Ice Stories: Dispatches From Polar Scientists » tides http://icestories.exploratorium.edu/dispatches Mon, 15 Nov 2010 20:40:36 +0000 http://wordpress.org/?v=2.9.2 en hourly 1 Pressure Ridges http://icestories.exploratorium.edu/dispatches/pressure-ridges-2/ http://icestories.exploratorium.edu/dispatches/pressure-ridges-2/#comments Fri, 08 Jan 2010 00:24:48 +0000 Mark Krasberg http://icestories.exploratorium.edu/dispatches/?p=2090 MCMURDO STATION, ANTARCTICA– Today I visited the (New Zealand) Scott Base. The New Zealand base is next to some spectacular pressure ridges, which are caused by tides where the sea ice meets the land – the ice literally buckles and rises upwards. While I was there I was invited to walk around this spectacular sight. (You have to be invited by a member of the New Zealand base.)


Members of the New Zealand base use flags to map out a safe route. The ice was starting to get soft and they were about to close down trips, but luckily the paths were still open.

Where the sea ice meets the land, the ice buckles and rises upwards under tidal forces, forming these pressure ridges.

Pressure ridges with Mount Erebus in the background.

Another view of the pressure ridges.

During the trip we encountered a Weddell seal lying close to the path. It was cute.

That’s me posing with the Weddell seal.

In the background, you can see a new feature on the Antarctic landscape: Scott Base has built three windmills for power.
]]> http://icestories.exploratorium.edu/dispatches/pressure-ridges-2/feed/ 2 The Power of the Wind and Tides http://icestories.exploratorium.edu/dispatches/the-power-of-the-wind-and-tides/ http://icestories.exploratorium.edu/dispatches/the-power-of-the-wind-and-tides/#comments Thu, 26 Nov 2009 03:09:56 +0000 Heidi Roop http://icestories.exploratorium.edu/dispatches/?p=1992 MCMURDO STATION, ANTARCTICA– We have been here a week now and the cargo is packed and loaded. Several planes have been able to get cargo out to WAIS and now all of the science crew and drillers need to get out to camp! Things are finally starting to look up. In the meantime, we have been having a grand time exploring the hiking trails, coffee house and entertainment that McMurdo has to offer (think craft room, gym, exercise classes, movie nights etc.)! Many of us are trying to stay healthy by going on runs, skiing, and hiking. We have had great weather (~15-20 °F) with sunny skies so that certainly provides the motivation to get out and have fun while we wait to get out to WAIS Divide. One of our adventures was over to the pressure ridges near Scott Base, the home of the Antarctica New Zealand program.

This short video sums up pressure ridges. The pressure ridges we explored here form where a large mass of sea ice buckles under pressure as it makes contact with land (in this case, Ross Island where McMurdo Station and Scott Base are located). The wind, tides, and sun are all variables that constantly change these ridges. With Mt. Erebus looming over the station, the views were quite dramatic. Surprisingly, every view along our ~2 mile walk seemed different! It was like walking through a park of ice sculptures! Like identifying shapes in clouds, we were able to see a dog, person, peace sign, and set of waves. I hope you enjoy this short video with photos from this little adventure onto the ice!

Music by Wayne Grim.



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]]> http://icestories.exploratorium.edu/dispatches/the-power-of-the-wind-and-tides/feed/ 0 How Do You Stop the Motion of the Ocean? http://icestories.exploratorium.edu/dispatches/how-do-you-stop-the-motion-of-the-ocean/ http://icestories.exploratorium.edu/dispatches/how-do-you-stop-the-motion-of-the-ocean/#comments Tue, 28 Jul 2009 16:58:14 +0000 Doug LaVigne http://icestories.exploratorium.edu/dispatches/?p=1725 JOIDES RESOLUTION, ON THE BERING SEA-- The JOIDES Resolution is equipped with some of the best devices available to do her job. She is designed to move quickly on the ocean carrying a great deal of equipment and people to remote locations, and the ocean can be a rough place...]]> ABOARD THE JOIDES RESOLUTION, ON THE BERING SEA– The JOIDES Resolution is equipped with some of the best devices available to do her job. She is designed to move quickly on the ocean carrying a great deal of equipment and people to remote locations, and the ocean can be a rough place. But a problem arises when you are on the ever changing surface of the ocean and you are trying to drill a hole thousands of meters below the surface. How do you hold the drill steady when it is mounted to a ship that moves with the flow of the water? That is today’s topic.


The JR.

As we stop in one spot to begin drilling, the ship’s dynamic positioning computer system goes to work. The two thrusters in the aft of the ship are joined by another ten placed around the ship. Running constantly once we are in place over our location, they keep us steady. The beacon is a device that is dropped to the ocean floor to aid in maintaining our location. It is somewhat redundant with the ships other navigational equipment, but it is there just in case we there are any failures.


Deployed thrusters on the port side, forecastle deck, help keep us steady.

In addition to the thrusters, the derrick has what are called heave compensators. Most drilling problems are related to variations of the composition of sediment being drilled, and or problems clearing out the hole. When you add a rocking ship into the equation, things could get complicated. To combat this, the JR employs both passive and active heave compensation. The passive compensator is a reactive air cushion that reduces vertical movement. But since it has to overcome friction in the seals, it reacts better in rougher seas. In six foot seas it keeps the drill steady to about 3 feet relative to the sea floor, while in twelve foot seas it can keep it within around 2 feet relative to the sea floor. Pretty impressive considering this is several kilometers beneath the ship! The active heave compensator uses hydraulic power to overcome that friction, and can improve the heave compensation to within about 4 inches of motion at the rig floor. How’s that for calm?


Heave compensators reduce vertical movement.

And now this positioning equipment is so precise that a new problem has emerged. Tides. Tides vary according to the position of the moon and sun, because of the changing gravitational forces they exert on the oceans. In the past it was difficult to see these effects, and in short time periods you’d never notice a difference. But now due to the quality of heave compensation and the accuracy of the depth measurements, tides can be seen affecting drilling depths when we are drilling at one site over multiple days. Now that’s pretty amazing. One of the new things we are looking at on this expedition is tidal charts for this area, in an attempt to predict and account for the variations in ocean depth at our location. Maybe this will play a part in all future IODP drilling projects?

]]> http://icestories.exploratorium.edu/dispatches/how-do-you-stop-the-motion-of-the-ocean/feed/ 0 Pressure Ridges http://icestories.exploratorium.edu/dispatches/pressure-ridges/ http://icestories.exploratorium.edu/dispatches/pressure-ridges/#comments Mon, 12 Jan 2009 22:16:09 +0000 Mark Krasberg http://icestories.exploratorium.edu/dispatches/?p=1490 SOUTH POLE STATION, ANTARCTICA– Before I left McMurdo, I got a tour of the pressure ridges near Scott Base (the New Zealand station very close to McMurdo). The pressure ridges are formed by tidal forces — there is a thick sheet of sea ice which meets the land, and tidal forces cause the ice to buckle. Members of the New Zealand base use flags to map out a safe route, and we were allowed to walk around these marvelous ice formations one evening. Our guide was Peggy Malloy. The trip was a lot of fun!


Aerial view of McMurdo Station (US – brown buildings) and Scott Base (NZ – green buildings).

View of Scott Base from the pressure ridges.

Pressure ridges.

Flags to map out a safe route through the pressure ridges.

Another photo of these marvelous ice formations.

Me and my guide, Peggy Malloy.
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