Geography of Greater Manchester - Geology

Geology

Further information: Geology of England and Geology of the English counties

The underlying geology of Greater Manchester is dominated by rocks from three main periods from the geologic time scale—Carboniferous, Permian-and-Triassic, and Quaternary.

Most of Manchester, and its suburban fringe to the south, is located on Permian sandstones and red Triassic sandstones and mudstones, mantled by thick deposits of till and pockets of sand and gravel deposited by glaciers at the end of the last glacial period, some 15,000 years ago. The oldest rocks, from the Upper Carboniferous period, are sandstones and shales of Millstone Grit present as outcrops and uplands in the north-east of Greater Manchester, such as the upland moors of Dark Peak and South Pennines to the east and northeast of Rochdale, Oldham and Stalybridge. These rocks are overlain by shales, mudstones and thin coals of Coal Measures upon which the towns of Oldham, Rochdale, Bolton and Wigan are located. An outcrop of Coal Measures extends southwards down through Tameside and into Hazel Grove.

Starting in October 2002, a relatively large number of earthquakes were recorded in Greater Manchester, some of which were among notable tremours in the British Isles. By the end of November 2002 more than 100 earthquakes had been recorded by the British Geological Survey. The first quake, of magnitude 3.2 on the Richter Scale, struck on Monday 21 October 2002, with an epicentre about 1 mile (1.6 km) east of Manchester Piccadilly station at a depth of 3.4 kilometres (2.1 mi) A second quake of magnitude 3.9 on the Richter Scale followed four hours later and was followed by a further two substantial earthquakes on 22 October 2002. The epicentres were within a region of about 1 kilometre (0.62 mi) in diameter, about 2 kilometres (1.2 mi) northeast of the University of Manchester, leading to the rare classification of "Earthquake swarm" for the geological events. This Earthquake swarm was probably caused by the movement of blocks of rocks at depth along faults that occur in the Upper Carboniferous and Triassic succession, underlying the area.

Shallow, primitive, and small-scale coal mining from the Upper Carboniferous Coal Measures in what became Greater Manchester started as early as the 13th century. The situation changed dramatically during and after the Industrial Revolution; the construction of the Bridgewater Canal and other canals in the area, enabled coal to be cheaply transported to Manchester and the River Mersey for shipment. In Oldham, relatively shallow pits were dug due to flooding problems. The writer Daniel Defoe, on a visit to Oldham, described it as a place of "... Coals ... upon the top of the highest hills" because the coal seams were so shallow and accessibile. Advances in mining technology during the late-19th century lead to the formation of deeper mines. The Long Depression aside, there was a rapid acceleration of coal mining until about 1920, when the collieries in the eastern part of the Manchester Coalfield were exhausted and closed. In the western part of the coalfield, however, coal mining was continued into the 1960s. Coal mining ceased in north Manchester in the late 1970s.