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Imaggeo on Mondays: Hot and cold – how ash influences glacial landscapes

16 Dec

This week’s Imaggeo on Mondays is brought to you by Joanna Nield, a lecturer in physical geography at the University of Southampton. Nield explains how volcanic eruptions can impact glaciers and how ash fall can both accelerate and slow down glacial melt…

“Fjallsjökull after the 2011 Grímsvötn eruption” by Joanna Nield, distributed by the EGU under a Creative Commons licence.

“Fjallsjökull after the 2011 Grímsvötn eruption” by Joanna Nield, distributed by the EGU under a Creative Commons licence.

This photo was taken at Fjallsjökull, Iceland in July 2011, shortly after the eruption of Grímsvötn volcano (21 – 30 May 2011).  The Grímsvötn volcanic eruption partially covered many of the surrounding glaciers in a spatially variable layer of tephra ash.

Fjallsjökull (and Hrútárjökull, the smaller lobe on the left of this photo) were south-east of the volcano, exposing them to the dominant wind moving the ash plume and the subsequent ash fall.  We were lucky enough to use terrestrial laser scanning to study the impact on nearby Svínafellsjökull soon after the eruption with funding from the Royal Society – our daily surface measurements showed that shortly after an eruption, ice melt rates could be reduced by as much as 59% compared to clean ice model predictions.

When ash covers an ice surface, it changes the rate that snow and ice is lost from the glacier (the ablation rate).  Dark coloured ash will reduce the albedo (reflectiveness) of the surface, causing it to absorb more heat. This causes an increase in melt rates for thin debris layers, but thick layers of ash insulate the ice and reduce melt.  On top of this, complex feedbacks between debris cover, meltwater and surface shape redistribute ash and change surface roughness – which also influences ablation rates.  It is important to understand these ash-ice interactions as well as feedbacks between the surface and atmosphere to better quantify the impact of volcanic eruptions in glaciated landscapes.

By Joanna Nield, University of Southampton

References:

Nield, J.M., Chiverrell, R.C., Darby, S.E., Leyland, J., Vircavs, L.H., Jacobs, B.:  Complex spatial feedbacks of tephra redistribution, ice melt and surface roughness modulate ablation on tephra covered glaciers. Earth Surface Processes and Landforms, 38: 95-102, 2013

Nield, J.M., King, J., Wiggs, G.F.S., Leyland, J., Bryant, R.G., Chiverrell, R.C., Darby, S.E., Eckardt, F.D., Thomas, D.S.G., Vircavs, L.H., Washington, R.: Estimating aerodynamic roughness over complex surface terrain.  Journal of Geophysical Research – Atmospheres, 2013

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. 

Call for abstracts: The 9th Alexander von Humboldt Conference

26 Nov

The Alexander von Humboldt Conference is part of the EGU’s Topical Conference Series, and will be taking place in Istanbul, Turkey (24 – 28 March 2014). The aim of the meeting is to open a forum on natural hazard events that have a high impact and a large destructive potential, focussing on the Euro-Mediterranean Region in particular.

The theme for the conference can be broken down into nine broad areas:

  • Physical and Probabilistic Approaches to Earthquakes
  • Physics and Characterisation of Tsunamis
  • Monitoring and Risk of Volcanic Hazards
  • Hydro-Meteorological Hazards
  • Other High Impact Mediterranean Hazards (e.g., asteroid impacts, wildfires, terrigenous and submarine landslides, flooding, storm surges)
  • Complexity Analysis Approaches to Natural Hazards
  • Loss Models and Risk Assessment for Natural Catastrophes
  • What constitutes a prediction, what does not? Good Practice when Proposing Predictions of Natural Hazards
  • Communications and Education of Natural Hazard Knowledge  in the Mediterranean Region to Policy Makers, Students and the Public

In addition to the broad scientific topics, the conference will address risk assessment, communicating with the public and policymakers, and what is appropriate good practice when proposing natural hazard “predictions”.

You can submit your abstract to any one of the topics listed above until 31 January 2014. You can  register for the conference here.

Looking out over the Bosphorus from the conference location – great science and a great view! (Credit: Ali Ozgun Konca)

Looking out over the Bosphorus from the conference location – great science and a great view! (Credit: Ali Ozgun Konca)

To find out more about the 9th Alexander von Humboldt Conference: High Impact Natural Hazards Related to the Euro-Mediterranean Region, please see the conference website.

Update (07/01/13): Abstract submission and registration deadline extended to 31 January 2014.

Geosciences column: Getting a handle on glacial lakes

21 Nov

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.

Natural hazards workshop videos are online!

28 Aug

Every year, the EGU host a two day workshop for primary and secondary school teachers during the General Assembly. Geosciences Information For Teachers (GIFT) workshops aim to shorten the time between discovery and textbook, while providing teachers with material that can be used in the classroom.

This year, the workshop was on natural hazards, with scientists from the fields of seismology, volcanology and meteorology and more describing the latest research in their fields and enabling teachers to take a wealth of natural hazards knowledge back to the classroom. Videos of these workshops are now available our YouTube channel, so you can catch up on the latest in natural hazards research and, if you’re a teacher, take it back to your classroom too.

Here’s a short introduction to what’s online:

And here’s the science – from extreme weather to earthquakes and eruptions:

  1. Increase of extreme events in a warming world
  2. Understanding the earthquake generation process – key results and grand challenges
  3. ESA Earth observation programme and its applications to natural hazards
  4. Convergent margins and mega earthquakes
  5. Triggered landslide events – statistics, implications and road network interactions
  6. Space weather – storms from the Sun
  7. Risk assessment of Vesuvius volcano

To find out more about the GIFT programme, please see the GIFT website. You also can watch videos from previous GIFT workshops on EGU TV.

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