Dispatches from Sea >>
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| March 2007 |  Laura Preston, educator, UNH/Salem High School, Salem, NH. |
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| April 2007 | |||||||
April 14-15, 2007
The Weekend Report
I thought it might be interesting to take a step back and look at the volcanism that is being studied here at the OSC (Overlapping Spreading Center). Most folks know what a volcano looks like, right? We all know what features Mount Saint Helens has – a nice “picture book” mountain, maybe a bit snow covered at the top, with an occasional bit of steam coming from the top vent.
OK…that’s NOT what the volcanoes look like on the seafloor! First of all, we are at a plate boundary of two oceanic plates (the Cocos plate and the Pacific plate), and secondly, the two plates are spreading apart from one another. (click here to link to the Ridge2000 venturedeepocean.org website on plate boundaries http://www.venturedeepocean.org/vents/moving.html. For information on mid-ocean ridges, see the Dive and Discover Infomod on ridges http://www.divediscover.whoi.edu/ridge/infomod.html ) The opening where the magma comes out is actually called a fissure. Simply put, where the spreading occurs, the magma underneath the seafloor escapes and is erupted onto the seafloor, making some very unique shapes due to the differences in temperature, composition and viscosity. Remember, we are looking at temperatures at the seafloor of about 2degrees C, and the magma comes up with an average temperature of 1100 -1200degrees C! The geologists have names for all the different types of structures – ropey, lobate, folded, and pillows, to name a few.
 A fissure where the magma comes up and flows out onto the seafloor. |
 A flow that appears ropey. |
 Lobate lava. |
 A sheet of lava that looks folded. |
 “Pillow” lava. |
 An extremely interesting swirled feature. |
The scientists on this cruise ultimately want to link the detailed geology, geochemistry, and hydrothermal activity to what they already know about where the magma chamber(s) is, and they are studying how the magma moves from the chamber to the surface, and the type(s) of magma formed at the OSC. More on those topics tomorrow.
 Several students enjoy the evening air. |
 Wow! |
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