Cueva de la Marniosa

Alternate Names: No. 19 Cueva de la Marniosa


CO-ORDINATES: 30T 0361359 4790462
LENGTH: >4700m
DEPTH: -284m


The entrance is about 1.5km from the dam up the Sobra Valley, on the left hand side as one walks up Valley. It is close to, and 50m above two cabanas. Between the entrance and the cabanas, stands an electricity pylon and to the left of an obvious entrance, in a small gulley, lies the entrance to Cueva de la Marniosa.

Picture: Marniosa Location


The entrance is well hidden until one ascends the gulley where a strong draught comes from a fissure, 1.5m high by 1m wide.

Picture: Marniosa Entrance


Immediately inside the entrance, a small chamber is encountered with old wires and pieces of wood hanging from the ceiling. At one time this part of the cave was used for storing cheese. After a short low section the passage continues as a high (10m) rift, probably the old abandoned inlet. A 4m pitch is followed quickly by a 12 m pitch. The cave continues steeply down before a 4m climb / pitch is reached, this leads to into an impressive chamber, Morning Chamber, with many fine formations. Several passages lead out of this chamber, all choke or become too small, apart from one strongly draughting passage at the bottom end of the chamber.

The passage becomes much smaller as one climbs over a mud and calcite floor and enlarges as one nears the head of the next pitch. A 22m pitch lands in a moderate size chamber with a passage leading off that goes to two seperate pitches. Both pitches may be by-passed by a slope to the right. A low crawl on right leads to Extra-Caverns Series)

The passage continues as a large, well decorated tube, with a mud floor, which in places has calcited over. There are numerous small crawls and side passages that have not been pushed to any conclusion. The main passage continues via a muddy chamber, Smoker's Corner, to a rift passage eventually appearing to close in a blank wall, but a climb 3m (ed. rigged pre-2011) up into a roof passage leads to a continuation, via a smaller, but very well decorated section. The larger passage is met again and soon leads to a 20m (very muddy) rope climb, Papoose Pitch, from the head of which the sound of falling water can be heard. A ledge is reached, from which a climb on the right as one looks downslope, leads straight to the stream via a 7m pitch.

Extra Caverns Series

One third of the way down slope of the chamber a concealed low crawl to the right leads to a rift and short climb down. The rift if 2m wide and about 15m high. A chamber lies over a 3m high mudbank on the left, but there are no ways on whilst opposite a grovel in an oxbow rejoins the main development 20m further on at Mud Chamber. Three ways go on from here. To the right a rift closes after 35m. Straight ahead up an unlikely calcite slope, the route has been pushed up a steeply inclined muddy calcite flow for 15m but to no conclusion.

To the left a narrow rift 1m wide follows a tricle upstream. After 50m a fork goes left whilst the rift narrows and becomes thrutchy for a further 50m, before a climb down and slot to reach a small chamber. From here two very awkward rifts continue. The left hand rift becomes too tight after 8m whilst the other continues and divides after 20m. Both routes from here reach waterfall avens after a further 10m. The avens are both about 10m high.

The left hand fork begins as a tight rift, but becomes a crawl after 10m. A squeeze and crawl on a mud covered false calcite floor before the passage divides after a further 3m. Straight ahead more squeezing and walking to a small terminal chamber. To the right a hole in the false floor reaches a rift in the floor which is too tight. Over this is a well decorated chamber with no way on. To the left the passage goes down a loose 3m climb to another well decorated small chamber. A hole in the floor leads to the rift downstream and has been followed to a series of climbs and waterfalls to its terminal point some 70m from the hole in the floor.


Upstream of the ladder pitch, leading into a streamway, lies a considerable length of passage, perhaps 2-3km, all of hich was not surveyed. The going is slightly more difficult than downstream, the passage being narrower, more restricted, and containing considerably more roof-fall. The first collapse is 100m from the ladder and blocks the way completely. The route on is up a climb through boulders and over the fall. Many of the boulders seem precariously perched and the smaller ones move under foot. Small inlets enter at the point of many of these falls and often there are large black holes in the roof. Climbs in the roof of these area many be very rewarding.

The upstream continuation was followed to an immense chamber, called The Hall of the Mountain King. It consists of numerous connected avens, some with waterfalls, others dry and could be anything from 150' high. The floor is littered with sandstone boulders, suggesting that there is a route through to the surface nearby. Probably this chamber is near the sinks in the upper Sobra Valley. (see No. 20 Numerous sinks)

There was evidence of flood debris 2.5m up the walls, probably from spring melt.

Yorkshire Inlet

Follow the main Marniosa stream way upstream for 700m until two obvious climbs are reached.  The second climb of 3m marks the start of the Yorkshire Inlet passage, on the right of the passage, just above the stream way.  The easiest way is via an obvious 1m high passage, a low crawl on the right, 3m further along, is a flat out crawl in water that connects to the same passage.  The main passage is largely easy walking, in a small stream, for 20m to a sharp left bend.  The passage continues for another 40m before another sharp left, followed by a sharp right.  After another 20m the passage height starts to dramatically increase.  A junction is then met, left leads to a flat out crawl in water (possibly sumped).  This was unexplored. 

The height of the right hand passage increases further, terminating in the Bradford Aven, a 50m high aven with a small amount of water entering.  The Yorkshire Inlet passage heads almost directly north, under the Sobra Valley and the top of the Bradford Aven lies approximately 100m south and 300m below the small obvious peak at the head of the valley. 


Downstream a fine high but narrow streamway leads to a wet 4m pitch. After this the going is easy with potholed floor and chert bands in the walls. Eventually a pitch is met, where water descends through an eyehole. This may be by-passed by easy traversing at a slightly higher level. After about 50m there is a 4m ladder climb back to the stream. The passage now becomes more difficult to negotiate, with many chert bands and nodules as the stream descends a series of small falls. the passage eventually gets larger, just before another pitch. It is somewhere before this pitch that the strong draught, which is evident throughout the rest of the system, disappears. It may well be worth exploring the roof (30m above) in this section for this reason.

The pitch is 10m long and afterwards there is a large pool. to the right, a chest deep section leads to a muddy ramp and at its top, phreatic passages lead to a small chamber. A very loose climb, the possible continuation, was not passed. To the left a series of chambers lead, with wading and swimming, to the final sump chamber.

Sump 1

(1986) A 35m sump leads to 650m of spectacular stream passage ending in a 15m pitch. At the bottom of the pitch a deep pool is crossed, but tight rifts lead to another sump. Opposite the 15m pitch. a climb leads to a further 600m of stream rift was found, terminating in Sump 2. (ed 2013: Sump 2 in the Marniosa - "1986 Extensions" is approx. 500m horizontally and 50-100m vertically from Agua, halfway between Parting Friends and the Far Upstream Sump, )

Sump 2 & Beyond

At the end of the 1986 extensions, beyond Sump 1, is Sump 2.  The large clear sump pool gradually dips down to a shallow 5m depth, where it continues at an elbow in the passage.  The sump continues for approx. 25m (2m high by 4m wide) to surface in continuing stream passage Approximately 40m of open, lightly cascading stream passage has been explored to a calcite/mud climb on the right and the stream passage, in a rift, on the left.  The climb is not high but is slippery and unfinished, though it appears to choke at the top.  Down on the left, the main stream passage continues in a roomy rift with no sign of an imminent sump.  Exploration was not continued due to time limitations.


Speleological Notes on Cueva de la Marniosa.

Marniosa may be divided into two distinct parts, the dry entrance series and the active vadose streamway. The dry entrance series is much older than the streamway. It appears to have been affected by earth movements and contains extensive fill. the entrance pitch series is an old abandoned inlet into the large phreatic passages that start from near the bottom of the 22m pitch. When this inlet was active, the valley floor must have been considerably higher, to account for the position of the entrance. The phreatic passages are left on descent to the stream but in fact the passage continues across the top of the streamway. Above the rope climb the high level phreatic continuation was choked with calcite and could not be followed. There is the possibility that this passage has no realtion at all to the streamway, the stream at a later date having dissected this old passage.

The streamway is a very high and narrow vadose canyon. In most places no roof can be seen. The passage direction appears to be determined by major joints and faults and the strike. In most of the streamway there are extensive chert bands and near the second pitch there is a very thick shale band. There are several areas of collapse, mainly upstream and these areas may represent points where this high vadose canyon has cut across the older high level phreatic passages.

On the southern side of the Urdon Gorge and its continuation, the Sobra valley, there are no major resurgences except Cueva del Agua. the stream in Marniosa is almost certainly a feeder for Agua. Were a connection made between the two a fine 600m deep through trip would result. The strong draught in Marniosa was sufficient enough to blow out the carbide lamps. This draught is encouraging, though to make the connection it will be necessary to resort to artificial climbing in the lower section of Marniosa.

The straight line distance between the Agua entrance and Marniosa – Hall of the Mountain King is 3.5km.  The height difference in the caves closest reaches is, at present, 33m. (ed.2017)  

Marniosa Location

Nacimiento Location

Horizontal (m)

Vertical (m)





Beyond Sump 2 (current limit of exploration)

Furthest point Far Upstream Sump



T20 Sinks (Sobra)




 Upstream in Marniosa may reveal a sporting through route, if the sinks below the sandstone in the upper Sobra Valley can be linked to (No. 20 in the list of caves).