CR
Cryospheric Sciences

geology

Image of the Week – Vibrating Ice Shelf!

Image of the Week – Vibrating Ice Shelf!

If you listen carefully to the Ekström ice shelf in Antarctica, a strange sound can be heard! The sound of a vibrating truck sending sounds waves into the ice. These sound waves are used to “look” through the ice and create a seismic profile of what lies beneath the ice surface. Read on to find out how the technique works and for a special Cryosphere Christmas message!


What are we doing with this vibrating truck on an ice shelf?

In early December a team from the Alfred Wegener Institute (AWI) made a science traverse of the Ekström ice shelf, near the German Neumayer III Station. Their aim was to make a seismic survey of the area. The seismic source (sound source) used to make this survey was a vibrating truck, known as a Vibroseis source (Fig. 2).

Fig. 2: The Vibroseis truck. It is attached to a “poly-sled” so that it can be easily towed across the ice shelf. The vibrating plate can be seen suspended below the centre of the truck. [Credit: Judith Neunhaeuserer]

It has a round metal plate, which is lowered onto the ice-shelf surface and vibrates at a range of frequencies, sending sound waves into the ice. When the snow is soft the plate often sinks a little, leaving a rather strange “footprint” in the snow (Fig. 3).

Fig. 3: The “footprint” of the Vibroseis truck plate in the snow [Credit: Olaf Eisen].

The sound waves generated travel through the ice shelf, through the water underneath and into the rock and sediment of the sea floor, they are reflected back off these different layer and these reflections are recorded back on the ice surface by a string of recording instruments – geophones (Fig 1). There are sixty geophones in a long string, a snow streamer, which can be towed behind the truck as it moves from location to location. By analyzing how long it takes the sound waves to travel from the source to the geophones an “image” of the structures beneath the ice can be made. For example, you can see a reflection from the bottom of the ice shelf and from the sea floor as well as different layers of rock and sediment beneath the sea floor. This allows the team to look into the geological and glaciological history of the area, as well as understand current glaciology and oceanographic processes!

 

As it happens, the team from AWI consists of your very own EGU Cryosphere Division President, Olaf Eisen and ECS Rep, Emma Smith! As this is the last post before Christmas, we wanted to wish you a merry Christmas from Antarctica!

Merry Christmas! As you can see the weather is beautiful here! [Credit: Jan-Marcus Nasse]

Edited by Sophie Berger

Image of the Week – It’s all a bit erratic in Yosemite!

Image of the Week – It’s all a bit erratic in Yosemite!

When you think of California, with its sun-soaked beaches and Hollywood glamour, glaciers may not be the first thing that spring to mind – even for ice nerds like us. However, Yosemite National Park in California’s Sierra Nevada is famous for its dramatic landscape, which was created by glacial action. With our latest image of the week we show you some of the features that were left behind by ancient glaciers.


What do we see here?

Although Yosemite is now largely glacier-free the imprint of large-scale glaciation is evident everywhere you look. During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice. Evidence of this can be seen in the strange landscape, shown in our image of the week. The bedrock surface in this area is polished and smoothed due to a huge ice mass that was moving over it, crushing anything in it’s path. When this ice mass melted rocks and stones it transported were released from the ice and left strewn on the smoothed bedrock surface. These abandoned rocks and stones are know as glacial erratics. Some of these erratics will have travelled from far-away regions to their resting place today.

During the last glacial maximum (LGM), around 26,000 to 18,000 years ago, much of North America was covered in ice.

Glaciers that still remain!

There are still two glaciers in Yosemite, Lyell and Maclure, residing in the highest peaks of the National Park. Park rangers have been monitoring them since the 1930s (Fig. 2), so there is a comprehensive record of how they have changed over this period. Sadly, as with many other glaciers around the world this means a huge amount mass has been lost – read more about it here!

Figure 2: Survey on Maclure Glacier by park rangers in the 1930s [Credit: National Parks Service]

On a more cheerful note – Here at the EGU Cryosphere Blog we think it is rather fantastic that the park rangers of the 1930s conducted fieldwork in a suit, tie and wide-brimmed hat and we are hoping some of you might be encouraged to bring this fashion back! 😀

If you do please make sure to let us know, posting it on social media an tagging us @EGU_CR! Here are a few more ideas of historical “fieldwork fashion” to wet your appetite: Danish explorers in polar bear suits, 1864-65 Belgian-Dutch Antarctic Expedition and of course Shackleton’s Endurance expedition!


Imaggeo, what is it?

You like this image of the week? Good news, you are free to re-use it in your presentation and publication because it comes from Imaggeo, the EGU open access image repository.