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.
The Earth’s layers, showing the Inner and Outer Core, the Mantle, and Crust. Credit: discovermagazine.com
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.
The Earth’s Tectonic Plates. Credit: msnucleus.org
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.
Igneous rock (aka. “fire rock”) is formed from cooled and solidified lava. Credit: geologyclass.org
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!
This is an artist’s depiction of a 10-kilometer (6-mile) diameter asteroid striking the Earth. New evidence in Australia suggests an asteroid 2 to 3 times larger than this struck Earth early in its life. Credit: Don Davis/Southwest Research Institute.
New evidence found in northwestern Australia suggests that a massive asteroid, 20 to 30 kilometres in diameter, struck Earth about 3.5 billion years ago. This impact would have dwarfed anything experienced by humans, and dinosaurs, releasing as much energy as millions of nuclear weapons. Impacts this large can trigger earthquakes and tsunamis, and change the geological history of Earth.
The evidence was uncovered by Andrew Glikson and Arthur Hickman from the Australian National University. While drilling for the Geological Survey of Western Australia, the two obtained drilling cores from some of the oldest known sediments on Earth. Sandwiched between two layers of sediment were tiny glass beads called spherules, which were formed from vaporized material from the asteroid impact.
Impact spherules formed from material vaporized by an asteroid impact. Image: A. Glikson/Australian National University
The enormity of this impact cannot be overstated. “The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble,” said Dr. Glikson, from the ANU Planetary Institute.
This asteroid impact is the second oldest one that we know of. It is also one of the largest found yet, and at 20 to 30 kilometers in diameter, it is 2 the 3 times the size of the famous Chicxulub asteroid that struck the Yucatan in Mexico. That impact is thought to be responsible for ending the age of dinosaurs on Earth.
This image shows a very faint circular outline of the Chicxulub crater. After 65 million years, it is barely visible. All evidence of craters billions of years old would now be gone. Image: NASA/JPL
The crater itself would have been hundreds of kilometers in diameter, though all traces of it are now gone. “Exactly where this asteroid struck the earth remains a mystery,” Dr. Glikson said. “Any craters from this time on Earth’s surface have been obliterated by volcanic activity and tectonic movements.”
“Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago,” said Glikson.
At 3.46 billion years ago, this puts this impact event close to a period of time 4.1 to 3.8 billion years ago known as the Late Heavy Bombardment. This was a period of time when a disproportionate number of asteroids struck the Earth and the Moon, and probably Mercury, Venus, and Mars, too. The Late Heavy Bombardment was probably caused by the gas giants in our Solar System. As these planets migrated, their gravity caused enormous disruption, pulling objects in the asteroid belt and the Kuiper Belt into trajectories that sent them towards the inner Solar System.
The Late Heavy Bombardment is thought to be a period of time when the Earth, and the rest of the bodies in the inner Solar System, were repeatedly struck by asteroids. Image: NASA/ESA
The surfaces of Mercury and the Moon are covered in impact craters. Samples of rock from the lunar surface, brought back to Earth by the Apollo astronauts, have been subjected to isotopic dating. Their age is constrained to a fairly narrow band of time, corresponding to the Late Heavy Bombardment. Obviously, the Earth would have been subjected to the same thing. But on geologically active Earth, most traces of impact events have been erased. It’s the sediment that hints at these events.
Australia is geologically ancient, and contains some of the most ancient rocks on Earth. Glikson and Hickman found the glass spherules in cores while drilling at Marble Bar in north-western Australia. Because the sediment layer containing the spherules was preserved between two volcanic layers, its age was determined with great precision.
The sediments at Marble Bar, north-western Australia, where the spherules were found. Image: A Glikson/Australian National University
For over 20 years, Dr. Glikson has been searching for evidence of asteroid impacts. When these glass beads were found in the core samples, he suspected an asteroid impact. Testing confirmed that the levels of elements such as platinum, nickel and chromium, matched those in asteroids.
This is not the first evidence of impact events that Glikson has uncovered. In 2015, Glikson discovered evidence of another massive asteroid strike in the Warburton Basin in Central Australia. At that site, buried in the crust 30 kilometers deep, in rock that is 300 to 500 million years old, Glikson found evidence of a double impact crater covering an area 400 kilometers wide.
This crater was believed to be the result of an asteroid that broke into two before slamming into Earth. “The two asteroids must each have been over 10 kilometers (6.2 miles) across — it would have been curtains for many life species on the planet at the time,” said Glikson.
“There may have been many more similar impacts, for which the evidence has not been found, said Dr. Glikson. “This is just the tip of the iceberg. We’ve only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds.”
Finding the sites of ancient impacts is not easy. Advances in satellite imaging helped locate and pinpoint the Chicxulub crater, and others. If there have been hundreds of enormous asteroid impacts, like Dr. Glikson suggests, then they would have had an equally enormous impact on Earth’s evolution. But pinpointing these sites remains elusive.
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.
The area around the volcano is now densely populated. Credit: Wikipedia Commons/Jeffmatt
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.
The island of Santorini, Greece. Credit: EOS/NASA/ Public Domain
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.
The roof of the Pantheon, as seen from nearby rooftops in Roe. Credit: Public Domain/Anthony Majanlahti
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.
Sarychev volcano, (located in Russia’s Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Credit: NASA
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.
Steam rising from the Nesjavellir Geothermal Power Station in Iceland. Credit: Gretar Ívarsson/Fir0002
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.
Roughly 2.5 billion years ago, towards the end of the Archaean Era, oxidation of our atmosphere began. Credit: ocean.si.edu
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.
An artist's image of an asteroid Impact. Image Credit: University of California Observatories/Don Davis.
All over the Earth, there is a buried layer of sediment rich in iridium called the Cretaceous Paleogene-Boundary (K-Pg.) This sediment is the global signature of the 10-km-diameter asteroid that killed off the dinosaurs—and about 50% of all other species—66 million years ago. Now, in an effort to understand how life recovered after that event, scientists are going to drill down into the site where the asteroid struck—the Chicxulub Crater off the coast of Mexico’s Yucatan Peninsula.
The end-Cretaceous extinction was a global catastrophe, and a lot is already known about it. We’ve learned a lot about the physical effects of the strike on the impact area from oil and gas drilling in the Gulf of Mexico. According to data from that drilling, released on February 5th in the Journal of Geophysical Research: Solid Earth, the asteroid that struck Earth displaced approximately 200,000 cubic km (48,000 cubic miles) of sediment. That’s enough to fill the largest of the Great Lakes—Lake Superior—17 times.
The Chicxulub impact caused earthquakes and tsunamis that first loosened debris, then swept it from nearby areas like present-day Florida and Texas into the Gulf basin itself. This layer is hundreds of meters thick, and is hundreds of kilometers wide. It covers not only the Gulf of Mexico, but also the Caribbean and the Yucatan Peninsula.
In April, a team of scientists from the University of Texas and the National University of Mexico will spend two months drilling in the area, to gain insight into how life recovered after the impact event. Research Professor Sean Gulick of the University of Texas Institute for Geophysics told CNN in an interview that the team already has a hypothesis for what they will find. “We expect to see a period of no life initially, and then life returning and getting more diverse through time.”
Scientists have been wanting to drill in the impact region for some time, but couldn’t because of commercial drilling activity. Allowing this team to study the region directly will build on what is already known: that this enormous deposit of sediment happened over a very short period of time, possibly only a matter of days. The drilling will also help paint a picture of how life recovered by looking at the types of fossils that appear. Some scientists think that the asteroid impact would have lowered the pH of the oceans, so the fossilized remains of animals that can endure greater acidity would be of particular interest.
The Chicxulub impact was a monumental event in the history of the Earth, and it was extremely powerful. It may have been a billion times more powerful than the atomic bomb dropped on Hiroshima. Other than the layer of sediment laid down near the site of the impact itself, its global effects probably included widespread forest fires, global cooling from debris in the atmosphere, and then a period of high temperatures caused by an increase in atmospheric CO2.
We already know what will happen if an asteroid this size strikes Earth again—global devastation. But drilling in the area of the impact will tell us a lot about how geological and ecological processes respond to this type of devastation.
A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University
“What happened to Mars?” is one of the most compelling questions in space science. It probably wasn’t always the dead, dry, cold place it is now. Did its core cool and stop rotating, allowing the full glare of the sun to blast away its atmosphere and water, and kill anything that may have lived there? Was it struck by a large body, which incinerated its atmosphere, and led to its demise? Were there other causes?
According to a new research paper from Sylvain Bouley at the University of Paris-South, and his colleagues, it may have been a massive, ancient outpouring of molten rock that threw Mars off kilter and helped change Mars into what it is today.
The Tharsis region is an ancient lava complex on Mars that dates back to between 4.1 billion and 3.7 billion years ago. It’s located in Mars’ Western Hemisphere, right near the equator. It’s made up of three huge shield volcanoes—Arsia Mons, Pavonis Mons, and Ascraeus Mons. Collectively, they’re known as Tharsis Montes. (Olympus Mons, the largest volcano in the Solar System, is not a part of the Tharsis complex, though it is near it.)
Tharsis is over 5,000 km across and over 10 miles thick, making it the largest volcanic complex in the Solar System. That much mass positioned after Mars was already formed and had an established rotation would have been cataclysmic. Think what would happen to Earth if Australia rose up 10 miles.
An image of the Syria-Thaumasia region of the Tharsis complex, showing the volcano Arsia Mons on the left, and Valles Marineris on the northern edge. Brown areas are the highest altitude. Open Source Image: Arizona State University, JMars.
The new paper, published on March 2nd, 2016, in the journal Nature, says that the position of the Tharsis complex would have initiated a True Polar Wander (TPW.) Basically, what this means is that Tharsis’ huge mass would have forced Mars to shift its rotation, so that the location of Tharsis became the new equator.
It was thought that the emergence of Tharsis made Martian rivers—which formed later—flow the direction they do. But the study from Bouley and his colleagues shows that Martian rivers and valleys formed first—or maybe concurrently—and that the Tharsis TPW deformed the planet later.
The authors of the study calculated where the Martian poles would have been prior to Tharsis, and looked for evidence of polar conditions at those locations. The location of this ancient north pole contains a lot of ice today, and the location of the ancient south polar region also shows evidence of water.
What it all adds up to is that the disappearance of water on Mars probably happened at the same time as the TPW. Whether the appearance of the Tharsis lava complex, and the resulting cataclysmic shifting of Mars’ rotational orientation, were the cause of Mars losing its climate is not yet known for sure. But this study shows that the ancient volcanic cataclysm did at least help shape Mars into what it is today.
Mount Everest from Kalapatthar. Photo: Pavel Novak
When beholding the sheer size and majesty of mountains, ancient humans could not help but feel that they were standing in the presence of something… godlike. And within the belief systems of many ancient cultures, it was generally felt that mountains were something spiritual – either serving as the home of the Gods, a result of their activity, or a place to get closer to God.
Thanks to modern geology, we now know the true story of how mountains are formed. Simply put, they are the result of tectonic forces or volcanism. But knowing this has not diminished their impressive and awe-inspiring nature. When a geological formation is created through forces that can only be described as titanic, this is to be expected. But just how are mountains formed?
In truth, there are three ways in which mountains are formed, which correspond to the types of mountains in question. These are known as volcanic, fold and block mountains. All of these are the result of plate tectonics, where compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features.
Over the course of many million years, these uplifted sections are eroded by the elements – wind, rain, ice and gravity. These gradually wear the surface of the mountains down, cause the surface to be younger than the rocks that form them, and lead to the types of formations and distributions we are familiar with today.
The East side of the Matterhorn, a fold mountain that measures 4,478 meters in height, mirrored in lake Riffelsee. Credit: Wikipedia Commons/Dirk Beyer
Volcanic Mountains:
Volcanic mountains are formed when a tectonic plate is pushed beneath another (or above a mid-ocean ridge or hotspot) where magma is forced to the surface. When the magma reaches the surface, it often builds a volcanic mountain, such as s shield volcano or a stratovolcano. Examples of this sort of mountains include Mount Fuji in Japan, Mauna Kea in Hawaii, Nyamuragira in the Democratic Republic of Congo, Skjaldbreiður in Iceland and Mount Etna in Sicily.
At other times, the rising magma solidifies below the surface and forms dome mountains, where material is pushed up from the force of the build-up beneath it. Examples of this formation include Navajo Mountain in San Juan County, Utah; the Chaitén lava dome of Chile, Torfajökull in Iceland, and Mount St. Helens in Washington State.
Fold Mountains:
As the name suggests, fold mountains occur when two tectonic plates collide at a convergent plate boundary, causing the crust to overthicken. This process forces the less dense crust to float on top of the denser mantle rocks – with material being forced upwards to form hills, plateaus or mountains – while a greater volume of material is forced downward into the mantle.
Satellite image of the Himalayan mountain chain, as imaged by NASA’s Landsat-7 satellite. Credit: NASA
The Jura Mountains, a series of sub-parallel mountain ridges located in the Alps, are an example of fold mountains. Other examples include the “Simply Folded Belt” of the Zagros mountains, which extends from northern Syria and southern Turkey to eastern Iran and the Persian Gulf. There is also the Akwapim-Togo ranges in Ghana and the Ridge-and-Valley Appalachians in the Eastern United States.
But perhaps most famous is the Himalayan mountain chain, located between northern India and Nepal. This chain formed as a result of the collision between the Indian subcontinent and Asia some 25 million years ago, and has given rise to the tallest mountain in the world – Mt. Everest.
Block Mountains:
Block mountains are caused by faults in the crust, a seam where rocks can move past each other. Also known as rifting, this process occurs when rocks on one side of a fault rise relative to the other. The uplifted blocks become block mountains (also known as horsts) while the intervening dropped blocks are known as graben (i.e. depressed regions).
Examples of this type of terrain can be found in the Upper Rhine valley, the Vosges mountains in France, the Black Forest in Germany, and the Vindhya and Satpura horsts in India. There is also the East African Rift, an active continental rift zone with several active volcanoes that extends from Eritrea to Mozambique.
Satellite image of the East African Rift, taken on December 18th, 2002. Credit: NASA/GSFC/METI/Japan Space Systems/U.S.-Japan ASTER Science Team
Mountain Erosion:
As noted, the final way in which mountains are formed is through erosion. This occurs during and after an uplift, where a newly formed mountainous region is subjected to the effects of wind, water, ice, and gravity. These forces actively shape the surface of mountain ranges, wearing down the exposed surfaces, depositing sediment in alluvial flows, and leading to the formation of characteristic landforms.
These include pyramidal peaks, knife-edge arêtes, and bowl-shaped cirques that can contain lakes. Plateau mountains, such as the Catskills, are formed from the erosion of an uplifted plateau. And after millions of years of erosion, mountains may cease to exist entirely.
Given the size and scale of a mountain, the immense forces involved in their creation, and the immense amount of time it takes to shape and form them, it is little wonder why they are considered such a big deal. Between their religious significance (i.e. Mount Zion, Mount Olympus, Mount Ararat, and Mauna Kea, to name a few), their scenic value, the challenge they present, and their importance to the Earth sciences, these geological formations continue to enjoy a special place in our hearts, minds and culture.
As we explore other planets, we have also found new and impressive mountain formations that have taught us much about the geological activity and composition of other worlds. For example, there the volcanic mountain on Mars known as Olympus Mons, which just happens to be the largest mountain in the Solar System. And this is merely a drop in the bucket. Wherever there’s a geologically active planet, there’s mountains to be found!
Igneous rock (aka. "fire rock") is formed from cooled and solidified magma. Credit: geologyclass.org
When it comes to the composition of the Earth, three main types of rock come into play. These are known as metamorphic rock, sedimentary rock, and igneous rock, respectively. Also known as “fire rock” (derived from the Latin “ignus”), these type of rock are the most common type of rock in the Earth’s surface. In fact, combined with metaphoric rock, igneous rock makes up 90 to 95% of all rock to a depth of 16 km from the surface.
Igneous rocks are also very important because their mineral and chemical makeup can be used to learn about the composition, temperature and pressure that exists within the Earth’s mantle. They can also tell us much about the tectonic environment, given that they are closely linked to the convection of tectonic plates. But just how are these rocks formed?
Tungurahua ("throat of fire"), an active stratovolcano in Ecuador. Credit: Patrick Taschler
Without a doubt, volcanoes are one of the most powerful forces of nature a person can bear witness to. Put simply, they are what results when a massive rupture takes place in the Earth’s crust (or any planetary-mass object), spewing hot lava, volcanic ash, and toxic fumes onto the surface and air. Originating from deep within the Earth’s crust, volcanoes leave a lasting mark on the landscape.
But what are the specific parts of a volcano? Aside from the “volcanic cone” (i.e. the cone-shaped mountain), a volcano has many different parts and layers, most of which are located within the mountainous region or deep within the Earth. As such, any true understanding of their makeup requires that we do a little digging (so to speak!)
While volcanoes come in a number of shapes and sizes, certain common elements can be discerned. The following gives you a general breakdown of a volcanoes specific parts, and what goes into making them such a titanic and awesome natural force.
Magma Chamber:
A magma chamber is a large underground pool of molten rock sitting underneath the Earth’s crust. The molten rock in such a chamber is under extreme pressure, which in time can lead to the surrounding rock fracturing, creating outlets for the magma. This, combined with the fact that the magma is less dense than the surrounding mantle, allows it to seep up to the surface through the mantle’s cracks.
Lava cooling after an eruption from Kilauea, a shield volcano near Kalapana, Hawaii Credit: kalapanaculturaltours.com
When it reaches the surface, it results in a volcanic eruption. Hence why many volcanoes are located above a magma chamber. Most known magma chambers are located close to the Earth’s surface, usually between 1 km and 10 km deep. In geological terms, this makes them part of the Earth’s crust – which ranges from 5–70 km (~3–44 miles) deep.
Lava:
Lava is the silicate rock that is hot enough to be in liquid form, and which is expelled from a volcano during an eruption. The source of the heat that melts the rock is known as geothermal energy – i.e. heat generated within the Earth that is leftover from its formation and the decay of radioactive elements. When lava first erupted from a volcanic vent (see below), it comes out with a temperature of anywhere between 700 to 1,200 °C (1,292 to 2,192 °F). As it makes contact with air and flows downhill, it eventually cools and hardens.
Main Vent:
A volcano’s main vent is the weak point in the Earth’s crust where hot magma has been able to rise from the magma chamber and reach the surface. The familiar cone-shape of many volcanoes are an indication of this, the point at which ash, rock and lava ejected during an eruption fall back to Earth around the vent to form a protrusion.
Throat:
The uppermost section of the main vent is known as the volcano’s throat. As the entrance to the volcano, it is from here that lava and volcanic ash are ejected.
Thurston lava tube is located on Kilauea in Hawaii. Credit: P. Mouginis-Mark, LPI
Crater:
In addition to cone structures, volcanic activity can also lead to circular depressions (aka. craters) forming in the Earth. A volcanic crater is typically a basin, circular in form, which can be large in radius and sometimes great in depth. In these cases, the lava vent is located at the bottom of the crater. They are formed during certain types of climactic eruptions, where the volcano’s magma chamber empties enough for the area above it to collapse, forming what is known as a caldera.
Pyroclastic Flow:
Otherwise known as a pyroclastic density current, a pyroclastic flow refers to a fast-moving current of hot gas and rock that is moving away from a volcano. Such flows can reach speeds of up to 700 km/h (450 mph), with the gas reaching temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill from their eruption site.
Their speeds depend upon the density of the current, the volcanic output rate, and the gradient of the slope. Given their speed, temperature, and the way they flow downhill, they are one of the greatest dangers associated with volcanic eruptions and are one of the primary causes of damage to structures and the local environment around an eruption site.
Ash Cloud:
Volcanic ash consists of small pieces of pulverized rock, minerals and volcanic glass created during a volcanic eruption. These fragments are generally very small, measuring less than 2 mm (0.079 inches) in diameter. This sort of ash forms as a result of volcanic explosions, where dissolved gases in magma expand to the point where the magma shatters and is propelled into the atmosphere. The bits of magma then cool, solidifying into fragments of volcanic rock and glass.
Because of their size and the explosive force with which they are generated, volcanic ash is picked up by winds and dispersed up to several kilometers away from the eruption site. Due to this dispersal, ash an also have a damaging effect on the local environment, which includes negatively affecting human and animal health, disrupting aviation, disrupting infrastructure, and damaging agriculture and water systems. Ash is also produced when magma comes into contact with water, which causes the water to explosively evaporate into steam and for the magma to shatter.
Volcanic Bombs:
In addition to ash, volcanic eruptions have also been known to send larger projectiles flying through the air. Known as volcanic bombs, these ejecta are defined as those that measure more than 64mm (2.5 inches) in diameter, and which are formed when a volcano ejects viscous fragments of lava during an eruption. These cool before they hit the ground, are thrown many kilometers from the eruption site, and often acquire aerodynamic shapes (i.e. streamlined in form).
While the term applies to any ejecta larger than a few centimeters, volcanic bombs can sometimes be very large. There have been recorded instances where objects measuring several meters were retrieved hundreds of meters from an eruptions. Small or large, volcanic bombs are a significant volcanic hazard and can often cause serious damage and multiple fatalities, depending on where they land. Luckily, such explosions are rare.
Secondary Vent:
On large volcanoes, magma can reach the surface through several different vents. Where they reach the surface of the volcano, they form what is referred to as a secondary vent. Where they are interrupted by accumulated ash and solidified lava, they become what is known as a Dike. And where these intrude between cracks, pool and then crystallize, they form what is called a Sill.
Cross-section of a stratovolcano: 1. Magma chamber 2. Bedrock 3. Vent 4. Base 5. Sill 6. Dike 7. Layers of ash 8. Flank 9. Layers of lava 10. Throat 11. Parasitic cone 12. Lava flow 13. Vent 14. Crater 15. Ash cloud. Credit: MesserWoland
Secondary Cone:
Also known as a Parasitic Cone, secondary cones build up around secondary vents that reach the surface on larger volcanoes. As they deposit lava and ash on the exterior, they form a smaller cone, one that resembles a horn on the main cone.
Yes indeed, volcanoes are as powerful as they are dangerous. And yet, without these geological phenomena occasionally breaking through the surface and reigning down fire, smoke, and clouds of ash, the world as we know it would be a very different place. More than likely, it would be a geologically dead one, with no change or evolution in its crust. I think we can all agree that while such a world would be much safer, it would also be painfully boring!
This image contains the initial, informal names being used by the New Horizons team for the features on Pluto’s largest moon, Charon. Names were selected based on the input the team received from the Our Pluto naming campaign. Names have not yet been approved by the International Astronomical Union (IAU). Click for a pdf. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
A big smile. That was my reaction to seeing the names of Uhura, Spock, Kirk and Sulu on the latest map of Pluto’s jumbo moon Charon. The monikers are still only informal, but new maps of Charon and Pluto submitted to the IAU for approval feature some of our favorite real life and sci-fi characters. Come on — Vader Crater? How cool is that?
This image contains the initial, informal names being used by the New Horizons team for the features and regions on the surface of Pluto. The IAU will still need to give final approval. Click for a large pdf file. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Pluto’s features, in contrast, are named for both real people and places as well as mythological beings of underworld mythology. Clyde Tombaugh, the dwarf world’s discoverer, takes center stage, with his name appropriately spanning 990 miles (1,590 km) of frozen terrain nicknamed the “heart of Pluto”. Perhaps the most intriguing region of Pluto, it’s home to what appear to be glaciers of nitrogen ice still mobile at temperatures around –390°F (–234°C).
A close-up slice of Plutonian landscape centered on Tombaugh Regio with informal names waiting for approval. Click for a large pdf file. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Pluto, being a physically, historically and emotionally bigger deal than Charon, comes with six themes. I’ve listed a few examples for each:
* Space Missions and Spacecraft – Sputnik, Voyager, Challenger
* Scientists and Engineers– Tombaugh, Lowell, Burney (after Venetia Burney, the young girl who named Pluto) * Historic Explorers– Norgay, Cousteau, Isabella Bird
* Underworld Beings– Cthulu, Balrog (from Lord of the Rings), Anubis (Egyptian god associated with the afterlife)
* Underworlds and Underworld Locales– Tartarus (Greek “pit of lost souls”), Xibalba (Mayan underworld), Pandemonium (capital of hell in Paradise Lost)
* Travelers to the Underworld– Virgil (tour guide in Dante’s Divine Comedy), Sun Wukong (Monkey king of Chinese mythology), Inanna (ancient Sumerian goddess)
Global map of Pluto’s moon Charon pieced together from images taken at different resolutions. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
There’s nothing like a name. Not only do names make sure we’re all talking about the same thing, but they’re how we begin to understand the unique landscapes presented to us by Pluto and its wonderful system of satellites. To keep them all straight, astronomers at the International Astronomical Union’s Working Group on Planetary System Nomemclature are charged with choosing themes for each planet, asteroid or moon along with individual names for craters, canyons, mountains, volcanoes based on those themes. Astronomers help the group by providing suggested themes and names. In the case of the Pluto system, the public joined in to help the astronomers by participating in the Our Pluto Naming Campaign.
Craters and fissures (fossae) on Charon photographed during the flyby. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
If you’ve followed naming conventions over the years, you’ve noticed more Latin in use, especially when it comes to basic land forms. I took Latin in college and loved it, but since few of us speak the ancient language anymore, we’re often at a loss to understand what’s being described. What’s a ‘Krun Macula’ or ‘Soyuz Colles’?
Image I dug out of New Horizon’s LORRI archive shows Pluto’s nitrogen ice flows in Tombaugh Regio also shows several clumps of “colles”. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The first name is the proper name, so Krun denotes the Mandean god of the underworld. The second name – in Latin – describes the land form. Here’s a list of terms to help you translate the Plutonian and Charonian landscapes (plurals in parentheses):
Regio (Regi): Region
Mons (Montes): Mountain
Collis (Colles): Hill
Chasma (Chasmae): Canyon
Terra (Terrae): Land
Fossa (Fossae): Depression or fissure
Macula (Maculae): Spot
Valles (Valles): Valley
Rupes (Rupes): Cliff
Linea (Linea): Line
Dorsum (Dorsa): Wrinkle ridge
Cavus (Cava): Cavity or pit
Another LORRI photo showing icy Tombaugh Regio butting up against rugged, mountainous (montes) terrain. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
A view of the Villarrica Volcano's Eruption In Chile on March 3, 2-15. Credit: Ariel Marinkovic/EPA /Landov.
Want some volcano facts? Here are 10 interesting facts about volcanoes. Some of these facts you’ll know, and others may surprise you. Whatever the case, volcanoes are amazing features of nature that demand our respect.
1. There are Three Major Kinds of Volcanoes:
Although volcanoes are all made from hot magma reaching the surface of the Earth and erupting, there are different kinds. Shield volcanoes have lava flows with low viscosity that flow dozens of kilometers; this makes them very wide with smoothly sloping flanks.
Stratovolcanoes are made up of different kinds of lava, and eruptions of ash and rock and grow to enormous heights. Cinder cone volcanoes are usually smaller, and come from short-lived eruptions that only make a cone about 400 meters high.
2. Volcanoes Erupt Because of Escaping Magma:
About 30 km beneath your feet is the Earth’s mantle. It’s a region of superhot rock that extends down to the Earth’s core. This region is so hot that molten rock can squeeze out and form giant bubbles of liquid rock called magma chambers. This magma is lighter than the surrounding rock, so it rises up, finding cracks and weakness in the Earth’s crust.
Lava fountain in Hawaii. Image Credit: Jim D. Griggs/HVO/USGS
When it finally reaches the surface, it erupts out of the ground as lava, ash, volcanic gasses and rock. It’s called magma when it’s under the ground, and lava when it erupts onto the surface.
3. Volcanoes can be Active, Dormant or Extinct:
An active volcano is one that has had an eruption in historical times (in the last few thousand years). A dormant volcano is one that has erupted in historical times and has the potential to erupt again, it just hasn’t erupted recently. An extinct volcano is one that scientists think probably won’t erupt again. Here’s more information on the active volcanoes in the world.
4. Volcanoes can Grow Quickly:
Although some volcanoes can take thousands of years to form, others can grow overnight. For example, the cinder cone volcano Paricutin appeared in a Mexican cornfield on February 20, 1943. Within a week it was 5 stories tall, and by the end of a year it had grown to more than 336 meters tall. It ended its grown in 1952, at a height of 424 meters. By geology standards, that’s pretty quick.
Detailed view from space of the ash plume caused by the Eyjafjallajökull volcano in 2010. Credit: NASA
5. There are 20 Volcanoes Erupting Right Now:
Somewhere, around the world, there are likely about 20 active volcanoes erupting as you’re reading this. Some are experiencing new activity, others are ongoing. Between 50-70 volcanoes erupted last year, and 160 were active in the last decade. Geologists estimate that 1,300 erupted in the last 10,000 years.
Three quarters of all eruptions happen underneath the ocean, and most are actively erupting and no geologist knows about it at all. One of the reasons is that volcanoes occur at the mid ocean ridges, where the ocean’s plates are spreading apart. If you add the underwater volcanoes, you get an estimate that there are a total of about 6,000 volcanoes that have erupted in the last 10,000 years.
6. Volcanoes are Dangerous:
But then you knew that. Some of the most deadly volcanoes include Krakatoa, which erupted in 1883, releasing a tsunami that killed 36,000 people. When Vesuvius exploded in AD 79, it buried the towns of Pompeii and Herculaneum, killing 16,000 people.
Image of Mt. Vesuvius, captured in 2000 by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard the Terra satellite. Credit: NASA/EO
Mount Pelee, on the island of Martinique destroyed a town with 30,000 people in 1902. The most dangerous aspect of volcanoes are the deadly pyroclastic flows that blast down the side of a volcano during an eruption. These contain ash, rock and water moving hundreds of kilometers an hour, and hotter than 1,000 degrees C.
7. Supervolcanoes are Really Dangerous:
Geologists measure volcano eruptions using the Volcano Explosivity Index, which measures the amount of material released. A “small” eruption like Mount St. Helens was a 5 out of 8, releasing a cubic kilometer of material. The largest explosion on record was Toba, thought to have erupted 73,000 years ago.
It released more than 1,000 cubic kilometers of material, and created a caldera 100 km long and 30 kilometers wide. The explosion plunged the world into a world wide ice age. Toba was considered an 8 on the VEI.
8. The Tallest Volcano in the Solar System isn’t on Earth:
That’s right, the tallest volcano in the Solar System isn’t on Earth at all, but on Mars. Olympus Mons, on Mars, is a giant shield volcano that rises to an elevation of 27 km, and it measures 550 km across. Scientists think that Olympus Mons was able to get so large because there aren’t any plate tectonics on Mars. A single hotspot was able to bubble away for billions of years, building the volcano up bigger and bigger.
Mauna Kea observed from space. Credit: NASA/EO
9. The Tallest and Biggest Volcanoes on Earth are side by side:
The tallest volcano on Earth is Hawaii’s Mauna Kea, with an elevation of 4,207 meters. It’s only a little bigger than the largest volcano on Earth, Mauna Loa with an elevation of only 4,169 meters. Both are shield volcanoes that rise up from the bottom of the ocean. If you could measure Mauna Kea from the base of the ocean to its peak, you’d get a true height of 10,203 meters (and that’s bigger than Mount Everest).
10. The Most Distant Point from the Center of the Earth is a Volcano:
You might think that the peak of Mount Everest is the most distant point from the center of the Earth, but that’s not true. Instead, it’s the volcano Chimborazo in Ecuador. That’s because the Earth is spinning in space and is flattened out. Points at the equator are further from the center of the Earth than the poles. And Chimborazo is very close to the Earth’s equator.
