Mars's volcanoes

The discovery of enormous volcanoes on Mars as a result of early images returned by the Mariner and Viking missions led to intensified study of Martian volcanic characteristics and activities. It is believed that this study will help scientists determine relationships between geological processes on Earth and Mars and develop a unified theory about the origin and evolution of the solar system.

Overview

Volcanoes on Mars are generally larger than those on Earth. In fact, one should approach the planet with the understanding that all of its major features are gigantic, including its craters, plains, valleys, volcanoes, and polar caps. That is one of Mars’s overall characteristics, and the enormous size of the Martian volcanoes is typical.

Observed Martian volcanoes seem to group themselves into two distinct regions: in the Tharsis region, atop the Tharsis Dome, and in the region known as Elysium, a large topographic region of crustal upheaval. Volcanoes in other areas tend to be smaller and older than those in these two regions, although the dispersion of Martian volcanoes is not broad. Sixteen principal volcanoes have been identified in these two prime areas, both of which are mostly in the planet’s northern hemisphere. According to researchers, there are very few or no volcanoes in other regions of Mars, although the reason for this absence is not completely understood. Scientists speculate that the Martian crust is much thicker, overall, than Earth’s crust and that it is much more difficult for magma to punch a hole through its surface. Also, the comparatively rigid Martian crust does not allow for tectonic plate movement as extensive as that which occurs on Earth.

Volcanoes on Mars are created in the same manner as terrestrial volcanoes: either by eruption through a central tunnel or by eruption through side vents in the volcano’s walls. There is ample evidence that both processes have been at work on Mars in its long geologic past. In the first process, material from the planet’s interior pushes up, overflows, and then cools rapidly, creating a cone with a hole in the top that eventually seals, plugging the eruption tunnel. In the second instance, magma oozes through breaks in the volcano’s flanks, called vents. The major characteristics of Martian volcanoes, however, are very different from those of terrestrial volcanoes.

For a long time, researchers studying Mars thought the planet's crust was solid, with no tectonic plates like on Earth. Further research indicated evidence of plate tectonics, although scientists believe Mars is divided into just two large plates, like an eggshell cracked in half. An enormous canyon system that runs roughly along Mars's equator, called Valles Marineris, contains a number of chains of volcanoes indicating the meeting point of these two plates—which are thought to be much younger and much less active than the many plates on Earth.

The second process, the eruption of magma through side vents in the volcano’s flanks, comes about by the interior materials bursting through the weakest points in the sides of the volcano. This kind of process occurs on Mars as on Earth, but the result is usually quite different. On Mars, lava flowing down the sides of the volcano spills beyond the volcano’s base perimeter, creating vast lava plains that completely surround the volcano. Because volcanoes on Mars are not subject to nearly as much movement as those on Earth, repeated eruptions through the side vents cause the lava plain to continue to grow broader and broader. On Earth, the buildup is considerably slower, if it occurs at all, because the volcano is moved away from its original eruption site by tectonic shifts.

Volcanoes on Mars dwarf those on Earth. The largest of the Martian volcanoes are part of a grouping of about eight near the equator in the Tharsis Bulge, or Dome, just west of Valles Marineris. The biggest is Olympus Mons, a shield volcano judged to be about twenty-seven kilometers high and 600 kilometers in diameter. The next largest three lie in a nearly straight line to the east of Olympus Mons. Beginning with the northernmost, their names are Ascraeus Mons, Pavonis Mons, and Arsia Mons. Although they are not as spectacular as Olympus Mons, their sizes are still quite impressive.

Martian calderas—large craters at volcanoes’ summits caused by the settling of the magma in their interiors—are similarly immense. The caldera of Olympus Mons, for example, is a highly complex collection of features measuring about three kilometers deep and twenty-five kilometers across, with its walls set at a slope of about thirty-two degrees. The complex is the result of repeated calderacollapse after extrusions of magma settle and stop. The calderas of Martian volcanoes are unique, at least among the inner planets, in having many circular fractures surrounding the main caldera. In addition, the entire Olympus Mons structure is surrounded by a scarp, or cliff, which at some points is six kilometers high. In numerous places, there is ample evidence that lava has flowed over the sides of the scarp. Scarp lava overflows are often referred to as flow drapes and are quite common to Martian volcanoes; they extend the main volcano structure into the surrounding lava plain, often for many hundreds of kilometers. Flow drapes at Olympus Mons extend the volcano structure at least 1,000 kilometers outward over the rigid surrounding planetary crust. Flow drapes indicate that the scarp was formed before the time of the eruption of the magma that created the lava flows, and they help geologists determine the age of the volcano and the extent of the extrusion of magma.

Terracing is a feature that is highly pronounced on the slopes of Martian volcanoes, created by the front lines of immense lava flows churning down a volcano’s sides. Multiple terracing is often seen; it results from repeated eruptions, which create well-defined blankets of lava. Olympus Mons exhibits many such terracing features. It is difficult to imagine the enormous volume and extent of the rolling lava required to produce the many examples of terracing on this volcano.

Arsia Mons rises some sixteen kilometers above the Tharsis Dome with a caldera measuring 140 kilometers in diameter. The caldera is surrounded by concentric rings of hummocky topography, some of which are graben (long, linear depressions usually found between two parallel faults). The lava flow reaches at least 1,500 kilometers into the surrounding plain, often covering earlier features of the region. Images from the Mariner 9 mission, especially, disclose many lava-flow fronts and ridges where the rolling lava came to a stop. Repeated eruptions on Mars have thrown out truly copious amounts of lava, which, in turn, have formed far-reaching, relatively smooth plains adjacent to the volcano cones. These plains may extend hundreds of kilometers or, as in the case of Alba Patera, more than 1,700 kilometers out from the central cone. Although relatively flat, these plains most often show many lava-flow patterns, such as ridges and hummocks at the leading edges of flows.

The flow of lava down the flanks of a volcano can take many different forms. All these forms are present on Mars. The thickness of the lava, the steepness of the slope, and the presence or absence of barrier features all cause the downward spread of lava to take different forms and speeds, creating a variety of patterns. Fine-edged flows, flat-topped flows, and flow ridges can be seen in various volcano complexes. Ages of lava flows can be determined by the presence or absence of craters and other features on the volcanoes’ flanks; numerous craters, for example, would indicate that the flows are relatively older and that the craters were formed after the lava flow, whereas lava that creeps into or flows over preexisting craters indicates that the flow came after the crater was created. Some ancient Martian volcanoes, such as Tyrrhena Patera, exhibit features that have been degraded over time, sometimes so much that it is impossible to determine the location of the primary volcano. Other features of some volcanoes suggest the downward flow of ash rather than of lava.

In sum, volcanoes on Mars are somewhat different from volcanoes on Earth. Martian volcanoes are significantly larger. The volcano cone is created differently, and the limited tectonic movement allows a Martian volcano to stand over the same site for millions of years. Earth volcanoes, in the process of eruption, spew out lava in large amounts, yet Martian volcanoes eject lava in still larger amounts. When lava flows down the sides of a terrestrial volcano, it is affected by the landscape—streams, trees, and boulders that may deflect the flow pattern this way or that. On Mars, however, the flanks of volcanoes have no such barriers; instead, they encounter impact craters and the patterned buildup of previous lava flows. Finally, terrestrial volcanoes do not change size appreciably; those on Mars, however, keep growing bigger.

Methods of Study

Planetologists have enlisted a wide range of analytical techniques to study Martian volcanoes. The most obvious and by far the most productive have been the early images of the Martian surface gained through six highly successful uncrewed missions conducted by the National Aeronautics and Space Administration (NASA) between 1965 and 1976: Mariner 4, 6, 7, and 9 and Viking 1 and 2. These flyby, orbiting, and surface-landing missions produced a huge amount of photographic material with which geologists have begun to piece together a profile of Mars’s evolution based on the study of volcanoes. The study of volcanoes is especially enlightening because it allows a view of material that originated from deep inside the planet. The success of these early missions permitted the development of new questions in the study of Mars, and led directly to more advanced spacecraft such as Mars Pathfinder, Mars Global Surveyor, Mars Observer, Mars Reconnaissance Orbiter, Mars Express, Mars Phoenix, and Mars Science Laboratory, many of which were and are committed in large part to the search for water on Mars rather than volcanic processes.

By comparing Mars’s topographic features with similar features on Earth, scientists can gain an enormous amount of information in a short time. By applying geometry to shadows and large-scale topography, they can determine the sizes and trace the short- and long-term development of evolutionary features. This information is critical in the case of volcanoes; lava-flow patterns, especially, are revealing about the structural evolution of volcanic sites and the surrounding terrain. Photographic evidence can be enlarged to a surprising degree, and often, extremely detailed images captured by remote-sensing technology can be studied simultaneously by scientists all over the world. Television cameras aboard the mission spacecraft gather and transmit digital image data, which are separated into shades of gray and then transmitted across space to receiving antennae on Earth. In special receiving stations, digital data are put together again and stored in computers. The data can be recalled from the computers at any time and can be manipulated by computer operators. Shadow areas can be lightened or darkened, color can be added and shaded, and mathematical computations can be applied to various features, all revealing the true nature of the topography.

The Viking landers, which descended to the surface of Mars, contained a multitude of scientific instruments that recorded data about wind direction and velocity, surface and atmospheric temperatures, the sizes of windblown material, the composition of Mars’s soil, and even the viscosity of the soil. There were two landers, each settling at a different location on Mars. An arm was extended from each spacecraft, and at the end of the arm was a specially designed scoop that dug a trench in the planet’s surface. By analyzing the characteristics of the trench, scientists could deduce such information as the ability of the soil to cling together, whether or not other surface material slid into the trench and the strength it took to dig the trench. Also, a series of three instruments aboard the landers received the collected soil, analyzed it chemically, and determined its composition. Data were collected in numerical formats and radioed back to Earth, allowing scientists to create a profile of the Martian environment. The profile was then applied to other regions on the planet, such as those where volcanoes existed. The picture of Mars that developed from these instrumented explorations is one of a cold, lifeless wasteland without the kind of environment that would allow humans to survive even for a short time.

Later landers provided circumstantial evidence for water and found samples of volcanic origin locally. In the first decades of the twenty-first century, the European Space Agency’s Mars Express Rover, as well as NASA’s Curiosity and Perseverance rovers continued to take images and produce new data for the continued discovery of volcanic activity on Mars. The next quantum leap in understanding the volcanoes of Mars would be to send geologists to the Red Planet to survey volcanic regions and perform field geology exercises in situ.

Context

Properties of Martian volcanoes are important for scientists to study because they partially reveal the planet’s present and past geology, providing clues to the planet’s age, formation, and activity. Considerable study of volcanoes has disclosed that there is comparatively little tectonic plate activity associated with Mars and that the Martian crust is far more rigid than Earth’s. While there is a scarcity of volcanoes on Mars in comparison with the large number on Earth, they do help to establish theories about Mars’s age and evolution. Volcanic ejecta can reveal something of the activities deep within Mars’s crust and of the composition of material in the planet’s mantle.

If scientists can decipher how Mars evolved into the planet it is today, they can compare it to Earth and the other planets and, perhaps, reach a greater understanding of Earth’s past and future. One of the keys to unraveling Mars’s mysteries is volcanic activity; it is a critical measure of what is or is not happening both on the planet’s surface and deep inside its interior. Martian volcanoes are instrumental in the creation of other topographic features, such as extensive lava plains and scarps. Most volcanoes are located in a relatively confined area on Mars, and scientists want to know why volcanoes are not formed in other locations as well. Close study of Martian volcanoes could give scientists some clues about the interior properties of the planet and allow them to gain new insights into Mars’s internal dynamics.

Commercially, Mars may harbor wealth in the form of natural resources. The Martian surface is characterized by planetwide iron deposits and iron oxide, from which Mars derives its pinkish-orange coloration. Other critical minerals and resources may exist there as well. It is important, therefore, to understand the reasons for the present dispersion patterns of volcanoes to determine how volcanic actions affect mineral deposits and perhaps to predict future volcanic eruptions in mineral-rich areas.

Mars and, indeed, all planets must be viewed as large, complex bodies with interacting physical systems and geological processes. Scientists, therefore, ask the following questions: what are the driving elements in the forces that sculpt, change, and characterize each planet, especially volcanic action? Is there a common thread among volcanic activities on all the planets and their satellites? How do these elements and forces behave on Earth? The study of Mars has enabled scientists to arrive at a new method known as Earth system science.

Bibliography

Barlow, Nadine. Mars: An Introduction to Its Interior, Surface, and Atmosphere. Cambridge: Cambridge UP, 2008.

Bell, Jim. Postcards from Mars: The First Photographer on the Red Planet. New York: Dutton, 2006.

Bhanoo, Sindya N. "Signs of Volcanoes in Mars Topography." New York Times. New York Times, 30 Apr. 2012.

Carr, Michael H. The Surface of Mars. Cambridge: Cambridge UP, 2007.

Hartmann, William K. Moons and Planets. 5th ed. Belmont: Thomson, 2005.

Hartmann, William K., and Odell Raper. The New Mars: The Discoveries of Mariner 9. NASA SP-337. Washington: GPO, 1974.

Kargel, Jeffrey S. Mars: A Warmer, Wetter Planet. New York: Springer, 2004.

Kuthunur, Sharmila. “Landslides on Mars Suggest Water Once Surrounded Olympus Mons, Tallest Volcano in the Solar System.” Space.com, 28 Aug. 2023, www.space.com/landslides-mars-water-surrounded-olympus-mons-solar-system-largest-volcano. Accessed 21 Sept. 2023.

Mars Exploration Program. NASA, 2013.

"Mars Surface Made of Shifting Plates Like Earth, Study Suggests." Space.com. TechMediaNetwork.com, 14 Aug. 2012.

National Aeronautics and Space Administration. Viking 1, Early Results. NASA SP-408. Springfield: Natl. Technical Information Service, 1976.

Sheehan, William, and Stephen James O’Meara. Mars: The Lure of the Red Planet. Amherst: Prometheus, 2001.

Squyres, Steve. Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet. New York: Hyperion, 2006.

Strickland, Ashley. “Perseverance Rover Makes 'Completely Unexpected' Volcanic Discovery on Mars.” CNN, 15 Dec. 2021, www.cnn.com/2021/12/15/world/perseverance-rover-mars-findings-scn/index.html. Accessed 21 Sept. 2023.

Zubrin, Robert. Entering Space: Creating a Spacefaring Civilization. New York: Tarcher, 2000.