When a volcano erupts, the explosion of molten rock and gases is impressive. Not all volcanic eruptions are the same because conditions specific to the volcano dictate the nature of the eruption. An eruption can take down a forest or force the evacuation of a major city. Sometimes eruptions cause additional weather events such as a tsunami, mudslide or earthquake.
What Volcanoes Are
A volcano is a spot in the crust, or surface layer, of the planet that is open to the second layer, or mantle. The mantle contains hot gases and liquid rock sandwiched between two sub-layers of hard rock. The best-known volcanoes are tall, cone-shaped mountains, but volcanoes can also appear as cracks, bulges or even wide flat spaces known as plateaus. Some volcanoes are entirely underwater or even under ice caps. Volcanoes occur primarily in the Pacific Ring of Fire, which includes Alaska, Hawaii, Oregon, Washington and California. Scientists have also found volcanoes on other planets and moons in our solar system.
Why Volcanoes Erupt
Although the Earth’s crust seems solid, it is made up of constantly shifting plates that fit tightly together. When these plates rub against each other, it causes friction. As the friction builds, it generates heat and pressure. To alleviate the pressure, volcanoes release hot gases, ash and lava. This process is known as an eruption. According to plate tectonics theory, the same process also causes earthquakes.
What Happens in an Eruption
An eruption is a pressurized discharge of hot gases and other material. The molten rock is known as magma when it is inside the volcano and lava once it begins flowing out. Pumice is a light, spongy rock that forms during the eruption. Ash and toxic gases also come out of an erupting volcano. The deadliest part of an eruption is the pyroclastic flow, a semi-liquid mixture of hot poisonous gas and pieces of debris that looks like an avalanche and moves at hurricane speeds. Lahar is a slower-moving thick liquid that contains some pyroclastic material mixed with rocks and water. When a lahar stops moving, it turns quickly to a solid, cement-like material.
Do All Volcanoes Erupt?
Not all volcanoes erupt. Volcanoes are divided into three categories. Active volcanoes erupt regularly. Dormant volcanoes have not erupted in a long time, but still show activity below the surface. A dormant volcano could erupt, but the likelihood is low at any given time. Extinct volcanoes last erupted thousands of years earlier. No current activity exists and the volcano will not erupt again.