Mini-documentary on YouTube Maps: our work sites, the Amery region, the Vestfold Hills

Antarctica is one of the seven continents on planet earth. It sits at the extreme southern end of the planet and is somewhat larger than the United States. The south pole of the earth's rotational axis is near the center of Antarctica. The south magnetic pole and the south geomagnetic pole are down there, too.

Antarctica is completely surrounded by the Southern Ocean and is very remote, so remote that no human being had ever set foot on Antarctica until the 1800s. The first explorers were seal and whale hunters, followed soon after by adventurers and scientists. Today many nations maintain scientific research bases in Antarctica, including the United States, Russia, Australia, China, the United Kingdom, New Zealand, Italy, Argentina, Japan, Chile, South Africa, France, the Ukraine, Romania, and India. Several nations made territorial claims in Antarctcia but they have all been suspended by the Antarctic Treaty.

Antarctica is almost completely covered by a thick layer of ice. There are only a few places along the coast and at the tops of mountains where bare rock is exposed.

antarcticaNASA
amery ice shelf

The ice stays frozen all year long. Ice may seem perfectly solid, but it actually flows like a liquid -- only very, very slowly. For this reason ice is called a viscoelastic material. When ice flows over rock, it is called a glacier. Some glaciers flow out over the ocean while staying connected to the land, these are called ice shelves.

The largest ice shelf in East Antarctica is the Amery Ice Shelf, pictured at left in a mosaic of satellite photos. It is approximately 150 km across at the seaward end, around 400 km long, and flows north (to the right in this image) out over the ocean at a rate of up to 3 meters a day. It is nearly 1 kilometer thick at the center, and thins to 400 meters at the northern edge.

The "Loose Tooth" is an area at the north edge of the Amery Ice Shelf where a large iceberg is in the process of rifting away. Rift L1 (so named becase it is longitudinal to the ice flow direction) started growing in 1985 and made it 30 kilometers in from the edge before branching off into two rifts transverse to the flow direction, T1 and T2, in 1995. Rift T2 grew faster for many years but now both rifts are growing at a similar rate, around 4 meters per day on average. Rift L2 has not grown at all since the early 1990s.

The Loose Tooth Rift Monitoring project began during the 2002-03 field season. (Antarctic field work is almost always done during the summer, which is November through February in the southern hemisphere, because it is warmer and there are 24 hours of daylight.) There are two parts to the project: one is to monitor rift growth using satellite images and data, and the other is to learn about rift T2 in particular by putting sensors on the ice all around the rift tip.

loose tooth zoom
gps antenna

One type of sensor deployed around the rift tip is a Global Positioning System (GPS) receiver. A GPS receiver determines its position by recording signals beamed down from special satellites that are in orbit around the earth. The GPS receivers we use at the Loose Tooth rift are similar to the type you can buy in a sporting goods store, but collect and store more data, and we use special antennas for extra accuracy. The GPS gear we use is provided by the UNAVCO instrument center.

The photo at left shows one of the antennas mounted on a wooden pole hammered into the surface of the ice shelf. The grey box holds the electronic equipment. We leave this set up all summer; at the end of the summer we return to collect the gear. We use computer programs to process the data, and can then examine how the ice shelf deforms millimeter by millimeter as the rift grows.

The other type of sensor deployed at the rift is a seismometer. A seismometer detects vibrations and is most often used to measure the ground motion that occurs during earthquakes. On the ice shelf, we use the seismometers to study "icequakes" that occur near the rift tip as it cracks its way forward. In the picture on the right, the seismic sensor is inside the orange block; spring-mounted magnets vibrate inside coils of wire when the sensor shakes, creating an alternating electric current that is recorded by a data logger inside the grey box. Marianne Okal, who participated in the 2005-06 field season, is taking notes as we install the equipment. The solar panels on the box convert sunlight into power that keeps the GPS and seismic sensor running. The seismic gear that we use is provided by the PASSCAL instrument center.

During the first few seasons, the rift was seen to open up and march forward in short bursts, lasting for a few hours and occuring once every week or two. The source of the shaking was focused at the tip of the rift. During the 2005-06 season, however, seismic activity was more like a constant rumble and was spread out across a larger area as the rift tip entered into heavily crevassed ice. A crevasse is a deep slot that has opened up at the surface of the ice shelf; there are many large crevasses aligned perpendicular to rift T2 near the present location of its tip.

seismic sensor
in the box

A peek inside the box shows off the electronic guts of the system. The orange parts are the seismometer and the yellow part is the GPS unit. Each has its own battery and its own power regulator; the regulators balance current flow between the solar panel, the battery, and the computer inside each instrument.

One thing learned from the satellite data is that the rifts grow in the summer, but very little or not at all in the winter. This means that even though we can collect seismic and GPS data at the rift only in the summer months, we are still capturing most of the action.

In this photo, taken from a helicopter and looking down the length of T2, one of the stations is visible on the lower right (you can also clearly see several crevasses). Two stations are visible in the photo on the intro page of this website, can you find them? For this season, 2006-07, we will be deploying 12 sites like this around T2, plus we are going to try to collect some new types of data: we are going to stretch a strain meter across the rift, use radar to look inside the ice shelf, and use electromagnetic induction to look for seawater in the rift. We hope these extra data will help us better understand the properties of the ice that fills in the rift.

Antarctica loses more ice through the rifting of large icebergs than by any other process. Studying this rifting process is thus crucial to an understanding the mass balance of Antarctica's ice cap, that is, the sum total of all the ways the ice cap grows and shrinks.

This is the first time people have had an opportunity to study a major rifting event on the Amery Ice Shelf. The last time a large iceberg detached from the Amery was in 1964. We are interested in learning about the rate at which rifting occurs today and how it is affected by the temperature and motion of the ocean and atmosphere. With this information we can better understand how the earth's changing climate will affect the Antarctic ice cap in the future.

Keep an eye on the blog page for news and updates as the season progresses, and feel free to contact any of us with questions or comments.

-Jim Behrens, December 2006

rift with station



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