Quaternary
The Quaternary Period is the shortest division of time in the geological column covering only the last two million years or so of Earth’s history. The period is characterised by extraordinary changes in global climate producing four major phases of ice-sheet advance, (glacial), and retreat (interglacial). Many minor cycles of advance and retreat are superimposed upon each major phase.
The Quaternary can be sub-divided into two epochs, the Pleistocene – which covers all deposits between two million years and ten thousand years ago, and the Holocene – encompassing deposits from around ten thousand years ago to the present day.
Devensian
The most recent ice-sheet to occupy the Tees Valley did so during the Devensian Stage, between around seventy thousand years and ten thousand years before present, when ice advanced on the area from the Lake District in the west, and Scotland in the north. Pressure, applied by Scandinavian ice from the North Sea Basin, affected the advance locally by forcing the Scottish ice stream inland at suitable low points in the landscape.
Some landforms, such as Freeborough Hill, were sculpted as the ice-sheet carved up the original landscape during advance. Others, such as Cat Nab at Saltburn, resulted as the ice melted and the material which had been acquired en-route was unceremoniously dumped. Immense amounts of melt water, unable to escape in any other direction, flowed along the ice margins forming temporary lakes where conditions allowed. Longer-lived water bodies tended to fill until they eventually overflowed, the escaping streams often cut distinctive channels which were abandoned as flow rates diminished.
The most extensive evidence of former occupation by ice-sheets are the thick deposits of boulder clay that cloak the landscape, softening its contours to heights of between 250 and 300 metres above sea level. This material has also in-filled some of the pre-Devensian features producing buried valleys, most notably at Upgang and Saltwick Bay, near Whitby.