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rock glacier

Imaggeo on Mondays: Sneaking up from above

Imaggeo on Mondays: Sneaking up from above

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. Looking at today’s featured image, you’d be forgiven for thinking the Morenas Coloradas rock glacier wasn’t a glacier at all. But appearances can be misleading; as Jan Blöthe (a researcher at the University of Bonn) explains in today’s post.

The picture shows the Morenas Coloradas rock glacier, a pivotal example of actively creeping permafrost (ground that remains frozen for periods longer than two consecutive years) in the dry central Andes of Argentina. The rock glacier is located in the “Cordon del Plata” range, some 50 km east of the city of Mendoza.

The rock glacier fills the entire valley and slowly creeps downslope creating impressive lobes and tongues with steep fronts. With more than 4 km length, the Morenas Coloradas is one of the largest rock glaciers of the central Andes.

Taken from a drone, the picture looks straight up the rock glacier into the main amphitheatre-like valley formed by glacial erosion located at ~4500 m.a.s.l. From there, large amounts of loose debris are moved down the valley at speeds on the order of a few meters per year. The creeping process forms tongues of material that override each other, producing the characteristic surface with steps, ridges and furrows.

The central Andes of Argentina are semi-arid, receiving less than 500 mm of precipitation per year, mainly falling as snow during the winter. The region is famous for its wines, which are grow in the dry Andean foreland that is heavily dependent on meltwater from the mountains. How much of this meltwater is actually stored in ice-rich permafrost landforms is unknown.

As opposed to ice glaciers, rock glaciers show a delayed reaction to a changing climate, as large amounts of debris cover the ground ice, isolating it from rising air temperatures. With large areas located above the lower altitudinal limit of mountain permafrost of ~3600 m.a.s.l., the central Andes of Argentina might store significant amounts of water in the subsurface.

Using mainly near-surface geophysics, our research tries to quantify the water storage capacities in the very abundant and impressive rock glaciers of the region. The Morenas Coloradas rock glacier is of special importance in this regard, as first geophysical measurements date back to the 1980s. Since then, active layer thickness has dramatically increased in the lower parts of the rock glacier, indicating that also the ground ice of the permafrost domain of the central Andes is suffering under the currently warming climate.

A final remark: Thanks goes to the entire team of this research project, namely Christian Halla, Estefania Bottegal, Joachim Götz, Lothar Schrott, Dario Trombotto, Floreana Miesen, Lorenz Banzer, Julius Isigkeit, Henning Clemens, and Thorsten Höser.

By Jan Blöthe, University of Bonn, Germany

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/.

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