A man suffered head injuries when he was hit on the head by a boulder while carrying out a rock study on Teesside.
The man was part of a team carrying out a geological survey of rock movement at cliffs at Boulby, near Redcar.
A team of eight rescuers from the Great North Ambulance Service and Coastguard were scrambled and the man was airlifted to hospital on Thursday.
The Coastguard said the victim, in his mid 40s, suffered head and leg injuries, but was stable in hospital.
Bev Allen, Humber Coastguard watch officer, said: "The man was knocked unconscious by a falling rock and a doctor was with him when he was airlifted to James Cook Memorial Hospital.
"As far as we know the group were doing a survey on rock movement when the incident happened."