Composite Volcanoes ASK A SMALL child to draw a volcano. Chances are that child will draw a composite cone. These are the most common types of volcanic edifice, the sites of the most well-known historic eruptions, and the sources of a wide array of volcanic products. Composite volcanoes occur in all regions of volcanic activity across the Earth. Human populations are drawn to composite volcanoes, attracted by the fertile and frequently renewed volcanic soils generated by the volcanoes, while at the same time threatened by the hazards associated with their frequent eruptions. I. Introduction A. Definition of Composite Volcanoes Surprisingly, the definition of a composite volcano is neither straightforward nor uniformly agreed upon. Most volcanoes are constructional features—they build an edifice from erupted material that extends above the original topography in the region of the vent. Exceptions to this are maars and calderas. Among constructional edifices, there are variations in shape and size (Fig. 1). FIGURE 1 Variations in volcanic landforms as a function of size and "steepness." The diagram is intended for illustrative purposes rather than a rigorous classification. The composite volcanoes discussed in this article are constructional features, each with a reasonably protracted history of eruptions. The erupted products typically comprise both lavas and pyroclastic materials, associated with reworked deposits. Shape is largely a function of slope angle; at the one extreme are very shallow slopes that characterize shields, and on the other are the steeper slopes that characterize cones and domes. Among the smaller edifices are cinder cones and domes, which are typically monogenetic (formed from a single eruption episode). Shield volcanoes and composite cones are the products of multiple eruptions spanning tens to hundreds of thousand of years, and, as a result, are larger and more diverse in terms of their products (types and compositions). Composite volcanoes are therefore defined as relatively large and long-lived volcanic edifices comprising both lava and volcaniclastic erupted products. Note that our definition is intended to be descriptive and not a rigid classification; composite volcanoes clearly overlap with many other edifice types and may incorporate smaller volcano types (cinder cones and lava domes) in their architecture. Composite cones are commonly taken as synonymous with stratovolcanoes; the latter term is preferred in many introductory texts. We choose to avoid the term stratovolcano, as it conveys an implication (albeit not necessarily intentional, but certainly perpetuated in diagrams from introductory texts) of regularly interlayered pyroclastic deposits and lavas. The term "composite" has been used to describe volcanic cones from the Andes that have a composite growth history, punctuated by one or more episodes of sector collapse, and the term "compound" to denote edifices comprising multiple cones, resulting from limited vent migration over time within a restricted area. Both composite and compound volcanoes in these senses are included under our definition of composite cones. Back to Contents