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383
SOME EFFECTS OF THE STORM OF JUNE 3RD, 1908, ON BARBED FELL.
BY ALBERT CILLIGAN, B.Sc. (Read \2ih November, 1908. MS. received 30tk November, 1908.) Storms of more or less violence occurred in many parts of the British Isles on June 3rd, 1908. The West of Yorkshire seems to have been unfortunate in being the neighbourhood where the greatest downpour of rain took place, and conse• quently suffered more destruction than any other district. The stretch of country affected by the storm extends from Airedale to Swaledale, embracing in its path four watersheds. Much havoc was wrought throughout the whole area, but the special district with which it is proposed to deal is that of Barden Fell. The highest point of the hill, near the Upper Barden Reservoir, is 1,661 feet above sea level. The hill is drained normally by a number of becks, which flow radially from its summit, the chief of which are Barden Beck and Gill Beck on the east ; Loburn Gill and Moor Beck, which join to form Embsay Beck, on the south ; while on the west there are Fell Gill, Waterfall Gill, and Red Gill, tributaries of Eller Beck (see Map, Fig. 1). These streams all run down scarp slopes of the Kinderscout Grit, of which the hill is composed, and have in consequence deep narrow channels, with many waterfalls, where they have encountered the beds of shale which are interbedded with the grit. I visited the district in the neighbourhood of Burnsall a few days after the storm, and explored the fell side, which is in the occupation of Mr. Thompson, Wood End Farm. In the field below the main road from Bolton Abbey to Bumsall deep trendies had been cut, and some of the solid grit removed. The field was strewn with blocks of grit, and the wall bounding the field on the lower side had been breached in two places (Plate LV., Fig. 1). Following the track of the torrent up the fell side, it was found that the main road had been ploughed Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
384 GTLLTGAN : EFFECTS OF STORM ON BARDEN FELL.
Fig. 1.
MAP OF PORTION OF THE AREA AFFECTED BY THE STORM. REPRODUCED FROM
THE 1 INCH ORDNANCE MAP. {With ilie sanction of the Controller of H.M. Stationery OJlce.) Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
GILLIGAN : EFFECTS OF STORM ON BARD EN FELL. 385
itp to a depth of six feet, and the walls on either side thrown down, leaving gaps about twenty feet wide. The height at which the water had stood at the fell side cf the top wall was easily traceable by reason of the bracken and grass infilling the chinks. This height varied from eighteen inches to three feet six inches, according to the lie of the ground. The water crossed the road at a point where the ground rises to a crest in the line of the new channel. In this new channel was found remarkable evidence of the cutting power of a mountain torrent. Careful measurements showed that in many places the solid grit had been removed to a depth of twenty feet, while the greatest width was twelve feet. The deepest holes were always found succeeding a place where the water had been imprisoned in a narrow channel, and the material scooped out of the hole has been piled up on the lower side to form a boulder bar. '; Scape-colks " similar in their mode of origin, i.e., con• striction of the water channel, have been described by Suess* as occurring in the bed of the Danube during the construction of dams for the purpose of diverting the river. Much of the rock in this part of the channel is crushed, as by faulting, and a vein was found at one part, but a search failed to reveal any metalliferous ore, though on the other side of the valley of the Wharfe the veins in the limestone bear galena, which has long been worked. It seemed at first as if the course of the stream had been determined by a pre-existing channel along a line of fault, but I was assured by those in the neighbourhood who knew the ground thoroughly that no channel had existed there prior to this storm. Another interesting feature, which was noticed both in this channel and at most other places round the fell, was that a stiff boulder clay, containing limestone pebbles, which covered the ground, had offered a powerful resistance to the cutting action of the current, and had preserved the underlying rock. The wall separating this field from the rock-strewn fell above had, in common with others, been breached, and afforded evidence of previous storms, not so violent perhaps as the present one, but nevertheless bringing down much material from the higher * Suess, "The Faoe of the Earth," Vol. II., p. 343. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
386 GILLIGAN : EFFECTS OF STOSM ON BAEDEN FELL.
part of the fell. The old foundations of the wall could be seen six feet below the present level of the ground, and stratified gravel, alternating with beds of peaty mud and angular pieces of grit, were exposed where the wall had been washed away (Plate LV., Fig. 2). This wall had fortunately determined the course of one of the tributary streams along the top of Thomp• son's Folly Plantation, or the farm which lies directly below might have been swept away. In the channel cut by this tributary stream evidence of the forces bringing about the folding and faulting of the whole district could be seen in the beds forming an unsymmetrical anticline, which had passed over into a reversed fault on the other side of the channel. Striking north-west across the fell two old channels were found, now quite dry and unaffected by the storm, which were probably the drainage channels of some previous storm, and helping to confirm the observations made regarding the stratified deposits near the wall. Another channel only fifty \ ards further on was one of the main drainage channels of the recent storm. The amount of material cut out of its bed was enormous, and has been spread out in a fan some distance below. In nearly all cases the cutting in the smaller channels branching from the larger ones commenced quite suddenly, due no doubt to the cutting back of the waterfalls formed by the rapid deepening of the main channels, each of the waterfalls having the usual boulder bar. A portion of one of these new channels is shown in Plate LVL, Fig. 1. An old cart-road leading up to a quarry on the fell side had during the first part of the storm formed an easy escape for the water, but as the volume increased the water could not follow the windings of the road, and burst through the sides at the sharp turns, just as rivers cut a shorter channel and leave the " ox-bow " channels on their sides as records of their former courses. To the north of this road a fault which runs south-west to north-east, and throws the Millstone Grit against the Pendlesides, has been well exposed, and some interesting points which need more careful study have been disclosed along this fault line. It seemed at first nothing more than a normal fault, but an Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
GDLLIGAN : EFFECTS OF STORM ON BARD EN FELL. 387
examination of the shales in the grit showed evidence of much crumpling, in one place, at least, the beds being vertical. The grit along the line of fault is much crushed, and has wisps of Pendleside shale caught up in it. Furthermore, the Pendle• sides here show beautiful slickensiding along horizontal planes. Confirmation of what appears to be thrusting is found again lower down the fell side, where the beds are inclined 45° in the direction N. 60° W., and appear to have been packed up over the beds below, which are nearly horizontal. The direction of •dip here is almost at right angles to the dip found near the fault in the shales of the grit series, and without very careful map• ping it is difficult to see clearly what has taken place here, but the evidence seems to point to thrusting in a direction from north-west to south-east. Gill Beck.-—The lower part of this beck was swept quite clean to the rock floor, and at the new bridge only a few very large boulders had been left behind. Higher up the beck the debris had completely choked the channel, being piled up at a point where the course of the beck takes a sharp turn. A waterfall in Nelly Park Wood had been cut back about ten feet, and a well-defined fault clearly shown. The weirs con• structed by the Bradford Corporation had been much damaged, several of the huge blocks of grit forming the aprons of the weirs having been displaced, and the residuum lodge near Gill Beck Head completely filled with sand. Barden Beck.— This was the main channel for the water, which rose at least ten feet, as shown by the grass still clinging to the trees up to that height. Into the Upper Reservoir the water carried about 10,000 tons of material, and removed stones weighing 13 cwt. from the embankment to the bed of the stream below. Blocks of grit weighing from one to three tons had been cut from the banks and carried down stream. Small tributary streams which ordinarily carry very little water had swollen to such proportions as to carry away large stone bridges. The residuum lodge for the Lower Reservoir was choked with hundreds of tons of material, and into the reservoir itself the stream had swept about 30,000 tons of sand, forming a huge delta. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
388 GILLIGAN : EFFECTS OF STORM OK BARDEN FELL.
Embsay Fell.—Here tlie damage done was of a very serious nature, as some mills which are situated on Embsay Beck, and use the fall of the water as their motive power, were quite wrecked. At Millholme Mill the stream is carried beneath the buildings by a culvert, which proved quite inadequate on this occasion, and the water rose at the back of the mill to such a height as to force the end wall inwards, and make its way through the mill, reaching a height of five feet, as shown by the mark on the wall (Plate LVII., Fig. 1). The mill is built upon Pendleside rocks, which dip upstream at an angle of 50°, and this no doubt proved a fortunate thing for the mill, as the water tore up the flagstones in the culvert, but could not remove the rock, as it lay, like the stones in a river bed, offering the least resistance to the onward rush of the water. At a spindle mill further up the same beck the water made its way through the back of the mill and pushed out the front wall (Plate LVII., Fig. 2). Still higher up the beck, and beyond the new Skipton Reservoir^ the tributary streams Loburn Gill and Moor Beck both give evidence of the destructive work of the storm (Plate LVL, Fig. 2, and Plate LVIIL, Figs. 1 and 2). The streams draining Rilstone and Cracoe Fells show the same phenomena as I have described, though the amount of debris carried was not so great.
SIMILAR OCCURRENCES IN YORKSHIRE.
The first I can find mention of in this neighbourhood is that cited by Phillips* as occurring in 168G in Upper Wharfedale, when gravel and sand filled the houses up to the bedroom windows. The village of Langtoft, on the Wolds, was visited by a great storm in 1657, and a stone recording this storm, built into one of the houses, was laid bare by the adjoining house being carried away during the flood of 1892. Storms have also been recorded in this neighbourhood in 1853 and 1888.f * Rivers, Mountains, and Sea Coast of Yorkshire, p. 79. | Waterspouts on the Yorkshire Wolds, by J. Dennis Hood. Driffield, 1892. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
BOUNDARY WALL ON BURNSALL FELL, SHOW 1NO EVIDENCE OF FORMER STORMS. J'roc. York*. Geo/. Soc, Vol. XVI., Plate LV. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
Fig. '2. —-LOBURN GILL, EMJiSAY FELL. Proc. York*. Geo!. Soc, Vol. XVI., Plate LVI. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
Fig. 2.—SPINDLE MILL ON EMBSAY BECK.
Proc. Yorht. Geo!. Soc, Vol. XVI., Plate LVII. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
Fig. 2.— WEIR IX MOOR BECK AFTER FLOOD.
Proc. York*. Geol. Soc, Vol. XVI.. Plate LVIII. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
GLLLIGAN : EFFECTS OF STORM ON BARD EN FELL. 389
A graphic description of what is called a " Gill-brack " is given in a letter quoted in the Geological Survey Memoir on the country around Ingleborough, p. 91. This occurred in Dentdale on January 28th, 1752, and was due to the heavy rain following a fall of snow, and so causing the snow to slide bodily down the mountain side.
Ilkley was the scene of a disastrous storm on July 12th, 1900, particulars of which have been supplied me by Mr. Albert Wilson, F.R.Met.Soc, of Ilkley. The rainfall on this occasion was as much as 5-40 inches, and as the rain gauge was somewhat shaded, probably 6 inches would represent the correct amount. Much damage was done in the town, houses being thrown down and property carried away. The Wharfe rose six to seven feet, but did not overflow its banks, as it was so low prior to the storm.*
PROBABLE CAUSE OF SUCH STORMS.
Storms such as I have described are well known in all moun• tainous districts, from which numerous valleys radiate, and the reason assigned for them is the following :—The air which has been in contact with the earth in the valley during the sunny hours of the morning gets wrarmed, and, rising along the slopes, carries up the water vapour of the lower strata of the atmosphere, so that the relative humidity of the air on top of the mountain increases in the afternoon, while it decreases in the valleys below. The dynamical cooling which takes place condenses the water vapour into clouds, and when the air is damp enough they en• velop the mountain tops, and not infrequently develop into thunderstorms. Dr. Julius Hannt says : " There is a tendency to afternoon rains among mountains, and during the warmer months to thunderstorms. Such rains occur even when the general weather conditions do not indicate any precipitation, and when the general lowlands are having the most beautiful weather. These
* Symon's British Rainfall, 1900, p. 16. f Handbook of Climatology. Downloaded from http://pygs.lyellcollection.org/ at University of St Andrews on June 15, 2015
390 GILL IG AN : EFFECTS OF STOBM ON BAUD EN FELL.
thunderstorms remain within the mountain district in which they originate, they break up towards evening, and are followed by a clear night." The weather chart for June 3rd, 1908, shows a disturbance in the Bristol Channel, and a terrible thunderstorm is recorded at Bristol, accompanied by deluging rain. This may in part account for the storm at Barden, as the disturbance travelled north• eastward. The great amount of material which was carried down by the storm on Barden Fell makes one realise vividfv the mechanical power which water possesses as a denuding agent. The quiet work of the streams and rivers of the world is great, but no doubt storms aid them in their destructive work more than we are accustomed to imagine, bringing down the material from the higher land in such a form that the river can easily transport it.