A volcanic belt is a geographical region in which very high levels of volcanic activity are present. They often are compared to mountain ranges in appearance, but unlike mountain ranges, volcanic belts are able to produce eruptions with gases, ash, rock, lava or other ejecta. Additionally, some volcanic belts have been dormant for so many years they have been eroded nearly flat. They may form in two distinct ways: plate subduction or due to hot spots in the Earth.
When temperatures below the crust are very high, around 1292 to 2552 degrees Fahrenheit (700 to 1400 Celsius), solid material in the Earth's crust and mantle is able to melt. This melted material, called magma, becomes less dense than rock because on the atomic level, heat causes atoms to become more excited, vibrating in a larger area of space. Materials that are less dense always try to rise, so the magma rises, seeking out any weak point in the Earth's crust. The result typically is a bulge in the Earth's crust, which eventually opens if the pressure becomes great enough. A volcanic belt is simply many of these bulges within an area.
Melting of solid materials in the Earth's crust and upper mantle happens with much greater frequency around the boundaries of the tectonic plates, which are large sections of the Earth's crust. These plates move over a layer of malleable rock called the athenosphere. Geologists think this movement happens at least in part because of the convection currents that are present deeper within the Earth. At a subduction plate boundary where one plate slides underneath another, melting of crust material happens at a greater rate, so subduction plate boundaries often are where volcanic belts form.
Sometimes a volcanic belt forms because a tectonic plate moves slowly over an area where the inner Earth is much hotter than usual. In this case, a volcanic belt can occur far away from a plate boundary. Perhaps the best example of a volcanic belt formed in this way is the Hawaiian Islands.
Volcanoes can take hundreds or even thousands of years between eruptions, depending on the rate at which material melts below the crust and how quickly pressure builds. As a result, many of the volcanoes within volcanic belts are dormant. This does not mean they will not erupt in the future. It just means they are not currently active. Geologists are using increasingly sophisticated technologies to try to predict when eruptions will happen, but people still build and live in close proximity to volcanic belts despite the dangers. Subsequently, the potential for loss of property and life due to an eruption still exists.