VOLCANOES IN CONTEXT: ISLAND ARCS AND HOT SPOTS

We address key misconceptions that arise in the study of volcanoes and their relationship to plate tectonics. (1) Many people are aware of the theory of continental drift, and can recognize an image of Pangaea. However, they may not associate volcanism with both convergent and divergent plate motions, nor do they distinguish plate boundary volcanism from that related to deep mantle plumes or hot spots. (2) Many people are familiar with the age progression recorded by hot spot volcanism. In contrast, it is uncommon for students to understand that volcanoes formed in subduction zones are all the same age. Considerations of geologic time likely contribute to this misunderstanding, because adjacent volcanoes that erupt several hundred years apart are considered to be active concurrently. (3) Volcanic features are often taught as unrelated to tectonic setting although characteristic lava types, eruptive styles, morphologies and life spans clearly indicate the specific tectonic environment. The three primary settings for volcanism (mid-ocean ridges, subduction zones, and hot spots on either continental or oceanic crust) are readily identified by the volcanic products and their styles of emplacement.

Volcanoes are a natural draw for students because they are beautiful and exciting. They are also critical to understanding plate motions and the convective circulation of Earth’s interior. Introductory instruction about volcanoes typically focuses on lower-order skills rather than higher-order approaches. This situation is unfortunate because volcanoes present an ideal opportunity to integrate challenging aspects of Earth science: three-dimensional visualization, geologic time scales, and scientifically complex processes and vocabularies. We present a learning unit designed to explore the differences between volcanoes from two different settings: hot spots (Kilauea, Hawaiian-Emperor chain) and convergent plate boundaries (Mount Merapi, Indonesia). The volcanic groups have different morphologies that reflect the lava composition, viscosity and eruptive style, as well as distinct age progressions, all of which reveal differences in tectonic setting. By integrating this information students can build a comprehensive model of volcanism that reinforces the challenging concepts of plate tectonics.