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Imaggeo on Mondays: Glacier de la Pilatte

Imaggeo on Mondays: Glacier de la Pilatte

The relentless retreat of glaciers, globally, is widely studied and reported. The causes for the loss of these precious landforms are complex and the dynamics which govern them difficult to unravel. So are the consequences and impacts of reduced glacial extent atop the world’s high peaks, as Alexis Merlaud, explains in this week’s edition of Imaggeo on Mondays.

This picture was taken on 20 August 2009 at the Pilatte Hutt (44.87° N, 6.33° E,  2572 m.a.s.l.), located in the massif des Ecrins in the French Alps. It shows the Pilatte Glacier, which  was recently described as being 2.64km2 wide and 2.6 km long.

As most of the glaciers in the world, the Pilatte Glacier has been retreating over the last decades as can be seen from the two pictures in figure 1, taken respectively in 1921 and 2003, and from quantitative measurements since the 19th century. The glacier has lost 1.8 km since the end of the Little Ice Age (1850).

Figure 1: Retreat of the Pilatte Glacier over the last decades (pictures adapted from Bonet et al, 2005, time series from Reynaud and Vincent, 2000).

Figure 1: Retreat of the Pilatte Glacier over the last decades (pictures adapted from Bonet et al, 2005, time series from Reynaud and Vincent, 2000).

Two climatic variables affect glacier extents in opposite directions: the amount of winter precipitations (which accumulates snow converting to ice on the glacier) and the summer temperatures (which determines the melting altitude and thus the glacier ablation area – the zone where ice is lost from the glacier, commonly via melting).

The initial retreat of the Alpine glaciers in the 19th century can’t be explained by summer temperatures which remained stable until the 20th century. It has thus been explained by a reduction in snowfall . On the other hand, a recent study suggests that industrial black carbon could have triggered the end of the little ice age in Europe, by reducing the glaciers’albedo. But the globally observed glacier retreat from the 20th century is attributed to the increasing summer temperatures.

Figure 2: Global mean temperature series (Oerlemans, 2005, supporting online material)

Figure 2: Global mean temperature series (Oerlemans, 2005, supporting online material)

Understanding the relationship between glacier dynamics and climate enables to use glacier extents  as proxies to reconstruct global temperature time series, as was done by Oerlemans (2005). Using 169 glacier across the globe, this study provided independent evidences on the timing and magnitude of the warming, that are useful to corroborate other time series obtained through other proxies (such as tree rings) or by direct temperature measurements (see Figure. 2), all showing a temperature increase by around 0.5K across the 20th century.

Glaciers continued to retreat in the 20th century, at an accelerating rate. In the 2015 foreword of the Bulletin of the World Glacier Monitoring Service, its director Michael Zemp writes: “The record ice loss of  the 20thcentury, observed in 1998, was exceeded in 2003, 2006, 2011, 2013, and probably again in 2014 (based on the ‘reference’ glacier sample)”. Using climate models, it appears now possible to distinguish an increasing anthropogenic signature in this phenomenon.

Figure 3: Average glacier retreat worldwide from 1980 in mm of water equivalent (mm.w.e), a unit representing the average thickness of a glacier (WGMS website)

Figure 3: Average glacier retreat worldwide from 1980 in mm of water equivalent (mm.w.e), a unit representing the average thickness of a glacier (WGMS website)

One of the many problems caused by glaciers depletion is the impact on water supplies: glaciers are huge reservoirs of fresh water and their vanishings affect drinking water stock and irrigation for the neighboring population. In the Alps, the idea of replacing the glaciers by dams is already studied. This solution would probably be more difficult to implement in other parts of the world, such as in nothern Pakistan, an area covered with over 5000 glaciers, whose melting is already problematic, causing in particular severe floods.

 

By Alexis Merlaud, Belgian Institute for Space Aeronomy, Brussels, Belgium

References

Bonet, R., Arnaud, F., Bodin, X., Bouche, M., Boulangeat, I., Bourdeau, P., … Thuiller, W. (2015). Indicators of climate: Ecrins National Park participates in long-term monitoring to help determine the effects of climate change. Eco.mont (Journal on Protected Mountain Areas Research), 8(1), 44–52. http://doi.org/10.1553/eco.mont-8-1s44

Ravanel, L., Dubois, L., Fabre, S., Duvillard, P.-A., & Deline, P. (2015). The destabilization of the Pilatte hut (2577 m a.s.l. – Ecrins massif, France), a paraglacial process? EGU General Assembly 2015, Held 12-17 April, 2015 in Vienna, Austria.  id.8720, 17.

Reynaud, L., Vincent, C., & Vincent, C. (2000). Relevés de fluctuations sur quelques glaciers des Alpes Françaises. La Houille Blanche, (5), 79–86. http://doi.org/10.1051/lhb/2000052

Pointer, T. H., Flanner, M. G., Kaser, G., Marzeion, B., VanCuren, R. A., & Abdalati, W. (2013). End of the Little Ice Age in the Alps forced by industrial black carbon. Proceedings of the National Academy of Sciences of the United States of America, 110(38), 15216–21. http://doi.org/10.1073/pnas.1302570110

Vincent, C., Le Meur, E., Six, D., & Funk, M. (2005). Solving the paradox of the end of the Little Ice Age in the Alps. Geophysical Research Letters, 32(9), L09706. http://doi.org/10.1029/2005GL022552

Oerlemans, J. (2005). Extracting a climate signal from 169 glacier records. Science (New York, N.Y.), 308(5722), 675–7. http://doi.org/10.1126/science.1107046

Farinotti, D., Pistocchi, A., Huss, M., al, A. A. et, Barnett T P, A. J. C. and L. D. P., Bavay M, L. M. J. T. and L. H., … Zemp M, H. W. H. M. and P. F. (2016). From dwindling ice to headwater lakes: could dams replace glaciers in the European Alps? Environmental Research Letters, 11(5), 054022. http://doi.org/10.1088/1748-9326/11/5/054022

Marzeion, B., Cogley, J. G., Richter, K., Parkes, D., Gregory, J. M., White, N. J., … Adams, W. (2014). Glaciers. Attribution of global glacier mass loss to anthropogenic and natural causes. Science (New York, N.Y.), 345(6199), 919–21. http://doi.org/10.1126/science.1254702

WGMS (2008): Global Glacier Changes: facts and figures. Zemp, M., Roer, I., Kääb, A., Hoelzle, M., Paul, F. and Haeberli, W. (eds.), UNEP, World Glacier Monitoring Service, Zurich, Switzerland: 88 pp

 

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: 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: 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: Heavy machinery

Imaggeo on Mondays: Heavy machinery

How do you get heavy machinery, such as a drill spool onto an ice sheet? This week’s imaggeo on Mondays’ photography captures the freighting of components of a hot water drill to directly access and observe the physical and geothermal properties at the ice-bed interface. In the image, SAFIRE principal investigator Bryn Hubbard and post-doc Sam Doyle help fly in the drill spool at the start of the Summer 2014 field campaign on Store Glacier, Western Greenland.

Freighting several tons of equipment onto the Greenland Ice Sheet for the sake of science may be slightly intense, but in doing so, it reveals an environment that is complex in history and dynamics.

The Greenland Ice Sheet is losing mass at an increasing rate, and since 2010 has contributed 1 mm/year to global sea level rise. The large majority of changes occur within the drainage basins of marine-terminating glaciers (those which end at the lands edge and drain into the sea), which flow rapidly and drain 88% of the ice sheet. While the surface melt processes of glaciers has been well-studied and quantified, very little is known about what happens below the glacier surface, especially where the ice meets the bedrock.

Recent studies from Greenlandic outlet glaciers have emphasized meltwater-enhanced basal lubrication as an increasingly important mechanism to explain the flow of ice down a glacier. In essence, meltwater generated at the glacier surface will eventually find its way down to the glacier bed through crevasses that connect these two systems. The sudden influx of water increases the pressure within the environment, causing the glacier to “lift” off the bed and flow faster. However, the mechanism is largely an untested theory, and its specifics at the ice-bed interface are still largely unknown, especially on fast-flowing outlet glaciers. In order to achieve accurate predictions of sea level rise in the near future, we need to fully understand the dynamics occurring at the ice-bed interface and its complex response to climate-induced ice melt.
Obviously, a great method to tackle this research question is to air freight tons of heavy machinery onto the Greenland Ice Sheet, and to gain access to the bed of the ice sheet by drilling a 600-metre tunnel with hot water. This is part of the Subglacial Access and Fast Ice Research Experiment (SAFIRE), a collaboration between the Scott Polar Research Institute at the University of Cambridge and Aberystwyth University in Wales.

The SAFIRE project has two specific goals: 1. to identify and characterise the mechanical and hydrological conditions at the base of a large outlet glacier in Greenland, using instruments installed in boreholes drilled to the bed; and 2. to determine the role of basal processes in governing ice flow and iceberg calving. With no previous observation ever made in a subglacial environment of this type of glacier, this project breaks new ground, and from the unique datasets acquired from instruments deployed in boreholes and on the glacier’s surface, higher order numerical ice-flow models can be written and constrained.

Our work is mainly on Store Glacier, which is a large tidewater glacier in the Uummannaq region of northwestern Greenland. Store has a large drainage basin (35,000 km2) and flows up to 5 km/year at the glacier terminus, discharging extremely large volumes of ice into the ocean every day. Since 2014, we have been working on-site at a campsite ~30 km from the terminus, and our results characterise an extremely dynamic and warm basal environment over a deformable sediment bed. A detailed analysis of these unexpected results will be forthcoming in the near future.

By TJ Young, Scott Polar Research Institute / British Antarctic Survey 

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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