Sutton Bank is one of the most spectacular inland cliffs anywhere in Britain. The near vertical drop from top to bottom is around 140 metres, and it crosses at least two major geological boundaries. More than 60 million years of earth’s history is covered by the rocks of Sutton Bank.
The platform at the top of the bank is made of hard limey gritstone formed in the Upper Jurassic period. This same rock forms the top of the escarpment that runs all the way from here to the coast at Scarborough – it even sits on top of Scarborough’s Castle Hill.
Going down the cliff you encounter softer Upper Jurassic clay and limestones, then the hard Middle Jurassic sandstone that underlies the central moorland of the North York Moors. The cliff then plunges down through the Middle Jurassic rocks and into the soft shales and mudstones of the Lower Jurassic.
But why is this cliff here? During the last Ice Age, around 20 thousand years ago, an ice sheet pushed its way down the depression that lay between the upland areas of the North York Moors and the Pennines. As it scraped along the western edge of the moors, the tremendous force of the ice gouged out the soft underlying rocks, causing the hard tops to tumble down. The result was a near-vertical escarpment, of the type usually seen at the coast.
As the ice melted, it left layers of mud along the bottom edge of the cliff, in what are known as lateral moraines. These mud deposits blocked up the normal drainage channels, causing small lakes to form – Gormire Lake, below Sutton Bank, is the last remaining glacial lake.
The edge of the bank is not a perfect straight line and, a little to the south of Sutton Bank, Hood Hill stood out above the ice sheet and became detached from the moors. A small cap of hard Upper Jurassic grit sits on top of the hill, giving it a spectacular profile.
The 'Lime & Ice' exhibition at Sutton Bank National Park Centre includes an introduction to the geology of the area.