Major Sites of Volcanism
Mars has the largest shield volcanoes in the solar system. It also has a wide range of other volcanic features. These include large volcanic cones, unusual patera structures, mare-like volcanic plains, and a number of other smaller features. However, volcanic features are not common. There are less than 20 named volcanoes on Mars, and only 5 of these are giant shields. Also, volcanism occurs mostly within three regions. Even the mare-like plains cluster near these regions. The main cluster of volcanoes and lavas is in Tharsis. A much smaller cluster of three volcanoes lies in Elysium. Lastly, a few paterae are near the Hellas impact basin.
Differences from Moon
Like the Moon, volcanism on Mars is very old. The mare-like plains on Mars are the same age as the lunar mare, roughly 3 to 3.5 billion years old. However, volcanism lasted much longer on Mars than on the Moon. It also seems to have changed over time. Volcanism in the highland paterae and mare-like plains on Mars stopped 3 billion years ago, but some of the smaller shields and cones erupted only 2 billion years ago. The giant shield volcanoes are even younger. These volcanoes formed between 1 and 2 billion years ago. The youngest lava flows on Olympus Mons are only 20 to 200 million years old. These flows are very small, however, and they probably represent the last gasp of martian volcanism. Thus, the odds of finding an active volcano on Mars today are very small.
Like the Moon, Mars shows no sign of plate tectonics. It has no long mountain chains, and there is no clear global pattern to the volcanism. Over half of Mars is heavily cratered like the lunar farside. Unlike the Moon, however, most martian volcanism lies outside large impact basins. Instead, the mare-like plains are mostly near the largest volcanoes. These plains also are not limited to the lowest elevations. Indeed, some lava plains are much higher than the cratered uplands. Lava plains may lie at lower elevations as well. However, thick layers of dust and sediment cover both the Northern Lowlands and the large basin floors. These layers reflect a long history of winds, glaciers and flood events. They also hide any volcanism that may have occurred in the low areas on Mars.
The concentration and duration of volcanism into these two regions are attributed to the evolution of a long-lived mantle hotspot.
More Mars Volcano Information can be found at the "Geology of Mars" website curated by Albert T. Hsui, University of Illinois at Urbana-Champaign.
As well as:
NASA’s Mars Exploration Program
NASA Human Spaceflight
Giant Shield Volcanoes
The giant shield volcanoes on Mars are truly huge. The largest are three times as high as the biggest Earth volcanoes. They also are bigger in diameter. Thus, the biggest volcano on Mars is comparable to a pile of nearly 100 Hawaiian volcanoes. Despite this difference in size, the Mars shields look a lot like shield volcanoes on Earth. Both have the same broad flat profiles, large central calderas, and similar lava flow features. The giant martian shields are also much older than any Earth volcano. The youngest lavas on the martian shields are about 20 to 200 million years old. The oldest lavas are near 2.5 billion years old. Thus, these giant volcanoes were active for billions of years. This may explain their large size. On Earth, plate tectonics is always moving volcanoes away from their magma sources. Such movements are very slow, but they mean that most Earth volcanoes have distinct lifetimes. In the Hawaiian islands, for instance, volcanism lasts fo only a few million years on any given island. In contrast, the lack of plate tectonics on Mars allowed volcanoes to just keep growing. The only limit on their final size was the volume of lavas available.
The giant shield volcanoes on Mars are much larger than any feature on Earth. Shown here is a graphic comparison of Olympus Mons to the two largest mountains on Earth. (Note: Mount Everest is not a volcano.) Olympus Mons is the largest and youngest volcano on Mars. It is nearly 27 km high, and about 700 km across. Its summit is nearly 72 km wide, which is close to the size of Mount Everest and Mauna Kea. Mauna Kea is the largest Earth volcano. It rises nearly 10 km from the ocean floor, and is about 120 km wide. Mount Everest is a plate tectonic feature, created by uplift and erosion in the Himalayan Mountains. It is about 9 km above sea level, and it sits in a mountain range roughly 200 km wide. (figure is from NASA SP-4212, p. 366, and has a 2x vertical exaggeration.)
This picture clearly shows how large and flat Olympus Mons is. Although the volcano is nearly 27 km high, it is over 20 times wider than it is tall. Thus, most of the volcano has a fairly gentle surface slope. The image also shows the distinct cliff which marks the base of Olympus Mons. In places, this scarp is up to 6 km high. In other places, it is hidden under lava flows cascading out into the surrounding lava plains. This cliff is unique among the giant shield volcanoes on Mars. The rough, crinkly patches around Olympus Mons are also unusual. They form the Olympus Mons Aureole.
Both the Aureole and the basal cliff are poorly understood. However, their origins may be related. In one theory, the basal cliff was formed by many large landslides. The Aureole marks material piled up at the bottom of these landslides.
Olympus Mons (from Orbit)
This picture clearly shows how large and flat Olympus Mons is. Although the volcano is nearly 27 km high, it is over 20 times wider than it is tall. Thus, most of the volcano has a fairly gentle surface slope. The image also shows the distinct cliff which marks the base of Olympus Mons. In places, this scarp is up to 6 km high. In other places, it is hidden under lava flows cascading out into the surrounding lava plains. This cliff is unique among the giant shield volcanoes on Mars. The rough, crinkly areas around Olympus Mons are also unusual. They form the Olympus Mons Aureole. Both the Aureole and the basal cliff are poorly understood. However, their origins may be related. In one theory, the basal cliff was formed by many large landslides. The Aureole marks material piled up at the bottom of these landslides. (Viking image mosaic from Carr et al, 1977, J. Geophys. Res., vol. 82, p. 3996.)
Olympus Mons (3D)
This image provides a perspective view of Olympus Mons. North is to the left of the image. Note the clear basal cliff and the gentle rolling slopes higher up the volcano. The faint radial texture above the basal cliff marks the traces of thousands of separate lava flows. To the left and lower right, we can also see places where lavas have flowed over the basal cliff.
Olympus Mons Caldera
This image shows the summit caldera on Olympus Mons. It is nearly 90 km long by 60 km wide, and it contains 6 overlapping pit craters. These craters resemble the calderas found on shield volcanoes on Earth. Thus, they are probably not eruption vents. Rather, they are probably collapse pits that formed in the roof of a deeper magma chamber. The size of these pits suggests that the magma chambers in Olympus Mons were fairly large. Likely diameters range from about 20 km to over 60 km. For comparison, calder as in the Hawaiian Islands range in diameter from ~3-5 km up to ~18 km. (Viking Orbiter image 890A68, from Lunar & Planetary Institute slide set Volcanic Features of Hawaii and Other Planets.)
This image shows the three giant volcanoes known as the Tharsis Montes. Arsia Mons is in the lower left, Pavonis Mons is in the middle, and Ascreus Mons is in the upper right. Olympus Mons lies off the image to the upper left. These volcanoes lie in the center of the Tharsis region, and they form a line nearly 1500 km long. They are nearly 700 km apart, and each reaches nearly the same height as Olympus Mons (~25-27 km). These volcanoes are located on a large pile of lava flows , however, which is nearly 10 km high. Thus, the volcanoes are really only about 15 km tall. (Note: This is still more than half again the height of the Hawaiian volcanoes on Earth.) All three volcanoes seem to have formed together, and they were active for a very long time. Still, Arsia Mons appears to be slightly older than Pavonis Mons, and Ascreus Mons seems to be slightly younger. Therefore, volcanism in the Tharsis region may have slowly shifted north over time. A similar progression of volcanism is found in the Hawaiian Islands. Thus, the giant shield volcanoes on Mars may have formed over a mantle hotspot like that in Hawaii. (from digital mosiac of Viking 1 images, prepared for NASA by the U.S. Geologic Survey, published on the Mars CD-ROM VO_2014.)
This image shows Elysium Mons. This volcano is much smaller than the Tharsis volcanoes. It is only 9 km tall, and is about 240 km in diameter. Thus, it is nearly the same size as the largest Hawaiian volcanoes. Like the Tharsis Montes, however, Elysium Mons sits on a large pile of lava flows. This lets it rise 12 km above the mean planetary elevation. It grades so smoothly into the surrounding lava plains that its base is hard to see. A smaller volcano, Albor Tholus, can also be seen. It is partly buried by the lava plains surrounding Elysium Mons. Note the number of channels in this image. In places, these features look a lot like lunar sinuous rilles. They are all large flat-bottomed valleys. They begin abruptly in broad depressions. And their sources seem to form a ring centered on Elysium Mons. Like sinuous rilles on the Moon, these valleys might be lava channels. However, water is a more likely cause for their formation. Specifically, ground ice appears to have been widespread in the Elysium region. Such ice is easily melted near hot magmas. Thus, melt water provides a ready source for erosion in the Elysium region. Further, the loss of a lot of ground ice can cause collapse depressions near the channel sources. (from digital mosaic of Viking 1 images, prepared for NASA by the U.S. Geologic Survey, published on the Mars CD-ROM VO_2014.)
Volcanic Cones (on Mars)
Mars has a number of volcanoes with diameters between 50 and 150 km. These volcanoes are thus the same size as many large Earth volcanoes. Most are found within the Tharsis and Elysium regions. However, they are all older than the giant shield volcanoes. Thus, many have been partly buried by younger lavas. These volcanoes are divided into two general types. The first type are called "paterae," after the Greek word for a shallow saucer or bowl. They are fairly flat, they generally have little relief, and they often have large calderas. The second class of volcanoes are called "tholi." These volcanoes have much steeper sides, and they typically are taller than the patera structures. Both types apparently formed mostly from basaltic lava flows. Thus, they are much like Earth shield volcanoes. Their different appearances may mark either different depths of burial or changes in the nature of volcanism.
Biblis Patera is one of two volcanoes located near the center of Tharsis volcanism. With Ulysses Patera, it lies almost halfway between Olympus Mons and the southern Tharsis Montes. It is nearly 170 km long by over 100 km wide, and it has a central caldera nearly 55 km in diameter. It appears to be some 2 to 3 km tall. Biblis Patera is probably between 2 and 2.8 billion years old. However, it is surrounded by much younger lava flows. These flows come from Pavonis Mons to the east, and are clearest in the lower left of the image. The elongate shape of Biblis partly reflects the slope of these flows. Biblis is also clearly cut by a number of faults and graben. Note that some of these faults are buried by younger lavas along the edge of the volcano. This suggests that Biblis was modified by several episodes of tectonism and volcanism. (Viking Orbiter images 44B48 & 44B50, from Plescia (1994) Icarus, vol. 111.)
Ceraunius Tholus lies on the northeast edge of the Tharsis region. It is roughly 120 km long by 95 km wide, and it is about 2-3 km in height. It is probably close to 3 billion years old. Although running water formed the vast majority of channels on Mars, Ceraunius also shows two likely lava channels. One is the large channel in the upper center. Note the size of this feature. It is much larger than any of the other (water-carved) gullies on Ceraunius. It also appears to feed a volcanic cone in the old impact crater at its base. The second example is the chain of lunar-like pits in the left center. This pit chain links up to a clear channel downslope and probably reflects a collapsed lava tube. Both of these features strongly resemble the sinuous rilles on the Moon. (mosaic of Viking Orbiter images 516A24, 622A56, 622A58, 622A59 & 622A60, from Gulick and Baker (1990) J. Geophys. Res., vol. 95, No. B9)
Jove's Tholus lies nearly due east of Olympus Mons and northwest of Ascreus Mons. Thus, it lies on the very northern edge of the lava plains surrounding the Tharsis Montes. It is roughly 80 km long by 60 km wide, and it has a large off-center caldera complex some 40 km in diameter. The total height is probably close to 2 km. Its age is very poorly constrained. The volcano could be anywhere from 2.3 to 3.5 billion years old. Like most tholi, Jovis Tholus is surrounded by younger lava flows. These lavas also cover a set of buried graben , however. The graben cut the easternmost and westernmost edges of the volcano. Jovis also shows signs of a long eruptive history. Its sprawling caldera contains no less than 5 craters. These calderas march southwest from the first, central caldera. Each younger caldera has a lower floor. (Viking Orbiter images 41B17 & 41B19, from Plescia (1994) Icarus, vol. 111.)
Ulysses Patera lies just east of Biblis Patera. It is also located near the middle of Tharsis volcanism, and it has been buried by lavas from Pavonis Mons. It is about 100 km in diameter and is about 2-3 km tall. The central caldera is nearly 56 km across . Like Biblis Patera, Ulysses Patera is surrounded by younger lava flows. It is also cut by a few graben. The most striking features on this volcano, however, are two large impact craters. These craters overlap the caldera and clearly postdate all major volcanism at this site. Large craters are rare outside of the cratered uplands on Mars. Thus, the presence of two such craters on Ulysses Patera is highly unusual. This volcano appears to be very old. It has an estimated age of ~3.4 billion years. (VIking Orbiter images 49B68, 49B70 & 49B85, from Plescia (1994) Icarus, vol. 111.)
Uranius Tholus is located just north of Ceraunius Tholus. It is ~57 km in diameter, and it shows a clear cone several kilometers high. It is heavily cratered and it seems to be quite old. It is probably over 3 billion years in age. It is also surrounded by fairly old volcanic plains, much older than those seen at Biblis and Jovis. These plains record a long history of faulting, partially seen at the upper left. Such fault systems have been buried closer to the giant Tharsis shields, but they may have strongly influenced the locations of both shield volcanism and of the smaller tholi. (Viking Orbiter image 516A23)
The highland paterae on Mars are unique. First, they are not part of the volcanoes in Tharsis and Elysium. They mostly lie in the Cratered Uplands far from other large volcanoes. They also are much older than the Tharsis and Elysium shields. Second, these paterae do not look like Earth volcanoes. There is no sign of actual lava flows. Rather, their central calderas are surrounded by sets of radial furrows. Third, these volcanoes are very flat. They typically are only 1-2 km high and 200-300 km across. These volcanoes are sometimes called ash shields. They seem to be (thin) piles of easily eroded volcanic ash. In contrast to the Earth, however, this ash seems to be composed of basalt. It probably formed when magmas met underground water and exploded into ash and steam. Such explosions help to explain the low height of these paterae. First, large ash eruptions tend to trap air beneath the ash clouds. This air helps support the ash and lets it spread out over wide areas. Second, Mars' gravity is about 1/3 the Earth's. Thus, an eruption on Mars can also carry ash much further than on the Earth.
Alba is not a true highland patera, but it is also unique. It is the largest volcano on Mars, and is roughly 1600 km across. Despite its size, however, it is very flat. Alba has a total height of only ~3 km. Alba differs from both the giant martian shields and the highland paterae. Unlike the paterae, there are no signs of any furrowed ash deposits. Also, it is not in the highlands. Rather, it lies north of the Tharsis Volcanoes. Unlike the giant shields, Alba's volcanism is incredibly widespread. Its lava flows look like those on the other shields, but they are not piled as deeply. Also, it sits on a major fault trend that runs north northwards from the Tharsis region. As shown here, the youngest of these faults curve around to neatly frame Alba's summit. Alba also shows a long history of very fluid volcanism. There are both large sheets of mare-like lava flows and hundreds of long, narrow flows with a central channel or lava tube. Most of these flows are over 100 km long, and some are well over 300 km in length. Many are nearly 10 times larger than Earth flows which look similar. This increase in size probably marks larger and longer eruptions than those on the Earth. However, it may also need more liquid lavas than those on Earth.
Amphitrite (AP) also lies on the edge of the Hellas basin. However, it is on the far side from Hadriaca. Although larger, it is also less striking in appearance than Hadriaca. The central ring structure is about 120 km in diameter. The furrowed ash shield is about 300 km across. It seems fairly thin, and it has little apparent relief. Like Tyrrhena Patera, it is located in a large unit of mare-like plains. Little else is known about the volcano.
NOTE: The circular feature PP may also be a highland patera. However, it shows no sign of any furrowed ash units. Thus, it may just be a large impact that was partly buried by plains lavas. (Viking orbiter images 94A74, 94A75, & 94A76, from Tanaka & Leonard (1995) J. Geophys. Res., v. 100).
Hadriaca is younger than Tyrrhena Patera. It is also larger and better preserved. The caldera in the upper left is nearly 60 km across. The furrowed deposits extend off the image to the lower left for over 300 km. However, they extend less than 100 km in the other directions. This is because Hadriaca lies on the edge of a large impact basin, and has mostly flowed down the side of this basin. It has a very low relief as well. Ignoring the slope into Hellas, it is only 1-2 km tall. This volcano also is linked to clear signs of martian ground water. It lies near the sources for a major martian outflow or flood channel. Several of these sources are seen to the right here as large, smooth-floored depressions. These features indicate that a lot of water or ice was buried near the volcano.
(Viking Orbiter image 106A09, from Lunar & Planetary Institute slide set Volcanoes on Mars.)
Tyrrhena is the most striking of the highland paterae. It is about 300 km across, and it has a total relief of about 2 km. The central caldera is 12 km across, but it lies within a larger ring of fractures. This fracture ring may mark an older, buried caldera. It is 45 km in diameter, and it encircles the whole summit. The most striking features, however, are the broad furrows that run away from the fracture ring. These furrows are up to 200 km in length, and they suggest a period of heavy erosion. This erosion is very old and likely dates back to the time of volcano growth. It may mark a time of strong hydrothermal activity. Note that the furrows east of the summit are buried by a smoother set of volcanic deposits.
(Part of Viking Orbiter Mosaic 211-5213.)
Mare Volcanic Plains
Most of the extruded lava ended up forming the vast volcanic plains on Mars. About 60% of the Martian surface is covered by plains. Unlike the Moon or Mercury, one cannot definitively conclude that these are volcanic plains because they could be alluvial plains formed by hydro-processes or dust deposit plains formed by aeolian processes.
One way to identify volcanic plains is by lava flow fronts. In this photo, one can see the advancing lava that filled a couple of ancient craters. Also note the smoothness of the lava plain and the rough ancient surface.
This image shows the front of a lava flow advancing from the upper right hand corner. The rough, parallel ridges are probably the cooler upper portion of the flow that crumpled as the flow advanced. The front formed a cliff of about 30 meters (100 ft) high. Light-colored dust particles accumulated at the foot of the cliff to form the bright-colored region of the image The volcanic plains on Mars cover about 60% of the planet. It is thought that volcanism may have contributed to the formation of these features. Plain-style volcanism probably occurred throughout much of Mars’ geologic history. This can be seen in the resurfaced highland and lowland regions of the planet. To form the plains the lava flows would have probably had to have a high eruption rate. These features usually display wrinkle ridges that can be 10s km in length and 1000s m wide.
Other Volcanic Features (Mars)
Besides the large volcanoes, Mars also has many other volcanic features. The most obvious are the mare-like plains near Tharsis and the largest impact basins. However, the Viking mission found other, much smaller features as well. These include Earth-like cinder cones, a few small shields and some very old, rugged mountains in the cratered uplands. Some examples from each of these groups are shown here.
Cinder Cones 2
This image shows a field of larger cinder cones (arrows). Each is 2-5 km in size, and they are located near the edge of the cratered uplands. Like large cinder cones on Earth, most show a lop-sided, horse-shoe like pattern. Also note the many irregular pits within this image. These may be magma drainage features or a mark of volcanically melted ground ice within the region.
(Viking Orbiter image 878A38, from Wichman and Schultz (1989) J. Geophys. Res. vol. 94, p.17343.)
Cinder Cones 1
This image shows one likely group of small volcanic cones on Mars. The features are all less than a kilometer in size, and they are located in the northern lowlands. Each shows a clear central pit, and several lie on or along older faults (arrow). They are similar in size to Earth cinder cones, but the central pits are larger due to MarsÕ lower gravity. Like Earth cones, they mark the sites of small explosive eruptions.
(Viking Orbiter image 070A04, from Wilson and Head (1994) Rev. Geophysics, vol. 32, p. 248)
Highland Volcano (?)
There are also some possible volcanoes in the cratered uplands. Because the cratered uplands are very rough, however, these volcanoes are very hard to find. This is one of the clearest examples. It is about 25 km in size, and it lies south of the Tharsis region. It is clearly an isolated mountain with an apparent (central?) caldera (arrow). It is also heavily furrowed and thus looks like a number of Earth volcanoes. The problem is that it has no clear lava flows. Thus, the inferred caldera could be just another small impact crater. Similarly, the peak itself might be just part of a very old impact crater. However, that seems unlikely in this case.
(Viking image 56A68, from Scott (1982) J. Geophys. Res., vol. 87, p. 9841.)
This image shows a small shield volcano in the Tempe region of Mars. It is about 5 km across (arrow), but it grades smoothly into a plains unit some 20 km in size. These plains may have erupted from the shield, but they also link up with other flows that came in from Alba Patera (upper left). The lava plains in turn bury a heavily faulted section of the old cratered uplands. These faults are part of a large, early deformation event around the Tharsis Montes. Note how both the shield and its summit fissure line up with the buried faults. (Viking Orbiter image 627A28, from NASA SP-460, The Geology of the Terrestrial Planets)
Plains with Calderas
Wind-blown sand and dust cover most surfaces on Mars. Thus, most of the mare-like plains on Mars show little sign of a volcanic origin. This is one of the exceptions. Shown here is a caldera located near the middle of Syrtis Major Planum. This plains unit is over 1200 km in diameter. Unlike the lunar mare, however, it does not fill the floor of a large impact basin. Rather, it covers the cratered uplands just outside the Isidis impact basin.
The caldera itself is 70 km across, and several hundred meters deep. It marks the collapsed roof of an old, shallow magma chamber. To the northwest, it is surrounded by faults and graben. To the southeast, the caldera wall has been buried by younger lava plains. Note the small volcanic cone (arrow) located on the caldera floor.
(Viking Orbiter image 375S13, from Schaber (1982) J. Geophys. Res. vol. 87, p. 9856)
Valles Marineris Pyroclastics
This image shows a small part of the Valles Marineris Canyon System. The upper half of the picture is a canyon wall. The lower half is part of the canyon floor. The band of dark splotches running through the middle is a set of minor volcanic vents. These splotches are fairly thin, and they seem to be centered on faults within the canyon wall. They are also very young. They are younger than almost every other feature in the canyons, and some may be less than 100,000 years old. Thus, they may be the youngest volcanic units on Mars. They probably mark very small pyroclastic eruptions, much like the smallest dark mantling deposits on the Moon.
(Viking Orbiter image 81A04, from Lucchita (1987) Science, vol. 235, p. 566.)