Traits of Shield Volcanoes
A shield volcano, unlike the two other types of volcanoes, is entirely built on lava flaws. Their name comes from their large size and somewhat low profile, giving the appearance of a warrior’s shield in ancient times. Shield volcanoes are the rarest type of volcanoes. Unlike the other two, stratovolcanoes and cinder cones, they need a long period of time (sometimes millions of years) to “mature” (gain the warrior shield-like shape) and they require specific geological condition to form.
Most shield volcanoes are the result of hotspot activity. Hotspots are nothing more than “holes” in the crust, from which lava flaws constantly. Unlike other type of volcanic eruptions, the hotspots do not release high amounts of energy, therefore they don’t have an explosion which propels rocks, ask and lava into the atmosphere. Instead, they act like relief valves, lava quietly flowing from the hotspot, cooling down and creating hard basaltic structures. Hot spots are usually found underwater, or on the slopes of other bigger volcanoes.
Shield volcanoes erupt in a quiet way. They release wave of lava, which travels down the slopes, cooling down over time. Because of this behavior, and because they are mostly formed underwater, shield volcanoes create islands around them over the years (millions of years). Due to their almost constant lava eruptions, the size of a shield volcano varies with the age of the volcano. The Hawaiian Islands, the best example of volcanic island, are based on two gigantic shield volcanoes, which created and nurtured the islands over the course of millions of years. Mount Mauna Loa is probably the biggest shield volcano on earth. It raises over 4000 meters above the sea level, and over 97km wide. Due to this iconic volcano, all shield-volcanoes-like eruptions have been named “Hawaiian eruptions”.
Another trait of shield volcanoes is the lava tube. These structures formed in the mount of the volcano and serve as pipelines for lava flows, allowing further propagation of the lava flow.
Most mature shield volcanoes have secondary hot spots on their slopes. These smaller cones are formed during times of increased volcanic activity and serve as relief valves for the main volcano. Over time, these smaller hot spots will create their own “shield volcano” but they will always be considered a part of the bigger volcano.
Calderas are another common feature of shield volcanoes. They are formed and reformed over the lifespan of the volcano. Intensive volcanic activity creates cones which will collapse after the pressure settles down, forming calderas. Usually, the calderas will be filled in future eruptions.
Unlike other volcanoes, shield volcanoes tend to have a nurturing behavior, creating islands in the middle of the oceans; their lava flows are usually very rich in mineral composites plants need in order to develop. There two most famous volcanic archipelagos, The Galapagos and Hawaii, are both rich in plant and animal life. Underwater hot spots (young shield volcanoes) provide heat and minerals for plants and animals to thrive, creating their own micro ecosystems. Some scientists believe that these shield volcanoes are the perfect candidates for creating the environments required for life forms to appear.