How can you tell if a volcano is dormant or extinct?

Answer 1

This is a very interesting and a very difficult question to answer.

I asked this question once to a volcanologist and he said that there are not really a clear way of telling and if a volcano is either extinct or dormant if it is located in an active volcano-tectonic belt (or arc), so it can not be ruled out as being dormant.

Hawaiian type volcanoes are active almost all the time. But Most volcanoes have volcanic eruptions every tens or twenty years. There are other that have volcanic eruptions every thousands of years or even more and this is why it is so hard to answer this question.

The case of the super-volcanoes is even worse, is in the order of tens of thousands of years (some even hundred thousand years).

Nevertheless, there is a consensus among volcanologists that volcanoes older than 1 million years can be considered extinct.
But anything less than 1 million years is really hard to tell apart.

Answer 2

well there is noo such scale from where we can know the type of volcano....we tell that on the basis of the activity or an eruption from any particular volcano.....

An active volcano is one that has erupted recently or on volcanologists might erupt soon. Active volcanoes are watched very closely so people and animals in the area can be moved to a save place.

dormant volcano or sleeping volcano is a volcano that has been quiet for a long time, but still has signs it may erupt again. A volcano becomes dormant when the vent is blocked by hardened lava, called a plug, or if the magma seeps back under the earth’s crust. Volcanoes can be dormant for hundreds of years. Then suddenly a volcano will erupt again. The eruption is usually very violent. The plug of a dormant volcano stops the magma from rising. Then pressure under the plug builds up, so the plug gives away and a large eruption is caused. The volcano is then classified again as an active volcano.

An extinct volcano is one that has not erupted for thousands of years. Sometimes it is hard to tell if a volcano is dormant or extinct. They will be listed as dormant until volcanologists are sure there will be no more eruptions

Answer 3

If you peer over the ridge of the volcano and smoke and heat shoot up towards you singeing your eyebrows, then huge boulders and vast amounts of lava are thrown into the air it isn't dormant!

Actually I think they take seismic readings on location and absence of readings means it's extinct - the volcano will have moved from over the magma chamber (hot spot) - due to platetectonics. The old volcano can't erupt again when there is no magma underneath it! The chamber can then erupt in a new place forming a new volcano. That is why you get lines of volcanoes in some parts of the world.

Answer 4

Volcanic activity
A volcanic fissure and lava channel. Mount St. Helens shortly after the eruption of May 18, 1980A popular way of classifying magmatic volcanoes goes by their frequency of eruption, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes, which was explained above.

There is no real consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By our lifespans, however, they are not. Complicating the definition are volcanoes that become restless (producing earthquakes, venting gasses, or other non-eruptive activities) but do not actually erupt.

Scientists usually consider a volcano active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in Hawaii, little more than 200 years. The Smithsonian Global Volcanism Program's definition of 'active' is having erupted within the last 10,000 years.

Dormant volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Confusion however, can arise because many volcanoes which scientists consider to be active are referred to as dormant by laypersons or in the media.

Extinct volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct.

For example, the Yellowstone Caldera in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

Read more here:

Answer 5

A dormant volcano is asleep and may reawaken because it is located over a hot spot deep in the earth or near the edges of tectonic plates that are diverging or converging that can supply fresh magma. The Hawaiian islands are a chain of extinct and active volcanoes. Only the active volcanoes are located directly over a rather limited hot spot.

Answer 6

Undersea plate movement opens and closes lava vents. So checking seismic readings can tell if a volcano is dormant or extinct. Dormancy is when plate movement is very minor and major movement could reopen then vent and cause eruption.Extinction is when plates fuse permanently and the chances of reopening are very low. e.g 1: 1 000 000 000 000 000

Answer 7

u have to check the volcanos history of eruptions and if it hasnt erupted 4 thousands of years then it extinct

Answer 8

none. just consider any volcano can erupt anytime.

Answer 9

ask a vulcanologist.