Thus substantial readjustments of mass are taking place within the landslip. The average movement rate of the whole mass is about 10 cm a −1, with the central region moving significantly faster, at almost 50 cm a −1. Since 1996 we have carried out annual monitoring by electronic distance measurement of the movement of a network of some 30 stations on the slipped mass.
The slipped mass is in a state of year-on-year creep motion, which over the 190 years since the construction of the highway has led to extensive damage to the road, culminating in its closure in 1979.
The slip is about 750 m long and nearly 300 m wide and has the old main road from Manchester to Sheffield built across it. A section of the Namurian Edale mudstones and overlying Mam Tor sandstones has collapsed, leaving an 80 m high scar on the eastern side of Mam Tor. The spectacular Mam Tor landslip, near Castleton, Derbyshire, formed over 3000 years ago on an oversteepened slope left after the last ice age.
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