Longtown Castle

 Longtown Castle 

It was 1978 when I worked at Longtown Castle,  a motte and bailey medieval castle on the Welsh border in Herefordshire.

The job was simple enough, dig out the destruction rubble in the floor of the keep, around 30 cubic metres of rubble.

The castle is on a ridge that carries an ancient track way from Abergavenny,  north to Hay- on-Wye. 

A deep valley runs parallel to the Longtown ridge, and beyond that was the Black Mountain, a high ridge, also connecting Abergavenny to Hay- on-Wye. 

The scenery, topography, and geology are difficult to ignore here, and I would sit in the site hut, sipping teaz and looking out and wondering how the valley and the ridges on either side of it were formed.

Anything I might have learned at school suggested that the valley must have been formed by either a glacier sliding along it, or by water flowing along it.

Neither option looked feasible here. The valley was roughly 10 kilometres long, 1 kilometre wide, and fell 300 metres along it's length.

Looking at the valley over the rim of a cup of tea, at tea break, I could never see that the amount of rainwater falling on the valley would ever be enough to erode the several million tons of rock that was missing from the valley,  not even in many millions of years.

I began to cook up an idea that the valley was actually created, not by a scraping glacier flowing along it, but by an ice sheet edge  collapsing.  

This would explain most British valleys, and  ribbon lakes, and the valleys that cross small islands,  from sea to shining sea (Anglesey).

It would also explain multiples of valleys that lie parallel to each other,  and that are separated by ridges like the ridge upon which Longtown Castle sits.

Gradually the idea took shape a couple of years ago, as i started to research more deeply into the recent, post-glacial geology of Britain and Norway.

I found that academia is completely locked onto the idea that mountain valleys were formed by the flow of glaciers along them.

In fact though, what is actually happening, is that ice sheet edges are collapsing, gouging out valleys as they fall, and the resulting ice blocks, dust, and broken rocks are sliding gently down any available slope until they reach water. 

Finally, this flow of meltwater, dust, ice and rocks reach water where the ice melts out leaving a moraine at the waters edge.

The passage of the ice, dust, and rocks mixture is marked by striations in the exposed geology, being  currently understood to be formed by the movement of solid glaciers rather than this looser mixture of materials. 

If my calculations are correct this melt would have supplied meltwater at a volume of over half a cubic kilometre for every day of deglaciation in that valley. This would have (did) raised sea level significantly in the brief periods when extreme temperatures and extreme melts took place.

Jeffery Nicholls 

Jiffynorm@yahoo.co.uk 





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