GEOLOGICAL-GEOTECNICAL CHARACTERISTICS OF THE "LACHA"
All these geologic processes have given rise to the peculiar terrain existing in Benamaurel today, sequences of fine strata, locally known as "lacha", in which the geological history of the last million years is perfectly recorded. Therefore, this is ground with lacustrine sediments formed by clay, Marly clay (known locally as "jabaluna", plaster locally known like "espejuelo" and other salts (epsonita, anhydrite, etc). These are thin layers (of several millimetres to at the most 1 metre), totally horizontal, whose deposit depended on the climatologic conditions of the environment. In warm periods the precipitation of chemical rocks took place (plaster and salts), and in cold periods the clay was deposited.
Also the presence of accumulations of fossil remains of lacustrine fauna is common, constituted by levels several centimetres thick in which shells of bivalves, molluscs and marine invertebrates are generally found. On other occasions, the shell dissolves leaving a mold in which the complete structure of the animal is perfectly conserved. The appearance of these levels is very common in the walls of some caves.
The confinement of all these litologias, plus the weight of the water column above them during thousands of years which has exerted an important pressure on the sediments, has contributed to the formation of a consistent type of ground, safe and of superb geotechnical properties for the excavation of cave-houses. The presence of the Marly clay layers, "Jabaluna", intercalated between the other strata, makes the cave a solid, robust and indeformable structure; this is the reason why it is so difficult for cave-ins to occur.
On the other hand, once the caves are excavated, as they lose the natural humidity of the ground land, they dry and harden acquiring more resistance with time and for this reason it is important that cave houses are always ventilated.
Normally, for greater security, the dome shaped ceilings of the caves are usually culminated by one of these levels of jabaluna. In some caves, the presence of cracks locally known as "madres" is common but these do not present any danger (as long as these cracks do not arise on the outside of the ground) since they usually remain unchanged for hundreds of years. Indeed, these cracks can be beneficial on occasions since they usually persist without alteration for some hundreds of years. Furthermore, these "madres" are sometimes beneficial, since they allow for better ventilation of the ground preventing humidity from taking place. The first inhabited cave houses in Benamaurel date from the Neolithic era and still perfectly conserved.
The only and the most common enemy of caves are the filtrations of water caused by damage to the drainage and other similar installations. Water is an agent capable of originating geotechnical problems in any type of land, although because this type of ground is extremely impermeable, the resistance to water is greater and is always apparent by the appearance of humid or brackish spots or stains.
Therefore, as far as time is concerned, the consequences that water produces on any other type of land (cave-ins, collapses etc) are quicker in manifesting themselves than in this type of land, which is a great advantage, since there is therefore more time to discover and suitably treat the problem. Problems caused by water in natural conditions are not usually common, since the phreatic level is deep and the pluvial waters do not infiltrate because as commented previously, the ground is very impermeable.
The predominance of the argillaceous fraction in the land, isolated from the exterior and producing isothermia in caves is able to maintain temperatures inside between 18 and 22ºC throughout the year, although the climate in Benamaurel is subject to very contrasting seasonal changes.
Therefore, it is pleasant to be inside one of these caves, with its peculiar architecture, completely isolated from noise and enjoy its pleasant temperature, and to be able to observe with total clarity a part of the geologic era, the passage of thousands and millions of years, in which all types of natural processes have occurred: great storms, periods of immense heat, turbulences, human beings who inhabited the cave, as if one went from a sea to a lake, from a lake to the mainland, etc, and all this within a few simple walls.