When a volcano is actively erupting, such as during Mauna Loa's late November 2022 to early
December 2022 eruption, it is universally accepted that the volcano in question is active. However,
when asking about the status of a volcano which is not actively erupting and has not erupted for some
time, depending on the scientist you ask, the word used to describe that volcano might widely
vary. And, whether a volcano is considered active, dormant, or extinct becomes all the more complex
when you realize that individual volcanoes and volcanic fields on rare occasions have
gone more than 50,000 years without a volcanic eruption before unexpectedly erupting again. Thus,
a volcano can for example be classified as active without it being actively erupting.
Due to the potentially confusing opinions on how to describe what exactly is an active,
dormant, or extinct volcano, I have decided to make my own definition and criteria for
each of these terms which are used across my channel's videos aka GeologyHub on YouTube.
A volcano which I consider to be active falls under the following definition which
is slightly modified from a definition stated in a U.S. Geological Survey post on their website;
simply put, an active volcano is one which has erupted since the end of the last ice age,
and/or has an active magma chamber. The end of the last ice age occurred 11,650 years ago, marking
the boundary between the end of the Pleistocene Epoch and beginning of the Holocene Epoch. Thus,
the actively erupting Great Sitkin volcano in Alaska could be considered as active as it has
erupted since the end of the last ice age and preusmably has an active magma chamber. And,
the Mount Hood volcano which is not erupting and last erupted more than 150 years ago in
1865 could also be considered as active. However, volcanoes which have not erupted during a longer
period of time such as Mount Edgecumbe in Alaska can also be considered as active,
as it has produced several Holocene eruptions, of which the last confirmed eruption occurred in 2186
BCE. In 2022, this volcano once again showed signs of life after an earthquake swarm occurred
as it was discovered that a section of the Mount Edgecumbe complex was being uplifted
by a geologically recent intrusion of magma. However, the U.S. Geological Survey also has
several volcanoes which have clearly not erupted since the end of the last ice age yet are largely
considered to be active. Three of these volcanoes are the Yellowstone supervolcano, Long Valley
Caldera, and Valles Caldera, which each have not erupted in 70,000 years, 16,000 years,
and 40,000 years respectively. Each of these systems are considered to be active because they
still have an active magma chamber which created geothermal features and in the case of Yellowstone
and the Long Valley Caldera this activity has even resulted in episodes of ground deformation.
The next term which volcanoes can fall under is dormant. Under my personal definition,
a volcano is classified as dormant if it could theoretically erupt again in the future, but
has not erupted since the end of the last ice age and does not have an active magma chamber.
For example, in the 1990s the remote Fourpeaked volcano in Alaska was considered to be dormant
as it had not produced a volcanic eruption during the Holocene period. Yet, after going more than
12,000 years without a volcanic eruption it went on to unexpectedly erupt in 2006,
meaning its classification changed from dormant to active. In my opinion,
generally speaking and with a few exceptions any volcano or volcanic field which has not
erupted in the last 11,650 years but has erupted in the last 50,000 years and does not have signs
of an active magma chamber could be considered as dormant. For example, the Mount Mcloughlin
volcano in Oregon could fall under this criteria. Yet, sometimes a volcano being considered dormant
is not so simplistic. For example, imagine a volcanic field which consists of a chain of
7 maar explosion craters. The craters all formed during the last 3 million years, which (ignoring
the first crater), each one forming between 5,000 and 800,000 years after the prior one. Thus,
if in this hypothetical volcanic field it had been 500,000 years since the last eruption it
could be considered as dormant if it displayed no signs of a present magma chamber since the
interval between some distinct eruptions has been recorded as being longer than 500,000 years.
Finally, my definition of an extinct volcano is any volcano which has not erupted since the end
of the last ice age and will never erupt again. Volcanoes such as Goat Rocks and
Three Fingered Jack fall under this designation. Thanks for watching! If you would like to request
a specific topic, please leave a comment below. Additionally, I would like to thank Ella
Hurrell for becoming a new channel member on YouTube of GeologyHub!