerful earthquakes, landslide dams, and outburst floods, consistently affected the ancient Shu inhabitants.     

Intrinsic bioremediation of a petroleum-impacted wetland

Following the 1994 San Jacinto River flood and oil spill in southeast Texas, a petroleum-contaminated wetland was reserved for a long-term research program to evaluate bioremediation as a viable spill response tool. The first phase of this program, presented in this paper, evaluated the intrinsic biodegradation of petroleum in the contaminated wetland. Sediment samples from six test plots were collected 11 times over an 11-month period to assess the temporal and spatial petroleum concentrations. Petroleum concentrations were evaluated using gas chromatography-mass spectrometer analyses of specific target compounds normalized to the conservative biological marker, C(30)17alpha,21beta(H)-hopane. The analyses of specific target compounds were able to characterize that significant petroleum biodegradation had occurred at the site over the one-year period. Total resolved saturate and total resolved aromatic hydrocarbon data indicated the petroleum was degraded more than 95%. In addition, first-order biodegradation rate constants were calculated for the hopane-normalized target compounds and supported expected biodegradation patterns. The rapid degradation rates of the petroleum hydrocarbons are attributed to conditions favorable to biodegradation. Elevated nutrient levels from the flood deposition and the unconsolidated nature of the freshly deposited sediment possibly provided a nutrient rich, oxic environment. Additionally, it is suggested that an active and capable microbial community was present due to prior exposure to petroleum. These factors provided an environment conducive for the rapid bioremediation of the petroleum in the contaminated wetland.     

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.     

On the age of the Hoxnian interglacial

Fifteen new radiocarbon datings from British Pleistocene deposits are described. The datings are related to the classic Pleistocene succession and shown to be consistent with the stratigraphic sequence of East Anglia. On the basis of these datings, an absolute chronology is developed. According to this chronology, the glacial drifts of East Anglia ought to postdate 40,000 B.P. and hence belong to the Last Glaciation of the British Isles. The Hoxnian interglacial of this chronology is dated between about 25,500-21,000 B.P. The conventional age for the Hoxnian interglacial is 175,000–120,000 B.P. The validity of the radiocarbon datings is considered and some of the implications and problems of a revised age for the Hoxnian interglacial are reviewed.