ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

and eastern England are assessed using the landsystems
model.
Landforms produced during surging include thrust and
push moraines, concertina eskers and subglacial crevassesqueeze
ridges. Sedimentary sequences are usually characterized
by multiple stacked diamictons and stratified interbeds,
which display severe glacitectonic contortion and
faulting. Hummocky moraine comprising interbedded
stratified sediments and mass flow diamictons has also
been associated with surge margins where large quantities
of englacial debris entrained during the surge event has
melted out in situ. Similar landform/sediment associations
appear to have been produced at the margins of fast
flowing palaeo-ice streams. In southern Alberta, western
Canada, a palaeo-ice stream within the southwest Laurentide
Ice Sheet has been identified from a mega-fluting
complex and an associated terminal moraine arc of glacitectonically
distorted and thrust bedrock. Thrust moraines
are common also at slow moving sub-polar glacier snouts
where surging is extremely rare. Complex stratigraphies of
glacitectonized diamicton and stratified interbeds have
been widely reported from palaeo-glacier margins in Britain
and northwest Europe where they are interpreted as
the products of glacitectonic thickening of deformable sediments
and are not necessarily associated with abnormal
glacier velocities.
Only concertina eskers and extensive networks of subglacial
crevasse-squeeze ridges can really be associated exclusively
with surging glacier margins. Contorted medial moraines
are also good indicators of surge behaviour but have
a very poor preservation record. In the absence of such
features (eg. East Yorkshire) the local and regional aspects
of the palaeogeography that are conducive to surge behaviour
(eg, former deep ice-contact water bodies) should be
assessed in conjunction with the glaciallandsystem.
IAN S. EVANS l
& NICHOLAS J. COX l
Analysis, presentation and interrelation of directional
data as applied to glaciers and glacial cirques
1Earth Surface Systems Research Group, Department of Geography,
University of Durham, South Road, Durham City DH1 3LE,
England, U.K.
Linear statistics are still frequently applied to 2-D directional
data (azimuths, data on the circle), although it is well
known that the results can be very misleading because the
point at which the circle is divided is arbitrary. One problem
is that most statistical program suites do not have
routines which address the special properties of data on
the circle, and users are tempted to use ordinary linear
routines especially when their data sets include both linear
and circular variables. Here the use of a number of routines
for circular data, available from the authors, is exem-
160
plified for data sets for whole mountain ranges specifying
the aspect, position, size and form of glaciers and glacial
cirques. Other applications include hillslope analyses, river
channel and network analyses, wind direction and
bedform analyses (dunes, bars, drumlins)
Univariate data presentation is not a trivial matter and three
different approaches all have their strong points: a cumulative
vector diagram, a histogram wrapped around a
circle, and a linear histogram with repetition either side of
the division point. For a linear histogram, repetition of a
quarter-circle on the left and the right usually permits modes
and minima to be properly appreciated. Alternatively,
for unimodal distributions a linear histogram can be recentred
so that the circle is divided opposite the mean resultant
vector. Smoothing by a moving kernel on the circle
can remove minor sampling or rounding fluctuations, but
the number of 'real' modes remains a subjective interpretation.
For bivariate scatter plots, the best solution is lateral
repetition so that every data point plots four times; this ensures
that the whole of a band or cluster of data points can
be appreciated, whatever its shape or position.
A special version of the correlation coefficient is available
to interrelate paired values of aspect or azimuth. For
example the correlation between axial aspect and headwall
aspect is +0.873 for 158 cirques in the English Lake District,
and +0.838 for 198 cirques in the Cayoosh Range,
British Columbia. Circular variables are related to linear
variables by Fourier regression, which can be summarised
by another version of the correlation coefficient. Further
tests deal with the randomness of a data set, compared
with different alternative hypotheses, and the difference
between two or more distributions.
Both glaciers and cirques in the southern Coast Mountains'
British Columbia show a landward trend to increased
azimuthal concentration in the drier, more continental
climate with higher snowline. Differences are significant in
concentration but not in vector mean azimuth. The strong
asymmetry is related to wind and solar radiation effects
which reinforce eachother. Cirques are less azimuthally
concentrated than glaciers in the same range; the climates
in which they developed were colder than present, with a
snowline about 400 m lower, but with no discernible difference
in snow-bearing winds. They are believed to have
developed before glacial maxima, at which they were inundated
in the Cordilleran Ice Sheet.
MARTIN EVANS
The geomorphic sensitivity of alpine-subalpine basins
in the Cascade Mountains, British Columbia, Canada
Department of Geography, University of British Columbia,
1984 West Mall Vancouver, British Columbia, Canada
Concerns over global change have highlighted the importance
of understanding the sensitivity of geomorphic sy-