The A57 Snake Pass between Glossop and Ladybower Reservoir has been shut for three days since Storm Franklin triggered landslips on the hills above it.
It is expected to be closed for several weeks for repairs, and access is being maintained for local traffic only.
Cyclist Simon Warren, author of the Greatest Cycling Climbs books, Tweeted photos of himseld alone on the pass with between Manchester and Sheffield with no vehicles in sight.
He wrote: "The Snake Pass is closed to traffic, will be for ages. Went over to Glossop and back this morning. Bloody awesome. It now belongs to cyclists. Get out there before it opens again."
Derbyshire County Council said: "The A57 Snake Pass was closed on Monday February 21 following damage caused by torrential rain as Storm Eunice and then Storm Franklin battered the county.
"Inspectors found movement in three locations along a mile-long section of the road and a decision was made to close the road between Glossop and Ladybower Reservoir to protect road users. Visitor facilities at Fairholmes are unaffected and can be accessed via Sheffield.
"Two of the areas of slippage were already being monitored carefully following previous movement but a third, more serious slip, has now appeared along the road where the verge has dropped by 2 metres.
"Teams will continually monitor the situation but as the ground is still moving they are unable to come up with any final designs to repair the road until it has stabilised, which will be dependent on many factors including the weather.
"At this stage, a one-month closure is in place however it is too early to say when the road will be able to reopen following any necessary repairs due to the unstable nature of the ground.
Councillor Kewal Singh Athwal added: “I know this will be a huge inconvenience to everyone who uses the A57 regularly.
“However, with the ground underneath the road surface expected to continue to move, in the interests of everyone’s safety we simply cannot allow traffic to use the road.
“This is an evolving situation but please be assured we will continue to monitor the situation closely.
“Once the land movement has stopped we will assess what needs doing to repair the sections of road. However, once in a position to do this it will be a complicated piece of work.
“I’d like to thank everyone for their patience as we deal with the aftermath of this unprecedented weather which has affected not only Derbyshire but much of the country.”
It's not known how long it will take the ground to stabilise before thorough assessments can be carried out.
Drivers are asked to follow the diversion route which is the A57, A6013, A6187, B6049, A623, A6, A6015, A624 and then back on to the A57.