What Lies Beneath Part4

Part4... Coal & Quakes

Please note: all diagrams are approximate, do not sell, purchase or worry about what is under your house based on this info !

Read part 1... info on the superficial geology of Prestwich

Read part 2... info on the bedrock geology of Prestwich

Read part 3... Mixing Sand with Water

Much deeper underground, underneath the superficial glacial and fluvial deposits, and through the layers of sandstones laid down in the Triassic Period, we find deposits of coal. These have been made from dead plant matter which initially created peat. Modern era peat deposits can be seen on the map below.

This ancient peat came from dead swamp plants, which was then buried and compressed deep underground to form coal. This took millions of years to compress and our coal dates from the Carboniferous Period (359 to 299 mya). At this time the UK was still near the Equator but beginning to get land locked as the ancient tectonic plates moved around.

The word Carboniferous means "coal-bearing", from the Latin carbō ("coal") and ferō ("bear or carry"). Terrestrial animal life was well established by the Carboniferous Period, and both plant/tree and marine fossils are present in these rocks. Dead marine creatures give us limestone, but dead plants either give us coal or oil. Oil tends to be formed from plant life in lakes, oceans and shallow seas, whereas coal tends to come from woodland or swamps. Our layers of coal are found to be between 300 to 800m thick.

To the North and West of Prestwich lie Pennine Middle Coal formations, as well as containing seams of coal, there are also siltstone, sandstone and ironstone formations running about 200-650m thick.

Coal had been foraged from the surface since Roman times, typically at the coast or on valley sides where the seams had been exposed. Subsequently the seams of coal were dug out and followed, through surface pits or tunnels, this is called surface or shallow mining.

Wilson, in his History of Prestwich writes:

Edward Barlow who was born in Prestwich in 1642, tells in his Journal that his father, a husbandman, earned £8 or £9 a year and that he, himself, when a boy went in rags until he was able to earn a few pence by working at harvest or carrying coal from the coal pits. With the money thus earned he was able to buy clothes and then was able to attend Prestwich Church.

Edward sailed on the Naseby, the ship that brought Charles II back from Holland in 1660. He left an illustrated journal of his life and you can read more about Edward Barlow here

The map of 1927 shows the Worsley Four Foot seam passing under Prestwich, beneath Bury Old Road at Polefield, and a 2nd 4ft seam passing under the Hospital towards Whittaker Lane. These seams were from 3 feet to 4 feet in thickness and were used to supply steam coal. As can be seen in the below diagram, the 4ft seam was at a greater depth under the Prestwich side of the fault, and it made more sense to exploit it on the Agecroft side. Records suggest that the seams under Prestwich were largely untouched until the 1950s.

The above section shows how the Pendleton Fault has displaced the geological structures by a vertically diagonal distance of over 600feet (182m). This also shows how the position of a seam varies over depth, and that mapping the position of a seam on a 2D surface map doesn't really show the true situation.

This section also shows that when you see the line of a seam on the above map, it doesn't show the full picture. The seams are actually a layer, sloping down towards the south west. The further south & west you sink a pit, the deeper you will have to dig before you reach the seam. That same seam might also be reached, and exploited, at a shallower depth further north. For example the Agecroft Colliery worked the Doe seam, which hits the surface at the bend in the River Irwell at Clifton.

Similarly showing the Pendleton fault as a line on a 2D map hides the truth, which is that the fault is also vertically diagonal, but slopes down towards the East.

No mine entrances were sunk in Prestwich, due to the depth of the seams and the amount of glacial deposits sat above them. Though there was a Colliery in Radcliffe, another at Ringley and the nearest mine was at Park Lane Whitefield, on the edge of what is now Whitefield Golf Course. This was called Stott's Colliery, operating from 1855-1902, on a 3 foot seam of coal about 150 feet deep. They also bore down to a lower seam, and it cost them a lot of money to hold back all the sand which runs very deep in that area.

Several pits were sunk along the Salford side of the River Irwell between Agecroft and Clifton.(Clifton Hall, Botany Bay, Robin Hood, Wet Earth, Doe Brow, Ringley etc...). This is where the coal seems had been snapped off by the fault and the river valley meant less drift to overcome before reaching the coal. The problem with these mines was to be water, and great effort was made to install pumps to keep the mines operating.

Clifton Hall Colliery, where Lumms Lane Recycle centre is today, is thought to have opened about 1820, and Agecroft Colliery opened about 1844. Both operated on the more easily exploited shallow seams to the south and west of the Pendleton fault (the seams were called Worsley 4ft, Rams, Doe, Bin and Trencherbone amongst others). All these seams ran deeper Westwards from the Irwell Valley, having been terminated at their eastern end by the Pendleton Fault.

The seams to the East of the fault, under Prestwich, were not easily reachable from Agecroft, but could have potentially been exploited from Stotts or Ringley/Outwood Collieries.

Sadly, in 1859 a leatherband indicator that had been refixed just 90 minutes earlier, slipped off leading the cage to be drawn into the head gear, causing seven men and eight boys to fall to their deaths. Although this was by far the worst incident, the below chart shows the regular occurrence of deaths throughout the colliery's first phase of operation.

[Ref: Durham Mining Museum - details of all the recorded deaths]

Of the 111 deaths during phase one of operations at Agecroft Colliery (1844-1932), 45 of the deaths were caused by the falling of coal/stone onto colliers, 12 deaths were related to being struck/crushed by the trams/tubs used to move the extracted material, and 6 were due to explosions - 2 due to firedamp (methane gas), and 4 due to premature explosions - 3 of which died on 1st Feb 1899. Five men were suffocated while tackling an underground fire on the 2nd December 1891.

Wilson again records:

In 1895 the Earl of Wilton had engaged a Whitehaven firm to bore for coal under Heaton Park. They bored just east of the fish pond about half a mile north of Heaton Hall. At 2,300 feet down they had not found a commercially workable seam, so boring ceased in February,1897. Later borings have proved that coal is there, but at a greater depth.

Holt also recalls :

A certain John Hope who used to bring coal from Outwood Colliery had a donkey which he used as a chain horse to help to draw the load. When not in use the donkey was put out to grass in the field [where Conway Ave. Whitefield is now]. One day the dyers from the mill got hold of John's donkey and dyed it. Great was the amusement of the public to see the donkey calmly grazing away with all the colours of the rainbow around it.

Worsley Navigable Colliery closed about 1887, with other Bridgewater mines working until the 1940-50's. Agecroft Colliery which had opened about 1844, sank two shafts and worked the Doe seam at a depth of 1740ft (530m). Shafts 3 & 4 were sank about 1894 to reach the Trencherbone seam at a depth of 2,100 ft (640m).

All shafts suffered from excess water and shaft 3 also hit a layer of quicksand. At it's peak in 1910 over 1,100 men were employed above and below ground. Work was restricted by the Pendleton fault to its North and East, hence the seams under Prestwich were largely unexploited until the mid 20th Century.

With improvements in machinery, mine workings from Agecroft started to head eastwards beyond the Pendleton Fault during the early 20th century, and it is thought that the Landslip site at Higher Broughton was further weakened by the mine.

Clifton Hall Colliery closed in 1929 and Agecroft Colliery closed the same year (shafts 1&2)- with shafts 3&4 closed in 1932, though the shafts remained in operation to continue pumping water out of nearby mines.

Further bore holes were made and recorded around Prestwich during the 19th century, and into the 20th century.

Wilson again records:

"In 1952 the National Coal Board began to make trial borings in Prestwich for coal seams. Italian workmen spent some months in boring for specimens of the strata in Heaton Park and on the ground of the Cricket Club at The Heys among other places. Since then, from the pit head at the old Agecroft Colliery, tunnels have been driven under Prestwich and Whitefield thus causing considerable damage to residential property through subsidence. The galleries extend as far as Stand Golf Club. During this period two minor earthquakes have occurred, one as recently as November 1975, but whether they were due to the mining activities or to movement in the Pendleton Fault is a matter for argument."

Just as removal or accumulation of water can affect the stability of the overlying glaciofluvial deposits (See Part1), the same can be true for the underlying geology, excessive withdrawal or supply of water can cause earthquakes, and of course the natural pressures along the fault line also have a hand to play.

Some of the locations of the bore holes sunk in 1952 were: Grand Lodge, Heaton Park; by the reservoirs of Butterstile Hill; in the fields at Clifton Lane, and other places on the Whitefield side of where the M60 Motorway is today.

Sadly, in 1958, a misunderstanding that everyone had left the pit led to a planned explosion during construction work killing one man and trapping twelve others.

The original colliery at Agecroft, with its 4 shafts had been demolished and much of the winding gear dumped in the shafts. The shafts weren't capped though, and 3 & 4 were cleared out, made good, and re-opened. A 5th shaft was bore down to 670m (2,200 feet) - that's four times the height of the Betham Tower in Manchester- and from the base of the shaft, tunnels reached out under Kersal, Prestwich, Simister, Broughton, Whitefield and over to Worsley.

The main tunnels are called Horizon1 & Horizon2, these ran diesel locos along the straight (and flat) tunnels towards Whitefield. These horizon tunnels intersect the various coal seams, and tunnels then branch out to exploit each seam. Once miners alighted, they then had a walk along a 1 in 3 or even 1 in 1.8 decline to reach the work face. In total there are about 25 miles of walkable tunnels.

A further railway tunnel, called The West Crosscut, was constructed Under Whitefield, and marked the western boundary of the Agecroft Take (permitted area of mining). To the West of this were the Outwood colliery tunnels.

To this day, and forever more, there is a network of methane gas monitoring and extraction in operation to avoid any build up of dangerous gasses in all the disused tunnels.

One of the earliest quakes reported as being felt in Manchester was in 1750 and another in 1753 (epicentre Skipton), with further quakes reported in 1768 (epicentre Wensleydale) and 1777 (epicentre somewhere between Manchester and Altrincham). The latter of which was felt as far away as Lancaster and York, and rang the bells of the Collegiate and old St Mary's Churches in Manchester and a chest of drawers knocked a servant to the ground in Blackley. This quake of Sept 1777 was described by a Fellow of the Royal Society, Thomas Henry, and he already had doubts that the idea that they were related to atmospheric conditions wasn't true, as it was a clam and clear day.

More quakes were felt in 1795,1816 and 1835.

In 1843, a quake was felt by residents on Kersal Moor and also in Prestwich where "a gentleman was awakened by the shock". With no other witnesses to the trembling furniture and rattling of windows, the gentleman put the event down to his imagination until he reached Manchester where it was the topic of conversation. The epicentre was suspected to be under the sea off the coast of Barrow in Furness, with ship reporting the quake too.

Further quakes were felt around Manchester in 1839,1843,1852,1863,1864,1868,1869,1871, 1889 - the last of which estimate to measure 6 on the Richter Scale (not introduced until 1935). Many quakes were recorded as being felt, but had epicentres some distance away e.g. Todmorden 1864, or Neath, South Wales, in 1868.

More recently, chimneys fell when Pendlebury suffered a 3.7 quake in 1931, felt as far away as Bolton and Altrincham, and Prestwich was hit by quakes from the Pendleton Fault in 1899,1900,1905, 1931 & the Yuletide quake of 1944 (December 27th). In 1905, people within a 4 mile radius heard the tremor (dotted line on the above diagram). Then in 1992, there were 32 quakes in four days, with Manchester town hall evacuated and the vibrations were so strong that many thought a bomb had exploded.

On the 21st October 2002, five quakes of 3.2, 2.3 & 3.9 (because of how the Richter scale works this 3.9 is actually 11 times stronger than 3.2) followed by a final quake of 3.2 magnitude, were felt across Manchester, then 4 days later a 3.1 magnitude quake also hit. At the time a temporary seismograph had been deployed at Heaton Park to help identify the epicentre, and these were traced to have come from between 3-6km beneath Beswick. Some of the smaller after shocks centred under the Broughton Park area.

[Ref:Telegraph] In 2007, Manchester experienced six quakes in a month, attributed to the Pendleton Fault (of magnitudes 2.2-2.5) Dr Brian Baptie, a seismologist at the British Geological Survey, said: "The UK is somewhere in the middle of the Eurasian Plate, and we are regularly subjected to pressures which activate such pre-existing fault lines."During 2002/3 there were 150 tremors recorded in the same area of Manchester as yesterday's quake. The most likely explanation is that a fault line has been activated."

To the North and East of Prestwich lies Pennine Lower Coal, a mix of mudstone, siltstone and pale grey sandstone, with rich coal seams towards the "top". These deposits are about 307 to 319mya, and are found to be 650-720m thick.

The Bradford Fault line which passes under Bowlee was reactivated in the 1960s due to mining work, and led to the demolition of Crompton Hall Residential Complex.

Possibly the strongest quake felt in Manchester was the 1984 Llŷn Peninsula earthquake which struck northwest Wales on Thursday 19 July 1984 at 07:56 BST. Measuring 5.4 on the Richter scale, it is the largest onshore earthquake to occur in the UK since instrumental measurements began.