A passenger train was derailed after heavy rain and a rapid thaw of snow caused a massive 1,000-tonne landslip, investigators have found.
The train, carrying five passengers and two crew, was travelling at 40mph on a remote track in Lochaber between Lochailort and Glenfinnan just before 7am on January 22 2018 when it struck a mass of tons of mud and stones.
A report by the Rail Accident Investigation Branch said a protective fence at the scene above Loch Eilt had been “overwhelmed” by 500 to 600 cubic metres of material, weighing over 1,000 tons.
Investigators said: “The combination of rainfall, snowmelt and ground thaw resulted in substantial amounts of water running down the hillside.
“This high-risk event was not apparent.
“The driver of [the] train was unaware of debris obstructing the track until about four seconds before impact.
“Prior to this, the debris was hidden by a curve and darkness. The driver applied the brake but could not avoid the collision.”
The report said the leading coach of the twocar train, travelling from Mallaig to Fort William, derailed to the left and came to a halt embedded in landslip debris.
It added: “There were no injuries, but some diesel fuel escaped from the damaged train. It was carried by flowing water into a lineside drainage channel.
“Due to the inaccessibility of the site, pollution control measures were not put in place until later the following day, and by this time some diesel fuel had entered nearby Loch Eilt.”
The investigators concluded that a greater understanding of snowmelt risk would not have avoided this crash.
“But it may mitigate or prevent accidents in other similar circumstances.”
The report added: “The absence of factors indicating a risk of a large debris flow meant that Network Rail did not install an automated landslip detection system as found at some higher risk sites on its infrastructure.
“However, Network Rail is considering more widespread implementation of enhanced landslip monitoring systems in future as technological advances make it practicable.”
It has recommended to Network Rail to continue a review into risks and to promote the development of weather forecasting processes to take account of snowmelt and ground thaw.