The Picos de Europa are a geological unit composed almost purely of limestone, and are the largest single mass of mountain limestone in Europe.
The limestone was caused by the
compression of sediments laid down beneath the ocean during the
Carboniferous period, 345 to 280 million years ago. Later periods of
uplift thrust the limestone high above sea-level, fracturing and folding
it due to the great stresses involved, until three huge lumps of
limestone remained - the three massifs. More recently, glaciations
during the ice ages widened the fractures into narrow but deep gorges,
such as the Cares Gorge. The actions of ice and rain continue to erode
and dissolve the rock, forming the characteristic landscapes we see
today.
Limestone dissolves in rainwater by a process
known as karstification, the most visible sign of which is the vertical
fluting of rock-faces. Also notable, and typical of karst landscapes,
are the sink-holes or "jous" (or "hous" in Asturian), formed by lakes
having drained through underground passages. The largest of these
seemingly-lifeless jous are over 1km across, and are just as dramatic as
the peaks surrounding them. The passages through which they drained
have formed an extensive and complex cave system.
The high dry karst landscape is typical for its
lack of surface water, but infrequent springs do arrive at the surface,
though not for long, and they are notorious to locate. There are few
lakes or tarns in the mountains (lakes Enol and Ercina being the obvious
exceptions), few streams or rivers (except in the gorge bottoms), and
not a single waterfall of note. Mining for zinc and lead ore used to be
an important economic activity, mainly centred in Ándara in the eastern
massif, and Áliva in the central massif, but all operations were
abandoned towards the end of the twentieth century.
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