Volcanic Pillows in Aci Castello
The Volcanic Pillows, that is the pillow lavas, present in the town of Aci Castello are of major importance worldwide in the geological field.
On these rocks, which in the Middle Ages formed a real island, the Normans built a castle in 1076, from which the place took its name.
The first eruptions began about 500,000 near the current Aci Castello below the sea surface, on the seabed. Plastic flow movements of the oceanic crust lead to the formation of deep faults, from which large quantities of molten basaltic material were erupted.
Unlike the eruptions on dry land, the typical craters were not created because the incandescent lava leaked directly into the sea undergoing a sudden cooling and furthermore, the high pressure exerted by the overlying water prevented the formation of violent explosions.
All these circumstances made possible the formation of pillow lava.
Cushion lava is, in fact, a type of lava formed by characteristic cushion-shaped solidification structures, i.e. rounded and / or elongated blocks.
The sudden cooling of the lava in contact with the water leads to the formation of a plastic and viscous mass enclosed by a thin glassy crust, which under the action of the internal pressure exerted by the fluid and hot lava, is deformed into rounded blocks.
If the pressure is too high, the vitreous crust brawls at its weakest point and new lava pours into the water to form a new "cushion" in seconds.
Other examples of pillow lava are present in the town of Aci Trezza and only in Iceland and New Zealand.
