INTRODUCTION
Although the mass
balance of glaciers in temperate zones typically fluctuates on scales from days
to millennia, most glaciers worldwide have undergone sustained recession in the
past century. Most projections anticipate continued, and possibly increased,
climatic warming during the twenty-first century. Rates of glacier volume loss
are already accelerating in many areas, particularly coastal regions. The rate of glacier loss in
the British Columbia Coast Mountains doubled in the late 1990s, most likely due
to increased temperatures and decreased snowfall associated with regional and
global climate trends.
Many consequences of glacier retreat have already been documented: declines in
late-summer streamflow from glacier-fed catchments, geomorphic hazards such as
outburst floods and debris flows, higher temperatures in glacier-fed streams,
and changes in suspended sediment fluxes and concentrations.
Retreating glaciers expose large denuded areas between heavily vegetated
ground and ice fronts, open lan
dscapes
broken only by outwash channels and the
occasional tarn. In these freshly uncovered proglacial zones, stream
channels
develop, reworking the postglacial landscape and generating new
ecosystems
(note: the terms 'proglacial' and 'postglacial,' while nearly
synonymous and
often used interchangeably, are here used to distinguish spatial and
temporal
orientation, with 'proglacial' referring spatially to the zone in front
of a
glacier, and 'postglacial' referring temporally to processes within the
proglacial zone). Proglacial zones are headwater systems, functioning
as strong controls on downstream hydrologic, geomorphic, and biological
processes. The unique process characteristics of headwater systems -
tight hillslope-channel and terrestrial-aquatic linkages, large
sediment inputs from mass wasting processes - are highly complex in
glaciated catchments, dominated by the topographic signature of former
ice flows.
The most recent, and
drastic, phase of glacial activity in southern British Columbia has
taken place since the end of the Little Ice Age. The Little Ice Age
(LIA), spanning most of the last millennium, was a period of variable
but generally cool climate when glaciers worldwide were at their
maximum Holocene extent. During the LIA, most glaciers made early
advances between AD 1100 and 1300 and later advances between 1700 and
1900. The precise cause of climate variability during the LIA is not
known. It was most likely due to interactions among several forcing
mechanisms, including volcanism, solar activity, and ocean-atmosphere
interactions.
LIA glacier fluctuations appear to have been synchronous on a centennial timescale in
the Americas. Recent studies 
focusing
specifically
on glacier activity in British Columbia have established a highly
synchronous
pattern here. Dates of glacial extents are established by studying
deposits in glacial forefields called moraines (see photo to
right, moraine complex at Colonel Foster Glacier, Strathcona Provincial
Park) using dendrochronology, lichenometry, and radiocarbon
dating. Glacier activity in the past century can often be established
by aerial
photographs and satellite images. In western
Canada, significant glacier recession from the LIA maximum did not
begin until the early to mid
twentieth century.
Understanding major processes and controls in upstream reaches is critical to effective resource management, especially as glaciers continue to retreat. Process domains, regions within which one or a collection of surface processes dominates the detachment and transport of mass, are a highly accurate way to describe and analyse drainage basins and stream morphology. Plots of local slope gradient vs. contributing drainage area can be used to delineate process domains. Highly variable slope-area plots indicate greater system complexity. The LIA maximum was used as a benchmark for this project. In order to capture morphological variability in the most recently exposed areas of postglacial streams, slope-area information was gathered from the entire area exposed post-LIA as well as stream reaches extending up to 300 m beyond the maximum LIA extent.
This project seeks to identify patterns in proglacial channel morphology and relate these patterns to glacier characteristics using variability in process domains as a basic quantitative description of fluvial system type. Building on data collected from field surveys in summer 2010, it represents both an initial qualitative analysis and an attempt to quantify variability in glacier type and stream morphology.
STUDY AREAS
Sites were selected within the same geographic region, the southern British Columbia Coast Mountains, in order to minimize inter-regional variability and highlight intra-regional variability. Initially, 60 glaciers in Canada and 36 glaciers in the US were hand digitized (see additional description on methods page), but time constraints limited actual analysis to 17 glaciers in Canada, grouped into four regions as indicated in the figure below.
1. Strathcona Provincial Park: Septimus, Colonel Foster, and Moving Glaciers. 2. Spruce Lake Protected Area: Lorna E and Lorna W Glaciers. 3. Pemberton: Miller S, Miller N, Matier, and Anniversary Glaciers. 4. Garibaldi: Black Tusk E, Black Tusk W, Overlord, Fitzsimmons, Helm, Lava, Wedgemount, and Diamond Glaciers.