Lava is molten or partially molten rock that has been expelled from the interior of a terrestrial planet or a moon onto its surface. It may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from 800 to 1,200 °C (1,470 to 2,190 °F) . The volcanic rock resulting from subsequent cooling is also often called lava. A lava flow is an outpouring of lava during an effusive eruption. The viscosity of most lava is about that of ketchup, roughly 10,000 to 100,000 times that of water.

Lava is made up of various minerals, including magnesium and iron-rich minerals, which are present in almost all types of lava flows. The chemistry of lava flows can tell scientists about where the lava came from beneath the surface and how it flowed over the surface. Silicon is a good element to use to understand where the lava came from and how it flowed over the surface.

The temperatures of molten lava range from about 700 to 1,200 °C (1,300 to 2,200 °F) . The material can be very fluid, flowing almost like syrup, or it can be extremely stiff, scarcely flowing at all. The higher the lava’s silica content, the higher its viscosity. There are different types of lava, including pillow lava, pahoehoe, and blocky lava flows. Pillow lava is the lava structure typically formed when lava emerges from an underwater volcanic vent or subglacial volcano or a lava flow enters the ocean. Pahoehoe and aa lava flows actually have similar chemistry, but they differ because of viscosity, or their stickiness (blocky is more viscous than aa which is more viscous than pahoehoe) . Blocky lava flows have a lot of silicon (over 55% by weight), which means they move slowly across the surface, similar to how a glacier moves on land.

In summary, lava is molten or partially molten rock that has been expelled from the interior of a terrestrial planet or a moon onto its surface. It is made up of various minerals, including magnesium and iron-rich minerals, and can be very fluid or extremely stiff. The viscosity of lava depends on its silica content. There are different types of lava, including pillow lava, pahoehoe, and blocky lava flows.