Magma vs Lava: What's the Difference?
What is Magma?
Magma, which is molten rock beneath Earth's surface, is rich in oxygen and silicon, along with elements such as aluminium, iron, magnesium, calcium, sodium, and potassium
Igneous rocks are formed when magma cools very slowly over thousands to millions of years.
What is Lava?
Lava is molten rock that reaches Earth's surface during a volcanic eruption.
The difference between lava and magma is that one is molten rock below Earth's surface, while the other is molten rock once on Earth's surface.
Although magma and lava are chemically similar, they behave differently. When beneath Earth’s surface, magma is exposed to immense pressure, which prevents dissolved gases from escaping.
Once it reaches the surface as lava, that pressure is released. The way the gases escape plays a major role in how calm or explosive a volcanic eruption is.
The temperature of magma and lava varies from around 700°C to over 1,200°C, depending on chemical composition. Once cooled and solidified, both magma and lava form igneous rocks. The key difference is the rate at which cooling occurs.
When magma cools slowly underground, it produces coarse-grained, intrusive igneous rocks with large crystals, such as granite. Lava that cools more rapidly at the surface produces fine-grained or glassy igneous extrusive rocks such as basalt or obsidian.
What Causes Magma to Rise to the Surface?
Magma rises to the surface mainly because it's less dense than the surrounding solid rock. Once molten rock forms deep within the Earth, it becomes buoyant in the same way as a hot air balloon rises through cooler air. The buoyancy is the primary force that drives magma upward.
As it rises, the pressure decreases, allowing dissolved gases to expand. This helps the magma move upwards, especially near the surface. Fractures, faults, and weaker zones in Earth's crust can provide pathways that make ascent easier.
Article Photos
The photo at the top of our article is from a video of the eruption of Litli Hrútur in Iceland in 2023. Courtesy of James St.John. The image is clickable and links to a series of videos, which are quite spectacular. For access, you may have to sign up to Flickr. Joining is free, and there are no hidden charges or additional fees.
The second photo, which is also clickable, is an eruption from Pu‘u ‘Ō‘ō (Mt Kīlauea) volcano in Hawaii. The eruption began in 1983 and ended in 2018. Courtesy of Stan Celestian.
