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How Magmas Form

Partial melting – how magmas form


How does melting take place?

Rocks are made up of different minerals that have different melting points. When hot rocks begin to melt deep down beneath the surface, some of the minerals start to melt but others stay solid.

Where does melting take place?

There isn’t a layer of molten rock waiting to burst out! The rock of the Earth’s mantle layer only begins to melt in a few zones where it is disturbed in some way (see volcanoes map on next page).

Why does melting take place?

Surprisingly, not just because it’s hot deep down beneath the Earth’s surface! Other factors that may cause rocks to melt include changes in pressure, or the presence of water within the rock.

How does magma reach the surface?

The huge pressure at these depths (20 to 100 km) squeezes the rock like a sponge, forcing the melted material (magma) to rise toward the surface.
Pittsburgh University

Pittsburgh University

Peridotite fragment (originally mantle rock) contained within basalt (partial melt) erupted from a volcano.
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