GeoLog

Geomorphology

Imaggeo on Mondays: Erosion

Imaggeo on Mondays: Erosion

In mountainous regions precipitation – be that in the form of rain, hail or snow, for example – drives erosion, which means it plays an important part in shaping the way the landscape looks. Precipitation can directly wear away at hillsides and creates streams and rivers, which leave their mark on the scenery by cutting and calving their way through it.

Take for instance the hills in the arid coastal region of Pisco Valley, in Peru (pictured above). Contrary to what you might think having first looked at the photograph, very little erosion of rock happens here. The solid rock which makes up the undulating hills is a hard-wearing grantic rock (not dissimilar to the stone you might covet for your kitchen countertops).

Over time, wind-blown sediments have blanketed the granites. Loesses, as the deposits are known, are very soft and range between 20 and 60 cm in thickness. The channels which slice the hillside are carved into the loesses, not the granites which lie below.

Rain is such a rare thing in these parts that soil barely forms (Norton et al., 2015) and it’s impossible for plants to grow on the soft substrate, leaving the slopes exposed to the elements. When the infrequent rains do come, small scale gullies, only a few centimetres deep cut their way into the sediments, taking away material loosened by torrential rainfalls at high speeds.

References

Kevin P. Norton, Peter Molnar, Fritz Schlunegger, The role of climate-driven chemical weathering on soil production, Geomorphology, Volume 204, 1 January 2014, Pages 510-517, ISSN 0169-555X, http://dx.doi.org/10.1016/j.geomorph.2013.08.030.

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 http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: Concord at midnight

Imaggeo on Mondays: Concord at midnight

The high peaks of the Alps are always awe inspiring, but this midnight shot, captured by Alessandro Lechmann, a PhD student at the Institute of Geological Sciences at the University of Bern, further enhance their fragile beauty. With a warming climate threatening snow availability to even the highest peaks, it has never been more important to appreciate the importance of the glaciers which drape the mountain slopes.

This photograph shows a view from the Jungfraujoch (a saddle in the Bernese Alps, connecting the two four-thousander peaks Jungfrau and Mönch, at an elevation of 3,466 metres above sea level) towards the south-east down the Jungfraufirn (an arm of the Great Altesch Glacier).

Originating amidst three of the most famous mountains of the Swiss Alps (Eiger, Mönch and Jungfrau), this glacier flows southwards towards the Concordiaplatz, where it merges with the Ewigschneefäld and the Great Aletschfirn into the Great Aletsch Glacier. Even today, despite reports of receding glaciers in the Alps, it forms the largest and longest Alpine glacier.

In the countries surrounding the Alps, glacial landforms dominate the landscape. From drumlins, moraines (accumulations of glacial debris) and overdeepenings in the foreland to U-shaped valleys (Lauterbrunnen is a marvellous example) and cirques in mountainous regions. Although retreating at rates not seen previously, these glaciers carved the face of central Europe during the last glacial-interglacial cycles.

The building of the railway to the Jungfraujoch research station started in 1896 and was completed in 1912; an impressive feat considering the limited technology before the First World War. Perched precariously 3500 m above sea level, the research station (known for its prominent sphinx observatory), has contributed significantly   to the understanding of the atmospheric sciences, glaciology and cosmic ray physics.

The ridge which the Jungfraujoch is built on, marks the northern margin of the exposed crystalline core of the Alpine orogeny. Interestingly, this mountain ridge, in addition to being a geological boundary, is also a major watershed. Rain that falls north, flows via the Aare into the Rhine, which eventually discharges into the North Sea. Precipitation on the southern flank and melt water from the Jungfraufirn, on the other hand, joins the Rhone in the Valais valley, that ends up in the Mediterranean Sea. This highlights the importance of Alpine glaciers as a water stores which continue to provide water throughout the year.

By Alessandro Lechmann PhD student at the Institute of Geological Sciences at the University of Bern

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 http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: a storm is coming

Imaggeo on Mondays: a storm is coming

Coastlines globally are immensely diverse: from the beautifully topical and sun kissed beaches of the Caribbean, to the wet and misty British coastline, through to the raw and wild Alaskan shores, they are home to scores of flora and fauna; rich habitats shaped by powerful forces of nature.

In stark contrast, some coastlines, (28,000 km worldwide to be precise) are dry almost barren places, where little grows. These long stretches of inhospitable seaside lands are known as hyperarid and arid coastlines. Due to the lack of protective vegetation the land is exposed to the action of winds and the sun, leaving behind pavements of bare rock, large dune formations and/or highly saline enclosed lakes (sebkhas).

The Gulf of Aqaba, in the north-western tip of Saudi Arabia, where the desert meets the Red Sea is one such place. Rivers here, which drain into the sea water, are fleeting. They appear after heavy rainfall, when flash floods deliver huge influxes of sediment to the coral-rich waters of the Red Sea.

Nadine Hoffman took today’s featured image while driving from Israel from the Red Sea. Pictured is the northern tip of Saudi Arabia, where a spring storm is coming into the desert bringing severe rain and flash floods. Eventually, the flood waters will drain into the Gulf of Aqaba.

 

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 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 http://imaggeo.egu.eu/photo-contest/information/.

Imaggeo on Mondays: America’s dead sea

Imaggeo on Mondays: America’s dead sea

On the blog today, Jennifer Ziesch, a researcher at the Leibniz Institute for Applied Geophysics, takes us on a tour of the Great Salt Lake, located in the north of Salt Lake City (Utah). Did you know it is one of the largest salt water lakes in the world?

The large salt lake and Salt Lake City, named after the lake, lie on a flat plain about 1300 m above sea level. The salt lake is bordered to the east by the beautiful high Uinta Mountains (3700 – 4100 m) – part of the Rocky Mountains – and to the west by a huge salt desert, which developed towards the end of the last Ice Age due to dehydration. A semi-arid climate characterizes the landscape of the lake and surrounding area.

Like the Dead Sea, the Great Salt Lake is shrinking rapidly. In the middle of the 19th Century, the lake was almost twice as large as it is today. Mankind diverts the inflow of freshwater from the rivers for agriculture and industry. Local people have reported problems with saline groundwater.

The Great Salt Lake is becoming more salty (up to 27%). How high the salinity is shown in the close-up of a footprint. Salt crystals are formed in their full beauty.

Salt precipitation after a walk near the Great Salt Lake. Credit: Jennifer Ziesch (distributed via imaggeo.egu.eu)

The economy uses the salt and other minerals for fertilisers and wintering products. Unfortunately, the ecosystem is becoming more and more fragile: bird species, crabs and other creatures are losing their habitat.

By Jennifer Ziesch, geoscientist at the Leibniz Institute for Applied Geophysics.

Editor’s note: This text was modified on 14/02/2017 with the addition of an extra photograph to show salt precipitation in the lake. 

If you pre-register for the 2017 General Assembly (Vienna, 22 – 28 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 http://imaggeo.egu.eu/photo-contest/information/.

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