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The Texas Creek rock avalanche is a prehistoric deposit in the Fraser River Canyon, 17 km south of Lillooet, southwestern British Columbia, Canada. Original mapping suggested that the debris consisted of two landslides: a 45 Mm3 event deposited after the Mazama tephra but before about 2 ka ago, and a 7.2 Mm3 event about 1.1 ka ago. The proposed timing of the younger landslide was correlated with a decline in the First Nations population and was proposed as an agent of cultural collapse driven by its impact on salmon returns vital to the population's sustenance. We provide six surface exposure ages using 10Be from boulder tops, with three samples from each surface that were originally posited to be older and younger debris. The six samples yielded similar ages suggesting the landslide deposit represents a single event with an average age of 2.28 ± 0.19 (2σ external error) ka before 1950 AD. Evidently, the landslide played no role in the cultural collapse. Fraser River Holocene incision rates, estimated pre- and post-landslide are between 13 and 24 mm/yr, consistent with previous estimates for the mid-Fraser River region. Landslide timing is coincident with the explosive eruption of Mount Meager, 120 km to the northwest, and with a possible landslide at Mystery Creek 85 km to the west and 65 km south of Mount Meager. The landslide may have been seismically triggered, but attribution is speculative. [ABSTRACT FROM AUTHOR]

The moose Alces alces is the largest herbivore in the boreal forest biome, where it can have dramatic impacts on ecosystem structure and dynamics. Despite the importance of the boreal forest biome in global carbon cycling, the impacts of moose have only been studied in disparate regional exclosure experiments, leading to calls for common analyses across a biome‐wide network of moose exclosures.In this study, we use airborne laser scanning (ALS) to analyse forest canopy responses to moose across 100 paired exclosure‐control experimental plots distributed across the boreal biome, including sites in the United States (Isle Royale), Canada (Quebec, Newfoundland), Norway, Sweden and Finland.We test the hypotheses that canopy height, vertical complexity and above‐ground biomass (AGB) are all reduced by moose and that the impacts vary with moose density, productivity, temperature and pulse disturbances such as logging and insect outbreaks.We find a surprising convergence in forest canopy response to moose. Moose had negative impacts on canopy height, complexity and AGB as expected. The responses of canopy complexity and AGB were consistent across regions and did not vary along environmental gradients. The difference in canopy height between exclosures and open plots was on average 6 cm per year since the start of exclosure treatment (±2.1 SD). This rate increased with temperature, but only when moose density was high.The difference in AGB between moose exclosures and open plots was 0.306 Mg ha−1 year−1 (±0.079). In browsed plots, stand AGB was 32% of that in the exclosures, a difference of 2.09 Mg ha−1. The uniform response allows scaling of the estimate to a biome‐wide impact of moose of the loss of 448 (±115) Tg per year, or 224 Tg of carbon.Synthesis: Analysis of ALS data from distributed exclosure experiments identified a largely uniform response of forest canopies to moose across regions, facilitating scaling of moose impacts across the whole biome. This is an important step towards incorporating the effect of the largest boreal herbivore on the carbon cycling of one of the world's largest terrestrial biomes. [ABSTRACT FROM AUTHOR]

Indoor concentrations of radon gas more than Health Canada guidelines have been reported throughout the Whitehorse area, yet only cursory measurements have been made to determine the concentration of radon [...]

The timing and dynamics of deglaciation of the Newfoundland Ice Sheet (NIS) represents a complex and poorly resolved portion of the North American Ice Sheet Complex. Establishing the flow dynamics [...]

Deglaciation of the northwestern Laurentide Ice Sheet in the central Mackenzie Valley opened the northern portion of the deglacial Ice-Free Corridor between the Laurentide and Cordilleran ice sheets and a drainage route to the Arctic Ocean. In addition, ice sheet saddle collapse in this section of the Laurentide Ice Sheet has been implicated as a mechanism for delivering substantial freshwater influx into the Arctic Ocean on centennial timescales. However, there is little empirical data to constrain the deglaciation chronology in the central Mackenzie Valley where the northern slopes of the ice saddle were located. Here, we present 30 new 10 Be cosmogenic nuclide exposure dates across six sites, including two elevation transects, which constrain the timing and rate of thinning and retreat of the Laurentide Ice Sheet in the area. Our new 10 Be dates indicate that the initial deglaciation of the eastern summits of the central Mackenzie Mountains began at ∼15.8 ka (17.1–14.6 ka), ∼1000 years earlier than in previous reconstructions. The main phase of ice saddle collapse occurred between ∼14.9 and 13.6 ka, consistent with numerical modelling simulations, placing this event within the Bølling–Allerød interval (14.6–12.9 ka). Our new dates require a revision of ice margin retreat dynamics, with ice retreating more easterly rather than southward along the Mackenzie Valley. In addition, we quantify a total sea level rise contribution from the Cordilleran–Laurentide ice saddle region of ∼11.2 m between 16 and 13 ka. [ABSTRACT FROM AUTHOR]

New geologic map, tectonic, geomorphologic, and terrestrial cosmogenic nuclide (TCN) geochronologic data document the geometry, style, kinematics, and slip rates on late Quaternary faults within the Queen Valley, California-Nevada area. These data provide important insight into the kinematics of fault-slip transfer from the dextral White Mountains fault zone northward into the Mina deflection. Queen Valley is an ~16-km-long, NE-trending basin bounded to the south by the White Mountains and underlain by four major Pleistocene to Holocene alluvial-fan surfaces. Four different fault types and orientations cut and offset all but the youngest surfaces: (1) The normal-slip Queen Valley fault, which consists of a set of NE-striking, NW- and SE-dipping normal fault scarps that cut across the SE side of the valley and offset all but the youngest surfaces; (2) discontinuons NE-striking, sinistral faults exposed on the north side of the valley; (3) the NW-striking dextral Coyote Springs fault, which merges into (4) a set of E-W--striking thrust faults. Measured offsets across normal fault scarps developed within [sup.10]Be TCN-dated surfaces yield minimum late Pleistocene horizontal extension rates of 0.1-0.3 mm/yr. Documented fault geometries and slip orientations across Queen Valley suggest that fault-slip transfer models, such as the extensional displacement transfer, block rotation, and simple shear models, within the dextral fault system proposed for the eastern California shear zone--Walker Lane belt are not applicable to this part of the Mina deflection. Rather, dextral fault slip is transferred by both a restraining westward step and a releasing eastward step. Restraining and releasing bends have been extensively documented at a range of scales in strike-slip fault tectonic settings globally, and they have been simulated in analog models; thus, it is not surprising to document both within the ~630-km-long dextral shear zone that makes up the northern eastern California shear zone--Walker Lane belt. Our results, combined with published slip rates for the dextral White Mountain fault zone and the eastern sinistral Coaldale fault, suggest that transfer of dextral slip into the Mina deflection is partitioned into three different components: horizontal extension along the Queen Valley fault, thrust faulting that merges into the dominantly dextral slip along the Coyote Springs fault, and dominantly sinistral slip along the Coaldale fault. A velocity vector diagram of fault-slip partitioning across Queen Valley predicts a small component of contraction across the Coyote Springs and western Coaldale faults. Contraction across the Mina deflection is consistent with global positioning system data. An observed reduction in late Pleistocene fault-slip rates at the northern end of the eastern California shear zone and across the southwestern part of the Mina deflection may be explained by distribution of slip across a much broader zone than generally thought. Keywords: normal faults, strike-slip faults, thrust faults, terrestrial cosmogenic nuclide geochronology, fault-slip transfer, Walker Lane belt, Eastern California shear zone.

Abstract: Controversy persists in western Newfoundland regarding Pleistocene, particularly Late Wisconsinan, glacial ice volumes. Independently, a set of alpine glacial deposits on the flanks of the Tablelands in Gros Morne [...]

Abstract: Light detection and ranging (LIDAR) is an emerging technology to generate high-resolution digital elevation models (DEMs). Subtle topographical differences among three flow units of the Jurassic North Mountain Basalt, [...]

We assessed annual home-range area for 23 adult, resident American martens (Martes americana atrata) in a low-density population in eastern Newfoundland, Canada (1996-2003), and evaluated seasonal habitat requirements during a peak in abundance of snowshoe hares (Lepus americanus). Home-range estimates were 29.54 [km.sup.2] and 15.19 [km.sup.2] for males and females, respectively, and reflect significantly larger territories than those maintained by martens across most of their geographic range. We suggest that these exceptionally large territories reflect the low diversity and abundance of small mammals available to martens as prey. Seasonal requirements were examined by using an index to home-range area. The relationship between the index and snowshoe hare abundance indicated that movement rates of individuals decreased during winters when snowshoe hares were abundant, but that this relationship was not apparent during summer. Analyses of stand-scale habitat use indicated that mature coniferous forest was the dominant cover type in most home ranges (49.6% of area) and was the only forest type used proportionately more than its availability by resident martens. Other forest types used in proportion to their availability included coniferous scrub and insect-defoliated stands. Open areas and sites recently disturbed by fire were avoided at this scale. Key words: American marten, habitat use, home range, Martes americana, Newfoundland, prey abundance

Reliable chronology of sediment landforms is required to establish rates for a wide range of pedogenic and geologic processes. Cosmogenic nuclide depth profile exposure dating provides a useful means of [...]

Glacial erosion exerts a dominant control on the earth's terrestrial landscape. Through the excavation of material, glacial erosion plays a fundamental role in mountain range exhumation, isostatic processes, and biogeochemical [...]

The late Miocene and Pliocene Beaufort Formation and equivalent units throughout the Canadian Arctic Archipelago captured a rich record of landscape evolution, Arctic paleoclimatology, and paleo-ecosystem changes caused by a [...]

Deglaciation of the northwestern Laurentide Ice Sheet in the central Mackenzie Valley opened the northern portion of the deglacial Ice-Free Corridor between the Laurentide and Cordilleran ice sheets and a drainage route to the Arctic Ocean. In addition, ice-sheet saddle collapse in this section of the Laurentide Ice Sheet has been implicated as a mechanism for delivering substantial freshwater influx into the Arctic Ocean on centennial timescales. However, there is little empirical data to constrain the deglaciation chronology in the central Mackenzie Valley where the northern slopes of the ice saddle were located. Here, we present 30 new 10Be cosmogenic nuclide exposure dates across six sites, including two elevation transects, which constrain the timing and rate of thinning of the Laurentide Ice Sheet from the area. Our new 10Be dates indicate that the initial deglaciation of the eastern summits of the central Mackenzie Mountains began at ~15.8 ka (17.1 - 14.6 ka), ~1,000 years earlier than previous reconstructions. The main phase of ice-saddle collapse occurred between ~14.9 and 13.2 ka, consistent with numerical modelling simulations, placing this event within the Bølling-Allerød interval (14.6 - 12.9 ka). Our new dates require a revision of ice margin retreat dynamics, with ice retreating more easterly rather than southward along the Mackenzie Valley. In addition, we quantify a total sea level rise contribution from the Cordilleran-Laurentide ice saddle region of ~11.2 m between 16 ka and 13 ka. [ABSTRACT FROM AUTHOR]

We measured cosmogenic 36Cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the Wind River Range, Wyoming. We also measured 10Be in 10 of the same samples. Most of the 10Be ages were in good agreement with the 36Cl ages, indicating that rock-surface erosion rates were very low. The oldest moraine investigated, the type Sacagewea Ridge site, yielded only a limiting minimum age of >232 ka. The oldest moraines in the type Bull Lake complex also could be constrained only to >130 ka. The main sequence of type Bull Lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka; the best estimates are closer to the upper limits of these ranges, and associated uncertainties are in the range of 10% to 15%. These uncertainties could permit deposition in either marine isotope stage 6 or stage 5d. We found no evidence of glacial deposits dating to marine isotope stage 4. Both Bull Lake-age moraines from Fremont Lake. on the opposite side of the Wind River Range, and boulders on a fluvial terrace above the Wind River, gave age distributions very similar to that of the second oldest Bull Lake advance (ca. 130 to 100 ka). The distribution of boulder ages for Pinedale moraines at Bull Lake indicated deposition between 23 and 16 ka, nearly identical to the distribution of 10Be ages previously reported for the type Pinedale moraines at Fremont Lake.

The Foothills Erratics Train consists of large quartzite blocks of Rocky Mountains origin deposited on the eastern slopes of the Rocky Mountain Foothills in Alberta between ~53.5°N and 49°N. The blocks were deposited in their present locations when the western margin of the Laurentide Ice Sheet (LIS) detached from the local ice masses of the Rocky Mountains, which initiated the opening of the southern end of the ice-free corridor between the Cordilleran Ice Sheet and the LIS. We use 10Be exposure dating to constrain the beginning of this decoupling. Based on a group of 12 samples well-clustered in time, we date the detachment of the western LIS margin from the Rocky Mountain front to ~14.9 ± 0.9 ka. This is ~1000 years later than previously assumed, but a lack of a latitudinal trend in the ages over a distance of ~500 km is consistent with the rapid opening of a long wedge of unglaciated terrain portrayed in existing ice-retreat reconstructions. A later separation of the western LIS margin from the mountain front implies higher ice margin–retreat rates in order to meet the Younger Dryas ice margin position near the boundary of the Canadian Shield ~2000 years later. [ABSTRACT FROM AUTHOR]

Terrestrial cosmogenic nuclide (TCN) exposure dating of boulders is frequently used for rockslide chronology. A well-recognized source of error that cannot be readily quantified is related to inheritance of TCN produced in the rock prior to failure. The effect of inheritance is not constant and will be greatest in the instance of a very recent shallow failure on a high-altitude surface with low event frequencies. We illustrate the effect by measuring 10Be concentrations in six boulders exposed for only 9 years before sampling, on a rock avalanche in Puerto Aysén, Chile. Their apparent exposure ages range from 216 ± 76 to 1755 ± 436 years. The mean apparent exposure age of a statistical cluster of three samples exceeds the real exposure time by 345 ± 36 years (3800%), implying that all sampled rock surfaces experienced pre-failure TCN production. A reconstructed pre-failure topography enables the analysis of possible pre-failure boulder positions and an estimate of the range of possible inherited concentrations along a 2D transect. Despite a maximum failure-mass thickness of 110 m, the boulders seem to have originated from depths shallower than 14 m. Because of the likelihood that large boulders, prioritized for TCN sampling, originate from relatively shallow pre-failure depths owing to surface-near transport with minor turbation, it is necessary to consider potentially inherited TCN concentrations and their effect on the age determination, especially in cases of young rockslides, where the commonly adjusted effects of boulder erosion and snow, ash, or vegetation shielding are negligible in comparison. [ABSTRACT FROM AUTHOR]

The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO2 concentrations because atmospheric CO2 concentrations are thought to have been comparable to the current day and yet the climate and distribution of ecosystems were quite different. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified Arctic temperature response and its impact on Arctic ecosystems. Only the most recent models appear to correctly estimate the degree of warming in the Pliocene Arctic and validation of the currently proposed feedbacks is limited by scarce terrestrial records of climate and environment. Here we reconstruct the summer temperature and fire regime from a subfossil fen-peat deposit on west–central Ellesmere Island, Canada, that has been chronologically constrained using cosmogenic nuclide burial dating to 3.9+1.5/-0.5 Ma. The estimate for average mean summer temperature is 15.4±0.8 ∘ C using specific bacterial membrane lipids, i.e., branched glycerol dialkyl glycerol tetraethers. This is above the proposed threshold that predicts a substantial increase in wildfire in the modern high latitudes. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that included an increase in abundance of fire-promoting Pinus and Picea. Paleo-vegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire-adapted boreal forests of North America and central Siberia. To our knowledge, this site provides the northernmost evidence of fire during the Pliocene. It suggests that ecosystem productivity was greater than in the present day, providing fuel for wildfires, and that the climate was conducive to the ignition of fire during this period. The results reveal that interactions between paleo-vegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO2 concentrations were similar to modern values. [ABSTRACT FROM AUTHOR]

Oversteepened valley walls in western Norway have high recurrences of Holocene rock-slope failure activity causing significant risk to communities and infrastructure. Deposits from six to nine catastrophic rock-slope failure (CRSF) events are preserved at the base of the Mannen rock-slope instability in the Romsdal Valley, western Norway. The timing of these CRSF events was determined by terrestrial cosmogenic nuclide dating and relative chronology due to mapping Quaternary deposits. The stratigraphical chronology indicates that three of the CRSF events occurred between 12 and 10 ka, during regional deglaciation. Congruent with previous investigations, these events are attributed to the debuttressing effect experienced by steep slopes following deglaciation, during a period of paraglacial relaxation. The remaining three to six CRSF events cluster at 4.9 ± 0.6 ka (based on 10 cosmogenic 10Be samples from boulders). CRSF events during this later period are ascribed to climatic changes at the end of the Holocene thermal optimum, including increased precipitation rates, high air temperatures and the associated degradation of permafrost in rock-slope faces. Geomorphological mapping and sedimentological analyses further permit the contextualisation of these deposits within the overall sequence of post-glacial fjord-valley infilling. In the light of contemporary climate change, the relationship between CRSF frequency, precipitation, air temperature and permafrost degradation may be of interest to others working or operating in comparable settings. [ABSTRACT FROM AUTHOR]