The Mystery of the Exploding Cores – Day 31, 8/4/2009

Why do some cores explode?  One of the problems we’ve had on this expedition is that some of the cores are a bit gaseous. As you go to the sea floor and below it, the pressure from the water above is tremendous. Styrofoam coffee cups dropped to the sea floor come back a fraction of their original size. Why is that?

Well, the reason is the pressure forces the gases to decrease in volume, and Styrofoam cups are full of pockets of air. That same air insulates your coffee from the air in the room, and keeps it warm longer.

Those of you who know about Boyle’s Law should remember that if temperature stays the same, pressure and volume are inversely proportional. So assuming the temperature at the bottom of the ocean was constant, we know the pressure is really high, so any gases present are super compressed, so much so that they are dissolved into the water. Think of the gas in a can of Coca Cola. It is dissolved in the can, and held in place by the pressure. If you don’t believe me, try dropping a can of Coke on a hard floor. Just don’t do it in my house! It could get very messy. When you open the can (or it pops open) the gases lose pressure, their volume increases proportionally... and you end up with a big mess wherever you opened the can.
 
Now at the bottom of the Bering Sea, it happens to be pretty cold. Much colder than it is at the surface. If you know about Charles’ Law you should know that if the pressure is constant, then the volume of a heated gas will expand.
 
Maybe you can see where I am going with this. In a very short time, we take a core that is under tremendous pressure, in some cases full of dissolved gas, and bring it up to the surface where there is significantly less pressure and bring it up to room temperature. Think a can of Coke outside on a hot day. At least where I live, it is a bad idea to leave unopened cans of carbonated drinks in a hot car. Trust me, the interior of my second car served as a painful reminder of this until I sold her.
Hydrates escaping the core cause "worms" of mud to be produced.  Photo by Kelsie Dadd 

 

 

 

 

 

 

 

 

 

 

 

 

 

So that’s why the cores explode. To combat this, the technicians drill holes in the core liners (the plastic sleeves the cores are recovered in) to release the pressure. They try to minimize disturbing the core, but leaving the gases to build up volume can be explosive.

An amusing byproduct of the holes are the "worms" of sediment that escape.  As with any sample, these are collected, documented and saved.

Comments

hello.

Hello, Mr. LaVigne
I think it's really cool that you are in the middle of the ocean exploring. Hpw cold does it really get at sea level? I would love to see a styrofome cup shrink in size. It is really brave of you to be in the middle of the ocean doing all of that stuff. I am so glad to be having such a cool teacher this year. I can't wait to meet you.

Sincerly,
Maraijha Davis
4th block

Temperature and Styrofoam Cups

Hi Maraijha! I look forward to meeting you as well. The temperature isn't too bad here right now. It has been hovering in the 40s. The wind can be bad on occasion, but it is nothing like winter must be up here! I'd love to smush some styrofoam cups for you, but we aren't doing any of the work that requires the drillers to reenter the drill holes. Sadly that means we don't get to send anything down to the ocean floor. I'll have to ask one of the later Teachers at Sea to do that for me!

COOL

Hey Mr. Lavinge,
Im in your 4th period class and i really think that you being on this experience and stuff is really a one-time thing. It's really incredible that you get to do something this AWESOME. Someone needs to. It really is something that people on this planet need to think about more often and realize that if we don't do something soon then something really really bad is gonna happen. I wish that they would realize how important this information is.&Why is the bottom of the Bering see colder than the surface?? Well hope to see you soon in class.
Sincerly,
Christina Birch

Hello 4th Block (and Christina)!

It is a little odd meeting my classes in a blog, instead of during the first week of school... but hopefully you guys will be able to adjust to me starting a little bit later than you do.

I'll try to answer your question about the temperature on the bottom of the ocean. You actually made me do a little research to be able to answer that one, which means it is a really good question, and you'll notice how much I wrote to answer it! Well, I think initially there is less sunlight that penetrates deeper in the ocean, so certainly that has the effect of keeping it cooler.

I think you are wondering why, when the pressure increases as you go deeper in the ocean, doesn't the water warm up? Normally increased pressure results in increased temperature. If you think about the force it takes to push water molecules together, that takes energy. The energy is converted to heat. This heating (or cooling) by pressure change in a gas or liquid is called adiabatic heating. We'll actually talk about this a little in physics class. See if you can remind me about this reply when we get there!

Another good example: Think about a hot air balloon. The air is heated. Its pressure on the inside of the balloon increases. The air inside the balloon spreads out as the hot air expands and that air becomes less dense as a result. That allows the balloon to rise up into the air.

But this only occurs when there is a pressure *change*. The pressure at the bottom of the ocean is effectively constant. It isn't increasing or decreasing, it is pretty much the same. I say effectively, because the tides change the level of the water, so it does change, but only a really small amount.

Water is actually at its most dense at around 4 degrees Celsius. Water temp seems to be pretty near that on the bottom of the ocean. Luckily, unlike other things, when water freezes it gets less dense. Most things get more dense as they cool, and are at their most dense when they are coldest. But think about ice cubes. They float on water. Because frozen water is less dense. So, we don't find ice on the bottom of the ocean, just dense water at somewhere around 4 degrees Celsius.

Probably a good thing too. If water got more dense as it got colder, the ice would sink to the bottom of the ocean and accumulate because there is no sunlight down there to heat it back up. We might end up with frozen oceans with only a small surface layers of water in warmer areas. Going to the beach would be a lot different.

That's my best explanation. Maybe someone else reading here can help me if I've missed something. See you in September Christina.

More Info

Okay, after posting this, I talked with one of the ship's Paleomagnetists (Steve Lund) about your question, and he reminded me about some important processes going on in the ocean. The temperature for salt water to freeze is a little lower than pure water. As water freezes nearer to the poles of the Earth, it expels the salt particles because of the orderly structure of waters polar molecules and the form of salt crystals. This means the ice is a bit colder, and the surrounding water has higher salinity (salt content). Cold water and salt water are denser than surrounding less salty water. So the cold salty water sinks to the bottom of the ocean from these ice forming regions. When it hits bottom, it follows the terrain of the ocean floor, filling in and moving down trenches, getting pushed back up some inclines, etc. What this results in, is a water flow deep in the ocean that is separate from (but connected to) some of the wind driven flow at the surface of the ocean. This is one of the founding ideas driving our understanding of oceanography today. And it causes the water temperature of the bottom of the ocean to be a little bit colder, but still have some variation depending on where you are, and if the water is upwelling cold or warm water.

I am still asking around, and want to see if there is more to this picture that I am missing...

Fascinating!

Hi Doug

Look forward to hearing about your adventures upon your return! I am a new employee at SCB HS and find this to be such an educational journey. Warmest regards! -Jo

Hello Jo

Thanks for checking in! I look forward to meeting you in person in a few weeks. Please make a point to come by and say hello. It'll only be a few more weeks, but time seems to move slowly our here. Could be the endless horizon? Hope your year is off to a good start.

Coca-Cola

Doug,
Thanks for the mention of Coke products in your blogs. It's the real thing! See you soon. :)
Love ya,
Laura

Coke

It was purely unintentional. I promise. Send the royalty checks to me at home! ;)

Seriously though, it is amazing how many principles of science you can demonstrate with soft drinks. Maybe we should seek endorsement from them!

Doug

Cores

Enlightening explanation Doug. Thank you. Isn't that Jamie in your picture? I love how you all take time for visual documentation of the expedition. Are you going to write about hitting basement? I hope so. Jamie's mom.

You Are Welcome!

Hiya Jamie's mom,
I do believe that is Jamie. I thought it was someone else at first, but you made me go back and look at the picture again, and I recognized the sticker on the back of her helmet.

Also, I noticed that if you zoom in on the picture and look at the detail on the core, you can see the layers of mud separating from the expanding gas. If you've ever opened a can of biscuits, and the dough starts to spread apart and you can see where you need to tear it... the mud layers do that and then some. The darker spots you can see through the core liner are actually areas filled with gas and the light isn't reflecting off anything, so it looks dark. Kristen is drilling into those spots to release the gas. Jamie is ably holding the liner steady for her. See what I meant about everyone helping out when they are needed?