Pillow lava is a lava flow that forms underwater, usually at the bottom of the oceans. Individual pillows are mostly up to one meter in diameter. Pillow lavas are extremely common on the Earth’s surface — they form the upper part of the oceanic crust, but we have a chance to see them relatively infrequently because very few of us have ever visited their natural birthplace.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415370720777906
Pillow lava near Choletria.
Sometimes though they get pushed on top of the continental crust for us to take a look. One very good place to admire pillow lavas is Cyprus. The Troodos ophiolite, which makes up large part of the island, is a complete section of the former ocean floor. Hence, pillows are common in Cyprus.
Pillow lavas may show radial cracks (when you have a chance to see the cross section). These cracks are similar to cracks in columnar basalt. The cracks are perpendicular to the margin of the pillow, that’s why they are radial. Cracks in columnar basalt are parallel because they formed in a lava flow that cooled as a sheet. Another common feature of pillows are chilled margins. This is very fine-grained or glassy outer part of the pillow which cooled very rapidly in cold seawater. This material is called tachylyte. Some of the pillows below show radial cracks and some have chilled margins, which may be altered to palagonite.
Pillow lava in Cyprus is very common. I often stumbled upon it unintentionally while looking for something else. It was even easy to get bored of pillows, but I tried to remind myself that as soon as I will go home there are pillows nowhere near, so I took many photos. Here are some of the pillows I saw in Cyprus:
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415373706691570
Near Fasoula.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415374667788530
Near Fasoula.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415389679172834
Near Fasoula.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415393971943618
Pillow lava (in the middle) near Petra tou Romiou.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415396820863458
Near Petra tou Romiou.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415416634024642
Near Petra tou Romiou.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415424082395122
Pillow lava in the Mathiatis open-pit mine.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415432616258850
Pillow lava in the Mathiatis open-pit mine. Note radial cracks.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415442622713378
Pillow lava in the Mathiatis open-pit mine.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415446990389586
Pillow lava in the middle between dikes along the Akaki River.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415465690619346
Along the Akaki River.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415470530644354
Pillow with a chilled (glassy) margin (Kamara River).
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415475151745026
Pillow lava along the Kamara River.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415494111151618
Along the Kamara River.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415498178617378
Along the Kamara River. Black chilled margin is partly preserved.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415505847697410
Pillow lava near Arediou (along the Akaki River).
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415537648989746
Near Arediou (along the Akaki River). Former chilled margin is altered to orange palagonite.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415538761772514
Pillow lava breccia near Arediou (along the Akaki River).
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415543655593986
Near Arediou (along the Akaki River) with palagonitic rim.
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415561395875554
Near Arediou (along the Akaki River).
http://picasaweb.google.com/107509377372007544953/PillowLavaInCyprus#5736415566819782546
Near Arediou (along the Akaki River) with radial cracks.
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