Mount Etna and Pillow Lava of Aci Castello
Shown above, at top, is a view of Mount Etna, on the island of Sicily, Italy. Some 600,000 years ago, friction between the Eurasian and African plates, resulted in a long period of submarine volcanic activity that occurred beneath an extensive clayey layer. Manifestations of this activity can be seen today in the pillow lavas that form the cliffs of Aci Castello.
Pillow lava is formed by the escape of molten material below the sea surface. Following a sudden cooling of the lava’s surface, a thin, glassy crust (hyaloclastite) is created, facilitating the lava to divide into roundish blocks that overfold each other (bottom photo). Photos taken on May 17, 2009.