A brief introduction to... Glaciation

Glen Nevis. www.thewalkingzone.co.uk

Back again! Today's brief intro is on the evolution of landscapes through the transition from interglacial to glacial. I'll try not to focus too much on global temperature changes or the causes of these, more on a hypothetical landscape. And we're off...

A gradual drop in temperature will result in periglacial conditions and the onset of permafrost. Periglacial processes occur on the surface and subsurface, resulting in patterned ground features, pingos, palsas (in wetlands), sorting of sediments and frost action processes on exposed rocks. 

Precipitation in winter months results in a build up of snow cover, with melting occurring during the summer months. Seasonality is considered one of the primary controls on glaciation. If the net snow accumulation is positive for an extended period of time, snow cover thickness increases. Pressure from the snow overburden causes the transition of snow into firn, the point where the pore spaces between ice crystals become enclosed (more on this in a further post), trapping the air at its present concentration within the firn. Under increasing pressure, firn becomes ice.

Once overburden reaches a critical point, the ice spreads out in all directions from this "ice cap". Just as a river will find the path of least resistance, ice will flow in a direction which is easiest, this could be a relict river valley or any natural depression in the land. The erosive power of a massive body of moving ice is huge. Imagine the base of the glacier includes fragments of rock like giant sand-paper. Through time, this ice carves the classic glacial troughs seen throughout the Yorkshire Dales, Lake District, Snowdonia and Glen Nevis (Ben Nevis is an amazing place to hike; see the picture above and follow the link for more). This is probably the most awe inspiring period to imagine; millions of tonnes of ice grinding away the rock it is forced over by more ice being produced at the ice cap it originated from.

The Last Glacial Maximum (LGM) was between 12 and 14 thousand years ago depending on where you were at the time. It is known as the Loch Lomond Stadial or the Younger Dryas, and was preceded by an interglacial, just as every other glacial within the Quaternary.

Just as these periods capture my fascination due to the pure scale of landscape change, I find the transition from glacial to interglacial, known as the paraglacial period (coined by Colin K Ballantyne), is by far the most interesting. Landscapes just go crazy! This will be covered in my next post, so make sure to check back for that!

I hope you found this interesting. Please have a go at the feedback below, let me know what you think and what you'd like to read about, I'd be grateful for the ideas!