A volcano is a geological structure defined by a vent or fissure in the Earth’s crust that allows molten rock, ash, and gases to escape from a magma chamber beneath the surface. These vents are found in diverse geological settings, most commonly where tectonic plates diverge or converge, but also in areas known as hot spots. Volcanoes display a vast range of sizes and shapes, from massive, gentle slopes to steep, symmetrical peaks. The distinct morphology of a volcano is largely controlled by the chemistry and viscosity of the magma that erupts from its vent.
Identifying the Most Common Volcano
The most frequently occurring type of volcano on Earth is the cinder cone, also known as a scoria cone. These structures are the smallest and simplest of the three main volcano types. Their prevalence is due to their formation process, often appearing quickly in large numbers within volcanic fields or on the flanks of larger volcanoes. Cinder cones are typically the shortest-lived and rarely rise more than 1,000 feet above the landscape. They are defined by steep, conical sides, usually maintaining slopes between 30 and 40 degrees, and a distinctive bowl-shaped crater at the summit.
How Cinder Cones Form and Erupt
Cinder cones are built almost entirely from loose, fragmented material called cinders or scoria, rather than continuous lava flows. This material forms when gas-charged, fluid basaltic magma is blown violently into the air during an eruption. The ejected liquid fragments quickly cool and solidify in flight, raining down as porous, black or reddish-brown rocks around the central vent.
The eruption style that creates cinder cones is often classified as Strombolian, characterized by short, explosive bursts or “lava fountains” that shoot molten material hundreds of feet high. The low viscosity of the basaltic magma allows gases to escape, but the sudden release of pressure causes the dramatic fragmentation of the liquid rock. This process of continuous ejection and fall rapidly builds the steep-sided cone.
A defining characteristic is that most cinder cones are monogenetic, meaning they only experience a single, relatively short eruptive episode. This activity typically lasts from a few weeks to several months. Once the gas pressure dissipates and the magma supply is depleted, the cone becomes extinct. This brief lifespan contributes significantly to their high global count.
Comparing Other Major Volcano Types
In contrast to the small, fragmented cinder cones, the two other major volcano types, shield volcanoes and stratovolcanoes, are built over much longer periods. Shield volcanoes, exemplified by those in Hawaii like Mauna Loa, are characterized by broad, gently sloping profiles that resemble a warrior’s shield laid on the ground. These massive structures are formed almost exclusively by the repeated effusion of highly fluid, low-viscosity basaltic lava that flows great distances before solidifying.
Stratovolcanoes, also known as composite volcanoes, are the tall, symmetrically conical mountains most people associate with the term, such as Mount Fuji or Mount St. Helens. They are constructed from alternating layers (strata) of viscous lava flows, ash, and rock fragments. The high silica content in their magma makes it thick and sticky, trapping tremendous amounts of gas. This leads to highly explosive and destructive eruptions. The viscous material solidifies quickly near the vent, which is responsible for the steep slopes, often between 30 and 35 degrees, that define the stratovolcano’s classic shape.