Erik Schiefer

Physiographically controlled allometry of specific sediment yield in the canadian cordillera: a lake sediment‐based approach

It is generally supposed that specific sediment yield declines as the drainage basin area increases, as part of the mobilized sediment becomes trapped in the downstream cascade of storage zones. In British Columbia, using fluvial suspended sediment load data, Church and Slaymaker (Nature 1989, Vol 337, pp. 452–454) have observed a pattern of increasing specific sediment yield at all spatial scales up to 3×104km2. This trend has been attributed to the dominance of secondary remobilization of Quaternary sediments over primary denudation of the land surface. Using a larger data set of lake sediment‐based estimates of long‐term sediment yield, sub‐regional patterns of specific yield have been investigated for the Canadian Cordillera. Between spatial scales of 0.9 and 190 km2 sediment yield trends are differentiated by physiography, as indicated by the variable allometry observed in the specific sediment yield–drainage basin area relations. Highest sediment yields were observed in the Coast Mountains where specific sediment yields conform to the regional pattern described by Church and Slaymaker. However, in flat‐lying plateau and major valley areas specific sediment yield decreases with increasing drainage area, thus conforming to the conventional model of sediment delivery. In several other sub‐regions of intermediate relief there were no significant relations between specific yield and drainage area. These results suggest that no single model of sediment yield is adequate to describe sediment transfer processes in the Canadian Cordillera at the sub‐regional scale.

Predicting sediment physical properties within a montane lake basin, southern Coast Mountains, British Columbia, Canada

Abstract 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.

Climatic and morphometric controls on the altitudinal range of glaciers, British Columbia, Canada.

To examine the relation between climate and glacier extent, we compared gridded, monthly temperature and precipitation data to the altitudinal range of glaciers in British Columbia, Canada. We related glacier relief to ablation season temperature (June—August), accumulation season precipitation (September— March), and morphometric variables that included slope, glacier order, and a shape index for 523 alpine glaciers that ranged from 5 to 15 km2 in surface area. A 1°C increase in mean June—August temperature equates to a 109 to 182 m decrease in glacier relief, and a 1 mm increase in mean monthly September— March precipitation equates to a 0.78 to 2.20 m increase in glacier relief. The most important morphometric controls on this glacier—climate relation include average surface slope, glacier order (analogous to stream order), and the ratio of upper accumulation area to lower ablation area width, all of which are positively related to glacier relief. We note strong relations between glacier relief and climate in all mountain regions of British Columbia, with glaciers of the interior ranges being most sensitive to spatial climatic variability. We show how our approach can be used to estimate past climatic conditions based on historical ice extents, such as at the ‘Little Ice Age’ maximum, and to predict potential future equilibrium glacier extents in a changed climate regime, such as those predicted by general and regional circulation models.

Fluvial suspended sediment yields over hours to millennia in the High Arctic at proglacial Lake Linnévatnet, Svalbard

Sediment yield can be a sensitive indicator of catchment dynamics and environmental change. For a glacierized catchment in the High Arctic, we compiled and analyzed diverse sediment transfer data, spanning a wide range of temporal scales, to quantify catchment yields and explore landscape response to past and ongoing hydroclimatic variability. The dataset integrates rates of lake sedimentation from correlated varve records and repeated annual and seasonal sediment traps, augmented by multi-year lake and fluvial monitoring. Consistent spatial patterns of deposition enabled reconstruction of catchment yields from varve- and trap-based fluxes. We used hydroclimatic data and multivariate modeling to examine annual controls of sediment delivery over almost a century, and to examine shorter-term controls of sediment transfer during peak glacier melt. Particle-size analyses, especially for annual sediment traps, were used to further infer sediment transfer mechanisms and timing. Through the Medieval Warm Period and Little Ice Age, there were no apparent multi-century trends in lake sedimentation rates, which were over three times greater than those during the mid-Holocene when glaciers were diminished. Twentieth-century sedimentation rates were greater than those of previous millennia, with a mid-century step increase in mean yield from 240 to 425 Mg km-2 yr-1. Annual yields through the twentieth century showed significant positive relations with spring/summer temperature, rainfall, and peak discharge conditions. This finding is significant for the future of sediment transfer at Linnevatnet, and perhaps more broadly in the Arctic, where continued increases in temperature and rainfall are projected. For 2004-2010, annual yields ranged from 294 to 1330 Mg km-2 yr-1. Sediment trap volumes and particle-size variations indicate that recent annual yields were largely dominated by spring to early summer transfer of relatively coarse-grained sediment. Fluvial monitoring showed daily to hourly sediment transfer to be related to current and prior discharge, diurnal hysteresis, air temperature, and precipitation.

Lillooet-Harrison Drainage Basin: Variable Landscapes Within the Coast Mountains

The Lillooet-Harrison watershed (7870 km2 in area, of which 459 km2 is glacierized) contains recurring morphological landscape elements that differ in terms of their level of connectivity with Lillooet River. First, ridge tops with low local relief are connected to Lillooet River primarily through dissolved solids moving along subsurface pathways. Second, small glaciers have little direct connection with Lillooet River because of their numerous proximal lakes, whereas larger valley glaciers are directly linked to Lillooet River. Third, hillslopes subject to infrequent, large mass movements are episodically connected, and fourth, debris flow channels are directly linked with valley-bottom rivers. Fifth, mid-valley and lower valley-bottom sites are sediment storage areas that are episodically coupled to the adjacent river channel. The Mount Meager Volcanic Complex dominates the supply of coarse clastic sediment to Lillooet River and is primarily responsible for the rapid rates of Lillooet delta progradation and aggradation. The 6 % of the watershed that is glacierized provides a high proportion of the fine clastic sediments to Lillooet and Harrison lakes, whereas solute production that has little influence on morphological elements is important in assessing the overall rate of landscape denudation in the Lillooet-Harrison watershed. More frequent extreme rainfall events and rapid glacier retreat together with intensified human occupancy in the valley can be expected to increase the coupling of each of the morphological elements to Lillooet River and expedite the movement of water, sediments, and solutes through the watershed.

LATE‐SUMMER PEAK IN SEDIMENT ACCUMULATION IN TWO LAKES WITH CONTRASTING WATERSHEDS, ALASKA

Abstract The timing of clastic sedimentation in two glacial‐fed lakes with contrasting watersheds was monitored using sequencing sediment traps for two consecutive years at Allison Lake (Chugach Range, Alaska) and four months at Shainin Lake (Brooks Range, Alaska). Shainin Lake is a weakly stratified lake fed by distant glaciers, whereas Allison Lake is more strongly stratified and fed predominantly by proximal glaciers. At Shainin Lake, sediment accumulation started in late June and reached its maximum in mid‐August, just before lake mixing and during a period of low river discharge. The grain size of the sediment reaching the sediment trap in Shainin Lake was homogenous throughout the summer. At Allison Lake, pulsed sedimentation of coarse particles during late summer and early fall storms were superimposed on the fine‐grained sedimentation pattern similar to that observed at Shainin Lake. These storms triggered underflows that were observed in the thermal structure of the lake and deposited abundant sediment. The sequencing sediment traps reveal a lag between fluvial discharge and sediment deposition at both lakes, implying limitations to interpreting intra‐annual sedimentary features in terms of inflow discharge.