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Cryospheric Sciences

lake ice

Image of the Week — ice tsunamis !

Image of the Week — ice tsunamis !

Tsunami is a word that became world famous after the so-called Christmas tsunami in 2004, when enormous waves hit the shores around the Indian Ocean with disastrous consequences for countries such as Sri Lanka, Thailand, Somalia and many others.

But did you know that tsunamis can be icy?

An ice tsunami is one of the many names associated with ice shoves (or ivu, shore ice override, ice pile-up, ice ride-up). This rare but impressing phenomenon happens when strong winds rapidly push slabs of sea/lake ice towards the shore.

  • Once on shore, the ice shoves can ride up and advance up to a few hundreds metres inland as a large but thinner sheet of ice (Mahoney et al, 2004; Whiteman, 2011)

  • Alternatively, the ice slabs can also pile up, forming a big ridge on the beach that can rise up to 200m high (Mahoney et al, 2004; Whiteman, 2011).

 

Conditions to get an ice shove

  1. Partial thaw: Ice shoves can only happen when the ice has started to melt but has not completely disappeared yet.  Spring is therefore the best time of the year to observe such a phenomenon.
  2. Strong winds: Only strong winds in the direction of the shore can push piles of ice ashore.
  3. Gentle slope of the beach: The gentler the slope of the shore, the less it prevents the ice pile to advance inland, and the more it can pile up.

This is a common phenomenon in Northern Canada and in Alaska but as these places are sparsely populated, the damages it causes are often limited.

Modis satellite images of Lake Huron, Michigan before (top) and after (bottom) strong winds broke up the ice on the lake and caused an ice shove on Linwood. [Credit: NASA earth observatory]

Modis satellite images of Lake Huron, Michigan, before (top) and after (bottom) a wind storm broke up the ice on the lake and caused an ice shove on Linwood (NOTE: the resolution of the image is too coarse to display the ice piled up on the shore) . [Credit: NASA earth observatory]

Reference/further reading

Edited by N. Karlsson

Image of the Week — Happy ValentICE’s day

Image of the Week — Happy ValentICE’s day

On the eve of 14 February, love and little hearts are everywhere, even trapped in lake ice!
The EGU Cryosphere blog team wishes you a happy Valentine’s Day 🙂

Behind this nice picture, there is also science

This picture was taken during a laboratory experiment that aimed to reproduce the bubbles observed in Arctic lake ice in the winter.

In this shot, we can see two types of gas bubbles in the ice. The elongated vertical bubbles are formed after the exsolution of gas at the water-ice interface. The gas present in “heart-shaped” bubbles originates from ebullition (i.e. it has been emitted as bubbles from the sediment) and it contains a large amount of methane, a significant greenhouse gas. In both cases, the gas is trapped in the ice during the downward evolution* of the freezing front but the shape and gas content of the bubbles largely depends on the velocity of the freezing front development.

The goal of this research is to better understand the origin of the methane emitted by Artic lakes and unravel the role of lake ice cover on the methane atmospheric burden.

*During the winter, the cold atmosphere cools down the water of the lake, when the freezing point is reached, a thin layer of layer of lake ice starts to form at the surface and extends downward.

Further reading/Reference

Boereboom, T., Depoorter, M., Coppens, S., and Tison, J.-L.: Gas properties of winter lake ice in Northern Sweden: implication for carbon gas release, Biogeosciences, 9, 827-838, doi:10.5194/bg-9-827-2012, 2012.

Sapart, C. J et al (in preparation).