Pillow Lava - John Seach

Pillow lava forms when lava flows come in contact with water.
The lava takes on a variety of shapes including -
pillow -shaped, blister-shaped, mattress-shaped, sack-like, balloon-like.

Basaltic pillow lava is usually less than 1 m in diameter , but may reach 7 m in some cases.
Clay and sand may fill the spaces between the pillows.
 

Pillow lava
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Copyright John Seach