Astronauts Capture Great Views of Mount Etna Eruption

Mount Etna is Europe’s most active volcano, and it’s been spouting off since late February 2017. It spewed lava and gas with a rather big eruption last week, where 10 people were actually injured. The Expedition 50 crew on board the International Space Station have been able to capture both day and nighttime views of […]

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What is the Difference Between Active and Dormant Volcanoes?

Volcano Vesuvius. Image credit: Pastorius

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!

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).

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 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.

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:

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Weekly Space Hangout – June 24, 2016: Dr. James Green

Host: Fraser Cain (@fcain) Special Guest: Dr. James Green is the NASA Director of Planetary Science. Guests: Morgan Rehnberg (MorganRehnberg.com / @MorganRehnberg) Dave Dickinson (www.astroguyz.com / @astroguyz) Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier ) Their stories this week: Evidence for volcanic history on Mars Impact of Brexit on UK science uncertain FRIPON: A New All-Sky […]

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What is the Difference Between Lava and Magma?

Lava fountain in Hawaii.

Few forces in nature are are impressive or frightening as a volcanic eruption. In an instant, from within the rumbling depths of the Earth, hot lava, steam, and even chunks of hot rock are spewed into the air, covering vast distances with fire and ash. And thanks to the efforts of geologists and Earth scientists over the course of many centuries, we have to come to understand a great deal about them.

However, when it comes to the nomenclature of volcanoes, a point of confusion often arises. Again and again, one of the most common questions about volcanoes is, what is the difference between lava and magma? They are both molten rock, and are both associated with volcanism. So why the separate names? As it turns out, it all comes down to location.

Earth’s Composition:

As anyone with a basic knowledge of geology will tell you, the insides of the Earth are very hot. As a terrestrial planet, its interior is differentiated between a molten, metal core, and a mantle and crust composed primarily of silicate rock. Life as we know it, consisting of all vegetation and land animals, live on the cool crust, whereas sea life inhabits the oceans that cover a large extent of this same crust.

However, the deeper one goes into the planet, both pressures and temperatures increase considerably. All told, Earth’s mantle extends to a depth of about 2,890 km, and is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause pockets of molten rock to form.

This silicate material is less dense than the surrounding rock, and is therefore sufficiently ductile that it can flow on very long timescales. Over time, it will also reach the surface as geological forces push it upwards. This happens as a result of tectonic activity.

Basically, the cool, rigid crust is broken into pieces called tectonic plates. These plates are rigid segments that move in relation to one another at one of three types of plate boundaries. These are known as convergent boundaries, at which two plates come together; divergent boundaries, at which two plates are pulled apart; and transform boundaries, in which two plates slide past one another laterally.

Interactions between these plates are what is what is volcanic activity (best exemplified by the “Pacific Ring of Fire“) as well as mountain-building. As the tectonic plates migrate across the planet, the ocean floor is subducted – the leading edge of one plate pushing under another. At the same time, mantle material will push up at divergent boundaries, forcing molten rock to the surface.

Magma:

As already noted, both lava and magma are what results from rock superheated to the point where it becomes viscous and molten. But again, the location is the key. When this molten rock is still located within the Earth, it is known as magma. The name is derived from Greek, which translate to “thick unguent” (a word used to describe a viscous substance used for ointments or lubrication).

It is composed of molten or semi-molten rock, volatiles, solids (and sometimes crystals) that are found beneath the surface of the Earth. This vicious rock usually collects in a magma chamber beneath a volcano, or solidify underground to form an intrusion. Where it forms beneath a volcano, it can then be injected into cracks in rocks or issue out of volcanoes in eruptions. The temperature of magma ranges between 600 °C and 1600 °C.

Magma is also known to exist on other terrestrial planets in the Solar System (i.e. Mercury, Venus and Mars) as well as certain moons (Earth’s Moon and Jupiter’s moon Io). In addition to stable lava tubes being observed on Mercury, the Moon and Mars, powerful volcanoes have been observed on Io that are capable of sending lava jets 500 km (300 miles) into space.

Lava:

When magma reaches the surface and erupts from a volcano, it officially becomes lava. There are actually different kinds of lava depending on its thickness or viscosity. Whereas the thinnest lava can flow downhill for many kilometers (thus creating a gentle slope), thicker lavas will pile up around a  volcanic vent and hardly flow at all. The thickest lava doesn’t even flow, and just plugs up the throat of a volcano, which in some cases cause violent explosions.

The term lava is usually used instead of lava flow. This describes a moving outpouring of lava, which occurs when a non-explosive effusive eruption takes place. Once a flow has stopped moving, the lava solidifies to form igneous rock. Although lava can be up to 100,000 times more viscous than water, lava can flow over great distances before cooling and solidifying.

The word “lava” comes from Italian, and is probably derived from the Latin word labes which means “a fall” or “slide”. The first use in connection with a volcanic event was apparently in a short written account by Franscesco Serao, who observed the eruption of Mount Vesuvius between May 14th and June 4th, 1737. Serao described “a flow of fiery lava” as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain.

Such is the difference between magma and lava. It seems that in geology, as in real estate, its all about location!

We have written many articles about volcanoes here at Universe Today. Here’s What is Lava?, What is the Temperature of Lava?, Igneous Rocks: How Are They Formed?, What Are The Different Parts Of A Volcano? and Planet Earth.

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.

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The Moon’s Other Axis

A six degree True Polar Wander occurred on the Moon due to ancient volcanic activity. Image: University of Arizona/James Tuttle Keane

It’s tempting to think that the Moon never changes. You can spend your whole life looking at it, and see no evidence of change whatsoever. In fact, the ancients thought the whole Universe was unchanging.

You may have heard of a man named Aristotle. He thought the Universe was eternal and unchanging. Obviously, with our knowledge of the Big Bang, stellar evolution, and planetary formation, we know better. Still, the placid and unchanging face of the Moon can tempt us into thinking astronomers are making up all this evolving universe stuff.

But now, according to a new paper in Nature, the Moon’s axis of rotation is different now than it was billions of years ago. Not only that, but volcanoes may been responsible for it. Volcanoes! On our placid little Moon.

The clue to this lunar True Polar Wander (TPW) is in the water ice locked in the shadows of craters on the Moon. When hydrogen was discovered on the surface of the Moon in the 1990s by the Lunar Prospector probe, scientists suspected that they would eventually find water ice. Subsequent missions proved the presence of water ice, especially in craters near the polar regions. But the distribution of that water-ice wasn’t uniform.

You would expect to see ice uniformly distributed in the shadows of craters in the polar regions, but that’s not what scientists have found. Instead, some craters had no evidence of ice at all, which led the team behind this paper to conclude that these ice-free craters must have been exposed to the Sun at some point. What else would explain it?

The way that the ice in these craters is distributed forms two trails that lead away from each pole. They’re mirror images of each other, but they don’t conform with the Moon’s current axis of rotation, which is what led the team to conclude that the Moon underwent a 6 degree TPW billions of years ago.

The paper also highlights the age of the water on the Moon. Since the TPW, and the melting of some of the ice as a result of it, occurred some billions of years ago, then the water ice that is still frozen in the shadows of some of the Moon’s craters must be ancient. According to the paper, its existence records the “early delivery of water to the inner Solar System.” Hopefully, a future mission will return a sample of this ancient water for detailed study.

But even more interesting than the age of the ice in the craters and the TPW, to me anyways, is what is purported to have caused it. The team behind the paper reports that volcanic activity on the Moon in the Procellarum region, which was most active in the early history of the Moon, moved a substantial amount of material and “altered the density structure of the Moon.” This alteration would have changed the moments of inertia on the Moon, resulting in a TPW.

It’s strange to think of the Moon with volcanic activity viewable from Earth. I wonder what effect visible lunar volcanoes would have had on thinkers like Aristotle, if lunar volcanic activity had occurred during recorded history, rather than ending one billion years ago or so.

We know that events like eclipses and comets caused great confusion and sometimes upheaval in ancient civilizations. Would lunar volcanoes have had the same effect?

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What Are The Benefits Of Volcanoes?

Tungurahua ("throat of fire"), an active stratovolcano in Ecuador. Credit: Patrick Taschler

Volcanoes are renowned for their destructive power. In fact, there are few forces of nature that rival their sheer, awesome might, or have left as big of impact on the human psyche. Who hasn’t heard of tales of Mt. Vesuvius erupting and burying Pompeii? There’s also the Minoan Eruption, the eruption that took place in the 2nd millennium BCE on the isle of Santorini and devastated the Minoan settlement there.

In Japan, Hawaii, South American and all across the Pacific, there are countless instances of eruptions taking a terrible toll. And who can forget modern-day eruptions like Mount St. Helens? But would it surprise you to know that despite their destructive power, volcanoes actually come with their share of benefits? From enriching the soil to creating new landmasses, volcanoes are actually a productive force as well.

Soil Enrichment:

Volcanic eruptions result in ash being dispersed over wide areas around the eruption site. And depending on the chemistry of the magma from which it erupted, this ash will be contain varying amounts of soil nutrients. While the most abundant elements in magma are silica and oxygen, eruptions also result in the release of water, carbon dioxide (CO²), sulfur dioxide (SO²), hydrogen sulfide (H²S), and hydrogen chloride (HCl), amongst others.

In addition, eruptions release bits of rock such as potolivine, pyroxene, amphibole, and feldspar, which are in turn rich in iron, magnesium, and potassium. As a result, regions that have large deposits of volcanic soil (i.e. mountain slopes and valleys near eruption sites) are quite fertile. For example, most of Italy has poor soils that consist of limestone rock.

But in the regions around Naples (the site of Mt. Vesuvius), there are fertile stretches of land that were created by volcanic eruptions that took place 35,000 and 12,000 years ago. The soil in this region is rich because volcanic eruption deposit the necessary minerals, which are then weathered and broken down by rain. Once absorbed into the soil, they become a steady supply of nutrients for plant life.

Hawaii is another location where volcanism led to rich soil, which in turn allowed for the emergence of thriving agricultural communities. Between the 15th and 18th centuries on the islands of Kauai, O’ahu and Molokai, the cultivation of crops like taros and sweet potatoes allowed for the rise of powerful chiefdoms and the flowering of the culture we associate with Hawaii today.

Volcanic Land Formations:

In addition to scattering ash over large areas of land, volcanoes also push material to the surface that can result in the formation of new islands. For example, the entire Hawaiian chain of islands was created by the constant eruptions of a single volcanic hot spot. Over hundreds of thousands of years, these volcanoes breached the surface of the ocean becoming habitable islands, and rest stops during long sea journeys.

This is the case all across the Pacific, were island chains such as Micronesia, the Ryukyu Islands (between Taiwan and Japan), the Aleutian Islands (off the coast of Alaska), the Mariana Islands, and Bismark Archipelago were all formed along arcs that are parallel and close to a boundary between two converging tectonic plates.

Much the same is true of the Mediterranean. Along the Hellenic Arc (in the eastern Mediterranean), volcanic eruptions led to the creation of the Ionian Islands, Cyprus and Crete. The nearby South Aegean Arc meanwhile led to the formation of Aegina, Methana, Milos, Santorini and Kolumbo, and Kos, Nisyros and Yali. And in the Caribbean, volcanic activity led to the creation of the Antilles archipelago.

Where these islands formed, unique species of plants and animals evolved into new forms on these islands, creating balanced ecosystems and leading to new levels of biodiversity.

Volcanic Minerals and Stones:

Another benefits to volcanoes are the precious gems, minerals and building materials that eruptions make available. For instance, stones like pumice volcanic ash and perlite (volcanic glass) are all mined for various commercial uses. These include acting as abrasives in soaps and household cleaners. Volcanic ash and pumice are also used as a light-weight aggregate for making cement.

The finest grades of these volcanic rocks are used in metal polishes and for woodworking. Crushed and ground pumice are also used for loose-fill insulation, filter aids, poultry litter, soil conditioner, sweeping compound, insecticide carrier, and blacktop highway dressing.

Perlite is also used as an aggregate in plaster, since it expands rapidly when heated. In precast walls, it too is used as an aggregate in concrete. Crushed basalt and diasbase are also used for road metal, railroad ballast, roofing granules, or as protective arrangements for shorelines (riprap). High-density basalt and diabase aggregate are used in the concrete shields of nuclear reactors.

Hardened volcanic ash (called tuff) makes an especially strong, lightweight building material. The ancient Romans combined tuff and lime to make a strong, lightweight concrete for walls, and buildings. The roof of the Pantheon in Rome is made of this very type of concrete because it’s so lightweight.

Precious metals that are often found in volcanoes include sulfur, zinc, silver, copper, gold, and uranium. These metals have a wide range of uses in modern economies, ranging from fine metalwork, machinery and electronics to nuclear power, research and medicine. Precious stones and minerals that are found in volcanoes include opals, obsidian, fire agate, flourite, gypsum, onyx, hematite, and others.

Global Cooling:

Volcanoes also play a vital role in periodically cooling off the planet. When volcanic ash and compounds like sulfur dioxide are released into the atmosphere, it can reflect some of the Sun’s rays back into space, thereby reducing the amount of heat energy absorbed by the atmosphere. This process, known as “global dimming”, therefore has a cooling effect on the planet.

The link between volcanic eruptions and global cooling has been the subject of scientific study for decades. In that time, several dips have been observed in global temperatures after large eruptions. And though most ash clouds dissipate quickly, the occasional prolonged period of cooler temperatures have been traced to particularly large eruptions.

Because of this well-established link, some scientists have recommended that sulfur dioxide and other  be released into the atmosphere in order to combat global warming, a process which is known as ecological engineering.

Hot Springs And Geothermal Energy:

Another benefit of volcanism comes in the form of geothermal fields, which is an area of the Earth characterized by a relatively high heat flow. These fields, which are the result of present, or fairly recent magmatic activity, come in two forms. Low temperature fields (20-100°C) are due to hot rock below active faults, while high temperature fields (above 100°C) are associated with active volcanism.

Geothermal fields often create hot springs, geysers and boiling mud pools, which are often a popular destination for tourists. But they can also be harnessed for geothermal energy, a form of carbon-neutral power where pipes are placed in the Earth and channel steam upwards to turn turbines and generate electricity.

In countries like Kenya, Iceland, New Zealand, the Phillipines, Costa Rica and El Salvador, geothermal power is responsible for providing a significant portion of the country’s power supply – ranging from 14% in Costa Rica to 51% in Kenya. In all cases, this is due to the countries being in and around active volcanic regions that allow for the presence of abundant geothermal fields.

Outgassing and Atmospheric Formation:

But by far, the most beneficial aspect of volcanoes is the role they play in the formation of a planet’s atmosphere. In short, Earth’s atmosphere began to form after its formation 4.6 billion eyars ago, when volcanic outgassing led to the creation of gases stored in the Earth’s interior to collect around the surface of the planet. Initially, this atmosphere consisted of hydrogen sulfide, methane, and 10 to 200 times as much carbon dioxide as today’s atmosphere.

After about half a billion years, Earth’s surface cooled and solidified enough for water to collect on it. At this point, the atmosphere shifted to one composed of water vapor, carbon dioxide and ammonia (NH³). Much of the carbon dioxide dissolved into the oceans, where cyanobacteria developed to consume it and release oxygen as a byproduct. Meanwhile, the ammonia began to be broken down by photolysis, releasing the hydrogen into space and leaving the nitrogen behind.

Another key role played by volcanism occurred 2.5 billion years ago, during the boundary between the Archaean and Proterozoic Eras. It was at this point that oxygen began to appear in our oxygen due to photosynthesis – which is referred to asthe “Great Oxidation Event”. However, according to recent geological studies, biomarkers indicate that oxygen-producing cyanobacteria were releasing oxygen at the same levels there are today. In short, the oxygen being produced had to be going somewhere for it not to appear in the atmosphere.

The lack of terrestrial volcanoes is believed to be responsible. During the Archaean Era, there were only submarine volcanoes, which had the effect of scrubbing oxygen from the atmosphere, binding it into oxygen containing minerals. By the Archaean/Proterozoic boundary, stabilized continental land masses arose, leading to terrestrial volcanoes. From this point onward, markers show that oxygen began appearing in the atmosphere.

Volcanism also plays a vital role in the atmospheres of other planets. Mercury’s thin exosphere of hydrogen, helium, oxygen, sodium, calcium, potassium and water vapor is due in part of volcanism, which periodically replenishes it. Venus’ incredibly dense atmosphere is also believed to be periodically replenished by volcanoes on its surface.

And Io, Jupiter’s volcanically active moon, has an extremely tenuous atmosphere of sulfur dioxide (SO²), sulfur monoxide (SO), sodium chloride (NaCl), sulfur monoxide (SO), atomic sulfur (S) and oxygen (O). All of these gases are provided and replenished by the many hundreds of volcanoes situated across the moon’s surface.

As you can see, volcanoes are actually a pretty creative force when all is said and done. In fact, us terrestrial organisms depend on them for everything from the air we breathe, to the rich soil that produces our food, to the geological activity that gives rise to terrestrial renewal and biological diversity.

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

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

Astronomy Cast also has relevant episodes on the subject Earth, as part of our tour through the Solar System – Episode 51: Earth.

 

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Robots Exploring Alien Volcanoes? NASA Lab Hopes To Get There One Day

We’ve seen volcanoes or geysers erupting on the moons of Io and Enceladus. Volcanic remnants remain on Mars and the Moon. But it’s tough for rovers to get inside these challenging environments. So NASA’s Jet Propulsion Laboratory is trying out a new robot here on Earth to one day, they hope, get inside volcanoes elsewhere […]

Robots Exploring Alien Volcanoes? NASA Lab Hopes To Get There One Day

We’ve seen volcanoes or geysers erupting on the moons of Io and Enceladus. Volcanic remnants remain on Mars and the Moon. But it’s tough for rovers to get inside these challenging environments. So NASA’s Jet Propulsion Laboratory is trying out a new robot here on Earth to one day, they hope, get inside volcanoes elsewhere […]

Were Lunar Volcanoes Active When Dinosaurs Roamed the Earth?

The Moon’s a very dusty museum where the exhibits haven’t changed much over the last 4 billion years. Or so we thought. NASA’s Lunar Reconnaissance Orbiter (LRO) has provided researchers strong evidence the Moon’s volcanic activity slowed gradually instead of stopping abruptly a billion years ago. Some volcanic deposits are estimated to be 100 million years […]