Volcano Roots is an open educational resource about volcano imaging

Magmatic systems: the plumbing of volcanoes

Volcanoes are just the tip of the iceberg of vast underground plumbing systems that transport magma to the surface. Scientists use seismic waves to image the roots of volcanoes. The methods are similar to the ultrasound scans that doctors use to image inside the human body, but at a much larger scale. How do these methods work and what do they reveal about the inner working of volcanoes?

Volcanoes are very diverse, from fissure vents to large stratovolcanoes, from cinder cones to colossal calderas. This diversity is the result of differences in the conditions and journey of the magma in the plumbing system

The source of most magma is in the mantle at 50 to 100 km depth beneath the Earth’s surface. This parent magma is transformed and distilled by chemical reactions as it rises through the Earth’s crust.

The processes that change the composition of the magma include heating, cooling, crystallization, degassing, and melting of the surrounding rocks. The roots of volcanoes are often composed of many levels and multiple magma reservoirs connected by dykes and channels. Magma moves between these layers driven by buoyancy and differences in pressure.

Magma and crystal mush

Magma is rarely fully molten. It is often a mixture of melt and crystals. Some magma reservoirs are mostly crystallized and are similar to a spongy cake saturated with syrup. This is called crystal mush. The melt can flow upward through the crystal mush and accumulate, sometimes forming melt lenses at the top of the reservoir.

Scientists have been trying to image the intricate plumbing of volcanoes to help understand their dynamics and better predict eruptions.