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Geodynamics

Imaggeo on Mondays: Rock glaciers

Imaggeo on Mondays: Rock glaciers

Picture a glacier and you probably imagine a vast, dense mass of slow moving ice; the likes of which you’d expect to see atop the planet’s high peaks and at high latitudes. Now, what if not all glaciers look like that?

Take some ice, mix in some rock, snow and maybe a little mud and the result is a rock glacier. Unlike ice glaciers (the ones we are most familiar with), rock glaciers have very little ice at the surface. Instead, the ice is locked in between the other components, or forms a solid, central structure. Looking at the rock glacier on the flanks of the Heart Peaks shield volcano in northwestern British Columbia (pictured above) you’d be forgiven for thinking this isn’t a glacier at all!

Rock glaciers move down slopes, slowly; typically at speeds which range from a few millimetres per year, up to a few meters. The movement is driven by gravity and usually due to gliding at the base of the glacier, or sometimes due to internal deformation of the ice.

How do the impressive landforms come about? The jury is still out, with the merits of a number of explanations still being debated. Some argue that they are due to geomorphic processes that result from seasonal thawing of snow in areas of permafrost; while others suggest the explanation is simpler: as a glacier wastes, it leaves behind an increasing amount of rock debris as the ice melts. It may be that rock glaciers are the result of a landslide covered glacier melting, or the mixing of a glacier with a landslide it encounters in its way down-slope…

Whatever the exact cause of the rock glacier on the flank of Hearts Peak, it remains a particularly striking example of the landform, given its unusual pink(ish) colour. The dormant volcano is characterised by steep-sided lava domes which are composed of porphyitic rhyolites  and, to a lesser extent, trachytic rocks, which give rise to the unusual colouring of this rock glacier.

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: an impressive testimony to the collision between Africa and Europe

Imaggeo on Mondays: an impressive testimony to the collision between Africa and Europe

The huge fold in the flank of the 2969 m high Dent de Morcles (in Waadtland Alps, Switzerland) is an impressive testimony to the collision between Africa and Europe (which began some 65 million years ago). The layers, originally deposited on the sea floor in a horizontal position, were compressed and shifted. The darker parts developed during the Tertiary period (66 million years ago). They are younger than the greyish and yellowish limestone of the Cretaceous period (which began 145.5 million years ago and ended 79 million years later).

With the aim to capture the Dent de Morcles, this spectacular geological feature, I took a photo flight in the Waadtland Alps in Switzerland. We started with a helicopter from a little airport around 20 kilometres away from this location. The weather was mixed – sunny with a few clouds around. But when we reached Dent de Morcles the sun was hidden by a cloud which didn’t move away. We circled and circled around waiting for sun rays to light up the fold structure. I got quite nervous because every minute up there costs a lot of money. Suddenly a little whole opened in this huge cloud and Dent de Morcles was illuminated,  exactly as I’d hoped for. Only for some seconds. But enough time to take this aerial shot.

By Angelika Jung-Hüttl (Freelance science author) and Bernhard Edmaier (geologist and photographer)

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: The glacial landscape of Yosemite

 Glacial erratic rocks . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu)

Glacial erratic rocks . Credit: Yuval Sadeh (distributed via imaggeo.egu.eu)

Yosemite National Park, in California, is renowned for its beautiful and striking landscapes. So much so, this is the second time it has feature on the blog this summer. While our last post on the park focused on the ancient volcanic history of its landscape, in this post we fast forward to the Plesitocene (some 110,000 to 12,000 years ago) to discover more about how glaciers shaped Yosemite’s landscape. Indeed, it is the glacier carved landscape which has made the park so famous!

During the last ice age, the high peaks and valleys of the Sierra Nevada (of which Yosemite belongs to) were covered by ice.  A vast continental ice sheet spread across much of the United States and Canada. Local climate variations as well as the geographical position of Yosemite meant that the accumulation of ice in the region was particularly unique, and didn’t belong to the vast continental ice sheet. Nevertheless, glaciers dominated the landscape during this time and the scars left behind by their presence resulted in a range of landforms observable today: including chatter marks (gouges left in granite by moving glaciers), glacier polish (shiny patches of granite), exfoliation (layered cracking of rocks which resembles onions peeling), and many others.

As glaciers move, they accumulate debris underneath their surface. As the vast frozen rivers advance, they carry the debris, which can range from pebble-sized rocks through to house-sized boulders, along with it. As the climate in the Yosemite region began to warm as the ice age came to an end, the glaciers slowly melted. Once all the ice was gone, the rocks and boulders, known as glacial erratics, were left behind.

One of the best examples of glacial erratics can be seen at Olmstead Point, near Mt. Hoffmann, in Yosemite National Park, as photographed by Yuval Sadeh. Yuval reminisces about the moment he reached the spot where the boulders are strewn across the landscape:

“I remember walking on this extremely smooth scraped surface, watching the glacial erratics rocks which looks like a giant artist placed them gently on the bedrock. Although the glacier melted many years ago, out there on the glacier carved surface it seems that time is standing still ever since.”

Imaggeo on Mondays: A sunrise over Kelimutu’s three-colour lakes

Imaggeo on Mondays: A sunrise over Kelimutu’s three-colour lakes

Volcanoes are undeniably home to some of the most beautiful landscapes on Earth. It doesn’t take much imagination to picture slopes of exceedingly fertile mineral rich soils, covered in lush vegetation; high peaks punching through cloud cover offering stunning vistas and bubbling pools of geothermally warmed waters were one can soak ones worries away.

What about strikingly coloured crater lakes? You’ll have to travel to Kelimutu volcano, on the Indonesia island of Flores, to catch a glimpse of those.  But the journey is guaranteed to be worth it. Picture three deep pools of water, at times turquoise blue; at others emerald green and even blood red!

The andesitic to basaltic (this simply means that the rocks which form the volcano are depleted in silica, sodium and potassium bearing minerals – compared to other types of igneous rocks that is – and you’ll predominantly find pyroxene, plagioclase and hornblende in them) volcano is capped by the three colourful lakes, formed as a result of a powerful ancient volcanic eruption.

In stratovolcaones (those which are cone shaped) the intensity of an eruption(s) can be so great that once all the magma, ash and rock in a caldera is erupted the edifice can no longer hold itself up and collapses in on itself, in a process known as a caldera collapse. When this happens, it is not uncommon for the crater left behind to gradually fill with water, both from within the volcano and from precipitation and other external sources.

What is unusual about the Kelimutu lakes is that they are very striking in colour, and even more remarkably, their colour changes over time! It is of great interest to geologists since it is rare that these lakes can have different colours even though they are from the same volcano and are located side by side at the same crest.

According to Indonesian folklore, these lakes are the resting places of the ancestors of the Indonesian people.

  • Tiwu Nuwa Muri Koo Fai (Lake of Young Men and Women) – This lake is turquoise.
  • Tiwu Ata Polo  (Bewitched Lake) – Home to those who have been evil in life. This lake is usually red or brown
  • Tiwu Ata Mbupu ( Lake of Old people) – This lake is usually blue/green

The reason for the changing colour of the waters is hotly debated. Some argue that it is fumaroles beneath the lakes which emit volcanic gases like sulphur dioxide, which are to blame. The fumaroles create upwelling within the lakes, forcing denser mineral rich water from the bottom of the lakes upwards and this interaction causes the visible colour changes in the lake. Others argue that it is the changing levels in the oxygenation, as a result of the injection of volcanic gases, of the waters which drives the colour fluctuations.

While the mystery is resolved, all that is left is to visit the enigmatic lakes, as Danielle Su (author of today’s imaggeo on Mondays image and researcher at the University of Western Australia) did. Danielle’s research typically deals with upwelling around oceanic islands in the Indian Ocean so it was exciting to see the parallels of the upwelling mechanism replicated within these volcanic lakes.

‘Upwelling generates high primary productivity in the ocean by bringing deep nutrient rich water to the surface and can be identified in remotely sensed data by the colour of the phytoplankton chlorophyll-a signatures. Although the source and output is different, the physics is similar and I really enjoyed finding this similarity in such different environments,’ describes Danielle.

The morning hike requires some commitment but the view from the peak makes it all worthwhile as the first rays of sunlight casts a glow over the volcano’s summit lakes.

‘When you see something so beautiful in nature, the questions take a backseat for a while because deconstructing it seems to diminish it temporarily. But when you do go back to the science to understand the process, admiration then changes to appreciation, an appreciation of how the complexity of the natural world constantly challenges our curiosity.’

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/.

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