The Formation of the Cave

The geomorphologic frame of La Valldigna is configured by the range of ‘les Creus’ towards the North with very eroded reliefs and strong slopes towards the valley, and the range of the Mondúver at the south. The center is occupied by the valley (La Valldigna) covered by strong quaternary sedimentary deposits. Towards the east, the Valldigna opens to the Mediterranean Sea in a landscape full of marsh and dunes which connect with the coastal plain.
Bolomor cave forms part of this frame and, is located on the right side of a small karst cliff (Bolomor Gorge) in the northern part of the Mondúver. The topographic relief of 300-400m of altitude is highly karstified, covered by fields of hills and crossed by fractured systems. This situation generates a very contrasted orography between the plain and the mountain.

FIG. 1 y 2: Modelo de evolucion karstica segun J. Guimera, modificado. FIG. 3 y 4: Diferentes fases evolutivas del karst de la Cova del Bolomor desde su origen hasta su desaparición.

Karstic evolution model according to J. Guimerà, modified. Different evolutionary phases of the karst of Bolomor Cave since its origin till its disappearance

The Mondúver Range presents a paleolandscape with formations of a tropical karst (pinnacle karst, cockpit karst, kegel karst,…) with conical sinkholes, isolated hills and pinnacles. This karstification and its morphoclimatical systems are attributed to the warm climate of the Upper Miocene-Pliocene which generated an old Mediterranean tropical humid karst during the Tertiary and which nowadays we observe next to the posterior Pleistocene modifications. The elements of the landscape which indicate an evolution of this karst are the sinkholes, the systems of fracturing, the fossilized breccias, the different phases of the cave formation and others.

Ensayo de evolucion karstica del Macizo del Monduver y la Cova del Bolomor.

Test of karst evolution in the Mondúver Range and Bolomor Cave

Relieve con formas karsticas tropicales y sistema de fracturacion NE-SW en el area de la Cova del Bolomor.

Relief with karstic tropical formations and a fracturing system of NE-SW in the area of the Bolomor Cave

Relieve con formas karsticas tropicales y sistema de fracturacion NE-SW en el area de la Cova del Bolomor.

Relief with karstic tropical formations and a fracturing system of NE-SW in the area of the Bolomor Cave

The groups of underground phenomenon identified in the Mondúver range are: spring caves with water activity, sinks and sinkholes in the absorption zone or recharge of the karst and cavities held on top of the piezometric level (residual caverns or relicts). Bolomor Cave can be considered between these last ones, although in the karstic apparatus, it’s a transitional element between absorbent cavities and springs, although in a partial and temporal way.

Reconstruccion de La Valldigna y Cova del Bolomor al principio de los tiempos cuaternarios hace mas de 1 millon de anos.

Reconstruction of the Valldigna and Bolomor Cave at the beginning of the quaternary 1 million years ago.

The evolution of Bolomor cave could have been the following:

– A phase of internal formation in which the cavity, conditioned by the characteristic of the stratiphication, where the dissolution and cracking would be major in hillsides E and S.

-Creation of a strong stalagmite level of very compact crystallization, and without exogenous elements (level XVIIIb), which would indicate constant environmental conditions during a wide space of time. This indicates that the incipient cavern was not open to the outside, or at least, there wasn’t a wide mouth. The chronology of this first and wide genetic phase could be located at warm moments of the final Pliocene (8-3 m.a).

– A hipogeo posterior and important change would be produced with the first incorporation to the karst deposit of small exterior elements which indicate the opening of a mouth or exterior conduct (level XVIIIa), possibly open in the north sector where there is a less dense rock layer and a favorable lithological structure. This event, by its characteristics, could be punctual and chronologically assignable to the Middle Pleistocene.

Reconstruccion de Cova del Bolomor con la primera presencia humana en el Pleistoceno medio, hace 350.000 anos.

Bolomor Cave reconstruction with the first human presence in the Middle Pleistocene , 350.000 years ago

– The tectonic phases of fracturing attributed to the Antique Quaternary would be the ones that would originate the basal fissure which acts as a principal sink of the cave and which already existed in the moment of the opening to the outside. In that period, the actual gorge of Bolomor wouldn’t exist with its actual morphology. The hillside would have a major protection towards the valley and there would be karstic functional conducts in the area that today is occupied by the gorge. These conducts, which have basal remains which can be observed in the slope in front, could have or not a link with the actual Bolomor Cave and configure a wide endokarstic apparatus, today totally disappeared.

Reconstruccion de La Valldigna y Cova del Bolomor al final del Pleistoceno medio, hace 150.000 anos.

Reconstruction of the Valldigna and of Bolomor Cave at the end of the Middle Pleistocene, 150.000 years ago

-The progressive regression of the north facade of this hillside and the transformation of the exokarstic formations of the mentioned apparatus, which nowadays are inexistent -sinkholes, poljes,..- would be the origin of the actual karstic canyon with a strong verticality which sections the cavern, leaving hanging and residual, as a lateral balcony, the small rocky shelter today known as Bolomor Cave. Between the capturing and sinking of the dome, there might have been a short geological time. From level XV, the strong incorporation of allochthonous material would indicate an opening of the cavity to the outside and a major incidence in the hillside. At the beginning of the Middle Pleistocene, according to the geomorphology of the environment and the stratigraphy of the filling, the site would offer, with total security, bigger dimensions which we can’t appreciate because of the collapse of the big parietal blocks and of the ancient dome. This sinking (level XVI ca 300 ka) could be related, by its characteristics, with seismic phenomena. This conduct worked as a sink, function which still has nowadays. At the end of the cave there is a vertical cavity which allows the flow of water towards lower areas in the karstic apparatus.

Reconstruccion de La Valldigna y Cova del Bolomor hace 100.000 anos.

Reconstruction of the Valldigna and Bolomor Cave 100.000 years ago

The formation of Bolomor Cave starts with the development of a cavity favored by an adequate stratiphication and cracking. Subsequently, it originates a strong stalagmite layer in the warm moments of the Final Miocene-Pliocene (8-3 million of years). The tectonic processes of fracturing of the cave, attributed to the Old Quaternary, 700.000 years ago, would originate the basal sinkhole which acts as a sink. In that period, the Bolomor gorge, with a different morphology to the one nowadays, would have a major projection towards the valley and hillsides. The progressive regression of this mountainous slope would give origin to the actual karst canyon, with a steep slope, which would section the cavern and would produce a mouth to the outside.

Between the opening of the mouth and the falling of the dome of the cave there might be some geological time relatively short. 350.000 years ago, the cave offered bigger dimensions, reduced from that moment after the collapse of the old dome which could be related with the frequent sismic phenomenon of the zone. The cavity always has worked as a sink which allows the flow of the water towards lower areas. However, the water activity didn’t erode the sedimentary filling as it was canalized by a system of fissures which have allowed the conservation of the archaeological deposit until nowadays.

In the present, Bolomor cave has morphology of rocky shelter, as a partial remain of an old and wide cavern. It presents an extension of 35m of length, in N-S, and 17m of width, in total, 600m2 with a depth of 20 m. The interior is very irregular due to the strong slopes of the stalagmite basal deposits, the big blocks product of the sinking of the ceiling and the filling of the breccied deposits. From its mouth, located in a wide rocky cliff which forms a hanging balcony over the valley, a wide coastal area can be viewed, up until the town of Cullera, crossed by the Vaca river.

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Topography of Bolomor Cave with its different sedimentological deposits

 

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Topography of Bolomor Cave with its different sedimentological deposits

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