Speak to me of dead ice
and glacial erratics.
Tell me the tales
of wandering stones* –
granodiorite from Southern Scotland,
Criffel granite, Shap granite, Eskdale granite,
granite from Loch Doon, Borrowdale volcanics,
Thornton limestone, Chatburn limestone.
Speak to me of glaciers that had no names.
Speak to me not of the death of your children
and how they laid their gravestones
in a ritual long long lost to us.
Speak to me not of your sacrifice in shaping this land.
We must be as stone
and not mourn the snowflakes
vanishing from the palms of our hands.
Outside the office at Brockholes Nature Reserve there is a 2.5 tonne boulder made of grandiorite which was extracted from Number One Pit beside the M6. Unlike the sandstone boulders nearby it does not fit with our local geology. This has led geologists to the conclusion it was transported from the Lake District or Southern Scotland by a glacier during the Last Ice Age 115,000– 11,700 years ago.
This reached its maximum 24,000 years ago and two of the ice advances, Heinrich 2 and 4**, extended to and covered Lancashire and Cheshire, whilst Heinrich 1 and Loch Lomond did not. When the glaciers melted they deposited their ‘suspended load’ of ‘boulder clay’ or ‘glacial till’. At Brockholes the sand and gravel were 20 metres thick leading to the area being used a quarry.
With these materials the grandiorite boulder was removed along with other erratics such as granite from South Scotland, Borrowdale Volcanics from the Lake District, and Chatburn Limestone from Clitheroe. The sandstone boulders near the car park may be local or from Pendle Hill or Longridge Fell.
Near Kirkham and Oldham, where ‘the rate of the ice melt’ was ‘equal to the movement of the ice sheet’ for a long period of time, lines of moraine (accumulations of glacial till), were deposited.
The vast volumes of water from the melting glaciers were also responsible for forging the valley of the Ribble – ‘the meander belt between the river cliffs is too wide to have been created’ by the river.
When dead ice was left behind by glaciers, became surrounded by sediment, then melted, it left kettle holes. This resulted in the formation of lakes such as Martin Mere and Marton Mere and the others that formed Lancashire’s Region Linuis ‘Lake Region’ and some of its numerous ponds.***
Since then we have dug out the sand and gravel and drained the lakes yet new lakes have formed in old pits. Number One Pit at Brockholes, where the grandiorite boulder was found, is now a lake and 182 species of birds have been recorded there including bittern, curlew, lapwing, and sand martins.
The Nature Reserve as we know it has originated from a combination of geological and man-made factors. In the shaping of the land during the Last Ice Age I see the work of Winter’s King and his glacial children. When I touch the glacial erratics or watch birds descending onto the lakes I see his hand.
*The term ‘erratic’ originates from the Latin errare ‘to wander’.
**Heinrich events are caused by the the collapse of northern hemisphere ice shelves and release of icebergs which affect the climate elsewhere.
***Most of the present-day ponds in Lancashire formed in former marl pits dug in the 18th century.
With thanks to Geolancashire from whose Brockholes Geotrail Guide I gained most of this information.