Pillow lava their shape reveals the attitude, or position, in which they were originally formed. Pillow lava shows it is still in its original orientation when: Pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or "subaqueous extrusion". Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in diameter. They form the upper part of Layer 2 of normal oceanic crust. Pillow lavas are commonly of basaltic composition, although pillows formed of komatiite, picrite, boninite, basaltic andesite, andesite, dacite
Lava Beds National Monument Beds. Aa is formed when pahoehoe cools and loses some of its gases. Aa is rough, sharp, and jagged; an excellent example is the Devils Homestead lava flow, which originated at Fleener Chimneys. Most of the rest of the lava in the monument is andesitic. Pumice, a type of rhyolitic lava, also is found covering the monument; this rained down around 900 years ago during the eruption of Glass Mountain. The flows from Mammoth and Modoc Craters comprise about two-thirds of the lava in the monument. Over 30 separate lava flows located in the park range in age from 2,000,000