What is the Difference Between Active and Dormant Volcanoes?

Volcanoes are an impressive force of nature. Physically, they dominate the landscape, and have an active role in shaping our planet’s geography. When they are actively erupting, they are an extremely dangerous and destructive force. But when they are passive, the soil they enrich can become very fertile, leading to settlements and cities being built nearby.

Such is the nature of volcanoes, and is the reason why we distinguish between those that are “active” and those that are “dormant”. But what exactly is the differences between the two, and how do geologists tell? This is actually a complicated question, because there’s no way to know for sure if a volcano is all done erupting, or if it’s going to become active again.

Put simply, the most popular way for classifying volcanoes comes down to the frequency of their eruption. Those that erupt regularly are called active, while those that have erupted in historical times but are now quiet are called dormant (or inactive). But in the end, knowing the difference all comes down to timing!

Sarychev volcano, (located in Russia's Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Credit: NASA
Sarychev volcano, (located in Russia’s Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Credit: NASA

Active Volcano:

Currently, there is no consensus among volcanologists about what constitutes “active”. Volcanoes – like all geological features – can have very long lifespans, varying between months to even millions of years. In the past few thousand years, many of Earth’s volcanoes have erupted many times over, but currently show no signs of impending eruption.

As such, the term “active” can mean only active in terms of human lifespans, which are entirely different from the lifespans of volcanoes. Hence why scientists often consider a volcano to be active only if it is showing signs of unrest (i.e. unusual earthquake activity or significant new gas emissions) that mean it is about to erupt.

The Smithsonian Global Volcanism Program defines a volcano as active only if it has erupted in the last 10,000 years. Another means for determining if a volcano is active comes from the International Association of Volcanology, who use historical time as a reference (i.e. recorded history).

Aleutian island #volcano letting off a little steam after the new year on Jan 2, 2016. #YearInSpace. Credit: NASA/Scott Kelly/@StationCDRKelly
Aleutian island #volcano letting off a little steam after the new year on Jan 2, 2016. #YearInSpace. Credit: NASA/Scott Kelly/@StationCDRKelly

By this definition, those volcanoes that have erupted in the course of human history (which includes more than 500 volcanoes) are defined as active. However, this too is problematic, since this varies from region to region – with some areas cataloging volcanoes for thousands of years, while others only have records for the past few centuries.

As such, an “active volcano” can be best described as one that’s currently in a state of regular eruptions. Maybe it’s going off right now, or had an event in the last few decades, or geologists expect it to erupt again very soon. In short, if its spewing fire or likely to again in the near future, then it’s active!

Dormant Volcano:

Meanwhile, a dormant volcano is used to refer to those that are capable of erupting, and will probably erupt again in the future, but hasn’t had an eruption for a very long time. Here too, definitions become complicated since it is difficult to distinguish between a volcano that is simply not active at present, and one that will remain inactive.

Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless, volcanoes may remain dormant for a long period of time. For instance, the volcanoes of Yellowstone, Toba, and Vesuvius were all thought to be extinct before their historic and devastating eruptions.

The area around the Vesuvius volcano is now densely populated. Credit: Wikipedia Commons/Jeffmatt
The area around Mount Vesuvius, which erupted in 79 CE, is now densely populated. Credit: Wikipedia Commons/Jeffmatt

The same is true of the Fourpeaked Mountain eruption in Alaska in 2006. Prior to this, the volcano was thought to be extinct since it had not erupted for over 10,000 years. Compare that to Mount Grímsvötn in south-east Iceland, which erupted three times in the past 12 years (in 2011, 2008 and 2004, respectively).

And so a dormant volcano is actually part of the active volcano classification, it’s just that it’s not currently erupting.

Extinct Volcano:

Geologists also employ the category of extinct volcano to refer to volcanoes that have become cut off from their magma supply. There are many examples of extinct volcanoes around the world, many of which are found in the Hawaiian-Emperor Seamount Chain in the Pacific Ocean, or stand individually in some areas.

For example, the Shiprock volcano, which stands in Navajo Nation territory in New Mexico, is an example of a solitary extinct volcano. Edinburgh Castle, located just outside the capitol of Edinburgh, Scotland, is famously located atop an extinct volcano.

An aerial image of the Shiprock extinct volcano. Credit: Wikipedia Commons
Aerial photograph of the Shiprock extinct volcano. Credit: Wikipedia Commons

But of course, determining if a volcano is truly extinct is often difficult, since some volcanoes can have eruptive lifespans that measure into the millions of years. As such, some volcanologists refer to extinct volcanoes as inactive, and some volcanoes once thought to be extinct are now referred to as dormant.

In short, knowing if a volcano is active, dormant, or extinct is complicated and all comes down to timing. And when it comes to geological features, timing is quite difficult for us mere mortals. Individuals and generations have limited life spans, nations rise and fall, and even entire civilization sometimes bite the dust.

But volcanic formations? They can endure for millions of years! Knowing if there still life in them requires hard work, good record-keeping, and (above all) immense patience.

We have written many articles about volcanoes for Universe Today. Here’s Ten Interesting Facts About Volcanoes, What are the Different Types of Volcanoes?, How Do Volcanoes Erupt?, What is a Volcano Conduit?, and What are the Benefits of Volcanoes?

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Sources:

What is the Earth’s Mantle Made Of?

The Earth's layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com

Like all the other terrestrial planets, (Mercury, Venus, and Mars) the Earth is made up of many layers. This is the result of it undergoing planetary differentiation, where denser materials sink to the center to form the core while lighter materials form around the outside. Whereas the core is composed primarily of iron and nickel, Earth’s upper layer are composed of silicate rock and minerals.

This region is known as the mantle, and accounts for the vast majority of the Earth’s volume. Movement, or convection, in this layer is also responsible for all of Earth’s volcanic and seismic activity. Information about structure and composition of the mantle is either the result of geophysical investigation or from direct analysis of rocks derived from the mantle, or exposed mantle on the ocean floor.

Continue reading “What is the Earth’s Mantle Made Of?”

Warm, Flowing Water on Mars Was Episodic, Study Suggests

Though the surface of Mars is a dry, dessicated and bitterly cold place today, it is strongly believed that the planet once had rivers, streams, lakes, and flowing water on its surface. Thanks to a combination of spacecraft imagery, remote sensing techniques and surface investigations from landers and rovers, ample evidence has been assembled to support this theory.

However, it is hard to reconcile this view with the latest climate models of Mars which suggest that it should have been a perennially cold and icy place. But according to a new study, the presence of warm, flowing water may have been an episodic occurrence, something that happened for decades or centuries when the planet was warmed sufficiently by volcanic eruptions and greenhouse gases.

The study, which was conducted by scientists from Brown University and Israel’s Weizmann Institute of Science, suggests that warmth and water flow on ancient Mars were probably episodic, related to brief periods of volcanic activity that spewed tons of greenhouse-inducing sulfur dioxide gas into the atmosphere.

The work combines the effect of volcanism with the latest climate models of early Mars and suggests that periods of temperatures warm enough for water to flow likely lasted for only tens or hundreds of years at a time.

The notion that Mars had surface water predates the space age by centuries. Long before Percival Lowell observed what he thought were “canals” on the Martian surface in 1877, the polar ice caps and dark spots on the surface were being observed by astronomers who thought that they were indications of liquid water.

Curiosity found evidence of an ancient, flowing stream on Mars at a few sites, including the "Hottah" rock outcrop pictured here. Credit: NASA/JPL
Curiosity found evidence of an ancient, flowing stream on Mars at a few sites, including the “Hottah” rock outcrop pictured here. Credit: NASA/JPL

But with all that’s been learned about Mars in recent years, the mystery of the planet’s ancient water has only deepened. The latest generation of climate models for early Mars suggests that the atmosphere was too thin to heat the planet enough for water to flow. Billions of years ago, the sun was also much dimmer than it is today, which further complicates this picture of a warmer early Mars.

“These new climate models that predict a cold and ice-covered world have been difficult to reconcile with the abundant evidence that water flowed across the surface to form streams and lakes,” said James W. Head, professor of earth, environmental and planetary sciences at Brown University and co-author of the new paper with Weizmann’s Itay Halevy. “This new analysis provides a mechanism for episodic periods of heating and melting of snow and ice that could have each lasted decades to centuries.”

Halevy and Head explored the idea that heating may have been linked to periodic volcanism. Many of the geological features that suggest water was flowing on the Martian surface have been dated to 3.7 billion years ago, a time when massive volcanoes are thought to have been active.

And whereas on Earth, widespread volcanism has often led to global dimming rather than warming – on account of sulfuric acid particles reflecting the sun’s rays – Head and Halevy think the effects may have been different in Mars’ dusty atmosphere.

To test this theory, they created a model of how sulfuric acid might react with the widespread dust in the Martian atmosphere. The work suggests that those sulfuric acid particles would have glommed onto dust particles and reduced their ability to reflect the sun’s rays. Meanwhile, sulfur dioxide gas would have produced enough greenhouse effect to warm the Martian equatorial region so that water could flow.

Image of the McMurdo Dry Valleys, Antarctica,  acquired by Landsat 7’s Enhanced Thematic Mapper plus (ETM+) instrument. Credit: NASA/EO
Image of the McMurdo Dry Valleys, Antarctica, acquired by Landsat 7’s Enhanced Thematic Mapper plus (ETM+) instrument. Credit: NASA/EO

Head has been doing fieldwork for years in Antarctica and thinks the climate on early Mars may have been very similar to what he has observed in the cold, desert-like.

“The average yearly temperature in the Antarctic Dry Valleys is way below freezing, but peak summer daytime temperatures can exceed the melting point of water, forming transient streams, which then refreeze,” Head said. “In a similar manner, we find that volcanism can bring the temperature on early Mars above the melting point for decades to centuries, causing episodic periods of stream and lake formation.”

As that early active volcanism on Mars ceased, so did the possibility of warmer temperatures and flowing water.

According to Head, this theory might also help in the ongoing search for signs that Mars once hosted life. If it ever did exist, this new research may offer clues as to where the fossilized remnants ended up.

“Life in Antarctica, in the form of algal mats, is very resistant to extremely cold and dry conditions and simply waits for the episodic infusion of water to ‘bloom’ and develop,” he said. “Thus, the ancient and currently dry and barren river and lake floors on Mars may harbor the remnants of similar primitive life, if it ever occurred on Mars.”

The research was published in Nature Geoscience.

Further Reading: Brown University

Mercury Had Quite The Explosive Past, Spacecraft Analysis Shows

Mercury — a planet once thought to have no volcanism at all — likely had a very active past, a new analysis of images from NASA’s MESSENGER spacecraft shows. After looking at 51 vents across Mercury, the team concluded that they show different amounts of erosion — hinting that the explosions happened at different times in the planet’s history.

“If [the explosions] happened over a brief period and then stopped, you’d expect all the vents to be degraded by approximately the same amount,” stated Goudge, a graduate geology student at Brown University who led the research.

“We don’t see that; we see different degradation states. So the eruptions appear to have been taking place over an appreciable period of Mercury’s history.”

Information came from orbital data collected from MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) since 2011, which provided more consistent data than the previous flybys, the researchers added. To better figure out the age of these vents, they examined those that are located in impact craters; any vents there before the impact occurred would have been wiped out.

Two pyroclastic vents in Mercury's Kipler crater in optical (top) and false-color views from NASA's MESSENGER spacecraft. Pyroclastic material is in brown-red in the bottom image. The vents were likely too fragile to survive the impact of the crater, scientists said, showing that they likely arose after the impact occurred. Credit: Brown University/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Two pyroclastic vents in Mercury’s Kipler crater in optical (top) and false-color views from NASA’s MESSENGER spacecraft. Pyroclastic material is in brown-red in the bottom image. The vents were likely too fragile to survive the impact of the crater, scientists said, showing that they likely arose after the impact occurred. Credit: Brown University/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The vents show up along with deposits of pyroclastic ash, which are leftovers of volcanic explosions. This shows that like Earth, the interior of Mercury has volatiles or compounds that have low boiling points. (Earth examples of these are water and carbon dioxide.)

By looking at the pattern of erosion in the craters, Goudge found that there are pyroclastic deposits in craters that are between 1 and 3.5 billion years old. By comparison, Mercury and the rest of the solar system formed about 4.5 billion years ago, and the finding shows the pyroclastic activity happened well after then.

“These ages tell us that Mercury didn’t degas all of its volatiles very early,” Goudge added. “It kept some of its volatiles around to more recent geological times.”

You can read more about the study in the Journal of Geophysical Research.

Source: Brown University

MESSENGER Sees a Smoother Side of Mercury

During its two years in orbit around Mercury — as well as several more years performing flybys — the MESSENGER spacecraft has taken over 150,000 images of the innermost planet, giving us a look at its incredibly rugged, Sun-scoured surface like never before. But not all areas on Mercury appear so harsh — it has its softer sides too, as seen above in an image released earlier today.

Here we see the smooth walls, floor and upper surfaces around an irregular depression on Mercury in high definition. The velvety texture is the result of widespread layering of fine particles, because unlike many features on Mercury’s  ancient surface this rimless depression wasn’t caused by an impact from above but rather explosively escaping lava from below — this is the rim of a volcanic vent, not a crater!

Previous images have been acquired of this irregularly-shaped depression but this is the highest resolution view MESSENGER has captured to date — about 26 meters per pixel.

A wide-angle view of the same depression, captured in July 2012
A wide-angle view of the same depression, captured by MESSENGER in July 2012

The full depression, located northeast of the Rachmaninoff basin, is about 36 km (22 miles) across at its widest. It’s surrounded by a smooth blanket of high-reflectance material — explosively ejected volcanic particles from a pyroclastic eruption that spread over the surface like snow.

Other similar vents have been found on Mercury, like this heart-shaped one in Caloris basin. The smooth, bright surface material is a telltale sign of a volcanic outburst, as are the rimless, irregular shapes of the vents.

The numerous small craters that are seen inside the vent and on the smooth surrounding surfaces would be from meteorite impacts that occurred well after the eruption.

On March 17, 2011, MESSENGER became the first spacecraft ever to orbit the planet Mercury. It is capable of continuing orbital operations until early 2015. Find out more about the mission here.

Image credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

Volcanoes on Venus May Still Be Active

Recent infrared data from an instrument on the Venus Express spacecraft indicate there could be active volcanism on Venus. “We are pretty sure that Venus still has volcanic activity,” said Joern Helbert and Nils Mueller from the DLR Institute of Planetary Research, members of the Visible and Infrared Thermal Imaging Spectrometer(VIRTIS) team. Nine ‘hotspots’ on Venus’ southern hemisphere have been identified as possibly active, according to a paper published in Science by an international team.

Focusing on areas that showed a lack of surface weathering – which indicates a young surface — the scientists looked at variations in surface thermal emissions to identify compositional differences in lava flows at three specific hotspots. They found that lava flows at the those areas emit abnormally high amounts of heat when compared with their surroundings. That the temperatures are higher does not indicate “heat” as such from volcanism, but means that not much rock degradation by exposure to the harsh Venusian weather took place.

For planetary scientists, that indicates recent active volcanos. How recent?

“Based on a wide range of estimates for rates of volcanism on the surface, we find an upper bound of 250 years to 2.5 million years,” lead author Suzanne Smrekar from JPL told Universe Today in an email. “From predictions about how fast rocks weather on the surface of Venus, we think they are likely on the young side of these estimates. However, there is nothing to preclude them from happening today – but we don’t have any data that demonstrates that.”
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The areas are analogous to Hawaii with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes – which are rising masses of hot molten rock.

Smrekar said the temperature variations aren’t huge. “Only a degree or two above the background temperature,” she said. “‘Hot spot’ refers to the geologic environment. On Earth, places like Hawaii where there is hot material coming up from deep inside the Earth to produce volcanism, are referred to as ‘hot spots’.”

Like on Earth, Venus’s valleys are warmer than its mountains. But the venusian atmosphere is so dense that it completely determines the temperature of the planet’s surface. This enabled the scientists to predict surface temperatures with computer models. Data obtained from VIRTIS last year shows that certain areas deviate from the predictions by as much as two or three degrees, and that was the focus of the team’s study.

Smrekar said the team was surprised at the findings. “Although we suspected that these areas could be volcanically active on geologic time scales from past data sets, this is the first data to confirm very recent volcanism, geologically speaking.”

Sources: Science, email exchange with Suzanne Smrekar, DLR

Mantle Plume

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One of the mysteries of Earth science is hotspots. While most volcanoes are found at plate boundaries, where two tectonic plates are rubbing against each other, volcanic hotspots can be anywhere, even in the middle of continents. What causes volcanic hotspots? One theory is the idea of a mantle plume.

A mantle plume is kind of like what’s going on inside a lava lamp. As the light heats up the wax in a lava lamp, it rises up through the oil in large blobs. These blobs reach the top of the lamp, cool and then sink back down to be heated up again.

Inside the Earth, the core of the Earth is very hot, and heats up the surrounding mantle. Heat convection in the mantle slowly transports heat from the core up to the Earth’s surface. These rising columns of heat can come up anywhere, and not just at the plate boundaries. Geologists did fluid dynamic experiments to try and simulate mantle plumes, and they found they formed long thin conduits topped by a bulbous head.

When the top of a mantle plume reaches the base of the Earth’s lithosphere, it flattens out and melts a large area of basalt magma. This whole region can form a continental flood basalt, which only lasts for a few million years. Or it can maintain a continuous stream of magma to a fixed location; this is a hotspot.

As the lithosphere continues to move through plate tectonics, the hotspot appears to be shifting its position over millions of years. But really the hotspot is remaining in a fixed location, and the Earth’s plates are shifting above it.

Two of the most famous places that might have mantle plumes underneath them are the Hawaiian Islands and Iceland.

We have written many articles about volcanoes and the interior of the Earth for Universe Today. Here’s an article about the difference between magma and lava, and here’s an article about magma chambers.

Here’s a great resource on mantle plumes, and here’s another.

We have recorded an entire episode of Astronomy Cast about volcanoes around the Solar System. Listen to it here: Episode 141: Volcanoes, Hot and Cold.

Barcena Volcano

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Barcena is a volcano located on the island of San Benedicto, the third largest island of the Revillagigedo Islands. The whole island is only about 4.8 km by 2.4 km and Barcena takes up a good chunk of the southern end. Barcena rises to an elevation of 332 meters, forming a volcanic crater.

There has only been on eruption from Barcena in recorded history, but it was a big one. On August 1, 1952, Barcena had a severe Vulcanian eruption measuring 3 on the Volcanic Explosivity Index. It released huge pyroclastic flows that rolled over the entire island, covering it in ash and pumice to a depth of 3 meters. Within less than 2 weeks, it had created a new volcanic cone more than 300 meters high. A second series of eruptions started up later in the year, releasing magma that broke out of the cone and flowed into the ocean. By late 1953, the volcano went dormant again.

The eruption wiped out all the plants and wildlife on the island, making the San Benedicto Rock Wren extinct. Within a few years the plants and wildlife made a return, although the island still looks barren.

We have written many article about volcanoes for Universe Today. Here’s an article about Tacana, a tall stratovolcano that straddles the border between Mexico and Guatemala. And here’s an article about Paricutin, a volcano that suddenly appeared in a farmer’s cornfield.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Basalt

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Basalt is a hard, black volcanic rock with less than 52% silica. Because of this low silica content, basalt has a low viscosity (thickness), and so it can flow for long distances after erupting from a volcano. During an eruption, a basalt lava flow can easily move more than 20 km away from a vent. Basalt is the most common rock type in the Earth’s crust. In fact, most of the ocean floor is made up of basalt.

Basalt is made up of dark colored materials like pyroxene and olivine, but it also contains lighter minerals like feldspar and quartz. These crystals form because the lava cools slowly after erupting out of a volcano. Although a lava flow might look cool shortly after an eruption, it might take months or even years to cool all the way through. The crystals are bigger in the middle of a cooled lava flow because that part had longer to cool. If a lava flow cools quickly, like when it falls into a lake or ocean, it becomes a glass-like rock called obsidian. This is because the crystals in the rock don’t have time to form.

Shield volcanoes are made up entirely of basalt lava eruptions. A good example of this are the volcanoes Mauna Loa and Mauna Kea on the Big Island of Hawaii. Over hundreds of thousands of years, they have built up tall volcanoes that are extremely wide because of the fast flowing basalt lava.

Geologists have found large outpourings of lava covering hundreds of kilometers of land called flood basalt. The largest of these is known as the Siberian Traps in northern Russia. This is a region of 1.5 million square kilometers covered by basalt.

We have written many articles about volcanoes for Universe Today. Here’s an article about obsidian, and here’s an article about different types of lava.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

What are Active Volcanoes?

Geologists classify volcanoes into three distinct groups: dormant, extinct and active volcanoes. Dormant volcanoes haven’t erupted in a long time, but they could again; extinct volcanoes have erupted for thousands of years and might be dead. Active volcanoes, on the other hand, erupted recently, and they’re probably going to erupt again soon.

There are approximately 500 active volcanoes in the world today, not including those underneath the oceans. In fact, as you read these words, there are probably 20 volcanoes erupting right now. Between 50-70 volcanoes are erupting every year, 160 have erupted in the last decade. And there are about 550 that have erupted since the beginning of recorded history.

The definition of an active volcano is difficult to pin down, since single volcanoes can have networks of volcanic vents across their flanks. And Iceland, there can be eruptions along volcanic fields hundreds of kilometers long. At Mexico’s Michoacan-Guanajuanto field, there are 1,400 cinder cones, maars and shield volcanoes coming from a single magma chamber.

And these are just the volcanoes on land. Scientists estimate that 3/4 of the lava that reaches the Earth’s surface happens underwater at the submarine midocean ridges.

So when does a volcano become dormant or extinct? A volcano is active if it’s currently erupting or showing signs of unrest. The Smithsonian Global Volcanism Program defines an active volcano as having erupted within the last 10,000 years. A volcano finally goes extinct when there’s no lava supply in the magma chamber beneath the volcano.

We have written many articles about volcanoes for Universe Today. Here’s an article about dormant volcanoes, and here’s an article about extinct volcanoes.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.