Wind direction and landscape change

This is a Bing satellite image and accompanying map to the same scale -- from the wonderful "side by side" web site created by the National Library of Scotland.

This is part of the main upland ride in the Brecon Beacons -- click to enlarge.

You can see here what a profound effect orientation and wind direction have on landscape change during the ice age.  Notice that the main cwms or cirques are oriented broadly NE.  The group of cirques and small glacial troughs in the NE quadrant of the photo were formed because this was the lee side of a ridge, where snow could accumulate and get converted into firn and then glacier ice, during the cold phases of the Ice Age when prevailing winds came from the W and SW.   The long escarpment running from top left to bottom right has been fashioned in a similar way, with a number of small cirques coalescing on the downwind flank of the upland ridge. 

In contrast, look at the valleys in the SW quadrant of the image -- these are "normal" river valleys with no trace of cirque formation.  In the Ice Age most drifting snow was blown up over the ridge to accumulate on the lee (shady) side, leaving the sunny flank largely unaffected. 

Here is another example, showing the Beacons landscape some way to the west, around the famous lakes of Llynyfan Fach and Llynyfan Fawr.   Here the coalescing cirques have a slightly different alignment -- there is a scarp face oriented NNW, but the cwm occupied by Llynyfan Fach is oriented NE, like most of the other cwms in the Beacons.  The scarp alignment may have something to do with the pre-glacial topography.  But note the long river valleys to the south, apparently unaffected by ice action.

  

The "upland glaciation" of this mountainous region must have occurred intermittently right through the Ice Age.  At other times the mountains were completely ice-free, and at the peak of each glacial episode the whole landscape hereabouts was deeply submerged by the ice of the Welsh Ice Cap.