Answer:
A volcano is a vent or chimney which transfers molten rock (known as magma) from depth to the Earth's surface through eruptions. Magma erupting from a volcano is called lava. Lava builds up around the vent and forms a cone.
A volcano is currently active if it is erupting lava, releasing gas or generating seismic activity. An active volcano is labelled dormant if it has not erupted for a long time but could erupt again in the future. When a volcano has been dormant for more than 10 000 years, it is considered extinct. Volcanoes can remain inactive, or dormant, for hundreds or thousands of years before erupting again. During this time, they can become covered by vegetation, making them difficult to identify.
How explosive a volcanic eruption is depends on how easily magma can flow or trap gas. If magma is able to trap a large amount of gas, it can produce explosive eruptions.
Predicting eruptions
Understanding how volcanoes work and how their eruptions can be predicted is essential for the well-being and preservation of people who inhabit volcanically vulnerable areas. Eruptions can occur without any preceding signals, making them extremely difficult to predict. However, sometimes there are useful clues for judging when a volcano is likely to erupt.
A volcano's eruptive history can provide some clues. However, because only a small number of the world's volcanoes have a known history it is extremely difficult to predict future eruptions, particularly for certain types of volcanoes. Scientists use the repose period, or the time between eruptions, to indicate the expected size and strength of an eruption. Consistently long repose periods may indicate that a volcano's eruptions are usually large and explosive. However, sometimes there is no clear relationship in the length of time between eruptions and the nature of the eruptions.
