An active volcano is one that has had at least one eruption in the past 10,000 years. An active volcano can be dormant or erupting.
Scientists use different terms to classify volcanoes. An erupting volcano is one that is having an eruption. A dormant volcano is an active volcano that is supposed to erupt again. An extinct volcano is one that has not erupted in the last 10,000 years and is not expected to erupt again.
There are around 500 active volcanoes throughout the world. Between 50 and 70 of these erupt each year and 160 have erupted in the last 10 years. Approximately 550 volcanoes have erupted since the beginning of recorded history and some of these are now extinct.
Generally, when speaking of volcanoes, geologists don't include those that are underwater. Scientists believe more than 75 percent of the lava that reaches the Earth's surface happens underwater.
Active volcanoes show signs of unrest or are currently erupting. A volcano is classified as extinct when the lava supply in the magma chamber of the volcano dries up. However, on occasion, extinct volcanoes will erupt.
Single active volcanoes may be part of long volcanic fields that can be hundreds of miles long.