The second example shows how directional optical filtering was applied to the study 
of crevasses occurring on the Karlinger Kees/Glacier in the Glockner Group, 
Austria. They are caused by tension in the ice due to changes in flow direction of 
the ice and to irregularities of the rock substratum. The portion of the glacier 
used for the experiment shows the pattern of crevasses produced where the ice 
from the catchment, coming from the upper right flows over a subglacial rock step 
or nose and thereafter gives way to the short glacier tongue to the left. Since ice 
crevasses are basically tension cracks they are formed perpendicularly to the 
stress produced by the direction of the iceflow over the substratum. It thus seems 
of interest to analyze the effect of the just mentioned change in flow direction in 
the transition zone where a cross-pattern of crevasses is formed. 
Photo 7 
Fourier spectra of the crevasse pattern of photo 6: 
(a) unfiltered (see photo 6); 
(b) with the vertical direction filtered out (see photo 8); 
(c) with the dominant oblique direction filtered out as 
well as possible (see photo 9). 
Photo 6 is the unfiltered laser image on which the two main crevasse directions 
are clearly visible, as is the snow-covered part of the glacier where no crevasses 
can be observed. The Fourier spectrum of photo 7a equally clearly indicates the 
dominance of the oblique crevasses formed under the influence of the stress pro 
duced by the flow direction occurring in the upper part of the glacier. The approx 
imately vertical crevasses, visible especially to the left of the snow patch in the 
lower portion of the image, reflect the beginning influence of the leftward tension 
produced by the ice flow in the glacier tongue further downstream. The subglacial 
rock step or nose, referred to above, is responsible for the irregular crevasses 
in the lower part of the image to the right of the snow patch.