Eastern Massif caving expeditions

In 2021 the Tresviso Caves Project continued work in Cueva del Nacimiento, Cueva de la Marniosa and ongoing work on the Andara mountain range.

Club D’Espeleologia L’Avern continued work in Portudera

Tresviso 2021 (TCP)


The 2021 expedition was to continue with ongoing exploration in the Cueva del Nacimiento cave in the Urdon Gorge (Tresviso, Cantabria).  Expeditions in the previous years have been slowly extending the cave up through the mountain range, with the intention of trying to connect the cave with the known deeper pot holes in the Andara region.  A number of the caves higher on the mountain (Sima 56, Sara) have previous been dye tested and the water is known to resurge in Cueva del Nacimiento.

Cueva del Nacimiento is a large resurgence cave in the gorge below Tresviso. Originally explored in the 1970’s and 80’s it was pushed to a terminal chamber ‘Death Race 2000’, ~400m above the entrance. Interest was re-kindled in 2009 with a lot of work put into regaining the original route over the following years and climbs above Death Race 2000 began with the hope of finding further extensions to the cave and a connection with the surface.

In 2019 a large new chamber, and secondary streamway was discovered in Cueva de la Marniosa, a feeder system into Nacimiento.  Although unexpected at the time, this has helped justified the extra time spent re-surveying old leads and revisiting known passage, but with improved equipment and lights.

Originally planned as an expedition with nearly 40 members, and a large student contingent, the global situation with the coronavirus pandemic forced some last minute changes and the expedition was run with a much reduced member basis and smaller objectives.


The main objectives of the 2021 expedition were:
1. Exploration in the far reaches of Cueva del Nacimiento. Work at the far end of Nacimiento has gradually been extending the cave upwards.  The 2021 saw the return of the ‘climbing contingent’ from early trips so further progress was hopeful.
2. Exploration in Cueva de la Marniosa, continuing from new second parallel streamway, discovered in 2019. 
3. Pushing the downstream sump of Marniosa – due to CoVid circumstances, this original objective was dropped.
4. With the expansion of the expedition by a large contingent of SUSS cavers, exploration of the alpine potholes, will continue. Due to CoVid circumstances, this original objective was dropped


In total over 2.6km of new cave was surveyed in 2021, a further 1km of existing cave was resurveyed, largely in Cueva del Nacimiento in order to correct known errors and incorrect passages in the entrance series. 

Exploration in Cueva del Nacimiento continues and after a few years of stalled progress the way on and the draft was discovered again.  Once more this has ended in a drafting choke, but perseverance is starting to bring rewards.

Cueva de la Marniosa once again has provided more unexpected discoveries and the continued increased in length and potential surface connections suggests this will provide more discoveries in the next few years.

The dye trace from Fallen Bear was also successfully completed and results are in progress.

The coronavirus pandemic provided some challenges to the management and running of the expedition, but this was largely confined to increased costs (for tests) and a constant state of worry for most that every sniffle and cough could be the onset of the virus and the heavy responsibility of being the group that brought the virus to a previously unaffected area of Spain.  Luckily the fears were unfounded and there were no major issues.

Cueva del Nacimiento

Jurassic World – Barney and Friends

The furthest point of Nacimiento has been at the end of the Jurassic World named section of passage, ending in a small draughty hole, The Sandy Dig.  After a few years of ignoring, for better leads, a solid 8 hours of digging and hammering, the hole was passed to a long section of walking passage, like the rest of Jurassic World.  Over 250m of passage was discovered, ending at a calcite choke with a draft

The B*stard

The large Pina Colada sump was crossed in 2018 to give access to an ascending rift / climb that led to another 150m of passage and and unclimbed aven.  The aven was scaled in 2021 for over 73m vertically and is still ascending, with a further bolt climb above.

Cueva de la Marniosa

The 42 Streamway

In 2019, a secondary streamway was discovered towards the end of that expedition.  A small climb in the stream was the limit in 2019.  This was quickly passed in 2021, and over a number of trips the passage was explored for over 1km


In addition to the major discovery in the streamway, the entrance series of Marniosa was resurveyed.  3 avens were scaled, with 1 still continuing and toward the end of the expedition, a climb above the original streamway, in the old part of the cave, has discovered a possibly continuation of the main relic passage.  A tantalising prospect for further progress on the next expedition.

Other Exploration


Several surface sites were identified, that were located above areas of Marniosa.  A few days were spent looking at shafts, including the discovery of a fine 80m shaft and a smaller pothole containing an unexploded WW2 grenade.  Unfortunately, no route through to Marniosa was discovered this year.


Phil WalkerBradford Pothole ClubUK2021Tresviso 2021
Bob ClaySouth Bristol Speleology SocietyUK2021Tresviso 2021
Howard JonesLancaster University Speleological SocietyUK2021Tresviso 2021
Derek CousinsLancaster University Speleological SocietyUK2021Tresviso 2021
Alastair GottTechnical Speleological GroupUK2021Tresviso 2021
Martin HoffSouth Wales Caving ClubUK2021Tresviso 2021
Toby DrydenSouth Wales Caving ClubUK2021Tresviso 2021
John RoeSouth Wales Caving ClubUK2021Tresviso 2021
Claire VivianSouth Wales Caving ClubUK2021Tresviso 2021
Tom SmithSouth Bristol Speleological SocietyUK2021Tresviso 2021
Jethro PrykeSouth Bristol Speleological SocietyUK2021Tresviso 2021
Glen SankeySouth Bristol Speleological SocietyUK2021Tresviso 2021
Chris JonesCardiff Hill DiversUK2021Tresviso 2021
Dave PowleslandCardiff Hill DiversUK2021Tresviso 2021
Leo BradleySouth Bristol Speleological SocietyUK2021Tresviso 2021

Thanks also due to Nick Airey, Colin Boothroyd, Ken Daykin, Fernando de la Fuente Moreno, Carolyn Ginnever, Tim Nichols, Mark Sefton, Jim Thomson, Ana Moradiellos Barreiros, UKCaving.com and the people of Tresviso.

Portudera 2021 (CEAO)


Since 2016 Club d’Espeleologia l’Avern de Ontinyent (Valencia) have been exploring the area of Portudera in the Eastern Massif. The project aims to catalogue and explore the caves in this area


7 new caves identified, exploration in Monte Obeson area and exploration of PO-84, 400m long


Individual members not recorded

Documents & Links

  • TBC