Geological formation of
the Bardenas Reales of Navarra
The Bardenas Reales are situated at the north edge of the hollow of
the river Ebro, a geographical feature, formed geologically by materials
from the continental Tertiary and Quaternary periods. As a result
of the supported pressure caused by the elevation of the Pyrenees
and the Iberian Mountain Range: the hollow of the river Ebro caves
in and receives the contribution of eroded materials from higher areas
since the late Eocene (38 million years ago) until the present.
In the areas nearer to the Pyrenees you can find the most heavy and
solid materials like conglomerate, gravel and sandstone. Towards the
centre of the hollow, where the slope is falling and the fluvial running
is lesser, you can find finer sandstone. In the plainer areas you
can find clay, gypsum, limestone and mineral salts.
The exceptional nature of the relief of the Bardenas is due to the
quality and the structure of the materials and due to the action of
water and wind. The alternation of clay, limestone and sandstone,
with predominance of clay, a soft and impermeable material, allows
that the erosion of the rain has a fast and severe effect because
of its sporadic but torrential character.
For example, the hillocks in the shape of a table are very typical
of this landscape. These hillocks are mounds composed of clay and
whose upper part is protected by a stratum of sandstone and limestone;
only their lower part is eroded.
Another demonstration of the erosion of the rain are the relieves
called “lunar”, “elephantskin” or “bad
lands”, formed in the plains and hollows where the torrent waters
act on the impermeable slime and clay. And also the formation of plateaus
and ravines, as well as other phenomenon caused by the absorption
of the water like cavities or cavernous spaces.
The wind is the other active agent which contributes to shape the
characteristic landscape of the Bardenas tirelessly. The “Cierzo”
a north wind with direction NE and NNE dominates over this territory
for more than a third part of the year. It can reach a speed of between
20 and 30 km/h.