Theories abound as to whether St Albans hole was caused by air raid shelter or chalk mine

PUBLISHED: 09:28 15 November 2018 | UPDATED: 09:35 15 November 2018

A bird's eye view of the sinkhole on Cedar Court. Picture: Sharon Minkin Conrich.

A bird's eye view of the sinkhole on Cedar Court. Picture: Sharon Minkin Conrich.

Archant

Was the Cedar Court chasm in St Albans caused by an old chalk mine, or an abandoned air raid shelter?

Police, firefighters, utility companies and councils sprung into action on Tuesday, November 13 following the discovery of a mysterious hole outside Cedar Court flats.

The flats’ inhabitants were evacuated and the building cordoned off as utilities were shut down.

Sinkhole specialist Tom Backhouse said: “Of course, this isn’t the first time this has occurred in St Albans, with a ‘sinkhole’ in 2015 on Fontmell Close gaining global media attention.”

“Although the site of [last] Monday’s ‘sinkhole’ is not directly related to this event, it is possible to have been caused by a similar problem, hidden beneath our feet.

Close-up pictures of the Cedar Court sinkhole. Picture: Joanne Smith.Close-up pictures of the Cedar Court sinkhole. Picture: Joanne Smith.

“The ground collapse in 2015 at Fontmell Close was later confirmed to be linked to ancient brick clay quarrying and its associated underground chalk mining.

“It was an area of St Albans that had been extensively exploited for clay and chalk over a period of several centuries, with the earliest recorded clay quarrying in the 15th century.”

Tom, who is CEO of environmental information company Terrafirma, continued: “A combination of expert interpretation of available records by Terrafirma and the results of extensive ground investigation proved an early prediction that this hole was linked to underground mining for chalk.

“A mine shaft, extending from the base of a historical clay pit had been poorly capped and the voids, associated with the chalk mine below the pit, had compromised the shaft, eventually leading to the collapse of the void and the infilled clay pit above.

Herts Fire and Rescue's aerial shot of the Cedar Court sinkhole.Herts Fire and Rescue's aerial shot of the Cedar Court sinkhole.

“The resulting crown hole, colloquially known as sinkholes, caused extensive damage to the surface, denied access and utilities to homes for many months and was seen across the world in global media.”

There was also an air raid shelter about 100 yards from Cedar Court, which is off Cedarwood Drive.

The residents have not been able to move back in yet, but have been allowed to collect items. The hole has been filled with cement to provide some stability for the building.

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