ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ground surface. The concentrations of these nuclides in
mineral grains at the ground surface reflects their rate of
erosion. If quartz grains exposed at the surface are subsequently
buried (for example by deposition in a cave or
deep within an alluvial terrace), then their 26AI and lOBe will
decay at different rates. The 26AI/1oBe ratio will therefore
decrease exponentially through time, recording the time
since burial. Thus the concentrations of 26AI and lOBe in
buried sediment record both the time since sediment emplacement
and the prevailing erosion rate at the time of sediment
burial.
We are currently measuring 26AI and lOBe concentrations in
cobbles of unmetamorphosed sediment, preserved high in
the Alpi Apuane in deposits within the Corchia cave complex,
and in alluvial terraces scattered throughout the region.
We anticipate that these analyses will constrain the
exhumation rate of these actively uplifting mountains, thus
dating the unroofing of the Alpi Apuane and establishing
the age of the developing mountain landforms.
GORDON E. GRANT\ SHERRI L. JOHNSON\
FREDERICK J. SWANSON 1 & BEVERLEY WEMPLE}
Anatomy of a flood: geomorphic and
hydrologic controls on channel
response to a major mountain flood
I Usda Forest Service, Pacific Northwest Research Station,
3200 Jefferson Way, Corvallis, OR 97331, U.S.A.
2 Department of Geosciences, Oregon State University,
Corvallis, OR 97331, U.S.A.
3 Department of Forest Sciences, Oregon State University,
Corvallis, OR 97331, U.S.A.
The flood of February 5-9, 1996 in the 'u.s. Pacific
Northwest provides unparalleled opportunities to examine
the interrelated effects of hydrologic and geomorphic processes,
landforms, and land use on watershed response to
major storm events.:We have examined how mass movements,
including landslides and debris flows, small stream
channels, and road networks interacted with mainstem
channels and valley floors to produce the pattern and magnitude
of floodclisturbances observed.
A coordinated program of inventory, field mapping, and
analysis of floodimp,acts on hillslopes, road networks,
stream channels.and riparian zones in the western Oregon
Cascades permits disentangling intrinsic and anthropogenic
controls on channel response. Flood effects were not
uniformly distributed either within or between watersheds.
Dynamics of melting snowpacks, as controlled by elevation,
determined the overall pattern of streamflows and
mass movements. Forest land-use activities on hillslopes
and in small and large channels contributed to channel response
by influencing the availability of water, sediment,
and wood delivered to mainstem channels. Mass failures
associated with road networks were prominent hillslope
disturbances, and delivered sediment and wood to down-
188
stream channels. Differences in the abundance of sediment
and large woody debris stored in the channel before the
flood and delivered during the event itself were primary
factors controlling the type and distribution of channel responses.
Large woody debris delivered to the channel by
debris flows and entrained from streamside forests played
multiple critical roles. At some sites, wood levies at the
margins of the active channel confined streamflows, thereby
increasing channel erosion while protecting riparian
forests. Alternatively, wood also caused channel avulsions,
battered and uprooted riparian forests, and promoted rapid
sediment deposition behind debris dams. Flood effects
were limited in narrow, bedrock-controlled channel sections
but extensive along many wide valley floors, particularly
where sediment supply was high.
Results from this flood analysis highlight the importance of
interpreting flood response within an overall geomorphic
context. Such a context includes recognizing the spatial distribution
of flood processes, variability in hillslope and
channel sensitivity to flood disturbances, and importance
of biogenic processes. It also includes placing response to a
particular flood within a larger temporal framework of
previous floods and evolving landscape conditions due to
changing land use patterns.
TAMES GRAY 1, CHRIS CLARK2, VINCENT DECKER 1,
JOHN GOSSE 3 & JEFF KLEIN 4
Patterns of mountain and continental glaciation of the
Torngat Mountains, Northern Quebec-Labrador:
the geomorphological evidence for cold-based ice
I Departement de Geographie, Universite de Montreal, Montreal,
Quebec, H3C 3J7, Canada
2 Department of Geography, University of Sheffield, Sheffield,
S10 2TN, U.K.
3 Department of Geology, 120 Lindley Hall, University of Kansas,
Lawrence, KA 66045, U.S:A.
4 Department of Physics, University of Pennsylvania,
Philadelphia, Pennsylvania, U.S.A.
Along the western flank of the Torngat Mountains, fronting
onto Ungava Bay, geomorphic evidence of ice flows
obtained from striae pits, and from erratic' provenance studies,
reveal that during the last glaciation, major lobes from
the continental Laurentide ice sheet to the west impinged
upon this uplifted mountain massif. In the northernmost
part of the peninsula, this continental ice clearly has overridden
the summits, situated at circa 500 m elevation. In
the Sheppard Lake region lateral and terminal moraine
complexes indicate late glacial stable phases near the eastern
front of the continental ice sheet. Further south, in
the vicinity of Abloviak Fjord, where relief is in excess of
1500 m, the striae evidence and erratic evidence, indicates
important outflow to the north-west, of locally developed
Torngat Mountain ice. Very well developed glacial lake
shorelines, and de Geer moraines, provide irrefutable evi-