Southern Coast Mountains Research Articles

Holocene Sediment Production in Lillooet River Basin, British Colombia: A Sediment Budget Approach

A sediment budget approach is used to investigate the sources, storage, and yield of clastic sediment in Lillooet River watershed, in the southern Coast Mountains. The 3150 km2 basin is heavily glacierised, and includes a Quaternary volcanic complex which has been active in the Holocene. The sediment yield has been determined from the rate of advance of the delta at the basin outlet. The floodplain of the main river valley is aggrading as the delta advances, and probably has been through most of the Holocene. Major sediment sources in the basin include glaciers and Neoglacial deposits, debris flows, and landslides in the Quaternary volcanic complex. Soil and bedrock creep, bank erosion of Pleistocene glacial deposits, and sediment from logging and agriculture are probably of minor importance. Estimates of sediment production from these sources explain only about half the observed clastic sediment yield plus the rate of valley aggradation. The unexplained sediment production may be associated with paraglacial sediments exposed by glacial retreat from the nineteenth century Neoglacial maximum; alternatively the frequency of occurrence of intermediate scale debris flows and landslides has been seriously underestimated. Sediment supply is highly episodic over time scales of centuries to thousands of years. Major factors in the temporal pattern of Holocene sediment supply are periods of volcanism, large landslides, the retreat of glaciers from the Neoglacial maximum, and recent river engineering works.

The Cordilleran Ice Sheet and the Glacial Geomorphology of Southern and Central British Colombia

This paper reviews the current state of knowledge about the Cordilleran Ice Sheet in southern and central British Columbia. Reconstructions of the ice sheet and the styles of ice expansion and déglaciation are based on extensive and varied glacigenic sediments and landforms that date from Late Wisconsinan (Fraser) Glaciation. Late-glacial lakes and sea level changes are also described and related to isostatic and eustatic effects. The timing of ice expansion and recession during Fraser Glaciation was markedly asymmetric: ice build-up commenced about 29 000 years BP, culminated between 14 500 and 14 000 years BP1 and déglaciation was largely completed by 11 500 years BP. Most of this interval appears to have been dominated by montane glaciation, which produced striking erosional landforms. A Cordilleran Ice Sheet existed from only about 19 000 to 13 500 years BP. An older glaciation, probably of Early Wisconsinan age, has been recognized from widespread exposures of drift that underlies Middle Wisconsinan non-glacial sediments. Pre-Wisconsinan drift is present near Vancouver. Drifts of late Tertiary to Middle Pleistocene age have been dated by association with volcanic sequences in the southern Coast Mountains and the central Interior, and by paleomagnetic studies in the southern Interior.

Glacier fluctuations during the past millennium in Garibaldi Provincial Park, southern Coast Mountains, British Columbia

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.

Fault locking, block rotation and crustal deformation in the Pacific Northwest

SummaryWe interpret Global Positioning System (GPS) measurements in the northwestern United States and adjacent parts of western Canada to describe relative motions of crustal blocks, locking on faults and permanent deformation associated with convergence between the Juan de Fuca and North American plates. To estimate angular velocities of the oceanic Juan de Fuca and Explorer plates and several continental crustal blocks, we invert the GPS velocities together with seafloor spreading rates, earthquake slip vector azimuths and fault slip azimuths and rates. We also determine the degree to which faults are either creeping aseismically or, alternatively, locked on the block-bounding faults. The Cascadia subduction thrust is locked mainly offshore, except in central Oregon, where locking extends inland. Most of Oregon and southwest Washington rotate clockwise relative to North America at rates of 0.4–1.0 ° Myr−1. No shear or extension along the Cascades volcanic arc has occurred at the mm/yr level during the past decade, suggesting that the shear deformation extending northward from the Walker Lane and eastern California shear zone south of Oregon is largely accommodated by block rotation in Oregon. The general agreement of vertical axis rotation rates derived from GPS velocities with those estimated from palaeomagnetic declination anomalies suggests that the rotations have been relatively steady for 10–15 Ma. Additional permanent dextral shear is indicated within the Oregon Coast Range near the coast. Block rotations in the Pacific Northwest do not result in net westward flux of crustal material—the crust is simply spinning and not escaping. On Vancouver Island, where the convergence obliquity is less than in Oregon and Washington, the contractional strain at the coast is more aligned with Juan de Fuca—North America motion. GPS velocities are fit significantly better when Vancouver Island and the southern Coast Mountains move relative to North America in a block-like fashion. The relative motions of the Oregon, western Washington and Vancouver Island crustal blocks indicate that the rate of permanent shortening, the type that causes upper plate earthquakes, across the Puget Sound region is 4.4 ± 0.3 mm yr−1. This shortening is likely distributed over several faults but GPS data alone cannot determine the partitioning of slip on them. The transition from predominantly shear deformation within the continent south of the Mendocino Triple Junction to predominantly block rotations north of it is similar to changes in tectonic style at other transitions from shear to subduction. This similarity suggests that crustal block rotations are enhanced in the vicinity of subduction zones possibly due to lower resisting stress.

Late Holocene vegetation and climate change at Moraine Bog, Tiedemann Glacier, southern Coast Mountains, British Columbia

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.

Effect of Alpine glaciation on thermochronometer age‐elevation profiles

Low‐temperature thermochronometers are widely used to quantify exhumation histories, typically by interpreting sample cooling age‐elevation relationships. However, the effects of specific geomorphic processes on age‐elevation profiles are seldom considered. We integrate apatite (U‐Th)/He [AHe], apatite fission track, and zircon (U‐Th)/He thermochronometry with numerical modeling to determine the effect of glacial erosion on an age‐elevation profile from the heavily glaciated southern Coast Mountains, British Columbia. AHe data show a distinct break in slope in age‐elevation between 1900–2100 m. We interpret this break in slope as an acceleration of erosion associated with the onset of alpine glaciation. We use a 3‐D thermo‐kinematic model to constrain pre‐ and synglacial erosion rates. Results indicate a preglacial erosion rate of ∼0.4 mm/yr that accelerated by a factor of ∼2 since ∼6 Ma. We propose that glacial valley widening and deepening are responsible for the observed nonlinear AHe age‐elevation profile.

Reconstructing morphometric change in a proglacial landscape using historical aerial photography and automated DEM generation

This paper explores the feasibility of using historical aerial photographs and digital photogrammetric procedures to reconstruct morphometric landscape changes in a proglacial setting of the southern Coast Mountains, British Columbia, Canada. The photographic record includes 12 sets of vertical photography, obtained at a range of large to medium nominal scales, for the period 1947 to 1997. An automated procedure of digital elevation model (DEM) extraction was employed and details of morphometric change were assessed by differencing the DEM surfaces obtained for different dates of photography. Results are used to describe terrain surface changes associated with glacier recession, moraine gully erosion, and forest growth in the glacial forefield. Methods are reviewed for the estimation and handling of systematic and random vertical errors in the DEMs that are suitable for this type of environment, where there are no historical surveys or monuments to use as a common benchmark and only natural features are available for establishing ground control. Digital photogrammetry, applied to scanned archived photography, can be used to generate high-resolution (sub-meter) DEM surfaces of proglacial terrain suitable for quantifying decadal-scale morphometric changes that have occurred since the mid-20th century to recent times. Potential applications of these techniques and the associated historical data are discussed.

Extreme sediment delivery events recorded in the contemporary sediment record of a montane lake, southern Coast Mountains, British Columbia

The extreme sediment delivery regime of a montane catchment was examined through the analysis of recent lacustrine varve deposits recovered from a high-density sampling program. Years of anomalously high sediment yield from the Green Lake watershed were identified over a 70-year period (1930–2000) based on whole-lake varve deposit volumes. Intra-annual sediment delivery events were categorized and described for those anomalous years using historical hydroclimatic data and the stratigraphic record observed within inflow proximal sediment cores. Extreme sediment delivery coincided with high discharge conditions and elevated sediment availability resulting from (1) rapid glacier recession of the early twentieth century, (2) late-summer and autumn rainstorm-generated floods, and (3) freshet floods caused by unusual snowmelt conditions. The thickness and physical characteristics of varves vary among years that experienced different types of moderate and extreme sediment delivery events in relation to the defined average-regime depositional model. Several hydroclimatic factors can interact to produce composite varve units of anomalous thickness. In some cases, geomorphic events, such as landslides and channel changes, contributed to extreme sediment delivery in the Green Lake catchment. The interaction of these geomorphic effects, coupled with the variable nature of associated hydroclimatic functions, complicate paleoenvironmental assessments based on the lacustrine varve record.

Multi-proxy record of Holocene glacial history of the Spearhead and Fitzsimmons ranges, southern Coast Mountains, British Columbia

Evidence from glacier forefields and lakes is used to reconstruct Holocene glacier fluctuations in the Spearhead and Fitzsimmons ranges in southwest British Columbia. Radiocarbon ages on detrital wood and trees killed by advancing ice and changes in sediment delivery to downstream proglacial lakes indicate that glaciers expanded from minimum extents in the early Holocene to their maximum extents about two to three centuries ago during the Little Ice Age. The data indicate that glaciers advanced 8630–8020, 6950–6750, 3580–2990, and probably 4530–4090calyrBP, and repeatedly during the past millennium. Little Ice Age moraines dated using dendrochronology and lichenometry date to early in the 18th century and in the 1830s and 1890s. Limitations inherent in lacustrine and terrestrial-based methods of documenting Holocene glacier fluctuations are minimized by using the two records together.

Statistical, remote sensing-based approach for estimating the probability of catastrophic drainage from moraine-dammed lakes in southwestern British Columbia

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.

Anomalous early 20th century sedimentation in proglacial Green Lake, British Columbia, Canada

Annually laminated sediments were recovered from Green Lake, a proglacial lake in the southern Coast Mountains in British Columbia, to examine their potential as a temperature proxy. Varve thickness is moderately correlated with temperature anomalies (A.D. 1900–1994) and annual maximum mean daily discharge of Lillooet River (A.D. 1930–1999), but these relations are not stable through time. Following A.D. 1977, the relation between varve thickness and annual maximum mean daily discharge is stronger. Prior to A.D. 1977, varve thickness is correlated with March to October air temperature, which controls the intensity and duration of glacier runoff. Varve thickness is weakly correlated with reconstructed air temperature records for North America and the Northern Hemisphere for the period A.D. 1600–1976. Less extensive glacier cover may explain the lack of a clear temperature signal in the varved sediment record prior to A.D. 1600 and following A.D. 1977. The period of highest lake sedimentation, from A.D. 1920 to 1945, coincides with rapid retreat of glaciers in the watershed. The lack of a similar level of sedimentation in the varve chronology suggests that glacier recession during the period 1920–1945 was higher than at any time in the past 600 years.

LATE EARLY SINEMURIAN (EARLY JURASSIC) AMMONITES FROM THE TASEKO LAKES MAP AREA, BRITISH COLUMBIA

Abstract: Abundant and well‐preserved Early Jurassic ammonite assemblages occur in the Taseko Lakes map area on the Cadwallader Terrane in the southern Coast Mountains of British Columbia. The ammonite assemblage described herein includes nine genera and 14 species, most of them already known from classical localities of northern and southern Europe. The presence in particular of Caenisites brooki (Sowerby) and C. turneri (Sowerby) permits high‐resolution correlation with the Turneri Zone of the north‐west European Sinemurian zonation. The specimens were collected at four localities but most come from an olistolith where the ammonite assemblage is dominated by Coroniceras (Paracoroniceras) mutabile Macchioni, Smith and Tipper, associated with Lytotropites fucinii (Bonarelli) and Hypasteroceras montii (De Stefani). The latter two species, whose exact age is here established for the first time, have a Mediterranean distribution.

Contemporary sedimentation rates and depositional structures in a montane lake basin, southern Coast Mountains, British Columbia, Canada

AbstractSpatial variability of recent lacustrine sedimentary structures and sedimentation rates are examined for Green Lake, a morphologically complex lake basin of the southern Coast Mountains, British Columbia. A dense, 100 m grid sampling scheme was used for sediment coring within the 2 km2 lake basin. Deltaic, massive, weakly laminated, and varved sediment sequences are identified within the sediment record. Spatial patterns among these sedimentary deposits are related to within‐lake sediment transfer processes, morphometric controls, and the extent of post‐depositional mixing by bioturbation. Unconformities, turbidites, and cohesive slump failure deposits, observed within the contemporary varve sequences, could all be correlated with major flooding events in the catchment area and direct anthropogenic disturbances along the shoreline. There is an overall, non‐linear decrease in sedimentation rates with increasing distance from the lake inflows; however, this pattern is disrupted in deep water sites of intervening lake sub‐basins where locally higher accumulation rates are observed. Spatial sedimentation patterns are quantitatively described by an empirically‐derived model. Systematic variations in the model parameters are observed for different lake sub‐regions and are associated with changing sediment transfer dynamics between proximal and distal sub‐basin settings. Copyright © 2006 John Wiley & Sons, Ltd.

Predicting Sediment Physical Properties within a Montane Lake Basin, Southern Coast Mountains, British Columbia, Canada

The variability of lacustrine sediment physical properties was examined for a small montane lake in the southern Coast Mountains of British Columbia. A high-density sampling scheme (1 core per 0.01 km2) was utilized for sediment sampling within the 2 km2 lake basin. Vertical patterns in the upper sediment record were controlled by compaction effects with interruptions by major sediment delivery event beds and organic debris deposits. Primary patterns of lateral variability were associated with proximity to the principal lake inflow. A simple sedimentation model based on Stokes Law was shown to reasonably predict down-lake variations of sediment texture. A significant influence of water depth was observed in shallow water settings where highly variable sediment characteristics were observed. Secondary spatial patterns were related to localized rapid deposition effects and past land-use activities. Sedimentary parameters of water content, bulk density, organic content, and particle size were shown to be interrelated to varying degrees. Water content may be used as a key parameter for predicting other physical properties because of its strong negative relation with sediment density, moderate positive relation with organic content, and non-linear association with mean particle size.

Apatite (U-Th)/He signal of large-magnitude accelerated glacial erosion, southwest British Columbia

Research Article| September 01, 2006 Apatite (U-Th)/He signal of large-magnitude accelerated glacial erosion, southwest British Columbia Todd A. Ehlers; Todd A. Ehlers 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Kenneth A. Farley; Kenneth A. Farley 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Search for other works by this author on: GSW Google Scholar Margaret E. Rusmore; Margaret E. Rusmore 3Department of Geology, Occidental College, Los Angeles, California 90041, USA Search for other works by this author on: GSW Google Scholar Glenn J. Woodsworth Glenn J. Woodsworth 4Geological Survey of Canada, 101-605 Robson St., Vancouver, British Columbia V6B 5J3, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Todd A. Ehlers 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Kenneth A. Farley 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA Margaret E. Rusmore 3Department of Geology, Occidental College, Los Angeles, California 90041, USA Glenn J. Woodsworth 4Geological Survey of Canada, 101-605 Robson St., Vancouver, British Columbia V6B 5J3, Canada Publisher: Geological Society of America Received: 07 Dec 2005 Revision Received: 24 Apr 2006 Accepted: 01 May 2006 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2006) 34 (9): 765–768. https://doi.org/10.1130/G22507.1 Article history Received: 07 Dec 2005 Revision Received: 24 Apr 2006 Accepted: 01 May 2006 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Todd A. Ehlers, Kenneth A. Farley, Margaret E. Rusmore, Glenn J. Woodsworth; Apatite (U-Th)/He signal of large-magnitude accelerated glacial erosion, southwest British Columbia. Geology 2006;; 34 (9): 765–768. doi: https://doi.org/10.1130/G22507.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Alpine glaciers are efficient agents of erosion and capable of significantly modifying topography. Despite recent advances in theoretical and field studies that quantify glacial erosion processes, few studies have documented glacial erosion rates over long (>106 yr) or large (more than tens of kilometers) scales. We use apatite (U-Th)/He (AHe) and apatite fission track (AFT) cooling ages to address the late Miocene to Holocene erosion history across two 60-km-long transects of the heavily glaciated southern Coast Mountains, British Columbia. Observed AHe cooling ages from equal elevation samples range between 1.5 and 8 Ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1.5–4.0 m.y. We evaluated temporal and spatial variations in erosion rates using a three-dimensional thermal-kinematic model that predicted AHe and AFT ages at the surface for different erosion histories. Comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300% over the past 1.5–7 m.y., coincident with the onset of glaciation of this range. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Rapid Glacial Erosion at 1.8 Ma Revealed by 4 He/ 3 He Thermochronometry

Alpine glaciation and river incision control the topography of mountain ranges, but their relative contributions have been debated for years. Apatite 4He/3He thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern Coast Mountains of British Columbia, Canada. Five proximate samples require accelerated denudation of the Klinaklini Valley initiating 1.8 +/- 0.2 million years ago (Ma). At least 2 kilometers of overlying rock were removed from the valley at >/=5 millimeters per year, indicating that glacial valley deepening proceeded >/=6 times as fast as erosion rates before approximately 1.8 Ma. This intense erosion may be related to a global transition to enhanced climate instability approximately 1.9 Ma.

Environmental reconstruction from a varve network in the southern Coast Mountains, British Columbia, Canada

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.

‘Little Ice Age’ proxy glacier mass balance records reconstructed from tree rings in the Mt Waddington area, British Columbia Coast Mountains, Canada

The intention of this research was to explore whether dendroclimatological relationships could be used to reconstruct long-term proxy records of ‘Little Ice Age’ glacier mass balance changes in the southern Coast Mountains of British Columbia. Tree-ring width chronologies from the Mt Waddington area were used in concert with historical glacier records to construct models spanning the past 450 years. The approach was to build models that were based on derived relationships between tree-ring growth and glacier mass balance: (1) warmer temperatures in the summer positively influence tree growth but are detrimental to glacier health; (2) colder temperatures during the winter and deeper snowpack have a negative impact on tree growth, whereas they are related to greater accumulation on the glacier during the winter season. Stepwise regression analyses were applied to tree-ring chronologies to predict glacier mass balance at local and regional scales. The models of net annual balance for the region (regional data set) show that periods of positive mass balance occurred in the AD 1750s, 1820s to 1830s and 1970s. Peaks of winter balance correspond closely to these periods, showing a sharp drop in winter mass balance towards the end of the nineteenth century. Wavelet analyses suggest that glacial mass balance regimes in the region respond synchronously to Pacific Ocean circulation systems such as the El Niño Southern Oscillation and the Pacific Decadal Oscillation.

Geomorphic and sedimentological signature of a two‐phase outburst flood from moraine‐dammed Queen Bess Lake, British Columbia, Canada

AbstractOn 12 August 1997, the lower part of Diadem Glacier in the southern Coast Mountains of British Columbia fell into Queen Bess Lake and produced a train of large waves. The waves overtopped the broad end moraine at the east end of the lake and flooded the valley of the west fork of Nostetuko River. The displacement waves also incised the outflow channel across the moraine. Stratigraphic and sedimentologic evidence supports the conclusion that the flood had two phases, one related to wave overtopping and a second to breach formation. Empirical equations were used to calculate the peak discharge of the flood at various points along the west fork of the Nostetuko valley and to describe the attenuation of the flood wave. The velocity of the flood was also calculated to determine the time it took for the flood to reach the main fork of Nostetuko River. The highest peak discharges were achieved in the upper reach of the valley during the displacement phase of the flood. Peak discharge declined rapidly just below the moraine dam, with little change thereafter for approximately 7 km. Empirical formulae and boulder measurements indicate a rise in peak discharge in the lower part of the west fork valley. We suggest that flow in the upper part of the valley records the passage of two separate flood peaks and that the rise in discharge in the lower part of the valley is due to amalgamation of the wave and breach peaks. Hydraulic ponding in confined reaches of the valley extended the duration of the flood. In addition, erosion of vegetation and sediment in the channel and valley sides may also have exerted an influence on the duration and nature of flooding. Sediments were deposited both upstream and downstream of channel constrictions and on a large fan extending out into the trunk Nostetuko River valley. This study extends our understanding of the variety and complexity of outburst floods from naturally dammed lakes. It also shows that simple empirical and other models for estimating peak discharges of outburst floods are likely to yield erroneous results. Copyright © 2005 John Wiley & Sons, Ltd.

Calibrated Rhizocarpon spp. Growth Curve for the Mount Waddington Area, British Columbia Coast Mountains, Canada

A calibrated Rhizocarpon spp. lichen growth curve spanning the last 680 yr was developed for the Bella Coola and Mount Waddington areas, southern Coast Mountains of British Columbia (Canada). It is based on 18 control surfaces whose ages were determined using radiocarbon dates, tree-ring dated moraines, and ice front positions derived from historical air photographs. Population distribution statistics were used to assess the validity of each control lichen measurement. The relationship is characterized by logarithmic growth during the first 100 yr following surface stabilization, and is described as linear for the successive 600 yr. Application of the curve at Tiedemann Glacier revealed evidence for six periods of late-Neoglacial moraine formation in ca. AD 620, 925, 1118, 1392, 1575, and 1621. The study confirms the importance of incorporating a multisite approach and a lichen population dynamic assessment. Large samples sizes and replication are also noted as necessary in order to adequately assess any dating errors.