Composite Volcano vs. Shield Volcano

Attribute	Composite Volcano	Shield Volcano
Shape	Steep-sided, conical shape	Gentle sloping sides
Eruption type	Explosive eruptions	Gentle eruptions
Lava composition	Viscous lava	Fluid lava
Height	Taller in height	Shorter in height
Location	Found at subduction zones	Found at hot spots

Formation

Composite volcanoes, also known as stratovolcanoes, are formed from alternating layers of lava flows, volcanic ash, and other volcanic debris. These layers are built up over time as the volcano erupts repeatedly, with each eruption adding a new layer to the cone. Shield volcanoes, on the other hand, are formed from multiple eruptions of low-viscosity lava that flows easily and spreads out over a wide area. This results in a broad, gently sloping volcano with a shield-like shape.

Shape

Composite volcanoes have a steep profile with a conical shape, often reaching heights of several thousand meters. The steep slopes are a result of the thick, viscous lava that does not flow very far from the vent before solidifying. In contrast, shield volcanoes have a much flatter profile with gentle slopes that extend over a large area. The low-viscosity lava flows easily and can travel long distances from the vent, creating the characteristic shield shape.

Eruption Style

Composite volcanoes are known for their explosive eruptions, which can be highly destructive. These eruptions are caused by the buildup of pressure from the thick, sticky lava and gas trapped within the volcano. When the pressure is released, it can result in ash clouds, pyroclastic flows, and lava bombs. Shield volcanoes, on the other hand, have relatively gentle eruptions characterized by the effusion of lava flows. These eruptions are less explosive and tend to be less hazardous to surrounding areas.

Volcanic Hazards

Due to their explosive nature, composite volcanoes pose a greater risk of volcanic hazards such as pyroclastic flows, ashfall, and lahars. Pyroclastic flows are fast-moving clouds of hot gas, ash, and rock fragments that can travel down the slopes of the volcano at high speeds, destroying everything in their path. Ashfall can blanket large areas, disrupting air travel and causing respiratory issues. Lahars are volcanic mudflows that can be triggered by heavy rainfall or melting snow, carrying debris and posing a threat to communities downstream. Shield volcanoes, with their less explosive eruptions, generally pose fewer hazards to surrounding areas.

Location

Composite volcanoes are typically found at subduction zones, where one tectonic plate is forced beneath another. The melting of the subducted plate creates magma that rises to the surface, leading to the formation of composite volcanoes. Examples of composite volcanoes include Mount St. Helens in the United States and Mount Fuji in Japan. Shield volcanoes, on the other hand, are often found in hot spot locations, where a plume of hot mantle material rises through the Earth's crust. This hot mantle material melts to form magma that erupts to create shield volcanoes. Examples of shield volcanoes include Mauna Loa in Hawaii and Mauna Kea in Hawaii.

Size

Composite volcanoes tend to be smaller in size compared to shield volcanoes. This is because the thick, viscous lava of composite volcanoes does not flow as easily or as far as the low-viscosity lava of shield volcanoes. As a result, shield volcanoes can grow to be much larger in terms of volume and area covered. Mauna Loa, for example, is one of the largest volcanoes on Earth in terms of volume, rising over 13,000 feet from the ocean floor.

Historical Eruptions

Composite volcanoes have a history of explosive eruptions that have had significant impacts on surrounding areas. Mount St. Helens, for example, had a catastrophic eruption in 1980 that resulted in the loss of lives and destruction of property. In contrast, shield volcanoes have a history of effusive eruptions that produce lava flows rather than explosive events. While these eruptions can still be dangerous, they are generally less destructive than the explosive eruptions of composite volcanoes.