Volcanoes are openings in Earth’s crust that allow molten rock, ash, and gases to escape. While many types of volcanoes exist, cinder volcanoes are distinct for their relatively small size and localized, explosive events. This article explores what defines these geological structures and how they form.
Defining Cinder Volcanoes
Cinder volcanoes, also known as scoria cones, are distinctive for their steep, conical shape and relatively small stature. They are primarily composed of loose pyroclastic fragments, which are pieces of volcanic rock ejected during an eruption. Scoria, a dark-colored, often reddish-brown or black, vesicular volcanic rock, contains numerous gas bubbles trapped as the molten material cooled rapidly.
The characteristic cone shape forms as these fragments accumulate around a central volcanic vent. Cinder cones typically have symmetrical slopes ranging from 30° to 40°, reflecting the angle at which the loose material can naturally pile up. Most also feature a bowl-shaped crater at their summit. Cinder cones are generally much smaller than other volcano types, such as stratovolcanoes or shield volcanoes. They commonly range from tens to a few hundreds of meters tall, with some of the largest reaching over 300 meters (around 1,000 feet) in height, like Parícutin in Mexico or Capulin Volcano in New Mexico.
Cinder volcanoes are often found in groups or as part of larger volcanic systems. They frequently occur on the flanks of bigger volcanoes, such as shield volcanoes or stratovolcanoes, or within extensive volcanic fields. For instance, numerous cinder cones dot the flanks of Mauna Kea in Hawaii.
How Cinder Volcanoes Form
The formation of a cinder volcano begins with explosive volcanic eruptions driven by gas-rich magma. As magma containing dissolved gases, such as water vapor and carbon dioxide, rises towards Earth’s surface, the pressure on it decreases. This pressure reduction causes dissolved gases to rapidly expand and form bubbles within the molten rock. This expansion fragments the magma into small pieces as it is violently ejected into the air.
These ejected fragments, known as cinders or scoria, cool quickly as they fly through the air. They then fall back to the ground around the central vent from which they were erupted. The continuous accumulation of these loose, solid fragments builds the characteristic conical hill. Larger, heavier fragments, like volcanic bombs, tend to land closer to the vent, contributing to the steepness of the cone’s sides.
Eruptions that form cinder cones are typically short-lived compared to the activity of larger volcanoes. Many cinder cones are monogenetic, meaning they result from a single eruptive episode that can last from a few weeks to several years. For example, Parícutin volcano in Mexico grew to over 400 meters in height over nine years from 1943 to 1952. Once the eruption ceases, the conduit connecting the magma source to the vent often becomes blocked, preventing further activity from that specific cone.