RRCPC Newsletter
Volume 41 Number 2 Article 1
May 2004

Introduction to the Caves of Matienzo

This article has been adapted from the version written for "The Archaeology of the Matienzo Depression" (Ruiz Cobo and Smith)

The Matienzo Polje: Geography and Geology

The enclosed karstic depression of Matienzo lies about 25km south east of the city of Santander on Spain's northern "green coast". The total area of the depression is 26.3km2 with the floor having an area of some 3km2. The basal altitude lies between 145m and 200m above sea level and the eastern slopes rise abruptly to 835m altitude on the mountain of Mullir. The depression has three "branches" - the western branch, called La Vega, has a narrow, flat floor. The southern branch, Ozana, has a gentle rise from the floor until it then rises steeply. The northern, lowest branch - La Secada - has a generally level floor sloping northwards towards the river sink. Two passes lead out of the Matienzo valley, Cruz Uzano to the south at 347m and to the north, Fuente las Varas at 450m. A river resurges from Cueva Comellante in La Vega and meanders for about 1200m along the valley floor before sinking into the impressive Cueva del Molino. After a kilometre flowing underground, the water resurges into the northern branch of the valley, meanders for a couple of kilometres through La Secada and finally sinks underground again into Cueva Carcavueso (altitude 145m). The water is seen on the surface again in the valley of Secadura, nearly 4km away to the north east, at an altitude of 50m.

The scenic hills around the depression display limestone scars and cliffs, with grass and scrub mingling with the lapiaz. In some places, the limestone is riddled with caves; in others, steep rubble slopes and pinnacles cover any possible entrances. At all altitudes, around and outside the depression, there are caves that would appear suitable for use by hunter-gatherers. At high level, where the ground is not too broken with steep limestone pinnacles or clints and grikes, the vegetation is grazed by cows, goats and horses. These animals find shelter beneath the rocky overhangs or in cave entrances and a number of the larger cave mouths have been adapted with pens to hold and husband the herds.

The valley floor is divided into walled fields and cultivated, often with a maize crop. The lower slopes are grazed or grass is grown and cropped using trad-itional scythes, although more modern mowing techniques are creeping in.

While scattered farms and cabanas are found above the lower regions, most of the population live along the floor of the depression and most within 100m of the metalled roads. The rapid rise in the standard of living since 1975 has not missed Matienzo, and a number of the houses are "holiday homes" or "week-end retreats" belonging to Spaniards or foreigners. Red tiled buildings are being renovated, both for locals and "in-comers". But overall the population of this essentially rural area is declining, young people move away while the older inhabitants die.

The extremes of climate that characterise the meseta in central Spain are mod-erated by the Atlantic so that Matienzo has a temperate to warm climate with an annual rainfall of about 1200mm per year. Snow is rarely seen on the valley floor and the summer afternoon temp-eratures can be pleasantly hot at 25-30oC. Prolonged rainfall is not uncommon and the result can be flooding along the valley floor as the river sink at Carcavueso becomes inundated. During clear summer nights, the moist air cools in the enclosed depression and produces thick mists. Early morning travellers approaching Matienzo from north or south are often treated to the spectacle of a "sea of cloud" surrounded by the characteristic green and white of the limestone scenery.

Practically the whole of the modern-day relief is in Cretaceous limestones that can be simplified into the following succession:

Albian   300m   Thin bedded limestones, with some massive beds
Aptian   100m   Massive limestone (Urgonian) with thin marls
Aptian   200m   Thin bedded limestones, with thin sandstones
Barremian   500m   Sandstones and marls (Wealdon)

The upper Aptian is a pure, compact limestone - typical of the facies known as Urgonian, which contains many caves in southern France. The controls on the initial formation and subsequent devel-opment of the caves are many. The rock is gently folded and has abundant faults. Local sandstone or sandy limestone lenses further complicate the geology and often have a deciding influence on cave passage direction. The valley bottoms have alluvial deposits and the valley sides and high levels have a thin layer of red soil. There was no Pleistocene glaciation.

It has been estimated that the depression below 347m (the altitude of the southern col) could have formed in the last two to three million years, with all of the dissolved limestone being carried away underground. There are many phreatic caves above this altitude and they must have formed much earlier. It has also been postulated that drainage may have occurred towards the south before both underground and surface waters were captured to flow north.

The Matienzo Caves: Exploration and Documentation

Madoz appears to have been the first to publish information about Matienzo in a scientific work. (Madoz Pascual, 1848). This volume mentions the village and the river. A few years later Puig in a work about the caves and shafts of Spain mentions some caves, sinks and resurgences in the depression, (Puig et al, 1896). But the systematic discovery and exploration of the caves under the hills around Matienzo has been due, first to Spanish spelaeologists in the 1960's and then to British cavers from the seventies to the present day. Joint exploration with Spanish groups has occurred for the last 10 or 11 years. A number of the caves have large entrances and the entrance passages will have been known, explored and possibly exploited since early times. As caves have been discovered, extended and documented, archaeological study has sometimes been the main thrust of investigation, for example in Cueva Grajas and Cueva del Dientes.

The British role in exploring and documenting the caves over the past thirty-three years has been crucial to obtaining a fuller understanding of the hydrology, geomorphology and arch-aeology of the caves. Programmes of scientific work have been carried out both above and below ground. Uranium series dating to determine the age of stalagmites (Openshaw S, 1996), magnetic resonance studies of cave sediments to determine possible cave system links (Quin Andrew, 1995) and radiocarbon analyses of pottery (Ruiz Cobo J and Smith P, 1997) have all added answers and more intriguing questions to the overall picture.

The passages discovered by many cavers, along with the scientific results, have led to particularly well documented knowledge (but incomplete understand-ing!) of the depression's cave systems. Each year of exploration has seen English and Spanish publications and recently a web site has been set up to share the information about the area and the caves, along with surveys, photos, history of exploration and scientific articles. (http://www.matienzo.org.uk).

At the end of the summer 2003 explorations, a total of 241.6km of cave passage had been explored and documented, with 1968 entrances and sites of speleological interest. The sites range from possible digs into caves, to cave networks over 40km long. Seventy of the sites have some archaeological interest, ranging from glimpsed medieval pottery in floor deposits to possible bronze age burials and caves used as shelters during the Civil War. Many sites remain to be excavated and the full archaeological potential of the area's caves has perhaps only recently been recognised. A number of these sites, although probably influenced by the Matienzo depression, are outside the depression and of the 70 archaeological sites in the "Matienzo database" some 46 lie within the boundary.

The South Vega Caves

The main spring or resurgence into the depression enters the Vega branch from the hills to the south. The cave behind the resurgence forms the South Vega System - a magnificent series of large passages which link to major entrances on the hillside above. The source of the water is likely to be percolation over a wide area. High level passages have often been truncated by surface lowering. It is a happy coincidence if caves occupied or visited in ancient times have their entrances blocked by rockfall or land-slip and artefacts sealed in, especially when modern day cavers in their search for cave passages can re-open these old entrances. This happened in Cueva Vallina where the finding of a complete prehistoric clay beaker on a slab 2 kilometers in, 100m down and 3 hours from the main entrance led to the excavation of an ancient opening that had collapsed.

The South Vega System with passages totalling 29km is close to linking with the 31.2km Cueva Vallina that has entrances over the hill on the Arredondo side. Connected into the system are Torca de Coterón, Torca de la Cabaña, Cueva-Cubio de la Reñada and Torca de Azpilicueta, sites 1338 and 675, and Torca de Papá Noel. The whole complex is essentially sets of sub-horizontal levels connected by vertical shafts. The bottom passages are partly formed below the current water table and sections of this level require diving equipment to proceed. The upper levels are mainly very dry with only the occasional sign of water. Even with very wet surface conditions, the percolating water is channelled away from many of the upper passages by perhaps a sandstone bed forming a roof. Alternatively shafts, faults and joints capture the water and divert it straight down to the bottom level, often making the descent of these drops a damp business. People visiting the caves must be proficient in single rope techniques to move between the levels up to 60m apart. Most of the passages in the system can be walked through and typically are 3 to 8m high and wide. Floor deposits range from boulders to sand, with crystals of gypsum often found in the sand-banks. Chambers often have pitches down to lower levels. In some places there are magnificent stalactites and stalagmites. These calcite deposits are often in the form of thin straw stalactites and massive bosses, sometimes coloured red or black by minerals. The damper areas of the South Vega System can be very muddy: knee-deep, sloppy and sticky clay slows the pace in sections of Cueva-Cubio de la Reñada and coats all the surfaces in sections of Torca de Azpilicueta.

The main levels of development in the South Vega System and through into Cueva Vallina are quite marked and appear to have their counterparts in the North Vega System. Indeed Quin (Quin A, 1993) has suggested that similar k values for sediments in Torca de Coterón and Cueva de Mostajo on the north side of La Vega show that the caves may have had a common morphogenic agent and were connected. It is certain that phreatic passages on both the north and south sides of the Vega valley must have formed well before the valley and it is quite feasible that the systems were joined.

At an altitude of 503m, the large entrance of Cueva Codisera to the east of the South Vega System has a height of 15m and width of 10m. Daylight reaches well into the magnificent passage. The ancient vadose entrance passage intersects old phreatic levels and the cave reaches a depth of about 140m, finishing at the base a steep shale slope. These major passages are some of the oldest around the depression, with levels between 500m and 360m altitude, compared with the 350m to 190m range for the majority of major routes in other caves. At least two of the levels in Cueva Codisera have been truncated by surface lowering.

The North Vega Caves

On the northern side of La Vega, the hanging Cubija valley runs down from the north west to the south east. At its head is the extensive network of the North Vega System, comprising Cueva Mostajo, Torca de Regaton, Cueva de Morenuca and El Cubio. Again, the 17.9km long system is basically a set of vertical shafts linking horizontal tunnels that have extensive layers of sediment (boulders, cobbles, gravel, sand and clay) and calcite deposits. Sections of the cave have superb helictites. The water met at the lowest level in this system is flowing away to the north and may resurge at Fuente Aguanaz, 5km to the north west.

The entrances to the system are shafts or tight squeezes and it is difficult to imagine hunter-gathers needing to enter such places. No archaeological artefacts have been found.

Four Valleys System

Most of the water in the Matienzo depression can only leave by evapo-transpiration or by sinking into the cave outlet at the lowest point of the valley - Cueva Carcavueso. (One low level cave in the southern Ozana branch appears to flow south and drain under the hill towards Ogarrio). The water in Carcavueso meets up with water from Cueva Hoyuca and Cueva Riaño in the Riaño valley to the north, flows east to pass through Cueva Llueva and flows under a ridge to resurge in Secadura. The whole cave system that links the Matienzo depression, Llueva, Riaño and Secadura is called the Four Valleys System, and the network has a length of 43.4km. It is possible for cavers to pass through from one valley to another but the routes require diving and passing through dangerous boulder chokes. The system lies under less limestone than the caves to the south and, at the moment, it would appear that there is basically one "level of development" at, and slightly above, river altitude. However, there are places where significantly higher pass-ages can be entered and the history of the Four Valleys System is certainly not that of a simple stream sink and resurgence.

To explore the caves within the Four Valleys System requires some stamina - for example, a caving trip to the end of Cueva Hoyuca and back involves traversing about 14km of passage and takes up to 18 hours, depending on the exploration carried out at the far end, near Cueva Carcavueso. The entrance series is a complicated phreatic maze that breaks out into the tunnels of Quadraphenia. About 10 minutes of quick walking on sandy floors, with occasional boulders leads to a stream where the going becomes more interest-ing. A crawl on sandstone cobbles enters a wet, flat-out crawl and a pop-out into a set of phreatic chambers. A drop down below a small boulder choke enters another crawl to the main river. The first 800m of river passage (the Gorilla Walk) is only about 1.5m high and involves wading through water up to a metre deep in places. Relief comes after a short bouldery section and the joining in of the second river from Cueva Riaño. The next 500m involves clambering up and down boulders or wading in the water. At Obvious Junction the water is left behind and a small passage at roof level crawled along for about 200m. At the end, the caver pops out on the side of the Third River. Wading and clambering characterise the going for the next 800m until the Fourth River is met and soon the cave's finest feature. By walking up a passage on the left of the streamway the magnificent 30m wide and 100m high Astradome aven is entered at the bottom. The aven has been climbed to enter small passages at the top, but the aven is just a diversion for people intent on reaching the end! The route continues downstream into the boulder piles of Armageddon that characterise about 250m of chambers. The route involves climbing up between large boulders, clambering up and down boulders in passage 20m wide and finally dropping back into the streamway. The river continues south and eventually the roof drops down towards the water. At Duckhams Sump the route is a walk through a wide passage with the water about 10cm from the roof. The sound of falling water guides the caver to a slot in the roof and a climb up into Rocky Horror. Huge boulders hinder route finding for some 400m and near the end there is a tortuous and dangerous route between smaller boulders that links with Cueva Llueva. Near the start of Rocky Horror, the higher levels in Trident Series can be entered. There are more than 2km of roomy passage in the Trident Series that come enticingly close to Cueva Carcavueso in Matienzo, but the link remains elusive. These higher levels could have been ancient water sinks for the depression and they may have been truncated by surface lowering.

Any trip to the end is a serious undertaking, but most of the major extensions were carried out in the seventies and eighties when clothing technology was not as advanced as it is today. The standard, modern wear for Cueva Hoyuca (and most other caves) is a one-piece fibre-pile body suit protected by a tough boiler suit. Twenty years ago to keep warm in wet caves, a neoprene wet suit was worn. Walking, crawling and wading in that outfit was hard work and it also trapped sand and grit behind the knees and in other delicate places!

It will come as no surprise that no prehistoric artifact has been found in any of the caves of the Four Valleys System, either placed or used in the caves, or washed in. However older, possible drainage routes for the depression may have been used by prehistoric people after the water found lower paths. At altitudes of 220m and 270m, the caves of Emboscados and La Cuvia may have been involved in the drainage of the valley in the past. It may also be no coincidence that these altitudes appear to mark cave passage horizons in other caves all around the depression.

The highest points around the depression are the mountains of Mullir and Muela on the east. The landscape is most inhospitable in places with sharp limestone edges, steep scree slopes and particularly nasty "jungles" of thorns and brambles on the lower slopes to the north. In places, deep shafts are to be found every few metres, but caves are less common. There are a few caves that must be more than 3 million years old but some of these are now shelters for cattle. Any remains buried deep in sediments may well be adversely affected by animal waste. The horizontal systems that must lie somewhere beneath the massive limestone have not yet been discovered, although at San Miguel the 30m wide passage in Cueva Cobrantes (on the north side of the Mullir / Muela range) gives some indication of the size that may exist.

It is unlikely that the more active and recently formed lower level caves will yield major archaeological finds. However, it is possible that some of the older, large cave passages above the floor of the depression will have been open and perhaps more or less in their present form for around a million years, e.g. Cueva Cofresnedo and Cueva Sotarraña. Some of the ancient sediments are hidden beneath massive stalagmite flows. With the finds at Atapuerca (300km to the south) pushing back the dates of substantial human remains to 800ka bp, there would appear to be little reason why our ancestors from the same age would not venture into these Matienzo caves that would be just above a higher valley floor.

Juan Corrin
18 November 2003

Recent reports

Bibliography

Matienzo Top Ten

Cave   Name   Alt   Length   Depth   Area
0107   Hoyuca, Cueva   175   43437   100   Riaño
0733   Vallina, Cueva   410   31169   157   Arredondo
0333   Azpilicueta, Torca de   480   29088   317   S Vega
0892   Regaton, Torca del   303   17922   147   Cubija
0025   Risco, Sima-Cueva del   196   9046   25   Ozana
0841   Fresnedo 2, Cueva   136   7045   30   Fresnedo
0258   Calleja Rebollo, Torcón de la   305   6531   67   Seldesuto
0122   Suviejo, Cueva de   183   3500   111   Secadura
0002   Coverón, Cueva del   265   3230   0   Ozana
0363   Colmenas, Fuente de las   180   2688   -66   N Vega

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