What Are Mafic and Felsic Lava?

Mafic and felsic lava are two types of lava that differ in the amount of silica present in the lava. Felsic lava has a high silica content, while mafic lava is low in silica. Silica forms chains in cooling lava, making it more viscous. This makes mafic lava able to travel longer distances than felsic lava before it cools.

Lava is molten rock that erupts from a volcano. This molten rock is known as magma before it reaches the surface. Mafic lava is approximately 50 percent silica. It can flow as fast as 20 miles per hour and reach a distance of as much as 60 miles from the volcano. It hardens into basalt, which is a black, grey or dark green rock. Most volcanoes formed from mafic lava are dome shaped.

Felsic lava is composed of approximately 70 percent silica. It usually occurs with explosive eruptions and forms steep-sided volcanoes. It hardens into a rock resembling granite called rhyolite.

Intermediate lava contains a silica amount between that of felsic and mafic lava. It hardens into a material called andesite.

Lava can damage properties and restructure landscapes. Most lava flows slowly, and advanced warning can save lives. Fast lava flows pose a greater risk to human life.