Once we came down from the viewpoint, all became clear. On revisiting the church, we found another "mine" next to it, and a similar sign. This time, however, the sign was written in English. It turns out that "Eledio Quartz Mine" is in fact "Eledio Sink Holes". What we have seen wasn't a mine, but a natural phenomenon.

Now, the sign had lots of information on sink holes. And I took a lot of photos from the viewpoint. So as I show the photos, in a clockwise direction, I will recite what the sign had to say about sink holes. That saves me from having to come up with lots of "ooo look, another view" captions.

The Sign Read:

Karstic processes result in the creation of surface and underground cavities. Each cavity may have a different shape (circular or linear), size (small or large), depth (shallow or deep) and, of course, genesis type. The most common strustures are sinkholes., usually of spherical shape, accompanied by ground subsidence (due to stress, earthquakes, reinfall etc). Other forms of cavities are dolines, crucibles etc.

Generally, karstic features are considered to be one of the most hazardous geological phenomena, as they often threaten the built environment and, furthermore they are not easily detected. The threat affects mainly residences - settlements, roads and bridges, water works (dams and canals) and verious other engineering works. Due to all of the above, particular attention is required from both geologists and engineers in order to deal wit such phenomena prior to construction. This provision, done properly, will save money.

Causes of the development of karstic features

The most common causes for the formation of karstic features, eg sinkholes, are changes in the water level and, generally, in the hydrological regime. Most sinkholes are often created after floods which increase river flow. They can also appear after pumping of underground water and the drop of the water level, assuming that the water, in such case, is to be chemically capable of dissolving the surrounding layer, e.g gypsum. Moreover, seismic movements can also contribute in the appearance of sinkholes. In cases when roofs collapse due to seismic shaking.

Generally, karstic structures do not have a specific arrangement or shape / pattern and that is why they are so difficult to be detected, especiaaly at greater depths. This fact alone indicates the greater severity of the hazard in engineering works' fuoundations and, eventually in their stability and safety.