Volcanoes can be defined by their eruption type, such as this Stromboli lava display.
The more than 500 active volcanoes that cover the earth's surface are capable of erupting at any time, given the correct conditions. Active volcanoes only account for a small portion of the world's total volcanoes, which comprise any vent in the planet's crust through which lava, rock fragments and gases erupt, according to the "Encyclopedia Britannica." Volcanologists have devised several classification schemes to aid them in their study of these phenomena, though no single system is the universal standard.
Three-Tier Volcano Classification Scheme
Most textbooks employ a simplified, three-tier system. Classifying all volcanoes into three basic types -- shield volcanoes, strato volcanoes and cinder cones -- for convenience, this system identifies volcanoes by their observable physical characteristics. While these three types of volcanoes are among the most commonly seen and known in the non-geological community, this model does not account for several large-scale volcano complexes, including monogenetic volcanic fields, which often lay under cinder cones, or caldera complexes, like the massive volcano under Yellowstone's famous Old Faithful.
Six-Volcano Classification Scheme
A more comprehensive system, used at the collegiate and graduate level, discards the cinder cone class as by-product of larger volcanic fields. Incorporating six separate types of volcanoes, this scheme adds caldera complexes, monogenetic fields, flood basalts and mid-ocean ridges to the standard shield and strato volcanoes. Several of these added classifications are poorly understood and hard to predict, such as the massive, slow-moving flood basalts that move more similarly to a glacier than a typical volcano or the unpredictable monogenetic fields that can vent at any point in the field when magma builds below the surface.
Classifying Volcanos with Modifiers
Another classification scheme, set out by leading volcanologists Tom Simkim and Lee Siebert in "Volcanoes of the World," outlines 26 types of volcanoes, minutely differentiated by physical and structural characteristics. Though this particular classification scheme is not widely used, it belies an important and commonly used hybridization of the six volcano classification system. Expanding on these six basic types, volcanologists use a series of descriptors when naming volcanoes to more specifically classify the volcano under discussion. For example, a volcano is not just a shield volcano -- a large, gently sloping volcanic peak constructed from slow-flowing lava -- but rather a small, steep-sloped, balsaltic shield.
Eruption-Related Classifications
One of the most typically referenced volcano classifications is a dual system: volcanoes are either active or dormant. However, "active" volcanoes do not only include volcanoes that are erupting or will probably erupt soon, but nearly any volcano that has erupted in historical memory. Within this seemingly all-or-nothing classification, there are grades of eruption potential and eruption type. The U.S. Geological Survey categorizes volcanoes by their potential to erupt in the immediate future, ranging from normal to advisory to watch to warning. Volcanoes which have erupted, and for which volcanologists have reliable pictorial or descriptive references, may be defined by the size, shape and content of their eruptions.
Tags: types volcanoes, active volcanoes, basic types, caldera complexes, cinder cones, Classification Scheme
