Pillow lava

Nur05018-Pillow lavas off Hawaii

Pillow lava Boatman's Harbour (Oamaru, New Zealand)

Pillow lava at Oamaru

Temagami greenstone belt pillow lava

ItalyPillowBasalt

Pillow basalt outcrop from Baras, Rizal, Philippines (closer view)

Pillow lava is a unique type of lava that forms underwater, typically at the ocean floor, though it can also form in subglacial environments. These formations are characterized by their distinctive pillow-shaped structures, which result from the rapid cooling and solidification of lava when it comes into contact with water. Pillow lavas are an important feature in the study of volcanology and geology, providing insights into underwater volcanic activity and the dynamics of the earth's crust.

Formation

Pillow lava is formed when magma erupts underwater. As the hot lava meets the cold water, a thin crust forms around the lava flow. However, the interior of the flow remains molten and continues to pressurize the newly formed crust. This pressure causes the crust to rupture, allowing more lava to ooze out and form a new pillow, repeating the process. This cycle results in the accumulation of pillow-shaped blobs of lava, which can vary in size from a few centimeters to several meters in diameter.

Characteristics

The most distinctive feature of pillow lava is its pillow-like shape, which is the result of the unique conditions under which it forms. The surfaces of these pillows are typically smooth, but can also be rough and feature striations and radial cracks caused by the contraction of the lava as it cools. The interiors of pillow lavas are usually more fine-grained than the exteriors, due to the rapid cooling effect of the water. In cross-section, pillow lavas can reveal complex internal structures, including concentric growth bands and vesicles (gas bubbles) that were trapped during the solidification process.

Distribution

Pillow lavas are found in various locations around the world, wherever volcanic activity occurs underwater. This includes mid-ocean ridges, where new oceanic crust is formed; submarine volcanoes; and areas of glacial meltwater. They are an important component of the oceanic crust and can also be found in ophiolites, sections of the oceanic crust that have been uplifted and exposed above sea level.

Scientific Importance

Pillow lavas are of significant interest to geologists and volcanologists for several reasons. They provide direct evidence of underwater volcanic activity and the processes involved in the formation of the oceanic crust. The study of pillow lavas can also offer insights into the thermal and chemical gradients of the earth's crust, as well as the dynamics of magma-water interactions. Furthermore, pillow lavas can serve as indicators of past environmental conditions, such as water depth and temperature at the time of their formation.

See Also

• Volcanology
• Magma
• Geology
• Oceanic crust
• Ophiolite