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Debate about relations between rates of fluvial incision and time (the "Sadler effect") continues, impeding the use of incision rates to infer tectonic and climatic processes. There is a dearth of detailed field evidence that can be used to explore the coupling between tectonics and climate in controlling alluvial channel geometry and incision rates over time scales of 102-105 yr. We present field data from the Rumei watershed of southeast Tibet, which we obtained by mapping and dating late Pleistocene (ca. 135 ka) fluvial terraces and related channels, measuring channel hydraulic geometry, and calculating channel steepness indexes and incision rates. The evidence indicates that climate forcing is the main driver of sediment production and delivery to streams in the watershed. New aggradation events altered alluvial valley and channel geometry and, coupled with tectonic uplift, affected the rate of channel incision in the catchment. We propose a conceptual model ... that links upliftdriven incision (II) to channel aggradation induced by climate change, which is valid in catchments and other areas. We conclude that the reduction in incision depth caused by climate-driven channel aggradation is significant on short time scales (10²-105 yr), and its cumulative effect contributes to the "Sadler effect" on long time scales (>106 yr). [ABSTRACT FROM AUTHOR]

A sedimentary exposure near the mouth of Serpentine River, about 25 km southeast of Vancouver, British Columbia, records evidence of a large earthquake that happened about 2000 years ago. The evidence includes sand dykes injected into late Holocene peat and mud. Vegetation changes based on pollen analysis and radiocarbon-dated wood match sedimentary changes at the Serpentine Fen site. A shift from herbaceous to woody peat is matched by a dramatic peak (∼ 45%) in pollen of Myrica shrubs, indicating uplift and a vegetation shift to drier shrubland from fen, also incorporating detrital spruce wood (Picea). At the top of the woody peat, Myrica pollen disappears and intertidal mud with Triglochin -type pollen increases, indicating subsidence and establishment of an intertidal environment. The section above the woody peat shows increasing amounts of halophyte pollen, especially Chenopodiaceae (or Amaranthaceae) which reaches values up to 60%, and scattered dinoflagellate cysts, indicative of a continued tidal influence. The combined evidence of uplift and subsidence over a short interval is rare at most sites in south-coastal British Columbia. • A new pollen diagram that records rapid vegetation changes linked to a paleoseismic event around 2000 years ago. Changes from marsh to shrubland with Myrica is followed by evidence of rapid submergence and increased halophyte vegetation. [ABSTRACT FROM AUTHOR]

Mount Meager is a deeply eroded quaternary volcanic complex located in southwestern British Columbia (BC) and is known for its frequent large landslides. In 2010, the south face of Mount Meager collapsed, generating a long-runout debris avalanche that was one of the largest landslides (50 × 106 m3) in Canadian history. Over the past 14 years, the landslide deposit has been reworked by stream action, delivering large amounts of sediment to Lillooet River, just downstream. In this study, we investigate 10 years of geomorphic evolution of the landslide deposit using orthophotos and digital elevation models (DEMs) generated using Structure from Motion (SfM) photogrammetry on aerial photographs acquired during unmanned aerial vehicle (UAV) and Global Navigation Satellite System (GNSS) surveys. The SfM products were used to produce a series of precise maps that highlight the geomorphological changes along the lower Meager Creek within the runout area of the landslide. Comparison of DEMs produced from 2010, 2012, 2015, and 2019 imagery allowed us to calculate deposit volume changes related to erosion, transport, and redeposition of landslide material. We estimate that about 1.1 × 106 m3 of sediment was eroded from the landslide deposit over the period 2015–2019. About 5.2 × 105 m3 of that sediment was redeposited inside the study area. About 5.8 × 105 m3 of sediment, mainly sand, silt, and clay, were exported from the study area and are being carried by Lillooet River towards Pemberton, 40 km from Mount Meager, and farther downstream. These remobilized sediments likely reduce the Lillooet River channel capacity and thus increase flood hazards to the communities of Pemberton and Mount Currie. Our study indicates a landslide persistence in the landscape, with an estimated 47-year half-life decay, suggesting that higher flood hazard conditions related to increased sediment supply may last longer than previously estimated. This study shows the value of using SfM in tandem with historic aerial photographs, UAV photos, and high-resolution satellite imagery for determining sediment budgets in fluvial systems. [ABSTRACT FROM AUTHOR]

In the past, researchers have disagreed over the maximum extent of the Cordilleran Ice Sheet in the Peace River valley during the Late Wisconsinan. Some workers argued that Cordilleran ice reached beyond the Rocky Mountains and briefly coalesced with the Laurentide Ice Sheet on the westernmost Interior Plains. In contrast, others asserted that Cordilleran ice did not reach beyond the eastern front of the Rocky Mountains. Stratigraphic interpretation of three sections within a Middle Wisconsinan paleovalley and re-examination of a previously published regional stratigraphic framework show that western-sourced ice (likely the Cordilleran Ice Sheet) extended east of the mountain front during the Late Wisconsinan, prior to the incursion of the Laurentide Ice Sheet into the area. This conclusion has implications for Cordilleran Ice Sheet reconstruction and modelling, and provides insight into the interactions between the Cordilleran and Laurentide ice sheets during the last glaciation. [ABSTRACT FROM AUTHOR]

Two adjacent glaciers in the Chugach Mountains of south-central Alaska have markedly different histories on decadal to perhaps centennial timescales. Sheridan Glacier has advanced and retreated hundreds of metres during the latest Holocene. Its recent fluctuations have markedly altered local base level of Sherman River, which drains Sherman Glacier and flows into Sheridan Lake. Sheridan Glacier advanced to its greatest extent during the Little Ice Age, raising base level of Sherman River and inducing aggradation there of up to 17 m of sediment. Retreat of Sheridan Glacier formed a series of lakes that have coalesced. As lower lake outlets have become available, base level of Sherman River has dropped, resulting in the evacuation of substantial volumes of sediment from Sherman River valley. In about 2000, the terminus of Sheridan Glacier began to disintegrate; retreat accelerated dramatically in 2010. By 2016, the glacier had retreated an average of 600 m from its 2010 terminus, although some areas retreated up to 1.9 km and others did not retreat at all. Meanwhile, Sherman Glacier continued a slow advance initiated by a rock avalanche that blanketed much of its ablation area in the 1964 Alaska earthquake. [ABSTRACT FROM AUTHOR]

Cheekye Fan is a large paraglacial debris flow fan in southwest British Columbia. It owes its origin to the collapse of Mount Garibaldi, a volcano that erupted in contact with glacier ice near the end of the Pleistocene Epoch. The fan extended across Howe Sound, isolating a freshwater lake upstream of the fan from a fjord downstream of it. Squamish River built a delta into this lake during the Holocene. We use 28 radiocarbon ages to describe the final infilling of the lake and the subsequent evolution of the Squamish River floodplain over the past 3300 years. These events are recorded in fine-grained lacustrine, wetland, river channel, and overbank sediments exposed in the banks of Squamish River over a distance of more than 10 km upstream of the fan. We link these deposits to construction, persistence, and eventual degradation of the dam formed by Cheekye Fan and a smaller inset fan formed by Cheakamus River, into which Cheekye River flows. The coupled Cheekye Fan - Squamish River floodplain system is similar to other low-gradient valley floors upstream of fans such as at Tulare Lake, California, and Alexandra River in the Canadian Rocky Mountains. Future debris flows and landslides in the headwaters of Cheekye River are likely to continue to affect base level on lower Squamish River. We speculate that future aggradation of Cheekye Fan would cause increased flooding and sediment deposition upstream of this barrier. These landscape linkages should be included in future land-use planning in lower Squamish River valley. [ABSTRACT FROM AUTHOR]

Our study combines new geological and paleoecological information to reconstruct the glacial history and terrestrial paleoenvironments on Haida Gwaii during the advance phase of the Fraser glaciation (Marine Isotope Stage 2). At Cape Ball on eastern Graham Island, five accelerator mass spectrometry radiocarbon ages ranging from 23,200±280 to 26,650±390 14C yr BP (ca. 27,000–31,400 cal yr BP) record the earliest approach of mainland glaciers to Haida Gwaii. Abundant marine dinoflagellate cysts indicate isostatic depression by glacial ice in Hecate Strait to the east. At Mary Point on the north coast of Graham Island, similar outwash of a piedmont lobe advancing westward along Dixon Entrance preserves plant remains dated from 19,270±360 to 23,740±300 14C yr BP (22,500–28,600 cal yr BP). These sediments also contain marine indicators. Plant macrofossils, pollen, and invertebrates support the geological evidence of a proglacial environment under a colder-than-present macroclimate. Although some trees were likely present on Graham Island at this time, tundra-like plant communities dominated low-lying areas. A large area that appears to have been ice-free during this time is a portion of the continental shelf off the east coast of Moresby Island, referred to provisionally as the “Hecate Refugium.” [ABSTRACT FROM PUBLISHER]

The relative magnitude of plate-boundary earthquakes at the northern end of the Cascadia subduction zone was assessed from the temporal concordance between the ages of coseismically buried late Holocene soils in southwest Washington, their counterparts in central and southern Cascadia, offshore turbidites, and paleoseismic deposits on the west coast of Vancouver Island. Only three of the seven buried soils in southwest Washington that can be reliably traced as buried soils or paleotsunami deposits in the coastal lowlands of south-central and southern Cascadia have well-dated counterparts in northern Cascadia. The three wide-ranging events date from Cascadia earthquakes Y (∼250 cal BP), U (∼1260 cal BP), and N (∼2520 cal BP). All three likely ruptured the entire plate margin, and therefore potentially qualify as “giants” (M w ≥ 9). Deposits that may derive from tsunamis generated by earthquakes S (∼1570 cal BP), L (∼2870 cal BP) and J (∼3360 cal BP) can also be found in northern Cascadia, but the ages of these deposits are not yet well-enough constrained to determine whether they are coeval with their southern counterparts. Earthquake W (∼850 cal BP), appears to be present in the northern Cascadia paleoseismic record, but yields considerably older ages than in central Cascadia, and may be missing from southernmost Cascadia. The onshore record of an offshore turbidite (T2) displays a similar spatio-temporal pattern to that of earthquake W. [ABSTRACT FROM AUTHOR]

During the last glaciation (marine oxygen isotope stage 2), outburst floods from glacial Lake Missoula deposited diagnostic sediments within glacial Lake Columbia. Two dominant outburst flood lithofacies are present within glacial Lake Columbia deposits: a flood expansion bar facies and a finer-grained hyperpycnite facies. We conclude that the flood sediments have a glacial Lake Missoula source because: (1) current indicators indicate westward flow through the lake, and upvalley flow followed by downvalley flow in tributary valleys; (2) no flood sediments are found north of a certain point; (3) there is a dominance of Belt–Purcell Supergroup clasts in a flood expansion bar; and (4) some of the finer-grained beds have a pink colour, reflective of glacial Lake Missoula lake-bottom sediments. A new radiocarbon age of 13,400 ± 100 14 C BP on plant detritus found below 37 flood beds helps constrain the timing of outburst flooding from glacial Lake Missoula. [ABSTRACT FROM AUTHOR]

Most alpine glaciers in the Northern Hemisphere reached their maximum extents of the Holocene between ad 1600 and 1850. Since the late 1800s, however, glaciers have thinned and retreated, mainly because of atmospheric warming. Glacier retreat in western Canada and other regions is exposing subfossil tree stumps, soils and plant detritus that, until recently, were beneath tens to hundreds of metres of ice. In addition, human artefacts and caribou dung are emerging from permanent snow patches many thousands of years after they were entombed. Dating of these materials indicates that many of these glaciers and snow patches are smaller today than at any time in the past several thousand years. This evidence, in turn, suggests that glacier recession in the 20th century is unprecedented during the past several millennia and that glaciers in western Canada have reached minimum extents only 150–300 years after they achieved their maximum Holocene extents. [ABSTRACT FROM AUTHOR]

Abstract: Glacier-dammed lakes and their associated jökulhlaups cause severe flooding in downstream areas and substantially influence glacier dynamics. Brady Glacier in southeast Alaska is well suited for a study of these phenomena because it presently dams 10 large (>1km2) lakes. Our objectives are to demonstrate how Brady Glacier and its lakes have co-evolved in the past and to apply this knowledge to predict how the glacier and its lakes will likely evolve in the future. To accomplish these objectives, we georeferenced a variety of maps, airphotos, and optical satellite imagery to characterize the evolution of the glacier and lakes. We also collected bathymetry data and created bathymetric maps of select lakes. Despite small advances and retreats, the main terminus of Brady Glacier has changed little since 1880. However, it downwasted at rates of 2–3m/y between 1948 and 2000, more than the regional average. The most dramatic retreat (2km) and downwasting (120m) have occurred adjacent to glacier-dammed lakes and are primarily the result of calving. Brady Glacier is a former tidewater glacier. With continued downwasting, Brady Glacier may return to a tidewater regime and enter into a phase of catastrophic retreat. The situation at Brady Glacier is not unique, and the lessons learned here can be applied elsewhere to identify future glacier-dammed lakes, jökulhlaups, and glacier instability. [Copyright &y& Elsevier]

Abstract: Most glaciers in western North America with reliable age control achieved their maximum Holocene extents during final advances of the Little Ice Age. Tiedemann Glacier, a large alpine glacier in western Canada, is an enigma because the glacier constructed lateral moraines that are up to 90 m higher, and extend 1.8 km farther downvalley, than those constructed during the Little Ice Age. Our data show that the activity of the glacier is more complex than originally documented and that the glacier advanced many times during the past six thousand years. Surface exposure dating and radiocarbon ages of stumps beneath till demonstrate that the glacier achieved its maximum Holocene extent at about 2.7 ka. We hypothesize that one or more rock avalanches delivered surface debris to the glacier and caused the 2.7 ka glacier advance to be much larger than can be explained by climate forcing. To test our hypothesis, we developed and used a surface debris advection routine coupled to an ice dynamics model. Our results show that even a moderately sized rock avalanche ( ) delivered to the top of the ablation zone could cause the glacier to thicken and advance far beyond its Little Ice Age limit. [Copyright &y& Elsevier]

Abstract: Some researchers propose that summer insolation controls long-term changes in glacier extent during the Holocene. If this hypothesis is correct, the record of glacier fluctuations at high latitudes in the Southern Hemisphere should differ from that in the Northern Hemisphere. Although the chronology of Holocene glacier fluctuations in the Northern Hemisphere is well established, much uncertainty remains in the ages of Holocene glacier fluctuations in the Southern Hemisphere, especially South America. Here we report on latest Pleistocene and Holocene glacier fluctuations at the southern end of the Andes north and west of Ushuaia, Argentina. Surface exposure ages (10Be) from glaciated bedrock beyond cirque moraines indicate that alpine areas were free of ice by ca 16.9 ka. One, and in some cases two, closely spaced moraines extend up to 2 km beyond Little Ice Age moraines within many of the cirques in the region. The mean age of five 10Be ages from two pre-Little Ice Age moraines is 14.27–12.67 ka, whereas a minimum limiting radiocarbon age for a smaller, recessional moraine in one cirque is 12.38–12.01 ka. Our ages imply that, following glacier retreat beginning about 18.52–17.17 ka, cirque glaciers first advanced during the Antarctic Cold Reversal (14.5–12.9 ka) and may have later advanced or stabilized in the Younger Dryas Chronozone (12.9–11.7 ka). Based on the distribution of thick, geochemically distinct, and well-dated Hudson tephra, no Holocene moraines appear to be older than 7.96–7.34 ka. At some sites, there is evidence for one or more advances of glaciers sometime between 7.96–7.34 ka and 5.29–5.05 ka to limits only tens of meters beyond Little Ice Age maximum positions. Taken together, the data: 1) do not support the summer insolation hypothesis to explain Holocene glacier fluctuations in southernmost Patagonia; 2) confirm paleobotanical evidence for a warm, dry early Holocene; and 3) suggest that some glaciers in the region reached extents comparable to those of the Little Ice Age shortly before 5.29–5.05 ka. [Copyright &y& Elsevier]

Glaciers are an important element of the Earth system. Glaciers provide numerous, though poorly appreciated, ecological and economic benefits. However, glacial processes can also be hazards. Local glacial hazards include catastrophic floods from lakes impounded by glaciers and their moraines, landslides and debris flows induced by glacier thinning and retreat and permafrost thaw, and enhanced seismicity and volcanism due to large-scale deglaciation. Regionally, rivers can be affected by changes in sediment supply from glacier forefields. Perhaps the greatest hazard that glaciers pose on a global scale of coastal erosion and flooding caused by sea-level rise. If Earth's climate continues to warm, as scientists forecast, the rate of sea-level rise will increase and some low-lying coastal areas will be flooded by the end of this century. [ABSTRACT FROM AUTHOR]

The current limited approaches to calculating hillslope erosion rate hamper the study of the relationships among the rates of hillslope erosion, river incision, and tectonic uplift and hence the discussion of steady-state landscape evolution. In this paper, we use remote sensing and geochronological methods to calculate the upper and lower bounding hillslope erosion rates in the Qilian Shan range, Tibet. Our analysis focuses on five convex landslide sediment units derived from the weathered hillslopes at Qingyang Mountain on the tectonically active northeastern Tibetan Plateau. These sediment units range in thickness from 5.5 to 12.8 m and in volume from 119 × 103 to 260 × 103 m3. Based on field observations, measurements extracted from high-resolution DEMs, and optical stimulated luminescence (OSL) ages on fluvial terraces, we obtain lower and upper bounding rates of 0.13 ± 0.03 and 0.21 ± 0.04 mm/yr, respectively. Finally, we calculate incision rates, ranging from 0.21 ± 0.02 to 0.39 ± 0.01 mm/yr, from heights of a dated fluvial terrace above the present river and the time of abandonment of the associated bedrock strath estimated from OSL ages. The rates of hillslope erosion and river incision at Qingyang Mountain and the tectonic uplift of the Qilian Mountains are estimated to be within a factor of two over the past 117 ka, suggesting that a state of dynamic equilibrium has likely existed on this timescale. [ABSTRACT FROM AUTHOR]

This article describes and compares the deposits of four large landslides on two glaciers in Alaska using field mapping and remote sensing. Digital image analysis is used to compare the sedimentological characteristics of nearly 200 000 individual surface blocks deposited by three landslides at Black Rapids Glacier in 2002. The debris sheets of one of the three landslides on Black Rapids Glacier and a landslide emplaced on Sherman Glacier in 1964 are also investigated. The three landslides on Black Rapids Glacier have undergone little post-depositional modification by glacier flow, whereas the Sherman Glacier landslide has been transported supraglacially up to ca 1 km over the past 46 years. The three debris sheets on Black Rapids Glacier have coarse blocky rims at their distal edges, and all four debris sheets have longitudinal flowbands characterized by differences in texture and produced by shearing within the moving debris. Elongated blocks are parallel to flow, except at the perimeter of the debris sheets, where they are aligned more perpendicular to flow. Blocks on the Sherman Glacier debris sheet have been reoriented by glacier flow. The matrix shows no systematic differences with depth or distance from the source. However, it appears to become coarser over a time scale of decades due to weathering. [ABSTRACT FROM AUTHOR]

Abstract: Moraine and glacier dams bordering the Homathko Icefield in the southern British Columbia Coast Mountains failed in the 1980s and 1990s, causing catastrophic downstream floods. The largest of the floods occurred in August 1997 and was caused by overtopping and rapid breaching of the moraine dam that impounds Queen Bess Lake. The floodwaters from Queen Bess Lake eroded Holocene-age sedimentary deposits along the west fork of Nostetuko River and caused a steep rise in the hydrograph of Homathko River at the head of Bute Inlet, ∼115km downstream. A field investigation of the eroded valley fill in 2008, revealed multiple paraglacial valley-fill units, many of which are capped by in situ stumps and woody detritus. Dendrogeomorphological field techniques were employed to develop a chronology for the buried forests. A regional tree-ring chronology spanning the interval CE 1572–2007 was constructed from living subalpine fir (Abies lasiocarpa) trees at seven sites in the southern Coast Mountains. In cases where subfossil stumps and boles predated the regional chronology, relative death dates constrained by radiocarbon ages were assigned to floating chronologies. By combining these dendrogeomorphological dating methods, we identified six floodplain aggradation episodes within the past 1200years. Comparison to local and regional glacial histories suggests that these events reflect climate-induced Little Ice Age changes in local glacier cover. [Copyright &y& Elsevier]

Radiocarbon and dendrochronological dating of glacially overridden stumps and detrital wood indicates that two outlet glaciers of the Juneau Icefield advanced shortly before the 'Little Ice Age'. Tulsequah Glacier advanced to within 2.4 km of its all-time Holocene limit between ad 865 and ad 940. Llewellyn Glacier, one of the largest glaciers in British Columbia, advanced sometime between ad 300 and ad 500, and reached to within 400 m of its Holocene limit between ad 1035 and ad 1210, well before the climactic, 'classical' 'Little Ice Age' advances of the past several centuries. Our data show that some glaciers in western North America were extensive and expanding at times when alpine glaciers have, in the past, been assumed to be restricted. The evidence raises questions about how to define the time of the beginning of the 'Little Ice Age' and, perhaps more importantly, about the utility of the term. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-two new radiocarbon ages from Skagit valley provide a detailed chronology of alpine glaciation during the Evans Creek stade of the Fraser Glaciation (early marine oxygen isotope stage (MIS) 2) in the Cascade Range, Washington State. Sediments at sites near Concrete, Washington, record two advances of the Baker valley glacier between ca. 30.3 and 19.5 cal ka BP, with an intervening period of glacier recession about 24.9 cal ka BP. The Baker valley glacier dammed lower Skagit valley, creating glacial Lake Concrete, which discharged around the ice dam along Finney Creek, or south into the Sauk valley. Sediments along the shores of Ross Lake in upper Skagit valley accumulated in glacial Lake Skymo after ca. 28.7 cal ka BP behind a glacier flowing out of Big Beaver valley. Horizontally laminated silt and bedded sand and gravel up to 20 m thick record as much as 8000 yr of deposition in these glacially dammed lakes. The data indicate that alpine glaciers in Skagit valley were far less extensive than previously thought. Alpine glaciers remained in advanced positions for much of the Evans Creek stade, which may have ended as early as 20.8 cal ka BP. [Copyright &y& Elsevier]

Abstract: Most Quaternary research in Canada during the first half of the twentieth century focused on Pleistocene glaciation. Given the dramatic shifts in climate during the Pleistocene, it is not surprising that the Holocene was viewed as a time of benign climate. Holocene climate variability was first recognized around the middle of the century when paleoecologists found evidence that the early part of the epoch was warmer and drier than the later part. In 1970s and 1980s, another generation of geologists, geographers, and botanists began to recognize more complexity in Holocene climate and vegetation in western Canada. Several millennial-scale glacier “advances” postdating the early Holocene warm interval were defined, including the Garibaldi Phase (6.9–5.6 ka), the Tiedemann–Peyto Advance (3.5–1.9 ka), and the Little Ice Age (AD 1200–1900). Subsequently, application of dendrochronological techniques and stratigraphic studies in glacier forefields showed that the Little Ice Age was itself more complex than previously thought. During that 700-year period, glaciers repeatedly advanced and retreated in response to climatic variability on time scales ranging from centuries to decades. Recent work shows that the glacier record of the Garibaldi Phase and the Tiedemann and Peyto advances are similar in complexity to the Little Ice Age, with multiple advances of glaciers separated by intervals of more restricted ice cover. Researchers have also identified other times in the Holocene when glaciers expanded from restricted positions – 8.20, 4.90–3.80, and 1.70–1.40 ka. Continued research undoubtedly will reveal additional complexities, but with what is currently known the appropriateness of terms such as “Tiedemann Advance,” “Peyto Advance,” and “Little Ice Age” can be questioned. Only short periods of time separate these episodes as currently defined, and it seems likely that intervals of restricted glacier cover within each of these millennial-length intervals are just as long as the intervals separating them. [Copyright &y& Elsevier]

Abstract: The hazard of any natural process can be expressed as a function of its magnitude and the annual probability of its occurrence in a particular region. Here we expand on the hypothesis that natural hazards have size–frequency relationships that in parts resemble inverse power laws. We illustrate that these trends apply to extremely large events, such as mega-landslides, huge volcanic debris avalanches, and outburst flows from failures of natural dams. We review quantitative evidence that supports the important contribution of extreme events to landscape development in mountains throughout the world, and propose that their common underreporting in the Quaternary record may lead to substantial underestimates of mean process rates. We find that magnitude–frequency relationships provide a link between Quaternary science and natural hazard research, with a degree of synergism and societal importance that neither discipline alone can deliver. Quaternary geomorphology, stratigraphy, and geochronology allow the reconstruction of times, magnitudes, and frequencies of extreme events, whereas natural hazard research raises public awareness of the importance of reconstructing events that have not happened historically, but have the potential to cause extreme destruction and loss of life in the future. [Copyright &y& Elsevier]

Evidence of at least three Early to Middle Pleistocene glaciations is recorded in the stratigraphic exposures near the outer limit of glaciation in southern Patagonia. At Cabo Vírgenes, at the mouth of the Strait of Magellan, up to 70 m of till, gravel, sand, and stony silt were deposited in a grounding-line environment at the front of the Magellan lobe along a front several tens of kilometres wide. Accommodation space for the sediments was produced by glacio-isostatic depression resulting from the advance of the Magellan lobe to the Atlantic coast. At that time, the 'moat' in which the sediments accumulated may have been seaward of the modern Atlantic shoreline because the continental shelf is shallow and sea level was much lower than it is today. The sediments at Cabo Vírgenes are normally magnetized, carry no reversed overprints, and thus probably date to the Brunhes Chron (<0.774 Ma). Seacliff exposures south of the Strait of Magellan along the Atlantic coast of northern Tierra de Fuego expose two tills separated by glaciofluvial sediments. Although not dated, the tills record two advances of the Magellan lobe onto the Atlantic continental shelf. The location of the exposures relative to Cabo Vírgenes indicates that the upper of the two tills may correlate with the Cabo Vírgenes drift. The Tres de Enero highway cut, 90 km northwest of Cabo Vírgenes, exposes lodgement tills deposited during the Great Patagonian glaciation (GPG) – two stacked, normally magnetized tills overlie a reversely magnetized till. Truncated sand wedges separate each of the three tills, indicating that the tills record three separate Early to Middle Pleistocene glaciations. The younger of the two normally magnetized tills, and perhaps both, were deposited in the Brunhes Chron; the lowest, reversely magnetized till records extensive glaciation late during the Matuyama Chron (2.608–0.780 Ma). At Bella Vista in the Río Gallegos valley, a 0.89-Ma-old basalt flow caps a thick unit of normally magnetized glaciofluvial gravel, which was probably deposited during the Jaramillo Subchron (1.075–0.991 Ma), but certainly not later. Sediments at Tres de Enero and Bella Vista show that the GPG is not a single event as originally thought, but rather at least three glaciations, perhaps spanning several hundred thousand years. • Seacliffs expose two tills separated by outwash, indicative of two advances of the Magellan lobe onto the Atlantic shelf. • A road cut south of Rio Gallegos exposes Great Patagonian (GPG) tills. • The GPG is a multi-phased, rather than a single, glacial event, possibly spanning several hundred thousand years. [ABSTRACT FROM AUTHOR]

Abstract: We reconstructed late Holocene fluctuations of Kluane Lake in Yukon Territory from variations in bulk physical properties and carbon and nitrogen elemental and isotopic abundances in nine sediment cores. Fluctuations of Kluane Lake in the past were controlled by changes in climate and glaciers, which affected inflow of Slims and Duke rivers, the two largest sources of water flowing into the lake. Kluane Lake fluctuated within a narrow range, at levels about 25 m below the present datum, from about 5000 to 1300 cal yr BP. Low lake levels during this interval are probably due to southerly drainage of Kluane Lake to the Pacific Ocean, opposite the present northerly drainage to Bering Sea. Slims River, which today is the largest contributor of water to Kluane Lake, only rarely flowed into the lake during the period 5000 to 1300 cal yr BP. The lake rose 7–12 m between 1300 and 900 cal yr BP, reached its present level around AD 1650, and within a few decades had risen an additional 12 m. Shortly thereafter, the lake established a northern outlet and fell to near its present level. [Copyright &y& Elsevier]

Sediment cores recovered from alpine and subalpine lakes up to 250 km apart in northern British Columbia contain five previously unrecognized tephras. Two black phonolitic tephras, each 5–10 mm thick, occur within 2–4 cm of each other in basal sediments from seven lakes in the Finlay River – Dease Lake area. The upper and lower Finlay tephras are slightly older than 10 220 – 10 560 cal year B.P. and likely originate from two closely spaced eruptions of one or two large volcanoes in the northern Cordilleran volcanic province. The Finlay tephras occur at the transition between deglacial sediments and organic-rich postglacial mud in the lake cores and, therefore, closely delimit the termination of the Fraser Glaciation in northern British Columbia. Sediments in Bob Quinn Lake, which lies on the east edge of the northern Coast Mountains, contain two black tephras that differ in age and composition from the Finlay tephras. The lower Bob Quinn tephra is 3–4 mm thick, basaltic in composition, and is derived from an eruption in the Iskut River volcanic field about 9400 cal years ago. The upper Bob Quinn tephra is 12 mm thick, trachytic in composition, and probably 7000–8000 cal years old. A fifth tephra occurs as a cryptotephra near the top of two cores from the Finlay River area and is correlated to the east lobe of the White River tephra (ca. 1150 cal year B.P.). Although present throughout southern Yukon, the White River tephra has not previously been documented this far south in British Columbia. The tephras are valuable new isochrons for future paleoenvironmental studies in northern British Columbia. [ABSTRACT FROM AUTHOR]

Two Cordilleran and three Laurentide glacial advances are recorded in Quaternary sediments and landforms in the Peace River valley, northeast British Columbia. The advances are inferred from fluvial gravels, glaciolacustrine sediments, and tills within nested paleovalleys excavated during three interglaciations and from the distribution of granitoid clasts derived from the Canadian Shield. Till of the last (Late Wisconsinan) Laurentide glaciation occurs at the surface, except where it is overlain by postglacial sediments. The advance that deposited this till was the most extensive in the study area, and the only advance definitively recognized in western Alberta south of the study area. Late Wisconsinan Cordilleran till has not been found in the study area, but Cordilleran and Laurentide ice may have coalesced briefly during the last glaciation. Support for this supposition is provided by the inferred deflection of Laurentide flutings to the southeast by Cordilleran ice. The earliest Laurentide advance may have been the least extensive of the three Laurentide events recognized in the study area. Erratics attributed to this advance occur only east of the Halfway River – Beatton River drainage divide. Deux avancées glaciaires de la Cordillère et trois de l’Inlandsis laurentidien sont évidentes dans les sédiments et la topographie du Quaternaire de la vallée de la rivière de la Paix, dans le nord-est de la Colombie-Britannique. Les avancées sont déduites à partir des graviers fluviatiles, des sédiments glacio-lacustres et des tills dans des paléovallées emboîtées excavées durant trois périodes interglaciaires et à partir de la distribution des clastes granitoïdes provenant du Bouclier canadien. Un till de la dernière glaciation laurentidienne (Wisconsinien tardif) se retrouve à la surface, sauf là où il est recouvert de sédiments post-glaciaires. L’avancée qui a déposé ce till a été la plus extensive dans le secteur à l’étude et c’est la seule avancée définitivement reconnue dans l’ouest de l’Alberta, au sud du secteur à l’étude. Aucun till de la Cordillère datant du Wisconsinien n’a été trouvé dans le secteur à l’étude. Cependant, la glace de la Cordillère et celle de l’Inlandsis laurentidien pourraient s’être unis durant une brève période au cours de la dernière glaciation. Cette hypothèse est soutenue par la déflexion inférée de rainures glaciaires laurentidiennes vers le sud-est par la glace de la Cordillère. L’avancée glaciaire laurentidienne la plus précoce pourrait être la moins étendue des trois événements laurentidiens reconnus dans le secteur à l’étude. Les blocs erratiques attribués à cette avancée ne se retrouvent qu’à l’est de la ligne de partage des eaux entre les rivières Halfway et Beatton. [ABSTRACT FROM AUTHOR]

Abstract: We recovered sediment cores from Cheakamus Lake in the southern Coast Mountains, southwest British Columbia, to reconstruct late Holocene environmental conditions in the watershed. The cored sediments are inorganic, rhythmically laminated clayey silt. Radiocarbon ages and correlation of lamina thickness with the magnitude of the annual flood recorded at a nearby gauging station indicate that the laminae are varves. We discriminate seven types of varves on the basis of couplet thickness and internal structure, and compare them to annual hydrographs over the period of record. The seven varve types record summer snowmelt floods, autumn floods, mid-season floods, years with two major floods, years with three major floods, years with more than three major floods, and periods of sustained glacier runoff. Varves attributed to autumn storms and glacier runoff are dominant, exhibit serial dependence, and are most common during six periods: AD 1300–1320, 1380–1410, 1470–1500, 1710–1730, 1880–1906, and 1916–1945. In contrast, varves attributed to summer snowmelt floods are randomly distributed through time. Thickest varves occur during the decades AD 1090–1110, 1120–1170, 1210–1250, 1310–1330, 1390–1450, 1720–1780, 1860–1900, and 1920–1945. The relation between Little Ice Age glacier activity and lake sedimentation is complex, but the thickest varves coincide with times of rapid glacier retreat and periods when air temperatures were warmer than average. The results confirm the importance of sediment transfers during the summer and autumn runoff season in the British Columbia Coast Mountains. [Copyright &y& Elsevier]

Abstract: Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550–10,250 cal yr BP (9230±50 14C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances. [Copyright &y& Elsevier]

Abstract: This review examines interpretive issues relating to catastrophic, long-runout landslides in the context of large numbers of recently discovered late Quaternary events. It links relevant research in landslide science, including some novel or hitherto-ignored complexities in the nature and role of these events, to broader concerns of mountain geomorphology. Attention is drawn to mountain ranges known to have large concentrations of events. In particular, discoveries in three regions are singled out; the Karakoram Himalaya, the coastal mountains of northwestern North America, and the Southern Alps of New Zealand. In each region, many new events, or previously unrecognized complexities, have been identified in the past decade or two. Research on the sedimentology and geomorphology of prehistoric, eroded deposits has been critical to identifying rock avalanches, including many that were formerly attributed to other processes. Discoveries of rock avalanches in the ancient stratigraphic record have helped with the field recognition of rock-avalanche materials and in developing facies models of deposits with complex emplacement histories. The stratigraphic record also provides insights into interactions of streaming rock debris with deformable substrates. Such interactions are responsible for “landslide-tectonized” forms and transformation of rock avalanches into debris flows. Of special interest are runout geometries involving the interactions of rock avalanches with topography or substrate materials, and travel over glaciers. Other emerging issues relate to reconstruction of detachment-zone geometries, and slow, deep-seated slope movements that may trigger catastrophic failure. Most previous landslide studies have focused on individual events or general models, whereas the questions addressed here arise from a comparative approach emphasizing common and contrasting features among events in sets and in different regions. The scale and frequency of landslides in the regions of interest mean they have an important role in denudation, regional landform development, watershed evolution, and Quaternary environmental change. A major developmental factor, largely neglected, is persistent disturbance of high mountain fluvial systems by many successive landslides. Damming of streams and subsequent breaching of landslide barriers strongly influence inter-montane sedimentation and denudation, with particular significance in post-, para-, and inter-glacial contexts. Although an individual landslide appears as a “catastrophe” lasting only a minute or two, its legacy can persist as a morphogenetic influence for millennia or tens of millennia through disturbance of other processes. The influence is permanently felt; in effect, multiple events make the event a “normal” one in regions such as the three considered here. [Copyright &y& Elsevier]

Abstract: Distributions of slope angles in tectonically active mountain belts point to the development of threshold conditions, where hillslopes attain a critical inclination or height at which they fail readily because of limitations in material strength. It has been proposed that hillslopes adjust to rapid uplift and bedrock incision through an increase in the rate of relief-limiting landsliding rather than gradual slope steepening. Here we test this concept by investigating the relationship between mean local relief H¯, which we take to be a proxy of long-term erosion rates E, and the occurrence of over 300 of the largest (V >108 m3) terrestrial landslides on Earth. We find that nearly two-thirds of these giant landslides have occurred in the steepest 5% of the Earth''s land surface, where relief is close to its proposed upper strength limit. They are primarily located in deeply incised valleys, along fault-bounded fringes of active mountain belts, and in volcanic arcs. This distribution coincides with areas of high long-term erosion rates (∼4 mm yr−1), confirming that giant landslides contribute to rapid denudation of mountains. Most of the eroded volume is concentrated in the smallest, but steepest parts of mountain belts and volcanic arcs. First-order estimates of minimum erosion rates accomplished by the largest landslides are ≥0.01 mm yr−1; these rates are between 1% and 10% of the Late Pleistocene to Holocene mean erosion rates in a given area. Importantly, the landslide erosion rates show a nonlinear increase with mean local relief, suggesting that the contribution of giant landslides in total and per event increases significantly with increasing overall erosion rates. However, giant landslides also occur in areas of lower-than-average relief (H¯ ∼300–700 m), irrespective of whether threshold hillslopes have developed or not. Factors contributing to these failures include soft rocks, extensive low-angle discontinuities, high rates of fluvial bedrock incision, and tectonically driven deformation and slope loading. [Copyright &y& Elsevier]

The Little Ice Age glacier history in Garibaldi Provincial Park (southern Coast Mountains, British Columbia) was reconstructed using geomorphic mapping, radiocarbon ages on fossil wood in glacier forefields, dendrochronology, and lichenometry. The Little Ice Age began in the 11th century. Glaciers reached their first maximum of the past millennium in the 12th century. They were only slightly more extensive than today in the 13th century, but advanced at least twice in the 14th and 15th centuries to near their maximum Little Ice Age positions. Glaciers probably fluctuated around these advanced positions from the 15th century to the beginning of the 18th century. They achieved their greatest extent between A.D. 1690 and 1720. Moraines were deposited at positions beyond present-day ice limits throughout the 19th and early 20th centuries. Glacier fluctuations appear to be synchronous throughout Garibaldi Park. This chronology agrees well with similar records from other mountain ranges and with reconstructed Northern Hemisphere temperature series, indicating global forcing of glacier fluctuations in the past millennium. It also corresponds with sunspot minima, indicating that solar irradiance plays an important role in late Holocene climate change. [ABSTRACT FROM AUTHOR]

Moraine Bog lies just outside the outermost lateral moraine of Tiedemann Glacier in the southern Coast Mountains of British Columbia. A sediment core taken from the wetland was analyzed for pollen, magnetic susceptibility, and loss on ignition to reconstruct changes in vegetation and climate during the late Holocene. Vegetation changed little between about 3500 and 2400 14C years BP. A period of local disturbance marked by deposition of a silty clay bed and increases in Alnus pollen, likely reflecting cooler moister conditions, coincides with an extensive Holocene advance of Tiedemann Glacier about 2400 14C years BP. Warm dry conditions between about 1900 and 1500 14C years BP are suggested by peak values of Pseudotsuga pollen and increasing Nuphar sclereids; the latter suggests lowered water levels. This period coincides with a time of drought and increased fire frequency in the southernmost Coast Mountains. About 1300 14C years BP, the forest became more coastal in composition with abundant Tsuga heterophylla and Abies. An increase in Tsuga mertensiana pollen suggests the onset of cool and wet conditions by ca. 500 14C years BP, coincident with the Little Ice Age. The record of inferred climate change at Moraine Bog is broadly synchronous with other paleoclimate records from the Coast Mountains and, at the centennial scale, with records elsewhere in the world. [ABSTRACT FROM AUTHOR]

Abstract: Safe development of glacierized regions requires a systematic and objective method for assessing the hazard posed by moraine-dammed lakes. Empirical relations exist for estimating outburst flood magnitude, but, until now, no standardized procedures have been developed for estimating outburst flood probability. To make quick and inexpensive preliminary assessments that are reproducible, we propose using a statistical, remote sensing-based approach to estimate the probability of catastrophic drainage of moraine-dammed lakes. We completed a comprehensive inventory of 175 moraine-dammed lakes in the southern Coast Mountains of British Columbia, Canada. By applying logistic regression analysis to the data set, we identified and weighted the following four independent predictor variables that best discriminate drained lakes from undrained lakes: moraine height-to-width ratio, presence/absence of an ice-core in the moraine, lake area, and main rock type forming the moraine. With an appropriate classification cutoff value, the predictive model correctly classifies 70% of drained lakes and 90% of undrained lakes, for an overall accuracy of 88%. Our model provides engineers and geoscientists with a tool for making first-order estimates of the probability of catastrophic drainage from moraine-dammed lakes in southwestern British Columbia. [Copyright &y& Elsevier]

Abstract: The level of Kluane Lake, the largest lake in Yukon Territory, was lower than at present during most of the Holocene. The lake rose rapidly in the late seventeenth century to a level 12 m above present, drowning forest and stranding driftwood on a conspicuous high-stand beach, remnants of which are preserved at the south end of the lake. Kluane Lake fell back to near its present level by the end of the eighteenth century and has fluctuated within a range of about 3 m over the last 50 yr. The primary control on historic fluctuations in lake level is the discharge of Slims River, the largest source of water to the lake. We use tree ring and radiocarbon ages, stratigraphy and sub-bottom acoustic data to evaluate two explanations for the dramatic changes in the level of Kluane Lake. Our data support the hypothesis of Hugh Bostock, who suggested in 1969 that the maximum Little Ice Age advance of Kaskawulsh Glacier deposited large amounts of sediment in the Slims River valley and established the present course of Slims River into Kluane Lake. Bostock argued that these events caused the lake to rise and eventually overflow to the north. The overflowing waters incised the Duke River fan at the north end of Kluane Lake and lowered the lake to its present level. This study highlights the potentially dramatic impacts of climate change on regional hydrology during the Little Ice Age in glacierised mountains. [Copyright &y& Elsevier]

Abstract: At least thirty-eight, large, catastrophic landslides, each either larger than 0.5 M m3 or longer than 1 km, have occurred in northern British Columbia in the last three decades. The landslides include low-gradient flowslides in cohesive sediments, long-runout rock slides (rock avalanches), and complex rock slide-flows. The flowslides have occurred in a variety of sediments, including glaciolacustrine silt, clay-rich till, and clay-rich colluvium. The rock failures have happened in weak shale overlain by sandstone and volcanic rocks. The frequency of large landslides in northern British Columbia appears to be increasing, suggesting a link to climate change. [Copyright &y& Elsevier]

Cores of annually laminated sediments (varves) from five lakes in the southern Coast Mountains of British Columbia, Canada, document clastic sediment response to climate and geomorphic change over the past 120 years. Interannual varve thickness correlates with annual flood magnitude. Interdecadal trends in varve thickness are influenced by other environmental factors such as glacier recession. Despite major differences in the lakes and their contributing watersheds, substantial concordance is observed among the records. A pronounced change in the nature of lake sedimentation, accompanied by higher interannual variability, occurred in 1980. The change coincides with an increase in the magnitude of autumn flooding and major re-organization of the North Pacific climate system. These results highlight new directions for palaeoenvironmental research using varved sediment records, specifically to study the magnitude and spatial extent of past hydro-climatic events. [ABSTRACT FROM AUTHOR]

Jökulhlaups from lakes dammed by Tulsequah Glacier in northwestern British Columbia have occurred regularly since the early twentieth century. The floods commenced after decades of downwasting and retreat of the glacier from its Holocene maximum position, which it achieved in the nineteenth century. Hydrometric data and other records are used to reconstruct the times and peak discharges of floods from two glacier-dammed lakes. Tulsequah Lake formed in the early 1900s when a tributary glacier separated from Tulsequah Glacier, creating an ice-free embayment between the two. The lake grew rapidly in surface area and volume in the first half of the twentieth century, but later, with continued glacier retreat, it decreased in size. The first jökulhlaups from Tulsequah Lake were the largest. Peak and total discharges decreased as the lake became smaller. Today, Tulsequah Lake is small, and it will disappear completely if Tulsequah Glacier retreats any further. A second lake (Lake No Lake), however, has formed and grown in size as Tulsequah Lake has diminished. Lake No Lake developed from a subglacial water body in a tributary valley, 7 km upglacier from Tulsequah Lake. Like Tulsequah Lake, Lake No Lake rapidly grew in area and volume during its youth, and in the 1970s it began to generate its own jökulhlaups. Lake No Lake appears to be following the same evolutionary path as Tulsequah Lake – its volume is now decreasing due to downwasting of Tulsequah Glacier, and its jökulhlaups are beginning to diminish. As Tulsequah Glacier continues to shrink in response to climatic warming, additional glacier-dammed lakes may form, renewing the cycle of outburst flood activity. Such behaviour can be expected in other high mountains because most alpine glaciers are retreating in response to global warming. [ABSTRACT FROM AUTHOR]

Abstract: Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation. [Copyright &y& Elsevier]

An integrated stratigraphic, paleoecological, and geochronological study of lake and fen sediments just beyond the terminus of Berendon Glacier provides insights into late Holocene climate, vegetation, and glacier change in the northern Coast Mountains of British Columbia. Cores collected from two small lakes in the foreland of Berendon Glacier and pits dug in a nearby fen record Little Ice Age and older glacier advances. The first Little Ice Age advance in this area began more than 500 years ago and peaked in the early 17th century. An earlier Neoglacial advance began about 2800–3000 cal yr ago and may have lasted for hundreds of years. There is also evidence for an intervening advance of even smaller magnitude around 1200–1300 cal yr ago. The advances are broadly synchronous with those in other parts of western North America, indicating that they were caused by regional, possibly global, changes in climate. Plant communities within the study area did not change dramatically during the late Holocene. The ranges of some plants, however, likely retracted or extended near treeline in response to changes in mean temperatures of perhaps 1–2°C, as well as changes in summer snow cover. The greatest changes in vegetation occurred within and just beyond the forefields of Berendon, Frank Mackie, and other nearby glaciers. The largest climate shifts of the last 3000 years took place during the late Little Ice Age and the last century. Climate warmed about 1–2°C during the 20th century, accompanied by a rise in treeline, an increase in coniferous tree cover in the subalpine zone, and an increase in the temperature and biological productivity of ponds. These trends are likely to continue if climate, as expected, continues to warm. [Copyright &y& Elsevier]

Holocene lateral moraines in the Coast Mountains of British Columbia are commonly composed of multiple drift units related to several glacier advances. In this paper, we document lateral moraine stratigraphy at Lillooet Glacier in the southern Coast Mountains. Five tills, separated by laterally extensive paleosols and layers of large woody debris, were found in three cross-sectional exposures through the northeast lateral moraine and two shallow gullies incised into its steep proximal face. Eighteen new radiocarbon ages constrain the timing of five separate advances of Lillooet Glacier: (1) prior to 3000 14C years BP; (2) ~3000 14C years BP; (3) ~2500 14C years BP; (4) ~1700 to 1400 14C years BP; and (5) during the Little Ice Age (LIA), after 470 14C years BP. The Lillooet Glacier chronology is broadly synchronous with other glacier records from the Coast Mountains. These records collectively demonstrate climate variability at higher frequencies during the late Holocene than is apparent from many paleoecological reconstructions. Reconstructions of glacier fluctuations are often hampered by poor preservation of landforms that predate the extensive LIA advances of the latest Holocene. Our results highlight the potential of lateral moraine stratigraphy for reconstructing these earlier events. [ABSTRACT FROM AUTHOR]

Self-reported questionnaires are frequently used to assess health status in epidemiological studies. The Cornell medical index is one such tool used to determine the presence of physical and psychiatric illness but its accuracy and value have been questioned. In this study we have assessed the ability of the CMI to predict health status in two separate patient populations (n=101, 88) by comparison to a structured medical assessment based on the SENIEUR protocol by two physicians. There was good agreement between medication use reported on the CMI and on medical assessment (k=0.79; CI: 0.70–0.88). Accuracy of prediction of the CMI for specific medical conditions was good 89–99%. A threshold score from the CMI was not predictive of health as determined by the SENIEUR protocol. In our older populations, we conclude that the CMI accurately predicted health status. The determination of normal health by a threshold score was poorly predictive of heath status. Self-reported medication use was the best predictor of health status. [Copyright &y& Elsevier]

Mount Meager massif, the northernmost volcano of the Cascade volcanic belt, has been the site of very large (>107 m3) landslides in the Holocene Epoch. We document two complex landslides at Pylon Peak, one of the peaks of the Mount Meager massif, about 7900 14C and 3900 14C years ago (about 8700 and 4400 calendar years ago). Together, the two landslides displaced ~ 6 × 108 m3 of volcanic rock from the south flank of Pylon Peak into nearby Meager Creek valley. Each landslide consisted of at least two phases, an early debris flow resulting from failure of hydrothermally altered pyroclastic rock at mid levels on the mountain and a later rock avalanche from a higher source. Both debris flows likely traveled down Meager Creek, and preliminary evidence from drilling indicates the 4400-year-old event traveled down Lillooet River into areas that are now settled and where population density is increasing rapidly. The mobility of the debris flows was due to the high content of fine, weathered volcanic sediment and the availability of sufficient water. The causes of the landslides are a wet climate and the presence of weak, hydrothermally altered volcanic rock containing abundant phreatic water on glacially oversteepened slopes. The landslides may have been triggered by earthquakes or by upwelling of magma to shallow depths within the volcano. However, they may also have occurred without specific triggers following extended periods of progressive weakening of the volcanic rocks. [ABSTRACT FROM AUTHOR]

Rivers flowing from glacier-clad Quaternary volcanoes in southwestern British Columbia have high sediment loads and anabranching and braided planforms. Their floodplains aggrade in response to recurrent large landslides on the volcanoes and to advance of glaciers during periods of climate cooling. In this paper, we document channel instability and aggradation during the last 200 years in lower Cheakamus River valley. Cheakamus River derives much of its flow and nearly all of its sediment from the Mount Garibaldi massif, which includes a number of volcanic centres dominated by Mount Garibaldi volcano. Stratigraphic analysis and radiocarbon and dendrochronological dating of recent floodplain sediments at North Vancouver Outdoor School in Cheakamus Valley show that Cheakamus River aggraded its floodplain about 1–2 m and buried a valley-floor forest in the early or mid 1800s. The aggradation was probably caused by a large (ca. 15–25×106 m3) landslide from the flank of Mount Garibaldi, 15 km north of our study site, in 1855 or 1856. Examination of historical aerial photographs dating back to 1947 indicates that channel instability triggered by this event persisted until the river was dyked in the late 1950s. Our observations are consistent with data from many other mountain areas that suggest rivers with large, but highly variable sediment loads may rapidly aggrade their floodplains following a large spike in sediment supply. Channel instability may persist for decades to centuries after the triggering event. [Copyright &y& Elsevier]

Paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from Glacial Lake Missoula, Montana, entered Washington's Yakima and Walla Walla Valleys during the last glaciation. In these valleys, the field evidence for hiatuses between floods is commonly subtle. However, paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at Zillah, Touchet, and Burlingame Canyon display consistent secular variation that correlates serially both within and between sections. The secular variation may further correlate with paleomagnetic data from Fish Lake, Oregon, and Mono Lake, California, for the interval 12,000-17,000 [sup 14]C yr B.P. Deposits of two successive floods are separated by two tephras derived from Mount St. Helens, Washington. The tephras differ in age by decades, indicating that a period at least this long separated two successive floods. The beds produced by these two floods are similar to all of the 40 beds in the slack-water sediment sequence, suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years. [ABSTRACT FROM AUTHOR]

Stratigraphy and landforms in the Brohm Creek basin and lowermost Mamquam River valley provide evidence for a readvance of a valley glacier in the southern Coast Mountains of British Columbia during the Younger Dryas interval. At Brohm Creek, till containing wood 10,500 and 10,700 14C yr old (ca 12,500–12,900 cal yr old), overlies an ice-contact terrace that is correlative with similar terraces at the mouth of Mamquam River, 11 km to the south and 900 m lower in elevation. A line linking the two sites has a slope of 5°, which is similar to slopes of termini of present-day valley glaciers in the southern Coast Mountains. We used these observations to reconstruct the Younger Dryas glacier in Squamish valley at the head of Howe Sound. The glacier deflected landslide debris, derived from steep slopes at the head of Cheekye River basin on the west flank of Mt. Garibaldi, southward to an ice-marginal lake at the mouth of Mamquam River. Foreset-bedded sediments in the core of a large fan at the mouth of Cheekye River indicate the glacier terminus had retreated up Squamish valley beyond Cheekye and Mamquam rivers by 10,200 14C yr BP (11,900 cal yr old). Radiocarbon ages on the oldest postglacial sediments in a kettle on the landslide debris show that stagnant ice in the study area had melted before 10,000 14C yr BP (11,500 cal yr BP). The readvance of the Squamish valley glacier during the Younger Dryas Chronozone was probably driven by a regional climate reversal. [Copyright &y& Elsevier]

The Late Wisconsinan Cordilleran ice sheet covered British Columbia, southern Yukon Territory, and parts of Alaska, Washington, Idaho, and Montana. Its major source areas were the high mountain ranges of the Canadian Cordillera, and flow was strongly controlled by topography. The last ice sheet began to develop about 30,000–25,000 14C yr ago, but it did not achieve its maximum extent until 15,000–14,000 14C yr BP. Ice sheet growth was interrupted locally by stillstands and retreat. Ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery, accompanied locally by brief readvances, and by downwasting and stagnation. By 10,000 14C yr BP, <5000 yr after the Last Glacial Maximum, ice cover in British Columbia was similar to that of today. The Cordilleran ice sheet depressed the crust over which it formed. Rapid isostatic rebound during deglaciation caused the sea to fall relative to the land along the southern British Columbia coast. A postglacial rebound model explains crustal tilting and rapid uplift in this region during retreat of the ice sheet in the late Pleistocene. Small values of modelled viscosity for the upper few hundred kilometers of the mantle deliver small present-day crustal tilt rates, consistent with mid- and late-Holocene sea-level observations. Rapid sea-level fall (land uplift) on eastern Vancouver Island during deglaciation requires, in addition to a low mantle viscosity, rapid unloading of the crust due to accelerated wastage of coastal portions of the southern Cordilleran ice sheet about 12,000 14C yr ago. [Copyright &y& Elsevier]

Many factors may contribute to the mortality and morbidity following hip fracture, including the provision of care. We wished to examine the contribution of potential factors to in-hospital mortality, length of hospital stay and 90-day mortality by statistical analyses of an audit database of all hip fractures admitted to a teaching hospital following the introduction of a fast track admission system. In-hospital mortality was predicted by ASA grade, the presence of any complications, cardiovascular complications, grade of surgeon, operation type and shorter admission time, a measure of time taken to admit a patient to a hospital bed (P<0.001). Length of hospital stay was predicted by increased age, presence of chronic cognitive impairment/dementia, presence of an implant complication, operation type, fracture type and longer admission time, r=0.455, P<0.001. Ninety-day mortality was predicted by the presence of chronic cognitive impairment/dementia, cardiovascular complications, pulmonary complications, ASA grade, grade of surgeon and admission day, P<0.001. Rapid admission following a hip fracture may not be the ideal management approach for all patient groups. Further study is required to identify factors in the process of care which are associated with better outcomes. [Copyright &y& Elsevier]

Human activities are a triggering factor for landslides in the Yellow River Basin (YRB, China). However, the extent to which the spatial distribution of landslides is affected by human activities is unclear. We constructed a human activity intensity index (HAII) based on nighttime light data and land cover data. Regression and dominance analyses were used to compare the effects of the HAII, precipitation, distance to river, distance to fault, topographic relief and slope on the landslides spatial density (LSD). The results showed that in the YRB, the HAII, as a dominance influencing factor, had a significant positive influence on the LSD. Moreover, regional differences in the human disturbance of nature intensify the spatial variation of LSD. To quantify the intensity of human disturbance to nature, a human-nature conflict index (HNCI) is constructed by quantifying the difference between the slope distributions of artificial and natural landscapes. The results show that in the middle section of the YRB, humans are developing more steep mountainous areas, leading to more dense landslides. This study provides a reference for landslide risk management and land use planning in the YRB. [ABSTRACT FROM AUTHOR]

Geotechnical drilling for a tunnel between Port Moody and Burnaby, BC, Canada, uncovered a buried fjord. Its sedimentary fill has a thickness of at least 130 m and extends more than 37 m below present mean sea level. Recovered sediments record cyclical growth and decay of successive Cordilleran ice sheets. The oldest sediments comprise 58 m of almost stoneless silt conformably overlying ice-proximal sediments and till, which in turn overlie bedrock. These sediments may predate Marine Isotope Stage (MIS) 4. Glacial sediments assigned to MIS 4 overlie this basal succession and, in turn, are overlain by MIS 3 interstadial sediments and sediments from two MIS 2 glacial advances. Indicators of relative sea-level elevations that bracket glacial deposits of MIS 4 and 2 indicate the cyclic existence of moat-like isostatic depressions in the front of expanding ice sheets. Compared with present sea level, these depressions were at least 160 m during the onsets of MIS 4 and MIS 2. Assuming a maximum eustatic drawdown of 120 m during MIS 2, isostatic depression may have exceeded 200 m during retreat of glacial ice from the Evergreen tunnel area. This is consistent with region-specific low mantle viscosity and rapid Cordilleran Ice Sheet buildup and wasting. [ABSTRACT FROM AUTHOR]