Localización: Mirador sobre el pantano de Mediano, en Morillo de Tou.
Coordenadas. 265971 4695727 31 N
Textos Esperanza Fernández (Geopage)
The castle of Morillo de Tou is built on a hill which is formed of two types of sedimentary rocks:..
Colina donde se asienta el castillo de Morillo de Tou. Se observa que el propio castillo está edificado en una capa de materiales de aspecto duro y consolidado. Son las areniscas y microconglomerados depositados en los canales submarinos. Bajo ella, la zona sin vegetación nos deja observar una roca blanquecina, muy erosionable y modela con pequeños barrancos. Se trata de margas y arcillas, depositadas en el abanico submarino, fuera de los canales. Fotografía: Esperanza Fernández.
Sandstone
These are sedimentary rocks formed from sand-sized mineral grains that have been bound together by cement. If the grains and the cement are rich in silica, these rocks are very resistant to erosion and stand out in relief.
Aspecto de rocas de tipo arenisca y, a la izquierda, microconglomerado. Fotografía: Esperanza Fernández..
Marlstone
These are sedimentary rocks consisting of a mixture of clays and limestone (calcium carbonate, often in the form of tiny shells of living beings). The higher the percentage of clay, the more plastic the rock and the more easily eroded.
Aspecto de rocas de tipo margas. Fotografía: Esperanza Fernández.
...and submarine canyons
Deep, steep-sided valleys known as submarine canyons cut into the sea floor. The rocks on which Morillo de Tou sits were formed in one of these canyons, on the floor of the sea which covered Sobrarbe about 42 million years ago.
On land, rivers act as huge collectors which carry materials to the sea, where they are deposited. Under certain circumstances (earthquakes, climate changes, the discharge of large amounts of material, etc.), the deposited materials are stirred up and begin to move, carried in the water, flowing through the canyons at high speed and forming what are called turbidity currents.
When these materials reach the base of the slope, the current is halted and the sediment is deposited by gravity. The largest particles (gravel and sand) settle first, and over time this produces layers of sandstone, which fill the channel through which they were carried. The finer sediments (clay) may remain in suspension for years and when they finally settle, they are mixed with particles of calcium carbonate and the remains of creatures that fall slowly but steadily to the sea floor. These deposits are very extensive and generate marlstone.
This process is repeated throughout geological time. The result is a regular sequence of rocks known as turbidites.
Esquema de un ambiente submarino en el que se depositan estas rocas especiales, las turbiditas. Dibujo de Albert Martínez.
The hills on which the castle of Boltaña or the esconjuradero de Guaso are located, among other viewpoints, have a formation similar to the hill on which Morillo de Tou sits: a layer of sandstone, formed in an ancient submarine canyon, protects the marls located beneath from erosion.
En diferentes puntos de Sobrarbe, las capas de arenisca sobre materiales más erosionables destacan en el relieve generando promontorios. Estos han sido utilizados históricamente para la edificación de torres vigía, castillos, esconjuraderos y otras construcciones que requieren una localización en zonas de gran visibilidad.
Avda. Ordesa 79. 22340 Boltaña. Huesca. 974 518 025.