Living Uplands


Natural History of Upper Weardale

4 - GEOMORPHOLOGY AND GLACIATION LEGACY

By David J A Evans: the Editor’s synopsis

Despite being a region that has been cloaked in glacier ice many times during the Quaternary geological period (the ice age), the physical landscape of the North Pennines is strongly controlled by the structure of its bedrock. Weardale is a valley with a very strong fluvial signature, being composed of a largely V-shaped cross profile and, together with its tributaries, a dendritic drainage network formed by the easterly flow of surface streams and rivers over the regionally eastward-dipping bedrock.

Glacial deposits are sparsely developed and Weardale has been little researched. Most knowledge comes from a substantial paper published in 1902 by Arthur Dwerryhouse, entitled The Glaciation of Teesdale, Weardale and the Tyne Valley, and their tributary valleys. This chapter is a compilation of old and new evidence on the landscape evolution and ice age legacy of Weardale.

During the most intensive glaciation period in the last 2.6 Ma (million years) the British-Irish Ice Sheet covered the region in several hundreds of metres of glacier ice. Despite this, Weardale is dominated by stepped hillslope profiles and tableland upland summits, features long central to notions of a very old and formerly extensive fluvial drainage surface called a ‘peneplain’. The age and origins of such peneplains are largely unknown but certainly predate the Quaternary glaciations.

The most recent (Quaternary drift) deposits in the Dale are not widely distributed and amount to a localised thickening on valley floors and lower slopes, thinning rapidly upslope to form a clear drift limit. There is no erratic material, and the glacial tills represent glacier ice that was seeded locally on the Pennine uplands and was capable of resisting the overriding of regional ice streams even during maximum ice sheet conditions.

The local Pennine till extends eastwards in Weardale only as far as Witton-le-Wear where it mixes with erratic materials transported by the Tyne Gap ice stream.

Our knowledge of glaciation history in Weardale is largely restricted to the events relating to the last cold stage, the Devensian Stage (116,000-11,500 years BP [Before Present]). Possibly repeated glacial readvance might show as landforms that constitute the Witton-le-Wear Moraine or in the lateral meltwater immediately west of Stanhope. The range of glacial landforms includes hummocky glacial terrain with glacitectonic forms, moraine ridges within valley floor hummocky drift, drumlins, glacifluvial assemblages (eskers and kames), glacial meltwater channels and terraces and deltas of likely glacier-dammed lakes. Each form is discussed in the chapter.

Concentrations of moraine and meltwater channel alignments are evident at Witton-le-Wear Moraine; Greenly Hills Moraine; Stanhope-Eastgate lateral melt channels. An invaluable example of dislocated strata has been reported from an opencast coal mine near Tow Law. An example of a composite glacitectonic ridge is the Greenly Hills Moraine, which records the thrusting of limestone and sandstone bedrock blocks into the lower Swinhope Burn by the Weardale valley glacier during its overall recession.

Weardale is an exception to the regional picture for it contains very few drumlins, largely located on the lower and intermediate slopes of the main valley between Westgate and Wolsingham. The paucity of subglacial streamlining is likely a reflection of the sparsely distributed and mostly thin till cover. Localised pockets of thicker glacial deposits, including till, provide some stratigraphic evidence of former glacial processes, an excellent example being exposed in Broadwood Quarry, Harehope.

The ice-marginal moraines of Weardale comprise predominantly subtle hummocky drift mounds within which short linear ridges can be traced, indicating that a former glacier margin was responsible for deposition. The oldest and most complex of the latero-frontal moraine assemblages occurs at the junction of the River Wear, Bedburn Beck and Linburn Beck (the Witton-le-Wear Moraine).

A prominent cluster of lateral meltwater channels occurs in upper Weardale between Stanhope and Wearhead and is associated with significant backfill moraines in both Westernhope Burn and Swinhope Burn Greenly Hills Moraine. Glacifluvial deposits have been identified on the lower slopes and valley floors around Weardale. They constitute either the discontinuous upper terraces located on the floodplain edges of the River Wear or linear assemblages of drift mounds, specifically in the lower Bedburn Beck valley and on the Waskerley Beck-Thornhope Beck interfluve. Evidence in Rookhope and Middlehope Burn on the north side of Weardale as well as in Swinhope Burn to the south suggests the uncovering of some tributaries to Weardale by ice recession appears to have given rise to the development of short-lived ice-dammed lakes.

The chapter concludes with a short discussion of postglacial geomorphology.

All the illustrations from Chapter 4 have been listed in this downloadable PDF to provide a larger format to explore.

 

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