Lava Flows
Lava forms when magma erupts from a volcano.
As pressure is released gases, dissolved in the magma, bubble out so the composition of lava changes.
As pressure is released gases, dissolved in the magma, bubble out so the composition of lava changes.
Most lava flows are formed by the eruption of hot (around 1200oC) basalt magma, (see video clip above).
As the lava moves away from the vent and cools, it can take many forms, some of which are shown here:
Pahoehoe
Richard Herd, University of East Anglia
Pahoehoe (ropy lava) forms when hot lava skins over as it is flowing. The skin rucks up to form shapes like coiled rope (see below).
Columnar Joints
Columnar Joints form as large lava flows cool and slowly contract. This causes the rock to break up to form hexagon-shaped joints.Aa
Aa or “blocky lava” is formed from a rubble of solidified lava lumps (often full of trapped gas bubbles), carried along by a relatively cool, slowly-moving lava flow beneath.