This entry was posted on August 6, 2023 by Anne Helmenstine (updated on February 10, 2024)
Magma and lava are terms that people use interchangeably in everyday conversation, but they are different stages in the life cycle of molten rock.
Difference Between Magma and Lava
The main difference between magma and lava is that magma is molten rock beneath the Earth’s surface, while lava is molten rock on the surface.
Magma: This refers to molten rock that exists beneath the Earth’s surface. It is a combination of molten or semi-molten rock, volatiles (such as water vapor and carbon dioxide), and solid minerals.
Lava: Once magma reaches the Earth’s surface and begins to flow, it is termed lava. The emergence happens through volcanic eruptions or fissures.
Comparing Magma vs Lava
In addition to location, magma differs from lava in other respects, too. These include chemical composition, temperature, composition, and behavior.
Location
Magma: Magma occurs beneath the Earth’s surface, in the mantle, and in chambers beneath volcanoes. The depth at which magma forms can vary. For instance, magma can form at tectonic plate boundaries where plates are diverging or converging.
Lava: Lava is on the Earth’s surface. Once magma reaches the surface through a volcanic vent or fissure, it becomes lava.
Temperature
Both magma and lava are hot! But, how hot they are varies. Magma is not necessarily hotter than lava.
Magma: Magma’s temperature ranges from 600°C to 1,300°C (1,112°F to 2,372°F), depending on its composition and depth. The hotter the magma, the more fluid it is.
Lava: Upon reaching the surface, lava starts to cool and solidify. Its temperature ranges between 700°C and 1,200°C (1,292°F to 2,192°F). The exact temperature depends on the type of lava and how long it has been exposed to cooler atmospheric conditions.
Composition
Both magma and lava have diverse compositions, depending largely on the source of the rock from which they form. However, upon reaching the surface, some gases and volatiles present in magma escape from the lava. This makes the composition of lava slightly different from that of its magma. It’s like the difference between an unopened can of soda (which contains dissolved gases) and an opened one (which eventually loses its bubbles).
Magma: Magma typically consists of three main components:
- Melt: The melt is the liquid portion, which is mainly made of silica.
- Solids: Magma contains solid mineral crystals like olivine, pyroxene, and feldspar.
- Volatiles: There are gases dissolved in the melt, including water vapor, carbon dioxide, and sulfur dioxide.
Lava: As magma erupts, it loses some volatiles. This leads to changes in viscosity and the potential for explosive eruptions. Eruptions release water as steam and also a variety of gases. The remaining melt solidifies and forms various types of volcanic rocks like basalt, andesite, or rhyolite.
Behavior
Magma: Magma behavior depends on its temperature, composition, and tectonic setting. For instance, magma with higher water content or silica is more viscous and may lead to more explosive eruptions when it reaches the surface.
Lava: The behavior of lava on the surface depends on its viscosity, which in turn is a function of its chemical composition. Pahoehoe lava is relatively fluid and smooth, while a‘a lava is chunkier and rougher.
Similarities Between Magma and Lava
- Origin: Both lava and magma result from the partial melting of the Earth’s crust or upper mantle.
- Composition: While there are differences due to the loss of volatiles, the fundamental elements and minerals in both magma and lava are essentially the same, sourced from the Earth’s mantle or crust.
- Formation of Rocks: Both magma (when it cools underground) and lava (when it cools on the surface) solidify and form igneous rocks. Magma forms intrusive or plutonic rocks like granite, while lava forms extrusive or volcanic rocks like basalt.
- Role in Earth’s Geology: Both play integral roles in the tectonic processes, helping shape the Earth’s crust and topography.
Magma and lava are intrinsically connected, representing different stages of molten rock’s journey from beneath the Earth’s surface to the world above. Understanding their differences and similarities helps volcanologists and geologists unravel the complexities of Earth’s dynamic processes.
References
- Harlov, D.E.; et al. (2002). “Apatite–monazite relations in the Kiirunavaara magnetite–apatite ore, northern Sweden”. Chemical Geology. 191 (1–3): 47–72. doi:10.1016/s0009-2541(02)00148-1
- Marshak, Stephen (2016). Essentials of Geology (5th ed.). W.W. Norton. ISBN 978-0-393-26339-8.
- Philpotts, Anthony R.; Ague, Jay J. (2009). Principles of Igneous and Metamorphic Petrology (2nd ed.). Cambridge, UK: Cambridge University Press. ISBN 9780521880060.
- Pinkerton, Harry; James, Mike; Jones, Alun (March 2002). “Surface temperature measurements of active lava flows on Kilauea volcano, Hawai’i”. Journal of Volcanology and Geothermal Research. 113 (1–2): 159–176. doi:10.1016/S0377-0273(01)00257-8
- Spera, Frank J. (2000). “Physical Properties of Magma”. In Sigurdsson, Haraldur (ed.). Encyclopedia of Volcanoes. Academic Press. pp. 171–90. ISBN 978-0126431407.
