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Discover the Sobrarbe-Pirineos Geopark

6 The legacy of ice. Linás de Broto

The legacy of ice( Linás de Broto)

Localización Entre la iglesia y las primeras casas del pueblo de Linás de Broto. Enfrente del abrevadero.

Coordenadas. 30T0732198 UTM 4722651

Textos Esperanza Fernández (Geopage)

Some of the most impressive landscapes in the Sobrarbe district were created by ice. If we were to travel back about 60,000 years into the past, we would find the northern part of this region covered with ice. In a world of ice, glaciers scoured out the terrain, leaving behind various traces of their existence: large cirques such as Marboré, tarns such as Basa de la Mora, open valleys such as the Pineta or Broto valleys, and chaotic sediment deposits such as those at Viú or Sarvisé, among others.

Glaciar actual (Saskatchewan, Montañas Rocosas, Alberta, Canadá) excavando el valle por el que se mueve. La suciedad está formada por material rocoso de diverso tamaño y procedencia, cuya acumulación se denomina morrena. Fotografía: Esperanza Fernández.

An example of these traces would be the "glaciolacustrine deposits" near to Linas de Broto, which are light-coloured sediments topped by a flat surface now covered with meadows. These sediments have become visible due to the erosive action of the Sorrosal stream and rainwater. Study of the geology has revealed that these sediments were deposited in an ancient lake fed by glacier meltwater, which has now disappeared.

Diversas vistas de los depósitos glaciolacustres de Linás de Broto.

vista tal y como se observa desde la carretera de entrada a esta localidad Fotografía: Ander Gómez.

El depósito al pie del mismo, y en ellas se pueden observar los diferentes tamaños de sedimentos depositados en el lago en función de la climatología y de otros factores geológicosFotografía: Ander Gómez.

Fotografía: Ander Gómez.

Detalle de estos depósitos. Fotografía: Ander Gómez.

Glaciar de casquete actual, en Groenlandia. Al deshacerse el hielo, todos los sedimentos que transportaba el glaciar se depositan. Estos depósitos glaciares (denominados morrenas) son caóticos, con sedimentos de todos los tamaños y formas. Sin embargo, cuando los sedimentos se depositan en una laguna alimentada por un glaciar, estos adquieren diversos estilos de depósito (capas de cantos, capas con arenas en láminas paralelas, capas de arcillas, etc) Algunas de estas formas de depósito glaciolacustre pueden reconocerse claramente en los materiales que afloran en las proximidades de Linás de Broto. Fotografía: Esperanza Fernández.

How was this deposit formed?

During the last ice age, the head of the Sorrosal Valley was occupied by a small glacier whose meltwater generated a stream that, like the present one, found its natural outlet in the Broto Valley. At the same time, a glacier flowed through this valley carrying large amounts of rock which had been torn away by the ice or had fallen from the surrounding hillsides. This glacier penetrated the Sorrosal valley, where it released much of the rock it was carrying and this deposit created a natural dam, blocking the stream's exit and forming a lake.

Autor: Albert Martínez

This lake was once about 2 km long and 500 m wide. The amount of water and sediment that entered it varied according to the prevailing climate at the time. As a result, the sediments which once filled the Linas de Broto lake present alternating layers of gravel and river pebbles, sands deposited in small river deltas and sedimentary clays from times when less sediment was deposited.

When the main glacier disappeared, the Sorrosal River opened a passage through the moraines, emptying the lake and continuing on its way to the River Ara.

Autor: Albert Martínez

El material que se observa desde el mirador de Linás de Broto, y al cual está dedicado el panel, no es el único depósito glaciolacustre de la zona. Diversos equipos de trabajo han investigado este valle en busca de sedimentos similares, hallando varios de ellos en diversos puntos y analizando la edad de cada uno de ellos. Estos depósitos han sido cartografiados en detalle y su estudio permite reconocer la existencia de, al menos, dos lagos situados a distinta altura y obturados por la presencia de morrenas

Mapa geomorfológico que muestra los lugares donde aparecen restos de depósitos glaciolacustres y de morrenas en los alrededores de Linás de Broto. Estos mapas son la herramienta básica del trabajo geológico, a partir de la cual se obtienen datos que permiten interpretar la historia geológica.

Did you know that…?

While most people associate the ice age with Pleistocene glaciation and the large woolly mammals which are now extinct, there have also been periods of intense cold in more recent times. The best known is the Little Ice Age, which took place between 1550 and 1850 and is thought to have been caused by a decrease in solar activity. The glaciers of the Pyrenees expanded during this period, but have been retreating since 1850. /p>

Glaciar de Monte Perdido, uno de los glaciares relictos que aún se conservan en Pirineos. Fotografía: Luis Carcavilla

Recomentations in your visit to Sobrarbe-Pirineos Geopark

• Safe visits, unforgettable experiences. There are companies who collaborate with the Geopark where you can hire specialized guides to make your tour a unique and safe experience.
• Respect the geological outcrops. Do not break off samples of rock, mineral or fossils.