The extent of the Eden Brows landslip has become clear as Network Rail warned the line could be closed between Carlisle and Appleby for “at least several months”.
Investigations showed that the incident near Armathwaite on the Settle-to-Carlisle line involved about 500,000 tonnes of earth and an area 130m by 70m.
Geotechnical specialists are carrying out detailed ground investigations using borehole equipment before designing a lasting repair.
Network Rail route managing director Martin Frobisher said: “Our monitoring has detected a twist fault in the tracks caused by the ground movement. The slip is accelerating and it is not safe to run trains in this situation.
“Our engineers on site are undertaking detailed ground surveys and this will enable us to design a permanent and lasting repair.”
This video highlights what caused the landslip and what is being done to tackle it.