Strange Landscapes on Mars were Created by Explosive Volcanoes

Scientists first observed the Medusae Fossae Formation (MFF) in the 1960s, thanks to the efforts of the Mariner spacecraft. This massive deposit of soft, sedimentary rock extends for roughly 1,000 km (621 mi) along the equator and consists of undulating hills, abrupt mesas, and curious ridges (aka. yardangs) that appear to be the result of wind erosion. What’s more, an unusual bump on top of this formation also gave rise to a UFO conspiracy theory.

Needless to say, the formation has been a source of scientific curiosity, with many geologists attempting to explain how it could have formed. According to a new study from Johns Hopkins University, the region was the result of volcanic activity that took place on the Red Planet more than 3 billion years ago. These findings could have drastic implications for scientists’ understanding of Mars’ interior and even its past potential for habitability.

The study – which recently appeared in the Journal of Geophysical Research: Planets under the title “The Density of the Medusae Fossae Formation: Implications for its Composition, Origin, and Importance in Martian History” – was conducted by Lujendra Ojha and Kevin Lewis, a Blaustein scholar and an assistant professor in the department of Earth and Planetary Science at Johns Hopkins University, respectively.

Perspective view of Medusa Fossae looking south-east. Copyright: ESA/DLR/FU Berlin (G. Neukum)

Ojha’s past work includes finding evidence that water on Mars occurs in seasonal brine flows on the surface, which he discovered in 2010 as an undergraduate student. Lewis, meanwhile, has dedicated much of his academic carreer to the in-depth study of the nature of sedimentary rock on Mars for the sake of determining what this geological record can tell us about that planet’s past climate and habitability.

As Ojha explained, the study of the Medusa Fossae Formation is central to understanding Mars geological history. Much like the Tharsus Montes region, this formation was formed at a time when the planet was still geologically active. “This is a massive deposit, not only on a Martian scale, but also in terms of the solar system, because we do not know of any other deposit that is like this,” he said.

Basically, sedimentary rock is the result of rock dust and debris accumulating on a planet’s surface and becoming hardened and layered over time. These layers serve as a geological record, indicating what types of processes where taking place on the surface at the time that the layers were deposited. When it comes to the Medusae Fossae Formation, scientists were unsure whether wind, water, ice or volcanic eruptions were responsible for the deposits.

In the past, radar measurements were made of the formation that suggested that Medusae Fosssae had an unusual composition. However, scientists were unsure whether the formation was made of highly porous rock or a mixture of rock and ice. For the sake of their study, Ojha and Lewis used gravity data from various Mars orbiters to measure the formation’s density for the first time.

An isolated hill in the Medusae Fossae Formation. The effect of wind erosion on this hill is evident by its streamlined shape. Credit: High Resolution Stereo Camera/European Space Agency

What they found was that the rock is unusually porous and about two-thirds as dense as the rest of the Martian crust. They also used radar and gravity data to show that the Formation’s density was too great to be explained by the presence of ice. From this, they concluded that the heavily-porous rock had to have been deposited by volcanic eruptions when Mars was still geologically active – ca. 3 billion years ago.

As these volcanoes exploded, casting ash and rock into the atmosphere, the material would have then fallen back to the surface, building up layers and streaming down hills. After enough time, the ash would have cemented into rock, which was slowly eroded over time by Martian winds and dust storms, leaving the Formation scientists see there today. According to Ojha, these new findings suggest that Mars’ interior is more complex than previously thought.

While scientists have known for some time that Mars has some volatiles – i.e. water, carbon dioxide and other elements that become gas with slight increases in temperature –  in its crust that allow for periodic explosive eruptions to occur on the surface, the kind of eruption needed to create the Medusa Fossae region would have been immense. This indicates that the planet may have massive amounts of volatiles in its interior. As Ojha explained:

“If you were to distribute the Medusae Fossae globally, it would make a 9.7-meter (32-foot) thick layer. Given the sheer magnitude of this deposit, it really is incredible because it implies that the magma was not only rich in volatiles and also that it had to be volatile-rich for long periods of time.”

An artist's impression of the ancient Martian ocean. When two meteors slammed into Mars 3.4 billion years ago, they triggered massive, 400 ft. tsunamis that reshaped the coastline. Image: ESO/M. Kornmesser, via N. Risinger
According to Ojha and Lewis’ study, the eruption that created the Medusa Fossae Formation would have covered Mars in a global ocean. Image: ESO/M. Kornmesser, via N. Risinger

In addition, this activity would have had a drastic impact on Mars’ past habitability. Basically, the formation of the Medusae Fossae Formation would have occurred during a pivotal point in Mars’ history. After the eruption occurred, massive amounts of carbon dioxide and (most likely) methane would have been ejected into the atmosphere, causing a significant greenhouse effect.

In addition, the authors indicated that the eruption would have ejected enough water to cover Mars in a global ocean more than 9 cm (4 inches) in thickness. This resulting greenhouse effect would have been enough to keep Mars’ surface warm to the point that the water would remain in a liquid state. At the same time, the expulsion of volcanic gases like hydrogen sulfide and sulfur dioxide would have altered the chemistry of Mars’ surface and atmosphere.

All of this would have had a drastic impact on the planet’s potential habitability. What’s more, as Kevin Lewis indicated, the new study shows that gravity surveys have the potential to interpret Mars’ geological record. “Future gravity surveys could help distinguish between ice, sediments and igneous rocks in the upper crust of the planet,” he said.

Studying Mars surface features and geological history is a lot like peeling an onion. With every layer we peel back, we get another piece of the puzzle, which together adds up to a rich and varied history. In the coming years and decades, more robotic missions will be studying the Red Planet’s surface and atmosphere in preparation for an eventual crewed mission by the 2030s.

All of these missions will allow us to learn more about Mars warmer, wetter past and whether or not may have existed there at some time (or perhaps, still does!)

Further Reading: AGU, Journal of Geophysical Research

Early Earth Was Almost Entirely Underwater, With Just A Few Islands

Earth's Hadean Eon is a bit of a mystery to us, because geologic evidence from that time is scarce. Researchers at the Australian National University have used tiny zircon grains to get a better picture of early Earth. Credit: NASA

It might seem unlikely, but tiny grains of minerals can help tell the story of early Earth. And researchers studying those grains say that 4.4 billion years ago, Earth was a barren, mountainless place, and almost everything was under water. Only a handful of islands poked above the surface.

Scientists at the Australian National University are behind this study, led by researcher Dr. Antony Burnham. The mineral grains in the study are the oldest rocks ever found. They’re 4.4 billion year old zircon mineral grains from the Jack Hills of Western Australia, where they were preserved in sandstone formations.

4.4 billion years ago, the Earth was in what is called the ‘Hadean Eon’. This time period is poorly understood, because there is no rock record dating from that time. This is where the zircon mineral grains come in.

“The history of the Earth is like a book with its first chapter ripped out with no surviving rocks from the very early period, but we’ve used these trace elements of zircon to build a profile of the world at that time.” – Lead Researcher Dr. Antony Burnham, Australian National University

In a sense, these zircon grains are the missing pages.

Zircon’s chemical name is zirconium silicate, and it’s found almost everywhere in the Earth’s crust. This study focuses on what’s called detrital zircon, which is formed in igneous rocks, but then survives over time until deposited in sedimentary rocks. Zircon grains are typically very small, about 0.1 to 0.3 mm in size.

Zircon crystals from the Jack Hills in western Australia are the oldest rock fragments ever found. Image: Stuart Hay, ANU
Zircon crystals from the Jack Hills in western Australia are the oldest rock fragments ever found. Image: Stuart Hay, ANU

Zircon commonly contains traces of thorium and uranium, which means they can be easily dated by modern dating methods. Zircon can survive a lot of geologic processes like metamorphism, which explains their usefulness in studying the early Earth. They’re not easily destroyed, and they have a story to tell us.

The zircon grains were crystallized in magma about 500 million years after the Earth formed. As a result, they offer rare insights into conditions on Earth at the time. The zircon grains in question are referred to as detritus, because they formed in magma but were deposited in the geologically-important sandstone at Jack Hills, Australia. The detritus grains were compared to a second type of zircon grain which were formed directly in the sedimentary formations.

By distinguishing between the two types, researchers gain a new geochemical tool to understand early Earth.

The Jack Hills in Western Australia contain the oldest rocks known to exist on Earth. A team studying them concludes that early Earth was mostly a water world. By NASA Earth Observatory - http://earthobservatory.nasa.gov/Study/Zircon/zircon.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=738512
The Jack Hills in Western Australia contain the oldest rocks known to exist on Earth. A team studying them concludes that early Earth was mostly a water world. By NASA Earth Observatory – http://earthobservatory.nasa.gov/Study/Zircon/zircon.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=738512

“We used the granites of southeast Australia to decipher the link between zircon composition and magma type, and built a picture of what those missing rocks were,” he said.

“Our research indicates there were no mountains and continental collisions during Earth’s first 700 million years or more of existence – it was a much more quiet and dull place,” says Dr. Burnham from the ANU Research School of Earth Sciences.

The detrital zircons formed elsewhere, but were deposited in the Jack Hills formation. By Robert Simmon, NASA - http://earthobservatory.nasa.gov/Study/Zircon/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4258701
The detrital zircons formed elsewhere, but were deposited in the Jack Hills formation. By Robert Simmon, NASA – http://earthobservatory.nasa.gov/Study/Zircon/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4258701

“Our findings also showed that there are strong similarities with zircon from the types of rocks that predominated for the following 1.5 billion years, suggesting that it took the Earth a long time to evolve into the planet that we know today.” The team’s results are published in the journal Nature Geoscience, and is titled “Formation of Hadean granites by melting of igneous crust.”

Dr. Antony Burnham from the Australian National University's Research School of Earth Sciences, led this study. Image: Stuart Hay, ANU.
Dr. Antony Burnham from the Australian National University’s Research School of Earth Sciences, led this study. Image: Stuart Hay, ANU.

This is not the first time that ancient, detrital zircons have been at the center of scientific studies of early Earth. In a previous study, they were used to conclude that Earth had a significant hydrosphere 4.3 billion years ago.

Earth Just Got A New Continent

We tend to lump New Zealand and Australia together. They’re similar culturally and share the same geographical position, relative to North America and Europe, anyway. But according to a new paper published in the Geological Society of America Today, it looks like New Zealand and their neighbor New Caledonia are actually their own continent: ‘Zealandia.’

Continent means something different to geographers and geologists. To be considered a geological continent, like Zealandia, the area in question has to satisfy a few conditions:

  • the land in question has to be higher than the ocean floor
  • it has to include a broad range of siliceous igneous, metamorphic, and sedimentary rocks
  • it has to have thicker crust than the ocean floor that surrounds it
  • it has to have well-defined limits, and be large enough to be considered a continent

In Geology, the first three points are well-understood. But as the authors say in the introduction to their paper, “…the last point—how “major” a piece of continental crust has to be to be called a continent—is almost never discussed… .” Since the Earth has so many micro-continents and continental fragments, defining how large something has to be to be called a continent is challenging. But the researchers did their homework.

They noted that the term “Zealandia” has been used before to describe New Zealand and surrounding regions. But the boundaries were never fully explored. 94% of this new continent is submerged, which helps explain why it’s taken this long to be identified.

This map shows the spatial limits of Zealandia. Note the dotted red line that delineates continental crust from ocean crust. Zealandia is also bisected by a plate boundary between the Pacific Plate and the Australian Plate. Image: Mortimer et. al. 2017, GSA Today

Zealandia seemed to be a collection of broken pieces, but new data collected over the years has challenged that interpretation. Recent satellite data has given us new gravity and elevation maps of the seafloor. This data has shown that Zealandia is a unified region large as large as India.

“This is not a sudden discovery but a gradual realization; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper.”

As the authors point out in their paper, it took a while to determine that Zealandia is a continent. There was no Eureka moment. “This is not a sudden discovery but a gradual realization; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper.”

Besides satisfying our intellectual curiosity about our planet, the discovery is important for other reasons. A proper understanding of the plate structures and continental boundaries is important to other sciences, and may trigger further understandings that we can’t predict yet. It may also point to other areas of research.

Also, many treaties rely on the agreed upon delineation of maritime and continental boundaries, including rights to fish stocks and underground resources. While the recognition of Zealandia seems clear from a scientific standpoint, it remains to be seen if it will be accepted politically.

Meteorite Confirms 2 Billion Years of Volcanic Activity on Mars

Color Mosaic of Olympus Mons on Mars

Mars is renowned for having the largest volcano in our Solar System, Olympus Mons. New research shows that Mars also has the most long-lived volcanoes. The study of a Martian meteorite confirms that volcanoes on Mars were active for 2 billion years or longer.

A lot of what we know about the volcanoes on Mars we’ve learned from Martian meteorites that have made it to Earth. The meteorite in this study was found in Algeria in 2012. Dubbed Northwest Africa 7635 (NWA 7635), this meteorite was actually seen travelling through Earth’s atmosphere in July 2011.

A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani
A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani

The lead author of this study is Tom Lapen, a Geology Professor at the University of Houston. He says that his findings provide new insights into the evolution of the Red Planet and the history of volcanic activity there. NWA 7635 was compared with 11 other Martian meteorites, of a type called shergottites. Analysis of their chemical composition reveals the length of time they spent in space, how long they’ve been on Earth, their age, and their volcanic source. All 12 of them are from the same volcanic source.

Mars has much weaker gravity than Earth, so when something large enough slams into the Martian surface, pieces of rock are ejected into space. Some of these rocks eventually cross Earth’s path and are captured by gravity. Most burn up, but some make it to the surface of our planet. In the case of NWA 7635 and the other meteorites, they were ejected from Mars about 1 million years ago.

“We see that they came from a similar volcanic source,” Lapen said. “Given that they also have the same ejection time, we can conclude that these come from the same location on Mars.”

Taken together, the meteorites give us a snapshot of one location of the Martian surface. The other meteorites range from 327 million to 600 million years old. But NWA 7635 was formed 2.4 billion years ago. This means that its source was one of the longest lived volcanoes in our entire Solar System.

This false color X-ray of NWA 7635 shows the meteorite’s mineralogy mineral textures. O, olivine; P, plagioclase (maskelynite); C, clinopyroxene (augite). Chemical compositions: Fe (purple), Mg (green), Ca (blue), Ti (magenta), and S (yellow). Purple colors in the mesostasis represent Fe-rich augite. You’re welcome, mineral nerds. Image: Lapen et. al.

Volcanic activity on Mars is an important part of understanding the planet, and whether it ever harbored life. It’s possible that so-called super-volcanoes contributed to extinctions here on Earth. The same thing may have happened on Mars. Given the massive size of Olympus Mons, it could very well have been the Martian equivalent of a super-volcano.

The ESA’s Mars Express Orbiter sent back images of Olympus Mons that showed possible lava flows as recently as 2 million years ago. There are also lava flows on Mars that have a very small number of impact craters on them, indicating that they were formed recently. If that is the case, then it’s possible that Martian volcanoes will be visibly active again.

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
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

Continuing volcanic activity on Mars is highly speculative, with different researchers arguing for and against it. The relatively crater-free, smooth surfaces of some lava features on Mars could be explained by erosion, or even glaciation. In any case, if there is another eruption on Mars, we would have to be extremely lucky for one of our orbiters to see it.

But you never know.

What is a Butte?

During the 16h century, Spanish explorers ventured north from Mexico looking for gold and the legendary “Seven cities of Cibola”. What they found instead were some of the most amazing natural formations in the world, which are today known as “buttes”. To the local Hopi, Navajo, and other indigenous nations, these features – which resemble tall, isolated plateaus – have been regarded as sacred sites since time immemorial.

By the beginning of the 19th century, the term “butte” entered common parlance and quickly became adopted by the geological community. And while their existence was something of a mystery for thousands of years, spawning mythological connections and folk tales, improvements in the fields of Earth sciences and geology have led scientists to understand what these features are and how they are formed.

Definition:

By definition, a Butte is a conspicuous isolated hill with steep, often vertical sides and a small, relatively flat top. The word “butte” comes from a French word meaning “small hill”. They are not to be confused with Mesas or Plateaus, which are typically differentiated based on the fact that their top surfaces are larger than their vertical faces, while a butte is taller than it is wide. However, definitions of the surface areas of mesas and buttes vary.

The Courthouse Butte, located near the town of Sedona, Arizona. Credit: Wikipedia Commons

One source states that a mesa has a surface area of less than 10 square kilometers, while a butte has a surface area less than 1,000 square meters. Another source states that the surface area of a mesa is larger than 2.59 square kilometers. However, all sides are in agreement that is the difference between their vertical and horizontal measurements that are key.

Formation:

Both buttes and mesas are formed by the same geological process, which involves the physical weathering of rock formations. Essentially, this involves the surface material of a hill or mountain (the cap rock) resists wind and water erosion, but the underlying materials do not. Over time, the underlying material is stripping away, leaving an isolated, standing feature with a flat top.

The top layer of a butte is a hardened layer of rock that is resistant to erosion. This top layer, called the cap rock, is usually composed of sedimentary rock, but sometimes is the remains of cooled and hardened lava that had spread out across the landscape in repeated flows from fissures or cracks in the ground.

Beneath this flat, protective cap of rock, horizontal layers of softer sedimentary rock are found. To varying degrees, these layers are not as resistant to wind and water erosion. As a result, when the softer rock is stripped away, a standing, isolated rock is left behind. Typically, buttes are found in arid and semiarid regions.

Merrick’s Butte, in Monument Valley, Utah. Credit: Wikipedia Commons/Ernst Brötz

Because water evaporates quickly in these normally dry environments, plants and other ground cover are scarce. Left exposed to the action of running water, the bare sides of the softer rock layers of buttes are eroded away over time. The base of these landforms is often gently sloped, contrasting with the almost-vertical sides leading down from the top. Rock material that has been eroded from the sides is carried downward, forming this sloping base.

Notable Buttes:

Because of their isolated and imposing nature, many buttes have become geographical land markers and major tourist destinations. They also figured prominently in the spiritual beliefs and creation myths of the indigenous peoples across North America. Buttes can be found all over North America, though they are most commonly found in the arid regions of the American Southwest.

For example, there is the Courthouse Butte, a prominent feature located just north of the Village of Oak Creek, and south of the town of Sedona in Yavapai County. Then there’s the Elephant Butte, which is located in the Elephant Butte Lake State Park in Sierra Country, New Mexico,. This geographical feature is so-named because of the combination of a vertical side and a sloping side, which resemble the shape of an elephant.

Bear Butte in South Dakota also has a long history of being a geological and cultural significant feature. Long before the arrival of European settlers, Bear Butte featured prominently in the religious and mythological traditions of the Lakota, Sioux and Cheyenne nations. To the Lakota and Sioux, the feature was known as “Matho Paha” (literally, Bear Mountain), while the Cheyenne referred to it as Nahkohe-vose (“bear hill”).

Bear Butte (aka. Bear Mountain or Bear Hill),, located in South Dakota. Credit: Jerrye & Roy Klotz, MD.

According to Cheyenne mythology, it was here that Ma’heo’o (God, or the Great Spirit) imparted the knowledge from which the Cheyenne base their religion, political, social and economic customs to the prophet Sweet Medicine. Today, the location remains a sacred site for many indigenous peoples, who make pilgrimages to leave prayer cloths and tobacco bundles tied to branches taken from the trees that surround the butte.

To the north, buttes can be found in the Canadian provinces of Saskatchewan, Alberta and British Columbia, in regions that are arid and semi-arid. For example, there is the Pilot Butte, which is located in southern Saskatchewan, near the town of the same name. This feature’s name is derived from the fact that the flat-topped butte served as a lookout for hunting buffalo and as a landmark for planes approaching the provincial capitol of Regina.

And there’s Lone Butte, a prehistoric basalt feature located in the southern Cariboo Plateau in central British Columbia. A part of the geological formation known as the Chilcotin Group, this feature was formed roughly six million years ago as a result of the extensive volcanic activity in the region.

Buttes on Other Planets:

Buttes have also been spotted on other planets in the Solar System, where they are also linked to geological activity and erosion. For example, NASA’s Curiosity rover mission has taken extensive images of the area currently known as the “Murray Buttes” region on Mars, which is located in the lower region of Mount Sharp (in the Gale Crater). In addition, Curiosity has taken drill samples from the surface rock in the region.

Wide-angle mosaic of a butte with sandstone layers showing cross-bedding, in the Murray Buttes region on lower Mount Sharp. Credit: NASA/JPL/MSSS/Ken Kremer/Marco Di Lorenzo

At one time, this crater was believed to be a standing body of water, which was largely responsible for the creation of these features. As Ashwin Vasavada, the Curiosity Project Scientist of NASA’s Jet Propulsion Laboratory, described the area as being “reminiscent of parts of the American southwest because of its butte and mesa landscape. In both areas, thick layers of sediment were deposited by wind and water, eventually resulting in a “layer cake” of bedrock that then began to erode away as conditions changed.  In both places, more resistant sandstone layers cap the mesas and buttes because they protect the more easily eroded, fine-grained rock underneath. ”

Buttes have also been photographed by the Mars Reconnaissance Orbiter’s (MRO) HiRISE instrument. These include the many buttes spotted in the Candor Chasma region – part of the Valles Marineris canyon system – back in 2007. The Viking 1 orbiter also noted the presence of many buttes in the Cydonia region during its flyby in 1976 – the occasion when it took pictures of the “Face of Mars” (later revealed to be a mesa).

Much like polygonal ridges that have been observed in the Medusae Fossae region and other locations across Mars (and Earth), these features are believed to be the remains of volcanic rock that remained in place after the surrounding rock was stripped away by erosion.

Ongoing studies into the various forces that shape our planet has allowed us to understand just how dynamic and changing it is. In addition, developments in space exploration and the planetary sciences have helped us to realize that Earth has a lot in common with other planets in our Solar System.

We have written many articles about geological formations for Universe Today. Here’s What is the Bakken Formation?, What is a Volcanic Neck?, What is the Earth’s Mantle Made Of?, What are Volcanoes?, What is the Difference Between Active and Dormant Volcanoes? and Stunning New Images of Mars from Curiosity Rover.

If you’d like more info on the Butte, check out the U.S. Geological Survey Website. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.

Sources:

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:

470 Million Year Old Meteorite Discovered In Swedish Quarry

Osterplana 65, the meteorite at the heart of a mystery. This meteorite is different than the thousands of other meteorites in collections around the world. Image: Birger Schmitz

470 million years ago, somewhere in our Solar System, there was an enormous collision between two asteroids. We know this because of the rain of meteorites that struck Earth at that time. But inside that rain of meteorites, which were all of the same type, there is a mystery: an oddball, different from the rest. And that oddball could tell us something about how rocks from space can change ecosystems, and allow species to thrive.

This oddball meteorite has a name: Osterplana 65. It’s a fossilized meteorite, and it was found in a limestone quarry in Sweden. Osterplana 65 fell to Earth some 470 mya, during the Ordovician period, and sank to the bottom of the ocean. There, it became sequestered in a bed of limestone, itself created by the sea-life of the time.

The Ordovician period is marked by a couple thing: a flourishing of life similar to the Cambrian period that preceded it, and a shower of meteors called the Ordovician meteor event. There is ample evidence of the Ordovician meteor event in the form of meteorites, and they all conform to similar chemistry and structure. So it’s long been understood that they all came from the same parent body.

The collision that caused this rain of meteorites had to have two components, two parent bodies, and Osterplana 65 is evidence that one of these parent bodies was different. In fact, Ost 65 represents a so far unknown type of meteorite.

The faint grey lines in this electron image of Ost 65 are called "shock deformation lamellae" and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt
The faint grey lines in this electron image of Ost 65 are called “shock deformation lamellae” and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt

The study that reported this finding was published in Nature on June 14 2016. As the text of the study says, “Although single random meteorites are possible, one has to consider that Öst 65 represents on the order of one per cent of the meteorites that have been found on the mid-Ordovician sea floor. “It goes on to say, “…Öst 65 may represent one of the dominant types of meteorites arriving on Earth 470 Myr ago.”

The discovery of a type of meteorite falling on Earth 470 mya, and no longer falling in our times, is important for a couple reasons. The asteroid that produced it is probably no longer around, and there is no other source for meteorites like Ost 65 today.

The fossil record of a type of meteorite no longer in existence may help us unravel the story of our Solar System. The asteroid belt itself is an ongoing evolution of collision and destruction. It seems reasonable that some types of asteroids that were present in the earlier Solar System are no longer present, and Ost 65 provides evidence that that is true, in at least one case.

Ost 65 shows us that the diversity in the population of meteorites was greater in the past than it is today. And Ost 65 only takes us back 470 mya. Was the population even more diverse even longer ago?

The Earth is largely a conglomeration of space rocks, and we know that there are no remnants of these Earthly building blocks in our collections of meteorites today. What Ost 65 helps prove is that the nature of space rock has changed over time, and the types of rock that came together to form Earth are no longer present in space.

Ost 65 was found in amongst about 100 other meteorites, which were all of the same type. It was found in the garbage dump part of the quarry. It’s presence is a blemish on the floor tiles that are cut at the quarry. Study co-author Birgen Schmitz told the BBC in an interview that “It used to be that they threw away the floor tiles that had ugly black dots in them. The very first fossil meteorite we found was in one of their dumps.”

According to Schmitz, he and his colleagues have asked the quarry to keep an eye out for these types of defects in rocks, in case more of them are fossilized meteorites.

Finding more fossilized meteorites could help answer another question that goes along with the discovery of Ost 65. Did the types and amounts of space rock falling to Earth at different times help shape the evolution of life on Earth? If Ost 65 was a dominant type of meteorite falling to Earth 470 mya, what effect did it have? There appear to be a confounding number of variables that have to be aligned in order for life to appear and flourish. A shower of minerals from space at the right time could very well be one of them.

Whether that question ever gets answered is anybody’s guess at this point. But Ost 65 does tell us one thing for certain. As the text of the study says, “Apparently there is potential to reconstruct important aspects of solar-system history by looking down in Earth’s sediments, in addition to looking up at the skies.”

Massive 400 Ft. Tsunamis On Ancient Mars

An artist's impression of the ancient Martian ocean. When two meteors slammed into Mars 3.4 billion years ago, they triggered massive, 400 ft. tsunamis that reshaped the coastline. Image: ESO/M. Kornmesser, via N. Risinger

About 3.4 billion years ago, (according to a new study) when the Late Heavy Bombardment had ended, and the first cells resembling prokaryotes were appearing on Earth, two enormous meteoroids slammed into the ancient, frigid ocean on Mars. These impacts generated massive 400 ft. high tsunamis that reshaped the shoreline of the Martian ocean, leaving behind fields of sediments and boulders.

It was long thought that ancient Mars had oceans. Sedimentary deposits discovered in the Martian north by radar in 2012 helped make the case for Martian oceans. 3.4 billion years ago, this ocean covered most of the Northern Martian lowlands. It’s thought that the ocean itself was fed by catastrophic flooding, perhaps fuelled by geothermal activity on Mars at the time.

These catastrophic tsunamis would have dwarfed most Earthly disasters. Waves 120 meters high would have swamped landmarks like the Statue of Liberty (93 m. high), and caused enormous destruction along the Martian coastline. If the research behind this new study stands up to scrutiny, then it will help prove the existence of the ancient Martian ocean.

The blue area in the above image is thought to be the location of a primordial ocean Mars. Image: NASA/JPL-Caltech/GSFC - Public Domain
The blue area in the above image is thought to be the location of a primordial ocean Mars. Image: NASA/JPL-Caltech/GSFC – Public Domain

The Martian surface shows the remains of an ancient ocean. In some areas, radar data shows a layer of water-borne sediment on top of a layer of volcanic rock. There’s also evidence of a shoreline, described by some scientists as being like a bathtub ring. The problems is, the shoreline can’t be seen everywhere it should be.

The tsunami hypothesis helps explain this missing shoreline.

According to the new study, led by Alexis Rodriguez, a Mars researcher at the Planetary Science Institute in Tucson Arizona, the tsunamis would have wiped away portions of the coastline, and left behind fields of sediment and boulders, and large backwash channels cut into the Martian surface.

The study is focussed on a specific region on Mars where a highland feature called Arabia Terra abuts the Chryse Planitia lowlands. This area was part of the shoreline of the Martian ocean. In that area, the team behind the study identified two separate geological formations that they say were created by two separate tsunami events.

The top image shows the shoreline of the ancient Martian shoreline at two separate times. The bottom images show debris left behind by the two tsunamis.  Image: Alexis Rodriguez.
The top image shows the shoreline of the ancient Martian shoreline at two separate times. The bottom images show debris left behind by the two tsunamis. Image: Alexis Rodriguez.

The first formation, and older of the two, looks every bit like a disturbed shoreline. An enormous wave washed over the beach, and in its wake deposited boulders over 10 meters across. Then, as the water drained back down into the ocean, it cut large backwash channels through its debris and boulder field.

A sequence of zoomed in images of the Martian surface in the study. A shows distances and elevations of backwash channels. B shows some of the channel-scoured, north-sloping highland mesas in blue. C shows the channelled surface, and D shows them in closer detail. Finally, E is zoomed in to show boulders as much as 10 m. in diameter. (Yellow bars are 10m.) Image: A,B:MOLA Science Team, MSS, JPL, NASA. C,D,E:  NASA/JPL/University of Arizona
A sequence of zoomed in images of the Martian surface in the study. (A) shows distances and elevations of backwash channels. (B) shows some of the channel-scoured, north-sloping highland mesas in blue. (C) shows the channelled surface, and (D) shows them in closer detail. Finally, (E) is zoomed in to show boulders as much as 10 m. in diameter. (Yellow bars are 10m.) Image: A,B:MOLA Science Team, MSS, JPL, NASA. C,D,E: NASA/JPL/University of Arizona

Then, some time passed. Millions of years, probably, until the second meteor hit, triggering another enormous tsunami. But this one behaved a little differently.

Conditions on Mars had changed by then, with temperatures dropping, and glaciers marching across the landscape, gouging out deep valleys on the surface of Mars. When the second tsunami hit the shore, its effect was different.

This time, the tsunami was more like an icy slurry, according to the team. Because of the cold temperatures, the icy water froze in place in some areas, before it could wash back into the ocean. The result? Deposits of frozen debris formed in dense lobes on the surface.

This long lobe of dark material on the surface of Mars was left behind when a tsunami of icy slush washed over the Martian coastline, freezing in place before it could wash back into the sea. Image: Alexis Rodriquez
This long lobe of dark material on the surface of Mars was left behind when a tsunami of icy flush washed over the Martian coastline, freezing in place before it could wash back into the sea. Image: Alexis Rodriquez

But according to Rodriguez, this is just a snapshot of a process that likely occurred multiple times in the history of Mars. Successive meteors could have caused successive mega-tsunamis that would have repeatedly wiped away evidence of a shoreline. This could have happened as often as every 3 million years.

This study isn’t the knockout blow that proves the existence of a Martian ocean in ancient times. But it is certainly intriguing, and is a reasonable hypothesis that explains missing shorelines.

Rodriguez intends to keep looking for other evidence of tsunamis on the Martian surface. If he finds more, it will help make the case for the meteor-tsunami explanation.

Rodriguez will also be visiting places on Earth that are analogues for the Martian surface of ancient times. This summer he plans on visiting high-altitude, cold, alpine lakes in Tibet, where he hopes to learn something about the processes and geological formations involved.

Even better would be a mission to Mars, to sample the area where the tsunamis came ashore. A group of small craters near the shore that were drenched by the tsunamis is of particular interest to Rodriguez and his team. Martian ocean water could have been trapped there for millions of years. This site could provide evidence about the briny nature of the ancient ocean on Mars, and possibly tell us something about the evolution of life there.

What is the Difference Between Lava and Magma?

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
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
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 magma. Credit: geologyclass.org
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!

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.

30 km Wide Asteroid Impacted Australia 3.4 Billion Years Ago

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
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
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 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
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.