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Imaggeo on Mondays: The most powerful waterfall in Europe

14 Jul

On the menu this Monday is the opportunity to indulge in some incredible Icelandic geology. Take a look at a tremendous waterfall and the beautiful basalt it cuts through…

Iceland is famous for its striking landscapes, from fiery volcanoes and fields of basalt to violent geysers and pools of the most fantastic blue. One of the country’s many geological gems is Dettifoss waterfall – a 100-metre-high mass of white, tumbling water within Vatnajökull National Park.

With about 200 cubic metres of water falling each second, Dettifoss is widely reported to be the most powerful waterfall in Europe. It certainly looks the part.

Dettifoss waterfall, Iceland (Credit: Neil Davies, via imaggeo.egu.eu)

Dettifoss waterfall, Iceland (Credit: Neil Davies, via imaggeo.egu.eu)

Dettifoss is fed by melt from the Vatna Glacier (Vatnajökull), and the spring spike in meltwater means the fall’s flow can reach some 1500 cubic metres per second. By putting your hand to the rocks beside the fall you can feel the thundering torrents as the basalt vibrates beneath your fingertips.

The Jökulsá river snakes through the park’s volcanic canyons, which are constantly being cut by the erosive force of the fall. Dettifoss isn’t the only great feature in this photo though: the canyon walls are layered with lava flows that – even at a glance – reveal when they were deposited. The relatively smooth deposit at the base of the wall and the thinner skin of smooth basalt in the middle are the product of interglacial eruptions. The two rough, blocky-looking layers are columnar basalt deposits – a feature that forms when lava meets ice and cools so rapidly that it fractures into long, hexagonal columns.

Dettifoss up close. (Credit: Roger McLassus)

Dettifoss up close. (Credit: Roger McLassus)

For many geoscientists, Iceland is the top spot on the geological destination list. If you went to Iceland, where would you go? Been before? Tell the tale. We’d love to hear from you.

By Sara Mynott, EGU Communications Officer

Reference:

Bamlett, M., and Potter, J. F.: Icelandic geology: an explanatory excursion guide based on a 1986 Field Meeting. Proceedings of the Geologists’ Association 99.3, 221-248, 1988.

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Turkey’s cotton castle

7 Jul

This week, Imaggeo on Mondays is brought to you by Josep Ubalde, who transports us to a wonderful site in western Turkey: a city of hot springs and ancient ruins dubbed cotton castle, after the voluminous white rocks that spread from the spring’s centre…

Pamukkale is lies in Turkey’s inner Aegean region, within an active fault that favours the formation of hot springs. The spring’s hot waters were once used by the ancient Greco-Roman city of Hierapolis, the remains of which sit atop Pamukkale. The entire area – city, springs and all – was declared a World Heritage site in 1988.

Travertine terraces in Pamukkale, Turkey (Credit: Josep M. Ubalde via imaggeo.egu.eu)

Travertine terraces in Pamukkale, Turkey (Credit: Josep M. Ubalde via imaggeo.egu.eu)

The materials that make up Pamukkale are travertines, sedimentary rocks deposited by water from a hot spring. Here, the spring water follows a 320-metre-long channel to the head of the travertine ridge before falling onto large terraces, each of which are about 60-70 metres long.

The travertines are formed in cascading pools that step down in a series of natural white balconies. These travertines are 300 metres high and their shape and colour lend them the name Pamukkale, meaning “cotton castle”.

At its source, the water temperature ranges between 35 and 60 degrees Celsius, and it contains a high concentration of calcium carbonate (over 80 ppm). When this carbonate-rich water comes into contact with the air, it evaporates and leaves deposits of calcium carbonate behind. Initially, the deposits are like a soft jelly, but over the time they harden to form the solid terraces you see here.

Putting Pamukkale into perspective (Credit: Josep M. Ubalde)

Putting Pamukkale into perspective (Credit: Josep M. Ubalde)

These travertines have been forming for the last 400,000 years. The rate they form is affected by weather conditions, ambient temperature, and the duration of water flow from the spring. It is estimated that 500 milligrams of calcium carbonate is deposited on the travertine for every litre of water. Today, thermal water is released over the terraces in a controlled programme to help preserve this natural wonder. You can no longer walk on them, but they are beautiful to behold.

By Josep M. Ubalde, Soil Scientist, Miguel Torres Winery

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Imaggeo on Mondays: Layers of leg-like sandstone

12 May

John Clemens, a researcher from Stellenbosch University and one of the winners in the EGU Photo Contest 2014, opens our eyes to erosional processes in the Grand Canyon in this week’s Imaggeo on Mondays…

The photo below was taken late in the afternoon while doing some geological tourism at the Grand Canyon in Arizona, USA. The light at this time of day is ideal for such locations as it has a yellow quality and the low sun angle emphasises the contours of the land. I was on a flying visit in connection with the South-Central Regional Meeting of the Geological Society of America (held in Austin Texas). I attended this meeting because it contained a special session in honour of the work of the late Bruce Chappell and the late Alan White – two giants of late 20th century granite geology. This has nothing to do with the visit to the Grand Canyon, and even less to do with the processes that sculpted the landforms depicted.

http://imaggeo.egu.eu/view/1933/

Middle Cambrian Bright Angel Shale in the Grand Canyon, USA – one of the winning images in the EGU Photo Contest 2014. (Credit: John Clemens via imaggeo.egu.eu)

I am not a geomorphologist, but while walking along the canyon’s south rim this feature – way down towards the bottom of the inner canyon – caught my eye. Here lies the Middle Cambrian Bright Angel Shale, a variably coloured sequence of relatively soft sedimentary rocks. This lies above the more recrystallised Proterozoic rocks of the Grand Canyon Supergroup, which provide a relatively hard and stable base for the shale. Above the shale, the rocks have been stripped off by mass wasting and water erosion, leaving this vulnerable sequence exposed to the elements. There are few hard layers amongst the shale, so rain storms and snow-melt from higher altitudes combine with the desert wind to efficiently carve its shape. The shale’s remains are then washed into the inner canyon for transport down the Colorado River. In the photograph you can see a hiking trail disappearing off the edge of the inner canyon and heading steeply down to the river, through the Palaeoproterozoic regional metamorphic rocks of the Vishnu Schist.

The erosional remnant of the Bright Angel Shale has been saved (temporarily) from destruction by the presence of the slightly harder brownish layers that you can see in the image. Nevertheless, the feature is not long for this world. The harder layers that give the spider-like shape to the outcrop are nearly gone and the ridge at the top is just a narrow remnant of what was once a more extensive butte. The numerous ephemeral streams that are responsible for the canyon’s destruction are clearly visible. There terrain is decorated by only a few small green desert shrubs, which offer scant resistance to the erosion that will eventually obliterate this fantastic feature.

Since this image was captured, I have invested in some higher-quality camera equipment and have taken up high-dynamic-range (HDR) photography. Readers interested to see some of these images, including some taken during the meeting in Vienna, can have a look here.

By John Clemens, Stellenbosch University

Imaggeo is the EGU’s open access geosciences image repository. Photos uploaded to Imaggeo can be used by scientists, the press and the public provided the original author is credited. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. You can submit your photos here.

Defining the age of humans

7 May

We are currently changing our planet like never before. But do these changes deserve a new name?

The Anthropocene – a geological period marking the length of time for which humans have had a significant impact on the planet – was first proposed in the 1980s. But the word has gained significant attention in recent years thanks to the popularising work of Nobel prize-winning chemist Paul Crutzen.

Humans are now responsible for moving more sediment around the face of the planet than all natural processes put together. Species extinction is thought to be operating at between 100 and 1000 times the ordinary background rate. Trace elements from weapons tests and coal burning can be found in ice cores. And climate change is altering the planet’s ecosystems in numerous ways. Yet despite all this, the Anthropocene isn’t officially recognised by geologists.

The International Union of Geological Sciences (IUGS) is the body responsible for changes to the geological timescale. Back in 2008 they acknowledged that the term had merit and in 2009 they set up a working group to investigate the issue.

An open pit mine in southern Arizona. (Credit: NASA)

An open pit mine in southern Arizona. (Credit: NASA)

Jan Zalasiewicz, a Senior Lecturer in Palaeobiology at the University of Leicester in the UK, is a member of the group. “We make the decision to mark out the great dynasties,” says Zalasiewicz, “and we are now in a new dynasty.” Zalasiewicz was speaking at a press conference at the EGU General Assembly 2014.

But the process remains a slow one: the working group isn’t presenting its initial findings until 2016. The issue explains Tony Brown, Professor of Geography at the University of Southampton in the UK, is that we need to be able to find the Anthropocene in the rock record; we need to be able to show that Anthropocene deposits extend for large horizontal distances and we need to be sure that they’ll remain there in the future.

The other major concern is when the Anthropocene actually started. “There’s probably a consensus that this is worth formalising,” says Zalasiewicz, “there’s less of a consensus as to when that should be.” Some, like Crutzen, pin the boundary at the start of the Industrial Revolution, but others think there is evidence for a much earlier start to the Anthropocene around 8000 years ago, when human agriculture first became widespread.

But do the details of the definition matter? John Burrows, Professor of Physics and Chemistry of the Atmosphere at the University of Bremen in Germany thinks we might be getting bogged down in the semantics. “We’re still behaving like hunter-gatherers with unlimited resources,” he says, “the question is: is the boat full?”

Perhaps, then, the Anthropocene is most useful as a tool for engagement, a way of reminding people how much of an effect we have on the planet – and that we need to think carefully about how we should be living in the age of humans.

By Tim Middleton, University of Oxford

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