Magma in the microwave

Abstract

Classroom demonstrations of volcanic processes are typically performed with low-temperature materials designed to exhibit behaviors conceptually analogous to magma. However, there are advantages to finding methods by which real magma can be created and used with audiences and students. Here, we describe a method by which magma can be made at home or in a classroom using a standard household microwave. We have tested a particular demonstration of how volatiles such as H₂O exsolve from natural obsidian to form pumice and ash, a direct replica of the volcanic phenomenon that drives eruptions on Earth and other planets. To demonstrate this, we used three obsidian samples—from Mono Craters (U.S.A.), Arteni (Armenia), and Hrafntinnuhryggur (Iceland)—within an off-the-shelf ceramics "microwave kiln" in both a 700 and 1000 W microwave. We found that millimetric obsidian chips will vesiculate to form pumice-like textures at low microwave power or low initial H₂O content and will fragment safely within the kiln at high microwave power or high initial H₂O content. This can be used to supplement existing well-known demonstrations using low-temperature analogs for magma. The demonstration results in real "products" that can be examined just as a geologist would examine natural specimens.