Imaggeo on Mondays: A hidden waterfall

Imaggeo on Mondays: A hidden waterfall

It’s fascinating how a relatively small outcrop, carved out by rivers and ancient ice, can reveal much about the geological history of an area. Today’s Imaggeo on Mondays post is one such example. Antonio Girona, a researcher at the University of Zaragoza, gives us a whirlwind tour of the geological history of the rocks revealed by the Sorrosal Waterfall, in Spain.

The visit to the Sorrosal Waterfall is an obligatory stop in your way to the Ordesa National Park, located in the Aragonese Pyrenees (NE-Spain). In the northern area of Huesca province, after a short walk from the town of Broto, this hidden waterfall can be found showing the geomorphological and geological history of the valley.

The Sorrosal Waterfall is located in the confluence of two valleys: Broto Valley, run by the Ara River (nowadays the longest river in the Pyrenees with 67 km) and Sorrosal Valley, a hanging valley 125 m above the position from which this photograph was taken. This waterfall was generated by the combined action of a glacier and the river. During the Ice Age, this site was covered by a 30 km long, 370 m deep glacier that shaped the valley that we nowadays call Broto Valley. At the same time Sorrosal river, fed by a small glacier in its headwaters, carved this valley transversely resulting in the Sorrosal Waterfall.

As a consequence of the slope between the two valleys, an interesting outcrop of geological interest can be observed. The rocks were originated from deep-marine sediments (turbidites) from the Eocene, which suffered a series of stepping folds as a result of the Pyrenees Alpine orogeny, becoming the wavy structure than can be appreciated nowadays.


By Antonio Girona Garcia, University of Zaragoza.


If you pre-register for the 2016 General Assembly (Vienna, 17 – 22 April), you can take part in our annual photo competition! From 1 February up until 1 March, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at



Imaggeo on Mondays: Mountains, rivers and agriculture

This week’s Imaggeo on Mondays image blends a range of geoscience disciplines. The post, by Irene Marzolff, a researcher at Johann Wolfgang Goethe-Universitaet, explores how the mountains, rivers and soils of the High Atlas in Morocco are intrinsically linked to the agriculture of the region.

High Atlas landscape. Credit: Irene Marzolff (distributed via

High Atlas landscape. Credit: Irene Marzolff (distributed via

The image was taken in the southern slopes of the Western High Atlas, north of the city of Taroudannt. The snow of these mountains, which in April is still prevailing on the highest ranges in the background of the photo, is a significant water resource for the region. The high interannual variability of precipitation and its changing patterns associated to climate change present a serious challenge for natural environment and for the sustainable use of water as a resource in agriculture and tourism, the two major economic sectors in the area.

A characteristic open cover of Argan trees (Argania spinosa) can be seen on the lower mountain slopes in the middle distance of the photo: an endemic species with small, oil-rich fruits resembling olives that yield high-quality oil used in medicine, food and cosmetics. The species is a relic of the Tertiary (66 to 2.8 million years ago) but has been under threat from human exploitation for centuries, by excessive grazing, fire-wood cutting, charcoal making and changes to the groundwater table. The area is part of the UNESCO-MAB Biosphere Reserve “Arganeraie” committed to the preservation and sustainable use of the trees.

The river bed in the foreground is formed by fluvial processes typical for this high-mountain region, with highly variable seasonal discharges controlled both by rainfall and snowmelt. It will in the near future drain into the Sidi Abdellah Reservoir that is currently being constructed near Tamaloukt. This reservoir will add to the 10 already existing water storage lakes in the region of Souss Massa Drâa, which is in urgent need of additional water resources: The Souss Valley to the South of the High Atlas is one of Morocco’s most intensely farmed agricultural regions, with agro-industrial production of bananas, vegetables and citrus fruit. Much of this, including 90% of Morocco’s tomato production, is exported to the European market.

By Irene Marzolff, researcher at the Institut fuer Physische Geographie, Johann Wolfgang Goethe-Universitaet, Frankfurt.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at