The inexorable ice front -- fact or fiction?

Beware!  Here comes the Ice Age........

Another myth that seems pretty widespread -- probably as a result of cartoons and disaster movies -- is the myth of the approaching ice age in the form of a vast ice cliff that approaches inexorably from the north and which eventually smashes everything to smithereens. "Glaciers in fiction" would be a nice doctorate thesis for somebody......

Let's get this straight.  At the onset of a glacial episode glaciers do not just form in the north and spread southwards, overtaking everything in their path.  They grow UPWARDS, not outwards, although of course when they have reached a critical thickness and mass, the ice does begin to flow and slide on its bed -- and at that time it can be said to be "advancing".  Not just southwards, but in any direction where there is an ice surface gradient.  You wouldn't believe (or maybe you would) the amount of time I have had to spend over the years explaining to archaeologists that northern hemisphere glaciers do not just flow north to south, and that it is perfectly OK for the Irish Sea Glacier to flow eastwards up the Bristol Channel without breaking any of the laws of physics.  It's also perfectly fine for the ice from the Scottish Highlands to flow northwards across the Orkneys, westwards across Harris and Lewis, and eastwards into the North Sea Basin.

At the beginning of each glacial episode in the British Isles, the process of glaciation is always started on a tundra landscape underpinned by permafrost, with seasonal snowpatches expanding and becoming permanent, so triggering a positive feedback mechanism as surface albedo increases.  The leads in turn to lower heat absorption from incoming solar radiation, with an inexorable thickening of the snowcover until in valleys and hollows it is converted into firn and then into ice.  Then it starts to flow as the landscape becomes covered with more and more small ice caps on plateaux and in the lee of upland ridges.  These ice caps begin to coalesce, and they keep on thickening until eventually we end up with in ice sheet, with its centre located in the area where accumulation rates are highest.  This will often be an area of high mountains or high plateaux.

I'll explore the birth of ice sheets in more detail in another post, but it's worth remembering that your average ice sheet starts off looking something like this:

The landscape of Byers Peninsula Livingston Island, South Shetlands, Antarctica. An undulating plateau, partly covered with semi-permanent snowfields. By the time glacier ice starts to move across a landscape like this, it will already have been covered with ice maybe more than 100m thick for many thousands of years.