A train route closed following a landslip looks set to reopen in around six weeks.
Engineers are likely to be on site for several months fixing the slip.
A spokesman for Network Rail said the area which is moving is around 120m by 120m.
He added: “Approximately 100,000 tonnes of material is believed to be moving.
“We are still carrying out investigations into the cause of the slip.
“The work we are doing now is to allow the railway to re-open safely.”
The line from Sheffield towards London is blocked and these trains are diverted.
Trains heading north are running past the site at approx 90mph.
The hillside above the railway line through Unstone became unstable during the recent wet weather.
Full details of changes:
East Midlands Trains services between Sheffield and St Pancras will operate via Beighton with extended journey times of around 20 minutes
Other East Midlands Trains services between Sheffield and Derby will start and terminate at Derby
Northern Rail services between Leeds and Nottingham will start and terminate at Sheffield. Replacement buses will run between Sheffield and Chesterfield, calling at Dronfield
East Midlands Trains will run between Sheffield and Nottingham via an alternative route (Beighton), calling additionally at Langley Mill and at Alfreton as timetabled
CrossCountry services will divert via Beighton with extended journey times
Freight traffic carrying cement aggregates and limestone from the peak district to the midlands, glia and the south west is also being diverted.