The area around Pleasley Colliery has an unusual and largely unexplained geological feature. Within the Lower Magnesian Limestone bedrock in the pit yard and the lands to the west and south-west are a large number of narrow fissures of unknown depth. It is reported that at some point the pit canteen had to be rebuilt after damage due to the effects of underlying fissures.

In November 2005, ground clearance work on the site of the colliery car-park exposed a section of old brick wall in which a length about 4yd long had sagged by about 12in at some time in the past. The sagging was probably due to collapes into an underlying fissure although this could not be seen at the time.

Section of disturbed brickwork near the SW edge of the old car-park area. (20/11/205)

As clearance work continued, several large interconnected fissures were exposed which presented considerable problems for the contractors, requiring excavation of the top of the fissures and the construction of reinforced concrete rafts.  Where possible the material excavated was used to infill the fissures but in places the fissure started to re-open as the material slipped into the depths.

During the excavations a large concrete plug was removed from the top of a fissure.  It’s not known when this was plug was cast but it’s clear that at some time in the past a serious problem had occurred.

large concrete plug excavated from a fissure   (08/01/06)

Small fissures had been noted during shaft sinking and several were exposed in the railway cuttings to the west where they were the home to a large colony of jackdaws.  The fissures in the LNER cutting extended almost the full height of the cutting - some had been closed off with stonework (which has since been removed) but others were open and sufficiently wide for teenage boys to penetrate inside for up to 10 feet.

In the 1960s problems began to occur with properties in New Terrace, Upper Pleasley, a few hundred yards to the south of the pit-top, where cracking started to appear in the walls of houses. Investigation revealed the presence of a number of fissures running in a NNE - SSW direction and extending for some distance under other nearby houses.

At about the same time a hole opened in a field about 1/2 mile further to the west to reveal a NNW - SSE trending fissure which could be descended for 8 - 10 ft.  A smaller hole with a similar trend later opened in the old railway track just north of the pit-top. These holes revealed the presence of pre-existing fissures 15 - 20 in wide, extending for an unknown distance and with only a thin surface seal just below soil level.

Although the National Coal Board denied any responsibility, there were workings active below these areas around that time. In December 1967, Pleasley opened a new face in the 1st Waterloo seam about 120 yds South of New Terrace.  To the West, Pleasley had worked the Dunsil seam in the mid 1950s and Teversal opened a nearby face in the same seam in 1963.

Some indication of the extent of the fissuring to the south-west of the colliery was revealed by an aerial photograph taken in May 1989. 

In the fields about 3/4 mile away crop-marks revealed the presence of an extensive network of interconnected features running along the rim of a small valley and extending  between the cuttings of the LMS and LNER railway lines. In the image below, the course of the LMS railway runs diagonally across the RH side with the LNER track just visible in the RH corner.

The crop marks seem to follow the trend of a tributary valley. The valley  contains a small  stream which follows the Lower Permian Marl outcrop.  A small area of Middle Coal Measures strata also outcrops in the valley bottom just outside the LH side of the image.

Crop marks about 3/4 mile SW of the colliery. May 1989.  (FoPP/JST)

A few years ago another fissure appeared in the front garden of a house in New Terrace, Upper Pleasley. It was about 12 inches wide, clear of debris and extending to a depth which could not be determined - the sides remaining parallel as far as could be seen. The trend was NE-SW and the dip was vertical. The length exposed was about 8 ft and at either end it was sealed by what appeared to be a layer of clayey - sandy soil about 12-15 in thick. The side walls appeared to have a fairly smooth surface, slightly undulating over a distance of a few feet.

Problems with fissures in the Magnesian Limestone were not confined to Pleasley in the 1960s, however. 

In the 1890s, Stanton Ironworks Co. had to rebuild Skegby church and vicarage after these are been damaged by subsidence caused by the advancing workings in the Top Hard seam from Teversal colliery.  The principle reason for the damage was identified as being due to the presence of pre-existing concealed fissures in the Magnesian Limestone ranging from 2 to 12 feet wide.  Several other similar cases occurred at Pleasley and in every instance when the foundations of the damaged buildings were examined it was found that concealed fissures were the principal cause of the damage.

In the early 1900s, Shirebrook colliery workings in the Top Hard seam resulted in considerable damage to nearby  Stuffynwood Hall although other nearby properties were not affected. This damage was believed to be due to subsidence disturbancing pre-existing fissures in the Magnesian Limestone running beneath the hall.

About a mile to the east of the colliery, in a railway cutting above the old Pleasley Vale cotton mills, there is a “cave” commonly known  locally as “Yew Tree Cave”. (NB this is not the cave referred to in the 19th century where prehistoric animal remains were found).  The cave consists of a series of vertical passageways and small interconnecting horizontal tunnels.  The actual extent of the cave is unknown but in my early twenties, by sliding along a narrow horizontal slot  and corkscrewing through a tiny aperture in the side, I penetrated into a large vertical chamber about 4ft wide with a sloping clay floor and walls extending upward for a considerable distance. There were two other vertical chambers of a similar dimension intersecting the main one. 

The roof of the chambers, which must have been close to the surface, appeared to be composed of jammed blocks and clay and it looked distinctly unstable. As there was no possibility of rescue by the route I had entered, discretion ruled the day and I retreated. When I got back to the small aperture I found that my friend, who was broader across the chest than me, had got stuck in the hole.   Panic time!!  I went back into the big chamber and left him to it, whilst I considered the possibility of digging my way out to the surface. Luckily he eventually managed to extricate himself and returned to the main entrance chamber. When I came to squeeze back through the aperture it really was tight and I had to take my T-shirt off to get through.  We were lucky but I guess we would have got out eventually because after a week of starvation he would either have slimmed down or I would have eaten him.

Anyway, looking back, I would say that the vertical chambers were examples of the fissures seen near the pit and the interconnecting tunnels were probably formed by the collapse of large blocks.  There were indications that the front of the cave had been exposed by a land slip and this could have provided space to allow the blocks to collapse.

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05 May, 2009