Are all volcanoes alike? While many people think of a volcano as cone-shaped mountain that spits red hot lava and has a plume of ash like the one shown below, in fact, there are multiple types of volcanoes.
The shape, size, and lifespan of a volcano depends on its location (under the ocean, at a convergent plate boundary, a hot spot etc.), the chemistry of the magma that erupts from it, and the amount of ash and lava in the eruption. Depending on the chemistry of the magma, the volcano can erupt either explosively or non-explosively; the style of eruption also affects the overall shape of the volcano.
While other types exist, there are three main types of volcanoes. They are cinder cones, composite volcanoes (stratovolcanoes), and shield volcanoes.
Diagram of a cinder cone, modified from image on DKfindout.
Cinder cones, the simplest type of volcano, are steep cone-shaped hills made up of cooled, air-filled lava, called cinder or scoria (commonly referred to as lava rock) that were ejected from a single vent. Cinder cones are commonly found near shield volcanoes or stratovolcanoes. Some only erupt once such as the famous Paricutin cinder cone, while others may erupt many times.
COMPOSITE VOLCANOES OR STRATOVOLCANOES
Diagram of a stratovolcano, modified from image on DKfindout.
Composite volcanoes or stratovolcanoes, are typically some of the world’s most beautiful and beloved mountains. All the major Cascade volcanoes including Mount Rainier and Mount St. Helens, as well as Mount Fuji, Mount Vesuvius, and Krakatoa are stratovolcanoes. These beautiful mountains are what most people think of when they picture a volcano—steep-sided, symmetrical cones that typically have a crater at the summit.
Stratovolcanoes can be very tall, many are more than 14,000 feet, and are built from alternating layers of volcanic ash, lava flows, and cinder. A stratovolcano forms from conduits where magma travels from deep within the Earth to the surface through a central vent which connects to multiple radiating dikes and secondary vents. Stratovolcanoes are commonly found at convergent plate boundaries, such as along the edge of the Pacific Ocean within the Ring of Fire.
Stratovolcanoes can erupt explosively (see video below) and can cause great damage to people living near them. The biggest hazard for people living near stratovolcanoes is not from lava, which moves slowly down the volcano, but from lahars (fast-moving volcanic mudflows) that can barrel down the slopes of the volcano at incredible speeds (up to 120 miles per hour!) destroying everything in their path.
Diagram of a shield volcano, modified from image on DKfindout.
Shield volcanoes are the largest volcanoes in the world. They are called shield volcanoes because when you look at them from afar they resemble a warrior’s shield. Mauna Loa, a shield volcano on Hawaii’s big island is the largest single mountain on earth. It reaches 30,000 feet above the ocean floor and is approximately 100 miles across at its base.
Shield volcanoes have shallow slopes and are made of layer upon layer of cooled lava that flowed down the slope in all directions from a central summit vent, or group of vents. Lava can also erupt from fractures or fissures along the edges of shield volcanoes.