GeoLog

glacier lake

Imaggeo on Mondays: Carving polar canyons

This week Ian Joughin, a research scientist from the Polar Science Center at the University of Washington, takes us on the polar express to put glacial processes into perspective and find out what makes a moulin…

“Water filled canyon” by Ian Joughin, distributed by the EGU under a Creative Commons licence.

“Water filled canyon” by Ian Joughin, distributed by the EGU under a Creative Commons licence.

This canyon formed when a melt lake on the surface of the Greenland Ice Sheet overflowed and created a stream that extended out toward a crevasse field. This outflow stream filled a crevasse, causing it to fracture under the pressure of the liquid, creating a hydrofracture that ran through the full thickness of the ice sheet. This fracture created a conduit to the base of the ice sheet, known as a moulin, through which the surface water drained to the bed.

Surface water entering a moulin on Athabasca Glacier (a much smaller Moulin than the one what would have drained the Greenland lake). (Credit: Wikimedia Commons user China Crisis)

Surface water entering a moulin on Athabasca Glacier. (Credit: Wikimedia Commons user China Crisis)

Over the course of several years, the turbulent overflow stream melted the ice down to create this canyon. By the time this photo was taken, snow had dammed canyon near the lake outlet, meaning it no longer actively drained the lake.

Most of the water in the photo is from melt at the sides of the canyon. The ice is flowing at approximately 100 m/yr, slowly moving the stream outlet toward higher ground so it is unlikely that the lake will overflow at this location again. And instead, we have found a new canyon forming in a lower part of the lake basin.

By Ian Joughin, University of Washington

The EGU’s open access geoscience image repository has a new and improved home at http://imaggeo.egu.eu! We’ve redesigned the website to give the database a more modern, image-based layout and have implemented a fully responsive page design. This means the new website adapts to the visitor’s screen size and looks good whether you’re using a smartphone, tablet or laptop.

Photos uploaded to Imaggeo are licensed under Creative Commons, meaning they can be used by scientists, the public, and even the press, provided the original author is credited. Further, you can now choose how you would like to licence your work. Users can also connect to Imaggeo through their social media accounts too! Find out more about the relaunch on the EGU website. 

Geosciences Column: Getting a handle on glacial lakes

Glacial lake outburst floods (GLOFs) are caused when masses of meltwater are released from behind a glacier moraine. Moraines are piles of unconsolidated debris that have either eroded from the glacier valley or have been deposited by melting glaciers. When they fail, a huge volume of water can be released, threatening populations further down the valley. Moraine failure can be caused by avalanches, earthquakes, erosion or an immense build-up of water pressure, but until recently there has been little in the way of a broadly applicable indicator of GLOF risk.

This is because, as far as field trips go, getting to a glacier is one of the hardest feats. So, if you can’t send a scientist to scope out the site, how can you rate the risk of flooding and assess its potential impact?

Recent research, published in Natural Hazards and Earth System Sciences suggests taking to the skies. Remote sensing is becoming an increasingly important part of Earth systems monitoring and provides great insight into the risks of a variety of natural hazards occurring, including tsunamis and volcanic eruptions.

Another use is investigating the risk of GLOFs, which present a serious hazard in the Himalayas. But detailed ground-based studies of them are rarely undertaken in here because they are so difficult to access.

A series of glacial lakes in Bhutan. (Credit: NASA)

A series of glacial lakes in Bhutan. (Credit: NASA)

The remote location of glacial lakes ensures the trigger of GLOFs remains a mystery, but the effect of the outburst of the damming moraine can give us clues. GLOFs leave in their wake a v-shaped channel that slices through the moraine, suggesting that moraine failure is a key factor in the onset of a GLOF.

Given the difficulty of getting to glaciers in high Himalayan locations, there is a pressing need to effectively assess risk using remote sensing techniques. Koji Fujita and his team have developed means of using satellite data and digital elevation models to do just that.

The steep lakefront area lies ahead of the lake and much of the moraine, and the steeper it is, the more likely the lake is to flood. Fujita identified a critical angle beyond which there is a significant risk of a GLOF occurring – that angle is 10 degrees. GLOFs are also more likely to occur when the moraine dam is narrow, as this makes it weaker and more susceptible to failure.

All these parameters can be calculated with some satellite data and a digital elevation model. The depression angle of the steep lakefront area, together with the minimum distance tell us how likely a moraine dam is to fail and the other parameters help calculate the potential flood volume. Since we know how area relates to lake depth, we can use satellite data to estimate lake depth without making any measurements on site. (Credit: Fujita et al, 2013)

All these parameters can be calculated with some satellite data and a digital elevation model. The depression angle of the steep lakefront area, together with the minimum distance tell us how likely a moraine dam is to fail, and the other parameters help calculate the potential flood volume. Since we know how area relates to lake depth, scientists can use satellite data to estimate lake depth without making any measurements on site. (Credit: Fujita et al, 2013)

In addition to monitoring the risk of moraine failure remotely, satellite data can be used to estimate the amount of water dammed behind it. Combining these approaches allows not just the risk of an event occurring to be estimated, but also its magnitude – fundamental factors in hazard assessment. The potential flood volume can be calculated from the lake area (which can also be used to infer how deep the lake is) and the level the lake surface is likely to drop by. Knowing the potential flood volume can help assess risk to populations downstream of the glacier.

The potential flood volume of glacial lakes in the Himalayas. (Credit: Fujita et al, 2013)

The potential flood volume of glacial lakes in the Himalayas. (Credit: Fujita et al, 2013)

GLOFs are a serious natural hazard in Himalayan countries, but when armed with the knowledge of which lakes have the greatest potential flood volume, scientists can prioritise areas for more detailed study. There are thousands of glacial lakes in the Himalayas, making the ability to screen them remotely and hone in on those that are most hazardous a very important development.

By Sara Mynott, EGU Communications Officer

References:

Fujita, K., Sakai, A., Takenaka, S., Nuimura, T., Surazakov, A. B., Sawagaki, T., and Yamanokuchi, T.: Potential flood volume of Himalayan glacial lakes, Nat. Hazards Earth Syst. Sci., 13, 1827-1839, 2013.

Hoechner, A., Ge, M., Babeyko, A. Y., and Sobolev, S. V.: Instant tsunami early warning based on real-time GPS – Tohoku 2011 case study, Nat. Hazards Earth Syst. Sci., 13, 1285-129, 2013.

Strozzi, T., Wiesmann, A., Kääb, A., Joshi, S., and Mool, P.: Glacial lake mapping with very high resolution satellite SAR data, Nat. Hazards Earth Syst. Sci., 12, 2487-2498, 2012.