lavas

Lavas are molten rock that erupts onto the surface of a planet or moon. When magma breaches the surface, it flows as lava. On Earth, lava temperatures commonly range from about 700°C to 1,200°C, with viscosity governed primarily by silica content and crystallization state. Mafic lavas (low silica) are relatively fluid, whereas felsic lavas (high silica) are very viscous.

Classification by chemistry yields basaltic, andesitic, rhyolitic and rhyodacitic lavas, associated with different rock types and tectonic settings. Basaltic lavas are common at mid-ocean ridges and hotspots; rhyolitic and andesitic lavas form in subduction zones.

Within flows, textures include pahoehoe (smooth, ropey) and a'a (rough, jagged). Pahoehoe can evolve into aa as cooling and disruption increase. Lava can also form tubes, resulting in lava caves, and surface features such as lava domes and lava plateaus. When viscous, lavas pile up near vents to form lava domes; when fluid, they create broad lava plains and shield volcanoes.

Eruptive styles range from effusive, producing lava flows that travel several kilometers, to explosive, ejecting ash clouds, pumice and other pyroclasts. Explosive activity can induce caldera formation and is common in high-viscosity lavas. Lavas shape landscapes on Earth and other planetary bodies and play a central role in volcanic hazard assessments.